(Radiographics. 2002;22:1139-1164.)
© RSNA, 2002
Anomalies of the Distal Ureter, Bladder, and Urethra in Children: Embryologic, Radiologic, and Pathologic Features1
Teresa Berrocal, MD, PhD,
Pedro López-Pereira, MD,
Antonia Arjonilla, MD and
Julia Gutiérrez, MD
1 From the Departments of Pediatric Radiology (T.B., A.A., J.G.) and Pediatric Urology (P.L.P.), Hospital Infantil La Paz, Paseo de la Castellana 261, Madrid 28046, Spain. Recipient of a Certificate of Merit award for an education exhibit at the 2000 RSNA scientific assembly. Received January 15, 2002; revision requested February 27 and received April 4; accepted April 23. Address correspondence to T.B. (e-mail: cprieto@.hulp.insalud.es).
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Abstract
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Congenital anomalies of the lower urinary tract are a significant cause of morbidity in infancy. Radiologic investigation is an important source of clinical information in lower urinary tract disorders but should not inconvenience the patient, expose the patient to unnecessary radiation, or delay surgical correction. In pediatric patients with suspected underlying urologic structural anomalies, screening ultrasonography is commonly the initial diagnostic study. If dilatation of the urinary tract is confirmed, voiding cystourethrography is performed to determine the presence of vesicoureteral reflux (VUR) and other causes of upper tract dilatation. If VUR is confirmed, follow-up with nuclear cystography or echo-enhanced cystosonography may be performed. If VUR is excluded, nuclear diuresis renography is the primary test for differentiating between obstructed and nonobstructed megaureter. Intravenous urography can be used to specifically identify an area of obstruction and to determine the presence of duplex collecting systems and a ureterocele. Computed tomography and magnetic resonance (MR) imaging are unsuitable for general screening but provide superb anatomic detail and added diagnostic specificity. MR imaging is mandatory in the evaluation of associated spinal anomalies. MR urography can demonstrate ectopic extravesical ureteric insertions, thereby providing a global view of the malformation. Familiarity with anomalies of the lower urinary tract is essential for correct diagnosis and appropriate management.
© RSNA, 2002
Index Terms: Bladder, abnormalities, 83.1444, 83.1465, 83.8771, 83.8779 • Bladder, diverticula, 83.1491 • Urachus, 839.1463 • Ureter, abnormalities, 82.143 • Ureter, enlarged, 82.1454, 82.1455, 82.849 • Ureter, reflux, 82.85 • Urethra, abnormalities, 84.245, 84.8781, 84.8783, 851.245, 851.8781, 851.8783 • Urethra, diverticula, 84.1491, 851.1491 • Urethra, stenosis or obstruction, 84.847, 851.847
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LEARNING OBJECTIVES FOR TEST 4
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After reading this article and taking the test, the reader will be able to:
- Describe the embryologic, radiologic, and pathologic features of a wide spectrum of congenital anomalies involving the distal ureter, bladder, and urethra.
- Discuss the utility of the imaging modalities that can be used in the management of these conditions.
- Identify the pitfalls, diagnostic difficulties, and differential diagnoses associated with evaluation of these conditions.
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Introduction
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Methods for imaging the urinary tract in children have proliferated significantly in recent years. Computed tomography (CT), magnetic resonance (MR) imaging, and echo-enhanced cystosonography have been added to the more traditional armamentarium of radiologic examinations, which include nuclear imaging, ultrasonography (US), voiding cystourethrography (VCUG), and intravenous urography (IVU). These procedures have a significant impact on diagnosis and management; therefore, it is important that the indications for and limitations and complications associated with these procedures be familiar to radiologists, urologists, and pediatricians who deal with urinary tract disease in children. The radiologist should tailor the imaging work-up of affected patients. With this approach, the number of examinations, the expense, the radiation exposure, and patient discomfort are minimized, whereas useful clinical information is maximized (1).
US is ideally suited for the evaluation of children with a suspected urinary tract abnormality because it is painless, involves no radiation exposure, and provides excellent anatomic images of the urinary system. US has replaced IVU as the initial examination, and the results of US usually determine what further evaluation is required. However, IVU may provide important additional information in certain uncommon cases. Diuresis renography is one of the most important diagnostic tools in the evaluation of neonates with hydroureteronephrosis. VCUG is essential for the evaluation of the anatomy and abnormalities of the bladder and urethra and should precede other examinations (IVU, MR imaging) because the results of VCUG may determine which additional examinations are required.
Anomalies of the urogenital tract are among the most common organ system anomalies found in the fetus or neonate. With use of real-time US as a screening test in healthy infants, Steinhardt et al (2) found that 3.2% of infants had an abnormality of the genitourinary tract and that one-half of these patients required surgical intervention. A complete understanding of the embryologic development of the urinary tract is very helpful in the evaluation and treatment of a child with a congenital genitourinary malformation.
In this article, we discuss and illustrate a wide spectrum of congenital anomalies of the distal ureter (vesicoureteral reflux [VUR], primary megaureter, ectopic ureter, simple and ectopic ureterocele), urachus, bladder (bladder agenesis, bladder duplication, bladder diverticula, prune-belly syndrome, cloacal malformation), and urethra (posterior and anterior urethral valves, complete and incomplete urethral duplication, urethral diverticula, megalourethra, urethral fistula, congenital urethral stricture). We also demonstrate the utility of various imaging modalities in the management of these conditions.
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Anomalies of the Distal Ureter
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The ureter first appears in the 3- to 5-mm stage at the end of the 5th gestational week as an outpouching on the mesonephric duct at the point where the duct bends sharply in a ventral direction just before it enters the cloaca. The segment of the mesonephric duct from the site of origin of the ureter to the primitive cloaca is known as the common excretory duct. During differentiation of the bladder and urethra, this segment widens as it is incorporated into the developing bladder base and proximal urethra, so that by the end of the 6th gestational week, the ureter and the remaining mesonephric duct have separate openings into the urogenital sinus. This absorption of the common excretory duct into the urogenital sinus occurs in such a way that the original meatus of the mesonephric duct migrates in a cephalic and lateral direction. Progressive development of the bladder, bladder neck, and urethra results in continued lateral and cephalic migration of the urethral orifice and more medial and caudal migration of the opening of the mesonephric duct (3). In males, this terminal end of the mesonephric duct that was proximal to the ureteral bud develops into the ejaculatory duct. Muscular bands persist between the ureteral orifice and the opening of the ejaculatory ducts and form the superficial muscular layer of the trigone. In females, further differentiation of the mesonephric duct ceases, and the structure involutes for the most part, although segments may persist as Gartner duct lying along the anterolateral vaginal wall and uterus and within the broad ligament. This normal muscular development results in the anatomically defined trigone of the normal bladder. Ureteral development occurs simultaneously with formation of the trigone and proximal urethra. As the ureter grows toward the metanephric blastema, it undergoes a series of dichotomous divisions that ultimately produce a complex pattern of infundibula, calices, and collecting ducts in the mature metanephric kidney (4).
Primary Vesicoureteral Reflux
VUR is the abnormal flow of urine from the bladder into the upper urinary tract. In the majority of cases, it occurs as a result of a primary maturation abnormality of the vesicoureteral junction or a short distal ureteric submucosal tunnel in the bladder that alters the function of the valve mechanism (5). VUR may be an isolated anomaly or associated with other congenital anomalies such as posterior urethral valves or complete duplication of the urinary tract (6).
Reflux predisposes to renal infection (pyelonephritis) because it carries bacteria from the bladder to the upper urinary tract (2). The majority of pediatric patients who develop renal scars after a urinary tract infection have VUR, and higher grades of reflux are associated with an increase in parenchymal scarring (7). Detection of VUR in neonates and infants is particularly important because these patients are more predisposed to the formation of renal scars than are older children (8). Reflux nephropathy is a common cause of renal failure; therefore, it is important that this condition be detected as early as possible to allow prompt prophylactic antibiotic treatment and hopefully reduce the risk of scarring and reflux nephropathy (9). Reflux is also the most common cause of antenatal hydronephrosis, being responsible for 40% of intrauterine cases (10).
The primary diagnostic procedure for evaluation of VUR is VCUG, which should be performed after the first well-documented urinary tract infection. VCUG should be used to document the presence of VUR and to determine the grade of reflux and whether reflux occurs during micturation or during bladder filling (Fig 1). Grading of VUR is based on the International Reflux Committee Study (Table 1) (11). Grade is determined on the basis of the most severe VUR, which usually coincides with the peak of voiding. The bladder volume at which VUR is first seen as well as any intrarenal reflux should be noted, although these are not relevant to the International Grading System (11).
Reflux can also be graded, although less precisely, with nuclear cystography. There is no universally accepted grading system for nuclear cystography, with most radiologists simply using the terms mild, moderate, and severe. The clear advantage of nuclear cystography is the lower radiation dosage, which makes it an excellent tool for screening female patients and for following up patients of both sexes (12). The disadvantages are (a) difficulty in recognizing important associated bladder disease (eg, bladder diverticula), (b) difficulty in visualizing the male urethra, and (c) lack of spatial resolution.
Echo-enhanced cystosonography has recently been proposed as a promising new method for detecting and grading VUR without exposing patients to ionizing radiation (13). This is important in pediatric patients, given the number of imaging evaluations for VUR that each child may undergo. Data show that cystosonography depicts not only more refluxing units but also higher-grade VUR than does VCUG. The main limitation of cystosonography is that it is incapable of adequately depicting the urethra, although this may be less of a consideration in female patients (14). Like nuclear cystography, cystosonography may be an excellent technique for screening female patients and for follow-up in patients of both sexes.
The prenatal detection of hydronephrosis, hydroureteronephrosis, or dilatation of part of a double collecting system is an indication for postnatal US. US is used to assess the renal parenchyma, the collecting system, and any associated abnormalities. Thickening of the wall of the renal collecting system has been described at US in patients with VUR. This wall thickening is probably due to intermittent dilatation of the collecting system during periods of VUR and can be attributed to infolding of the epithelium when a dilated upper urinary tract is in an empty contracted state (15). However, findings at conventional US do not exclude VUR. When hydroureteronephrosis is detected at US, refluxing megaureter may be differentiated from obstructed primary megaureter. In refluxing megaureter, the juxtavesical segment is not narrowed; indeed, it is quite patulous (16).
Occasionally, VUR may be suggested incidentally at IVU by the presence of pelvic striation (17) or ureteral dilatation. However, findings at both IVU and US are nonspecific and may be completely normal in patients with high-grade reflux. The most sensitive method of identifying pyelonephritis and renal scarring is cortical scintigraphy with dimercaptosuccinic acid (8).
Primary Megaureter
Megaureter is a generic term indicating the presence of an enlarged ureter with or without concomitant dilatation of the upper collecting system. The normal ureter in children rarely exceeds 5 mm in diameter (18). In practice, a ureter with a diameter of 7 mm or more should be considered a megaureter (19). Megaureter may be primary or secondary, refluxing or nonrefluxing, obstructed or nonobstructed, and nonrefluxing unobstructed (20). Primary megaureter is an inherently compound term that includes all cases of megaureter due to an idiopathic congenital alteration at the vesicoureteral junction. There are three major categories of primary megaureter: obstructed primary megaureter, refluxing primary megaureter, and nonrefluxing unobstructed primary megaureter (8). Secondary megaureter occurs as a result of some abnormality involving the bladder or urethra (eg, urethral valves, neuropathic bladder dysfunction, urethral strictures, ureteroceles, acquired causes of obstruction).
In obstructed primary megaureter, there is dilatation above a short (0.5–4-cm), aperistaltic, normal-caliber juxtavesical section of a normally inserted ureter (17). The ureteral orifice and the submucosal tunnel are normal. The normal ureter proximal to the aperistaltic segment dilates because of relative obstruction. This phenomenon is somewhat similar to achalasia and Hirschsprung disease. The cause of distal ureteral aperistalsis is not known. It may be due to a paucity of ganglion cells in the connective tissue that surrounds the distal ureter (21); however, aganglionosis has not been proved to be the problem. Tokunaka et al (22) reported a muscular derangement and increased interstitial connective tissue in the nondilated terminal ureteral segment. All investigations with electron microscopy demonstrated an excess of collagen between muscle cells (22). Refluxing primary megaureter is caused by a short or absent intravesical ureter, congenital paraureteric diverticulum, or other derangement of the vesicoureteral junction (20). Lee et al (21) assumed that the marked increase in collagen and significant decrease in smooth muscle could be major contributing factors in the pathogenesis of refluxing primary megaureter. In nonrefluxing unobstructed primary megaureter, there is neither reflux nor stenosis of the vesicoureteral junction, but the ureter is dilated beginning at a point just above the bladder (Fig 2). The cause of this phenomenon is unknown, but several theoretic explanations have been given based on transitional (prenatal to postnatal) renal physiologic and histoanatomic features of the developing ureter. Most primary megaureter in neonates falls into this category (20).
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Figure 2. Primary megaureter in a 7-month-old boy. Longitudinal US image through the bladder ( ) demonstrates a dilated distal ureter (u) and a narrowed juxtavesical ureteral segment corresponding to the aperistaltic segment (arrow).
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Because of the widespread use of prenatal US, hydroureteronephrosis is usually diagnosed at fetal screening. The evaluation of an infant with prenatally diagnosed megaureter begins with renal and bladder US to confirm the persistence of urinary tract dilatation (Fig 3a). If this condition is confirmed, VCUG is performed to exclude VUR. The primary nature of megaureter must be confirmed by excluding secondary causes such as urethral valves or neuropathic bladder dysfunction (23). In obstructed primary megaureter, VCUG demonstrates no VUR. US shows hydronephrosis and ureteral dilatation above the persistently narrowed distal aperistaltic segment. Real-time US reveals active peristaltic waves passing to and fro in the dilated ureter above the narrowed segment (16) and disproportionate dilatation of the lower ureter relative to the upper ureter and renal pelvis. In primary megaureter, once VUR has been excluded, perfusion studies and diuresis renography (Fig 4) are indicated. These imaging modalities are useful in differentiating dilatation that is functionally obstructive and requires surgical treatment from dilatation that represents a variant in normal ureteral development and can be conservatively treated initially. Because it is quick, noninvasive, and nontoxic, an isotope study is also a very adequate test in the follow-up of conservatively treated primary megaureter, which accounts for approximately 49% of all cases of primary megaureter (23,24). The findings of obstructed primary megaureter are also demonstrable with IVU, which shows ureteral dilatation above a distal segment of normal caliber (Fig 3b). However, the use of IVU is controversial in this setting, and some authors believe that it does not add significant information to that provided by US and isotope studies (24). Although the aperistaltic segment and the ureteral dilatation above it can be well demonstrated with MR imaging, this technique is not indicated in the routine management of primary megaureter.
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Figure 4. Bilateral obstructed primary megaureter. Nuclear diuresis renogram obtained 20 minutes after administration of furosemide demonstrates no washout of the radiotracer, a finding that indicates obstructed megaureter.
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Ectopic Ureter
Ectopic insertion of the ureter stems from abnormal ureteral bud migration and usually results in caudal ectopia. Normally, the primitive ureteral bud travels cephalad, whereas the wolffian duct, from which it originates, travels caudad (25). However, if the ureteral bud fails to separate from the wolffian duct, it may be carried into a more caudal position than normal. Consequently, the opening of the ureter becomes caudally ectopic and, in the female, inserts into the lower bladder, urethra, vestibule, or vagina. More rarely, it can empty into the uterus or a wolffian duct remnant such as Gartner duct or cyst (26). In males, it empties into the lower bladder, posterior urethra, seminal vesicle, vas deferens, or ejaculatory duct. In very rare instances, it can empty into the rectum (25,27). The fundamental difference between ureteral ectopia in females and in males is that in females, ectopic ureters can terminate at a level distal to the continence mechanisms of the bladder neck and external sphincter and thus may be associated with incontinence. Approximately one-half of female patients with ectopic ureters present with a classic history of continuous dribbling incontinence despite what appears to be a normal voiding pattern (25,28).
An ectopic ureter can drain a single kidney (28), but about 70% are associated with complete ureteral duplication (Fig 5). In complete ureteral duplication with each segment having its own ureteral orifice in the bladder, the Weigert-Meyer rule applies. This rule states that the ureteral orifice of the upper pole moiety inserts into the bladder medial and inferior to both its normal location and the orifice of the ureter draining the lower renal segment. In these cases, the ureter draining the upper pole moiety frequently ends in a ureterocele, whereas reflux into the lower moiety typically occurs (Fig 5).
The most frequently encountered anomaly associated with an ectopic ureter is hypoplasia or dysplasia of the renal moiety. There is fairly good correlation between the degree of ectopia and the degree of renal abnormality, although it appears to hold better for duplex systems with ectopy than for single systems with ectopy (25,28). The classic radiologic work-up of abnormal duplex kidneys includes US, VCUG, and IVU. Initial screening must be performed with renal US. US usually allows exclusion of a duplex kidney and of obstruction due to a ureterocele. It delineates the abnormal fluid-filled ureter in most cases and allows the ureter to be traced into the pelvis and into an abnormally low position beyond the bladder. Occasionally, the upper moiety may be too small to be detected, and the diagnosis may depend on recognizing the absence of an upper pole calix or apparent excessive thickness of the renal tissue on the medial aspect of the upper pole. The ectopic ureter and its insertion point may be visualized directly with IVU, although IVU is now performed less frequently because the dilated upper pole often shows reduced function and rarely opacifies (29). In ectopic insertion of a ureter of a single collecting system, the involved kidney is usually small and dysplastic and may not be visible at IVU or US. Renal scintigraphy is required to assess renal function, and CT may be useful on occasion in locating a small, poorly functioning dysplastic kidney (30). VCUG is performed to demonstrate reflux into the ectopic ureter and to identify the endpoint of the ureter (Fig 5). However, when an ectopic ureter drains outside the urinary system (Fig 6), the ectopic insertion may not be visible at VCUG. Recently, MR urography has proved capable of displaying dilated collecting systems, ectopic ureters, and ureteroceles (30). It has an advantage over US and IVU in that it is capable of demonstrating ectopic extravesical ureteric insertions, thereby providing a global view of the malformation. MR urography is a promising imaging modality in selected cases (29,31).
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Figure 6a. Ectopic ureter draining into the seminal vesicles. (a) IVU image shows an abdominal mass displacing the bladder () to the left. The left ureter (arrowheads) is also displaced by the mass. The right renal pelvis is seen (arrows), but not the right ureter. (b) Photograph of the gross specimen shows the right ureter (u) draining into a widely dilated seminal vesicle (SV), which produced the mass effect observed at IVU.
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Figure 6b. Ectopic ureter draining into the seminal vesicles. (a) IVU image shows an abdominal mass displacing the bladder () to the left. The left ureter (arrowheads) is also displaced by the mass. The right renal pelvis is seen (arrows), but not the right ureter. (b) Photograph of the gross specimen shows the right ureter (u) draining into a widely dilated seminal vesicle (SV), which produced the mass effect observed at IVU.
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Ureterocele
Ureteroceles represent cystic dilatation of the intravesical segment of the ureter. Ureteroceles may be associated with either a single or a duplex ureter. The congenital defect is the obstruction of the meatus, and the ureterocele is simply a hyperplastic response to this obstruction. The outer wall is composed of bladder epithelium and the inner wall of ureteral epithelium, with connective tissue and muscle fiber in between (32). A ureterocele may be as small 1 cm, or it may fill the entire bladder and prolapse through the urethra (Fig 7). Ureteral duplication is present in about 75% of patients with ureteroceles (33).
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Figure 7a. Prolapsing ureterocele. (a) On an IVU image, the bladder is filled with a large ureterocele (u) that projects through the neck of the bladder (arrow). (b) Clinical photograph obtained in a different patient shows a ureterocele manifesting as an interlabial mass () that prolapses through the perineal orifice.
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Figure 7b. Prolapsing ureterocele. (a) On an IVU image, the bladder is filled with a large ureterocele (u) that projects through the neck of the bladder (arrow). (b) Clinical photograph obtained in a different patient shows a ureterocele manifesting as an interlabial mass () that prolapses through the perineal orifice.
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Ureteroceles may be either simple or ectopic. In simple ureteroceles, stenosis of the distal end of the normally positioned ureteral orifice leads to ballooning of the segment immediately above it, forming the ureterocele. In young patients, the stenosis is presumed to be congenital, although in older children and adults it can be secondary to an inflammatory stricture. The defect leading to this anomaly is thought to be a persistent Chwalla membrane with consequent obstruction at the fusion point between the mesonephric duct and urogenital channel (34). This anatomic defect is more often seen in lesions wholly contained within the bladder. A simple ureterocele may be demonstrated at US, VCUG, or IVU (35). At US, the ureterocele is identified as a cystic intravesical mass, contiguous with a dilated ureter and arising from a normally positioned ureteral orifice near the lateral margin of the trigone (Fig 8c). The wall of the ureterocele is visualized as a rounded echogenic structure located near the lateral margin of the trigone (35). Typically, a simple ureterocele demonstrates a narrow base. It can often be followed into a dilated ureter deep within the bony pelvis and can occasionally obstruct the bladder (36). With real-time US, partial or complete collapse of a simple ureterocele secondary to ureteric peristalsis can be demonstrated. In such cases, further imaging should be performed to exclude a mass in the bladder. At VCUG, a collapsed simple ureterocele usually manifests as a rounded filling defect within the bladder. It is important to use diluted contrast material in small amounts to avoid flattening, intussusception, or even eversion of the ureterocele. When performed, IVU will usually demonstrate a collection of contrast material within the ureterocele, which produces the classic "cobra head" appearance consisting of a round or oval area of increased opacity surrounded by the radiolucent halo of the wall of the ureterocele (Fig 8a). In other cases, the ureterocele produces a negative filling defect in the contrast material–filled bladder (Fig 8b) representing an ectopic ureterocele filled with nonopaque urine.
An ectopic ureterocele is the cystlike protrusion into the bladder lumen of the dilated submucosal distal portion of an ectopic ureter. It is almost invariably associated with a duplex collecting system and represents the distal portion of the ureter of the upper renal moiety. An ectopic ureterocele is more inferiorly located than a simple ureterocele. It is usually unilateral and is far more common in girls than in boys (37). The US appearance of an ectopic ureterocele is characteristic. The upper pole collecting system of a duplex kidney is typically dilated and is connected with a dilated, tortuous ureter. At the level of the bladder, the hydroureter terminates in a round, thin-walled, anechoic intravesical cavity (Fig 9) (38) located out of the normal ureteral meatus. Further diagnostic studies should include VCUG for identification of VUR into other ureteral segments and evaluation of bladder neck obstruction. When complete ureteral duplication is present, reflux typically occurs into the lower moiety via a ureter with an abnormally caudal origin on the mesonephric duct, leading to a laterally ectopic ureteral orifice with a shortened submucosal tunnel (38). Cecoureterocele is an uncommon form of ectopic ureterocele in which the intravesical portion dissects submucosally below the trigone and urethra. A domelike protrusion into the bladder and urethra is seen. The lumen extends beyond the orifice like a tongue or "cecum" (4). A ureterocele can herniate into the urethra and manifest as a perineal mass. This occurs most commonly in females but can also be seen in males (39).
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Figure 9a. Ectopic ureterocele in a 3-month-old boy. (a) IVU image shows a duplex left kidney. There is nonvisualization of the upper moiety and moderate dilatation of the lower pole pelvicaliceal system (*). Note the increased distance between the spinal column and the left kidney produced by the upper moiety. A large filling defect (u) is seen in the bladder, a finding that represents a ureterocele. (b) Longitudinal US scan through the bladder shows a rounded, well-defined cystic mass (u) that represents an ectopic ureterocele. (c) Clinical photograph shows the ureterocele () protruding into the open bladder.
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Figure 9b. Ectopic ureterocele in a 3-month-old boy. (a) IVU image shows a duplex left kidney. There is nonvisualization of the upper moiety and moderate dilatation of the lower pole pelvicaliceal system (*). Note the increased distance between the spinal column and the left kidney produced by the upper moiety. A large filling defect (u) is seen in the bladder, a finding that represents a ureterocele. (b) Longitudinal US scan through the bladder shows a rounded, well-defined cystic mass (u) that represents an ectopic ureterocele. (c) Clinical photograph shows the ureterocele () protruding into the open bladder.
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Figure 9c. Ectopic ureterocele in a 3-month-old boy. (a) IVU image shows a duplex left kidney. There is nonvisualization of the upper moiety and moderate dilatation of the lower pole pelvicaliceal system (*). Note the increased distance between the spinal column and the left kidney produced by the upper moiety. A large filling defect (u) is seen in the bladder, a finding that represents a ureterocele. (b) Longitudinal US scan through the bladder shows a rounded, well-defined cystic mass (u) that represents an ectopic ureterocele. (c) Clinical photograph shows the ureterocele () protruding into the open bladder.
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Urachal Anomalies
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The urachus develops from the superior portion of the urogenital sinus and connects the dome of the bladder to the allantoic duct during fetal life. The urachus is located behind the abdominal wall and anterior to the peritoneum in the space of Retzius. Before birth, the urachus is obliterated and becomes a vestigial structure known as the medial umbilical ligament. In the absence of complete obliteration, the urachus persists as either a patent urachus, urachal cyst, urachal sinus, or urachal diverticulum (40). A persistent urachus frequently coexists with congenital lower urinary tract obstruction such as posterior urethral valves or prune-belly syndrome. It may also coexist with ventral abdominal wall defects such as omphalocele (40). Although adenocarcinoma of the urachus is rare, it has been reported in patients as young as 15 years of age.
Patent urachus represents the failure of the entire course of the urachus to close, resulting in an open channel between the bladder and the umbilicus (41). A patent urachus is usually diagnosed in the neonate when urine is noted leaking from the umbilicus. This anomaly is demonstrated by retrograde injection of contrast material into the orifice of the channel at the umbilical end or during VCUG in the lateral projection. A patent urachus manifests at longitudinal US as a tubular connection between the anterosuperior aspect of the bladder and the umbilicus (42). Patency is better assessed with a linear high-frequency transducer due to the superficial location of the urachus. Occasionally, patency of the urachus can be demonstrated at CT (42).
A urachal cyst forms when both the umbilical and vesical ends of the urachal lumen close while an intervening portion remains patent and fluid filled. Urachal cysts usually remain obscure until complicated by infection or bleeding. At radiology, an uncomplicated urachal cyst appears as a collection of simple fluid localized in the midline of the anterior abdominal wall, between the umbilicus and the pubis and often contiguous with the bladder dome. Diagnostic evaluation should begin with US, which usually allows localization of the mass and delineation of its limits. A urachal cyst may become infected and demonstrate (a) features of mixed echogenicity at US, (b) attenuation and signal intensity that deviate upward from those of water at CT and MR imaging, respectively, and (c) thickening of the urachal wall (43). The differential diagnosis includes bladder diverticulum, vitelline cyst, mesenteric cyst, Meckel diverticulum, umbilical hernia, and even ovarian cyst.
Urachal sinus is a noncommunicating dilatation of the urachus at the umbilical end, whereas urachal diverticulum is a similar deformity that communicates with the anterosuperior aspect of the bladder as a result of failure of the urachus to close at the bladder. A urachal diverticulum frequently coexists with congenital obstruction of the lower urinary tract. This anomaly is identified as a urine-filled anterosuperior extension from the bladder dome at VCUG (Fig 10), US, CT, orMR imaging (44). An umbilical-urachal sinus manifests at US as a thickened tubular structure along the midline below the umbilicus (45). If seen at CT, it is usually an incidental finding that appears as a midline cystic lesion just above the anterosuperior aspect of the bladder. At US, it manifests as an extraluminally protruding, fluid-filled sac that does not communicate with the umbilicus (42,45).
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Anomalies of the Bladder
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Bladder Agenesis
Agenesis of the bladder is an extremely rare congenital anomaly, with approximately 45 cases reported to date in the radiology literature written in English. Most infants with the anomaly are stillborn and have other urogenital tract anomalies as well as neurologic and orthopedic disorders. The cause of agenesis of the bladder is uncertain. Because the hindgut is normal in these infants, it may be assumed that embryologic division of the cloaca into the urogenital sinus and anorectum proceeded normally (46). Bladder agenesis may be the result of secondary loss of the anterior division of the cloaca, perhaps owing to a lack of distention with urine caused by failure of incorporation of the mesonephric ducts and ureters into the trigone, thus preventing urine from accumulating in the bladder (47). In most cases in which the bladder is absent, the ureters have the same course as ureters with ectopic vestibular openings (Fig 11). In these cases, there is usually some preservation of renal function. US is useful in demonstrating absence of the bladder and the severe bilateral renal dysplasia that is usually present. Retrograde catheterization of a ureteral opening must be performed to study the kidneys and ureters (46,47).
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Figure 11. Agenesis of the bladder in a 5-day-old girl with wetting. Image from bilateral ureterography performed with catheters placed in ectopic ureteral orifices shows dilated and tortuous ureters (u) with dilatation of the renal pelves and calices. Intrarenal reflux is also noted. IVU showed poorly functioning hydronephrotic kidneys.
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Bladder Duplication
Complete duplication of the bladder and urethra is a rare anomaly. The English radiology literature contains only a few reports (48). The cause of complete duplication of the bladder remains obscure, although several hypotheses have been proposed. Abrahamson (49) offered two explanations: (a) excessive constriction between the urogenital and vesicourethral portions of the ventral cloaca, and (b) a supernumerary cloacal septum that indents the epithelial wall of the bladder. Disturbances in the embryogenesis of the hindgut may result in duplication of the lower urinary tract (50). The primitive hindgut is the anlage of the terminal ileum, colon, and cloaca. The cloaca is divided into anterior and posterior positions, which form the lower genitourinary and lower gastrointestinal systems, respectively. Early embryologic duplication of the hindgut could cause complete duplication of the two systems (48,50). Duplication of the bladder may occur in the sagittal or coronal plane. The most common form is sagittal duplication, in which two bladders lie side by side and are separated by a fold of peritoneum and loose areolar tissue. Each bladder receives the ureter of the ipsilateral kidney and is drained by its own urethra, the ureter and urethra lying side by side (1,4). In some cases, only one bladder communicates with a single urethra, leaving the opposite side obstructed with no outlet (51,52). Most obstructed systems are associated with renal dysplasia and nonfunction. Complete duplication of the bladder in the coronal plane is much more unusual. In this form of duplication, there are two bladders lying one in front of the other and separated by a fibromuscular septum that runs obliquely in a posterosuperior to anteroinferior plane (Fig 12). In this anomaly, each urethra originates from a separate bladder (52–54). A review of the literature showed that multilocular bladders were frequently misdiagnosed as complete duplications (49,53). In cases of true duplication, the internal bladder septum includes a muscular component or the absence of communication between the two bladders is noted at gross examination.
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Figure 12a. Complete duplication of the bladder and urethra in the coronal plane. (a) Lateral retrograde cystourethrogram through both separate urethral openings shows two bladders, one (a) anterior to the other (b). (b) Transverse US image also shows the two bladders (a, b), one lying in front of the other and each with its own muscular wall.
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Figure 12b. Complete duplication of the bladder and urethra in the coronal plane. (a) Lateral retrograde cystourethrogram through both separate urethral openings shows two bladders, one (a) anterior to the other (b). (b) Transverse US image also shows the two bladders (a, b), one lying in front of the other and each with its own muscular wall.
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Associated congenital anomalies of other systems are present in the majority of cases of complete duplication of the bladder and urethra. In 90% of cases, there is some type of duplication of the external genitalia, and in 40% there is duplication of the lower gastrointestinal tract. Other reported associated abnormalities include spinal duplication and fistulas between the rectum, vagina, and urethra (53,54).
Bladder Diverticula
Congenital bladder diverticula that are not associated with posterior urethral valves or neuropathic bladder are unusual but not rare and occur almost exclusively in boys. In an extensive study of a pediatric genitourinary database of 5,084 children, bladder diverticula were found in 1.7% of cases (55). Bladder diverticula can be unilateral or bilateral and are caused by congenital bladder muscular anomalies (55,56). A diverticulum that occurs at the ureterovesicular junction is usually called periureteric diverticulum (Fig 13), classically known as Hutch diverticulum (56), and is often associated with VUR. This is because the presence of the diverticulum alters the normal slanted insertion of the ureter into the bladder. In male infants, bladder diverticula must be distinguished from protrusions of the urinary bladder bilaterally into the inguinal rings anteriorly. These outpouchings, known as "bladder ears," are transient and usually disappear with age. Lateral VCUG usually helps differentiate between the two conditions.
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Figure 13. Periureteric diverticula in a male neonate. Lateral VCUG image shows that the left ureter (U) inserts into a bladder diverticulum (D) in a periureteric location. A small urethral diverticulum is also seen (arrowheads). = bladder.
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Most bladder diverticula are diagnosed during evaluation for urinary tract infection, incontinence, or urine retention (57). Diverticula are easy to diagnose at VCUG (Fig 13). At US, diverticula appear as round or oval anechoic fluid collections that arise from the base of the bladder or around the ureteric orifice. Congenital bladder diverticula have been described in children with Ehlers-Danlos syndrome, a congenital connective tissue disorder characterized by abnormalities of collagen structure and function (58). Potential spontaneous rupture of the diverticulum is a typical feature, as is postsurgical relapse (58). In children with incidentally discovered primary congenital diverticula, no therapy is needed unless the diverticulum involves the vesicoureteral hiatus to such an extent that it contributes to the occurrence of VUR. In such cases, as well as when the diverticula are causing infection or obstruction, they should be excised. Because of the potential for the development of carcinoma in bladder diverticula, many surgeons would argue for immediate prophylactic diverticular excision (57).
Prune-Belly Syndrome
The term prune belly refers to a lax, wrinkled abdominal wall, which is frequently associated with other anomalies. Prune-belly syndrome is a specific constellation of anomalies consisting of three major findings associated with a number of other respiratory, gastrointestinal, musculoskeletal, and cardiovascular anomalies (59). The syndrome is named for the wrinkled appearance of the distended and lax abdominal wall that results from the absence of rectus muscles. Bilateral, nonpalpable undescended testes are present, and there is an abnormal urinary tract characterized by tortuous, dilated ureters; a megalocystic, dilated prostatic urethra; and renal dysmorphism. This syndrome is also called Eagle-Barrett syndrome and triad syndrome. Prune-belly syndrome occurs almost exclusively in males, with only occasional female involvement being recorded (60). The condition is of unknown cause. One theory suggests that there is a mesenchymal insult to the fetus at about 6 weeks gestation that produces deficient abdominal muscular development. A second theory suggests that the problem may be secondary to chronic intrauterine abdominal distention and pressure atrophy of the abdominal muscles (61). There appear to be two groups of patients. The first group has an obstructing lesion of the urethra (urethral atresia or posterior urethral valves) that leads to death soon after birth. The second group presents with a functional abnormality of bladder emptying but no urethral obstruction and usually survives the neonatal period, developing chronic urinary tract disease. The first group is less numerous than the second group. A variety of skeletal, gastrointestinal, cardiac, and pulmonary anomalies are occasionally associated with prune-belly syndrome (62). The bladder is often enlarged and elongated but lacks trabeculation. The wall of the bladder is thickened by replacement of normal smooth muscle with connective tissue. A similar process involving the ureters produces ureteral dilatation, although ureteral dilatation may be secondary to VUR, which is present in approximately 85% of cases (59,62).
At US, dilated and tortuous ureters with bilateral hydronephrosis are common findings, and kidneys usually show varying degrees of dysplasia and, sometimes, cystic changes. VCUG is used to demonstrate a large, elongated bladder with an irregular contour and bilateral VUR (Fig 14). A urachal diverticulum is frequently present. During voiding, the prostatic urethra typically dilates, tapering down to the membranous urethra, and there is occasionally evidence of a small, opacified prostatic utricle (59).
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Figure 14a. Prune-belly syndrome. (a, b) IVU (a) and VCUG (b) images show the characteristic large floppy bladder () and marked bilateral hydronephrosis and hydroureter (u) with renal parenchymal wasting. Note the anomalies in the pelvic bones and both femurs due to renal osteodystrophy in b. (c) Clinical photograph obtained in a different patient shows a large, floppy abdomen due to congenital deficiency of the abdominal wall musculature.
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Figure 14b. Prune-belly syndrome. (a, b) IVU (a) and VCUG (b) images show the characteristic large floppy bladder () and marked bilateral hydronephrosis and hydroureter (u) with renal parenchymal wasting. Note the anomalies in the pelvic bones and both femurs due to renal osteodystrophy in b. (c) Clinical photograph obtained in a different patient shows a large, floppy abdomen due to congenital deficiency of the abdominal wall musculature.
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Figure 14c. Prune-belly syndrome. (a, b) IVU (a) and VCUG (b) images show the characteristic large floppy bladder () and marked bilateral hydronephrosis and hydroureter (u) with renal parenchymal wasting. Note the anomalies in the pelvic bones and both femurs due to renal osteodystrophy in b. (c) Clinical photograph obtained in a different patient shows a large, floppy abdomen due to congenital deficiency of the abdominal wall musculature.
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Cloacal Malformation
The urinary, genital, and distal gastrointestinal tracts empty into a common channel called the cloaca in the 3- to 5-week-old embryo (63). The confluence of the allantois and hindgut in this common chamber is a widely accepted stage in embryonic development. The cloaca is covered by a membrane that occupies the space between the tail and the body stalk and is not opened externally at this stage of development (64). By the 6th gestational week, the cloaca is segregated into an anterior urogenital sinus and a posterior intestinal canal by the cranial-to-caudal descent of the urorectal septum. This descent is accompanied by migration of the lateral folds of the cloaca toward the midline. The urorectal septum, a wedge of mesoderm, normally extends to the cloacal membrane by the 7th week. The caudal extension of the urorectal septum develops into the perineal body, dividing the perineum into the urogenital triangle ventrally and the anal triangle dorsally. In the male, the inner and outer genital ridges fuse to form the anterior urethra. In the female, these ridges do not coalesce, and so develop into the labia minora and majora. The urogenital sinus is divided into three parts: a cranial vesical part that is continuous with the allantois, a middle pelvic part, and a caudal phallic part that is closed externally by the urogenital membrane (4,64). Arrest of division of the cloaca by the urorectal septum at varied times between the 4th and 12th weeks of gestation leads to the wide spectrum of anorectal malformations. The intimate association of the embryologic development of the anorectal, genital, and urinary systems also explains the frequency with which simultaneous associated malformations in these systems are encountered (65).
Cloacal malformation represents persistence of an early embryonic state in which the urinary, genital, and gastrointestinal tracts all drain through a common perineal opening. This anomaly is believed to result from failure of the urorectal septum to join the cloacal membrane during the 4th to 6th week of embryonic life (52). This rare anomaly occurs only in phenotypic girls (66). The perineum of the typical patient has a single opening that serves as the outlet for urine, genital secretions, and feces or meconium, and the abdominal wall is normal (Fig 15) (67). Lower urinary tract abnormalities, genital abnormalities, and abnormalities of the bony pelvis and lower spinal cord are common associated findings. Contrast material–enhanced studies of the cloaca and the distal end of the colostomy with fluoroscopy in various projections are essential for diagnosis. US is valuable for imaging the kidneys, and MR imaging is very useful in evaluating anomalies of the lower spinal cord (67).
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Figure 15a. Cloacal malformation. (a) Lateral VCUG image obtained after contrast material injection through a single perineal orifice demonstrates opacification and connectedness of the sigmoid colon (S), vagina (V), and bladder (B). (b) Clinical photograph shows the single perineal orifice.
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Figure 15b. Cloacal malformation. (a) Lateral VCUG image obtained after contrast material injection through a single perineal orifice demonstrates opacification and connectedness of the sigmoid colon (S), vagina (V), and bladder (B). (b) Clinical photograph shows the single perineal orifice.
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Cloacal malformation must be differentiated from cloacal exstrophy. Although both of these anomalies contain the word cloaca, which is Latin for "sewer," they differ greatly in their embryogenesis and clinical features. Exstrophy of the cloaca is seen in both boys and girls and involves a failure of the lower abdominal wall to close. Superficially, the anomaly resembles exstrophy of the bladder, but the defect is larger. As presently understood, cloacal exstrophy results from a migration failure of the lateral mesodermal folds of the infraumbilical anterior abdominal wall and rupture of the resulting enlarged, persistent cloacal membrane before the 8th week of gestation (68).
Urogenital sinus is the persistence of an embryonic state in which the urinary and genital tracts drain through a common perineal opening but the gastrointestinal tract drains separately. In this anomaly, there are two perineal orifices: the anterior orifice for the bladder and vagina, and the posterior anal orifice (Fig 16). Like cloacal malformation, this anomaly occurs only in phenotypic girls.
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Figure 16a. Persistent urogenital sinus. (a) VCUG image through the anterior perineal orifice shows the bladder (B) and vagina (V). The rectum (r) is located posteriorly and drains through a normally placed anus. (b) Transverse US image obtained after filling the bladder with saline solution shows a dilated vagina (V) located behind the bladder (). (c) Endoscopic image through the anterior perineal orifice shows communication between the bladder opening (B) and the vaginal opening (V).
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Figure 16b. Persistent urogenital sinus. (a) VCUG image through the anterior perineal orifice shows the bladder (B) and vagina (V). The rectum (r) is located posteriorly and drains through a normally placed anus. (b) Transverse US image obtained after filling the bladder with saline solution shows a dilated vagina (V) located behind the bladder (). (c) Endoscopic image through the anterior perineal orifice shows communication between the bladder opening (B) and the vaginal opening (V).
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Figure 16c. Persistent urogenital sinus. (a) VCUG image through the anterior perineal orifice shows the bladder (B) and vagina (V). The rectum (r) is located posteriorly and drains through a normally placed anus. (b) Transverse US image obtained after filling the bladder with saline solution shows a dilated vagina (V) located behind the bladder (). (c) Endoscopic image through the anterior perineal orifice shows communication between the bladder opening (B) and the vaginal opening (V).
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Anomalies of the Urethra
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Posterior Urethral Valves
Posterior urethral valves are by far the most common congenital obstructive lesion of the urethra, occurring only in phenotypic boys. Young (69) initially classified posterior urethral valves into three types, but it is now clear that there is only one type (formerly called type I). Posterior urethral valves result from the formation of a thick, valvelike membrane from tissue of wolffian duct origin that courses obliquely from the verumontanum to the most distal portion of the prostatic urethra. In essence, the valve is a diaphragm, but because it is more rigid along its line of fusion, progressive distention during voiding causes it to become bilobed or saillike (70). The Young type III valve is a congenital, disklike membrane that is oriented across the urethral lumen at the level of the membranous urethra. An orifice of variable size is typically located centrally.
VCUG is the best imaging technique for the diagnosis of posterior urethral valves (Fig 17). Radiologic findings include dilatation and elongation of the posterior urethra and, occasionally, a linear radiolucent band corresponding to the valve (71). The bladder neck becomes hypertrophic and appears narrow in relation to the dilated posterior urethra. Any cause of bladder outlet obstruction such as posterior urethral valves will cause bladder trabeculation or wall thickening (Fig 17). VUR with gross hydronephrosis, dysplastic kidneys, and urine ascites are common findings (71). VUR occurs in 50% of patients. Bladder trabeculation, hypertrophy, and diverticula are also demonstrated at VCUG (70,71).
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Figure 17a. Posterior urethral valve. (a) VCUG image shows the typical distention of the posterior urethra and abrupt change in caliber in the region of the external sphincter (arrow) at the junction of the posterior and anterior urethra. Note also the bladder wall thickening and trabeculation. (b) Transverse US image through the bladder shows significant thickening of the bladder wall (arrows).
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Figure 17b. Posterior urethral valve. (a) VCUG image shows the typical distention of the posterior urethra and abrupt change in caliber in the region of the external sphincter (arrow) at the junction of the posterior and anterior urethra. Note also the bladder wall thickening and trabeculation. (b) Transverse US image through the bladder shows significant thickening of the bladder wall (arrows).
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Prenatal US is actually the usual method of detecting posterior urethral valves (72). Abnormalities are most evident when the valves are severely obstructing and may include oligohydramnios, bladder distention, and, occasionally, fetal ascites (72). Both prenatal and postnatal US usually show bilateral hydroureteronephrosis with parenchymal thinning and a thick-walled bladder (73). At postnatal US, careful examination of the posterior urethra with a perineal approach may demonstrate a dilated prostatic urethra (72,73). Occasionally, parenchymal cysts or increased echogenicity of the kidneys is noted secondary to associated cystic renal dysplasia. Other findings include urinary ascites and subcapsular or perirenal urinomas (71,74).
Anterior Urethral Valves
Anterior urethral valves are rare congenital anomalies that cause lower urinary tract obstruction in children. They can occur as an isolated entity or in association with a proximal diverticulum; in either case, they probably represent a spectrum of disease (75). The embryologic development of anterior urethral valves remains unclear. Various proposed etiologic mechanisms include an abortive attempt at urethral duplication (76), failure of alignment between the proximal and distal urethra, imbalanced tissue growth in the developing urethra resulting in a remnant of excess tissue acting as a valve, and congenital cystic dilatation of periurethral glands resulting in a flaplike valve (77). Anterior urethral valves may be found anywhere in the anterior urethra. Forty percent of the valves are located in the bulbar urethra, 30% at the penoscrotal junction, and 30% in the pendulous urethra (78). The clinical manifestation of anterior urethral valves is highly variable and depends on patient age and degree of obstruction. It may range from severe obstruction with bilateral severe hydroureteronephrosis, end-stage renal disease (78), and even bladder rupture to minimal obstruction (79). VCUG is the diagnostic modality of choice for anterior urethral valves. Typically, the urethra appears dilated proximal to the valve and narrowed distal to it (Fig 18). A valve may appear as a linear filling defect along the ventral wall, or it may be indicated by a dilated urethra ending in a smooth bulge or an abrupt change in the caliber of the dilated urethra (79). In addition to demonstrating a lesion in the urethra, VCUG may also reveal an associated anomaly. VUR has been reported in one-third of cases and upper tract deterioration in one-half (78,79). Endoscopic examination of the urethra usually helps confirm the diagnosis.
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Figure 18. Anterior urethral valve. VCUG image shows urethral dilatation proximal to an anterior urethral valve (arrow) and narrowing distal to it. Note the abrupt change in the caliber of the urethra below the valve.
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Urethral Duplication
Duplication of the urethra (accessory urethra) is a rare anomaly. In the vast majority of cases, it occurs in the coronal plane; however, collateral (side-by-side) duplication in the absence of bladder duplication also exists (80). The embryologic development of urethral duplication is vague because there are probably different provocations for the various types of anomalies. There appears to be a misalignment of sorts between the termination of the cloacal membrane and its relationship with the developing genital tubercle and urogenital sinus. It appears that in almost every instance, however, the ventral urethra is the most normal-caliber portion of the urethra. The most complete classification scheme for urethral duplication has been offered by Effmann et al (Table 2) (81). This classification scheme can be applied to either dorsal or ventral duplications (82). A perineal or rectal fistula (Y-type fistula) associated with a stenotic, normally located penile urethra is placed in the IIa category. This Y-type fistula usually originates from the prostatic urethra and is commonly associated with stenosis of the anterior portion of the normally situated urethra (83). If the two channels join above the sphincter, there is no incontinence and the lesion is usually discovered incidentally. When the ectopic channel communicates directly with the bladder, the child often presents with wetting. Infection in the partially stenotic orifice is sometimes the presenting symptom. A proper clinical examination, VCUG, and urethrocystoscopy will provide a complete picture of the altered anatomy (Figs 19 –21) (80,83). An effort to determine the length of the defect should be made with retrograde urethrography, which may require two catheters in some patients. For urethras that are complete, standard VCUG may be diagnostic by demonstrating the two urethral channels (Figs 20, 21). Urethral duplication in girls is exceptional and is usually associated with other caudal anomalies or bladder duplication (Fig 21) (84).
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Figure 19. Incomplete urethral duplication. VCUG image shows two different urethral channels (1, 2) arising from two different bladder orifices (arrows). In the midurethra, the two channels join to form a single anterior urethra.
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Figure 20a. Complete urethral duplication. (a) VCUG image obtained in a 6-month-old boy shows two complete urethral channels. The duplicate urethra (arrowheads) is located in the dorsal surface of the penis. The ventral urethra () is normal. (b) Clinical photograph obtained in a 13-year-old boy during voiding shows complete urethral duplication.
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Figure 20b. Complete urethral duplication. (a) VCUG image obtained in a 6-month-old boy shows two complete urethral channels. The duplicate urethra (arrowheads) is located in the dorsal surface of the penis. The ventral urethra () is normal. (b) Clinical photograph obtained in a 13-year-old boy during voiding shows complete urethral duplication.
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Figure 21. Complete urethral duplication in a 2-week-old girl. VCUG image shows two complete urethral channels: the normal channel (arrows) and the duplicate channel (arrowheads). Note the coexisting VUR. U = ureter. This anomaly is extremely rare in females.
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Urethral Diverticula
Anterior urethral diverticulum, although uncommon, is the second most common cause of congenital urethral obstruction in boys (85). A diverticulum of the anterior urethra develops on the ventral surface of the penile urethra as a result of either incomplete development of the corpus spongiosum focally or incomplete fusion of a segment of the urethral plate (86). A lip of tissue may be seen around the diverticulum. As the diverticulum distends, the lip of tissue is pressed against the urethral wall and results in a valvelike obstruction (57). Congenital urethral diverticula have a wide spectrum of clinical manifestations, although most children are diagnosed in infancy with dribbling-type micturation or infection. The dribbling may be due to emptying of the diverticulum or to overflow incontinence. If the obstruction is distal, ballooning of the urethra may occur with voiding (85). VCUG is the key to diagnosis. During VCUG, the typical saccular diverticulum of the anterior urethra fills with contrast material and appears as an oval structure on the ventral aspect of the anterior urethra (Fig 22) (87).
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Figure 22. Syringocele. VCUG image shows an oval structure on the ventral aspect of the anterior urethra (arrowheads), a finding that represents tubular dilatation of the Cowper gland.
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An uncommon diverticulum occurs with retention cysts of the Cowper ducts. The Cowper glands are paired paraurethral glands located in the urogenital diaphragm near the bulbous urethra. They are involved in the immune defense of the genitourinary tract, play a role in infertility, and secrete many glycoproteins (88). They can be visualized as a ductlike structure parallel to the urethra, sometimes associated with opacification of the gland at IVU. This finding can be differentiated from a fistula, contrast material extravasation, urethral duplication, or artifact by the course parallel to the urethra and the position of the orifice (88). A retention cyst of a Cowper gland is seen as a filling defect on the floor of the bulbous urethra during VCUG. The cyst can erode into the bulbous urethra, either spontaneously or after surgery, leading to filling of the cyst during voiding and a resulting diverticulum. Tubular or cystic dilatation of the Cowper gland duct has been called a syringocele (Fig 22) (89).
The prostatic utricle is a short, blind-ending pouch located on the verumontanum (ie, the floor of the prostatic urethra) that represents a mesodermal remnant of the Müller tubercle formed by the fused, paired distal müllerian ducts (1). In males, the müllerian ducts regress under the influence of müllerian inhibiting factor produced by the fetal testis, leaving the prostatic utricle as a vestige. Because regression of the utricle is androgen mediated, utricular cysts are found with increased frequency in boys with other disorders, such as hypospadias or prune-belly syndrome (4). An opacified prostatic utricle is usually well demonstrated at lateral VCUG, appearing as a posterior urethral diverticulum (Fig 23). Occasionally, urethral diverticula may be gigantic (Fig 23b).
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Figure 23a. Prostatic utricle. (a) VCUG image shows a diverticulum () resulting from spontaneous opacification of a prostatic utricle. (b) VCUG image depicts a large prostatic utricle manifesting as a diverticulum (D) that arises from the posterior wall of the urethra.
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Figure 23b. Prostatic utricle. (a) VCUG image shows a diverticulum () resulting from spontaneous opacification of a prostatic utricle. (b) VCUG image depicts a large prostatic utricle manifesting as a diverticulum (D) that arises from the posterior wall of the urethra.
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Megalourethra
Megalourethra is a rare congenital disorder. The scaphoid type is due to poor development of the corpus spongiosum, whereas in the more severe fusiform variety the corpora cavernosa are also affected (90). In the milder form, which involves only the urethra and corpus spongiosum, the urethra dilates in a scaphoid (boat-shaped) fashion during voiding because the dorsal aspect is supported by the intact corpora cavernosa (Fig 24) (90).
Fusiform megalourethra is characterized by a long, dilated, floppy urethra that results from a congenital deficiency of the corpora cavernosa (91). The condition is extremely uncommon and is usually associated with other life-threatening congenital anomalies (eg, lower urinary tract duplication, prune-belly syndrome, urethral fistula). Less than 20 cases of fusiform megalourethra have been reported in the English radiology literature (91). VCUG allows visualization of the dilated urethra (Fig 25).
Urethral Fistula
Imperforate anus is the most common abnormality of the anorectal segment and occurs when the terminal bowel fails to descend normally, resulting in a lack of communication with the anus. As a result, the bowel may open via a fistula at an abnormal location (92). Boys with high imperforate anus frequently have a connection from the rectum to the lower urinary tract, usually at the level of the prostatic urethra, although more distal and proximal communications occasionally occur (93). The fistula is well demonstrated with VCUG (Fig 26).
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Figure 26. Urethral fistula in a neonate with a high imperforate anus. VCUG image demonstrates a fistula between the posterior urethra and the rectum (arrow). An associated dysraphic spine is also noted.
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Congenital Urethral Stricture
A true congenital urethral stricture is limited to a localized narrowing at the junction of the posterior and anterior urethra. Less frequently, it can be located below the bladder neck. Other types of congenital stenosis are rare and may occur at any level of the penile and bulbous urethra (94). Segmental urethral stenosis or complete atresia is rarely seen. Findings above the stenotic segment are similar to those of posterior urethral valves and include wall bladder thickening, hydronephrosis, and renal dysplasia. VCUG demonstrates the stenotic segment and the associated alterations (Fig 27) (94).
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Figure 27. Congenital urethral stenosis. VCUG image shows a narrowed segment in the posterior urethra near the bladder neck (arrow). High-grade VUR is also seen. = bladder, u = ureters.
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Conclusions
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Radiologic investigation continues to be one of the most important sources of clinical information in the evaluation of lower urinary tract disorders. The role of diagnostic imaging is to help determine as closely as possible the exact nature of the abnormality, but the need for radiologic examinations should be carefully weighed to avoid inconveniencing the patient, exposing the patient to unnecessary radiation, or delaying surgical correction.
When an infant or child is suspected of having an underlying urologic structural anomaly, screening US is commonly the initial diagnostic study. The results of this study guide the selection of subsequent imaging modalities. The evaluation of an infant with prenatally diagnosed hydroureteronephrosis includes renal and bladder US. If dilatation of the urinary tract is confirmed, VCUG is performed to determine the presence of VUR and other causes of upper tract dilatation (eg, posterior urethral valves, neuropathic bladder). If VUR is confirmed, follow-up with nuclear cystography or echo-enhanced cystosonography may be performed. If VUR is excluded, nuclear diuresis renography is the primary test for differentiating between obstructed and nonobstructed megaureter.
The indications for and use of IVU have decreased steadily over the past 10 years because of the increased availability of US and isotope imaging. IVU can be used to specifically identify an area of obstruction and to determine whether the patient has duplex collecting systems and a ureterocele. Bladder and urethral anomalies are usually well depicted at VCUG. CT and MR imaging are unsuitable for general screening but provide superb anatomic detail and added diagnostic specificity. They are especially useful in the evaluation of complex anomalies affecting multiple pelvic organs. MR imaging is mandatory in the evaluation of associated anomalies of the spine. MR urography plays an expanding role in displaying dilated collecting systems, ectopic ureters, and ureteroceles and has an advantage over US and IVU in that it can demonstrate ectopic extravesical ureteric insertions, thereby providing a global view of the malformation.
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Footnotes
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Abbreviations: IVU = intravenous urography,
VCUG = voiding cystourethrography,
VUR = vesicoureteral reflux
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References
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Abstract
LEARNING OBJECTIVES FOR TEST...
