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Pediatric Presacral Masses¹

¹ From the Department of Radiology, Gulhane Military Medical School, Ankara, Turkey (M.K.); and Division of Pediatric Radiology, Department of Radiology, 1905 McGovern-Davison Children’s Health Center, Box 3808, Duke University Medical Center, Erwin Rd, Durham, NC 27710 (D.P.F.). Presented as an education exhibit at the 2004 RSNA Annual Meeting. Received April 25, 2005; revision requested May 26 and received July 20; accepted July 29. Both authors have no financial relationships to disclose. Address correspondence to D.P.F. (e-mail: frush943{at}mc.duke.edu).

	Abstract

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Congenital and Developmental... Neurogenic Masses Inflammatory Masses Mesenchymal Masses Lymphomatous Masses Sacral Masses with Presacral... Other Masses Conclusions References

 
Various types of masses may affect the presacral area in children. A presacral mass may be congenital or developmental or may arise from inflammation. The mass may have neural, vascular, lymphatic, or mesenchymal origins and may be primary (as in focal disease) or systemic (as in multifocal disease). Because the clinical manifestations of presacral masses are often nonspecific, imaging plays an important role in the detection and differentiation of these masses. Information obtained from imaging is also critical for management, especially for surgical planning. For these reasons, it is important that radiologists be familiar with the anatomy of the presacral region and with the imaging features of the various lesions that may occur in this region in children. For the accurate interpretation of findings, radiologists also must know the specific advantages and limitations of each of the imaging modalities used to evaluate this category of abnormalities.

© RSNA, 2006

	LEARNING OBJECTIVES FOR TEST 5

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Congenital and Developmental... Neurogenic Masses Inflammatory Masses Mesenchymal Masses Lymphomatous Masses Sacral Masses with Presacral... Other Masses Conclusions References

 
After reading this article and taking the test, the reader will be able to:

• Describe the clinical manifestations and the frequency of occurrence of lesions in the presacral region in children.
  
• Recognize the imaging characteristics of pediatric presacral masses.
  
• Develop imaging algorithms for evaluation of pediatric presacral masses.
  

	Introduction

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Congenital and Developmental... Neurogenic Masses Inflammatory Masses Mesenchymal Masses Lymphomatous Masses Sacral Masses with Presacral... Other Masses Conclusions References

 
The presacral or retrorectal space is located between the rectum and the sacrococcygeal part of the spine. In embryologic development, the remodeling and regression of the neuroectoderm, notochord, hindgut, and proctoderm help to define this space. The levator ani and coccygeus muscles form the inferior boundary, peritoneal reflections define the superior boundary, and the ureters and iliac vessels define the lateral borders of this space. The presacral space contains a variety of tissues, including fat, mesenchymal tissue, lymph nodes, nerve plexuses, and vessels (1,2). Hence, a variety of tumoral lesions may affect this area (Table).

Imaging is often pivotal for the detection of a presacral mass and the demonstration of its extension to or involvement of neighboring organs and tissues. In addition, certain imaging features can provide important and sometimes definitive clues for the classification of a mass. Because of the complexity of the anatomy in this region, the results of conventional radiography and gastrointestinal and urinary contrast material–enhanced studies are usually unsatisfactory. Instead, ultrasonography (US), computed tomography (CT), and magnetic resonance (MR) imaging are usually performed, alone or in combination (2,3,6), to obtain superior anatomic delineation and improved depiction of various tissue types (eg, fat, fluid) in pediatric presacral masses.

	Congenital and Developmental Masses

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Congenital and Developmental... Neurogenic Masses Inflammatory Masses Mesenchymal Masses Lymphomatous Masses Sacral Masses with Presacral... Other Masses Conclusions References

 
Sacrococcygeal Germ Cell Tumors
Sacrococcygeal germ cell tumors are secondary to the disorganization of some of the totipotent primitive neural cells during embryogenesis. Various benign and malignant germ cell tumors may occur, depending on the degree of differentiation of these cells. Teratoma and teratocarcinoma result from the differentiation of totipotent cells along an embryonic pathway. The stem cells also may progress along an extraembryonic pathway and produce a yolk sac tumor (ie, endodermal sinus tumor) or carcinoma. Embryonal carcinoma results from undifferentiated totipotent cells.

Sacrococcygeal teratoma is the most common presacral germ cell tumor in children and the most common solid tumor in neonates (7–9). The prevalence of the benign form of sacrococcygeal teratoma is approximately one in 35,000–40,000 births. The benign form accounts for 60% of all sacrococcygeal teratomas (7–9). The other germinomatous and nongerminomatous germ cell tumors of the presacral region are extremely rare (10). The majority (60%) of non–central nervous system teratomas originate in the sacrococcygeal region, followed by the ovaries and testicles (30%), the mediastinum (5%), and the retroperitoneum (4%) (6).

Most sacrococcygeal teratomas manifest as presacral or pelvic masses that are palpable at rectal examination. The masses also may extend into the abdomen. The most commonly used system for classification of sacrococcygeal masses comprises four groups: type I, predominantly external masses with a small presacral component; type II, external masses with a significant intrapelvic component; type III, external masses with a pelvic and abdominal component; and type IV, internal masses with an intrapelvic and abdominal location (9) (Fig 1). About 50% of sacrococcygeal teratomas are type I lesions. Approximately 50%–70% of sacrococcygeal teratomas are manifested within the first few days of life, and 80% are diagnosed before the age of 6 months. Less than 10% are diagnosed after the age of 2 years. This older age at the time of diagnosis is associated with an increased prevalence of malignancy (7); therefore, early diagnosis and surgical intervention are important (6,9,12). Seventy-five percent of children with sacrococcygeal germ cell tumors are female; however, malignant sacrococcygeal teratomas are equally distributed between the sexes (8,9). The diagnosis of type IV germ cell tumors is usually delayed, and this type is the most likely to be malignant (38% of lesions), although tumors of the other three types also may be malignant (6,13–16).

View larger version (43K): [in this window] [in a new window] [Download PPT slide]   Figure 1.  Schema shows the Altman classification system for sacrococcygeal teratomas. Type I (A, left) and type II (A, right) teratomas have predominant extrapelvic components. Type III (B, left) and type IV (B, right) teratomas have a primarily intrapelvic location. Types II and III resemble a dumbbell. (Reprinted, with permission, from reference 11.)

The imaging characteristics of these tumors depend on their contents. Benign teratomas contain only mature tissues, including fluid, fat, calcification, and a small amount of soft tissue; tumors that are predominantly cystic are likely to be benign (19). The presence of a large amount of immature tissue in a teratoma is suggestive of malignant potential and the possibility of local recurrence (6). In some cases, conventional radiographs of the sacral region may show calcification. Contrast-enhanced examination of the colon demonstrates displacement of the intestines by a retrorectal mass.

Cystic components typically appear as anechoic areas on US images, but they may demonstrate internal areas of echogenicity due to fat or debris. Although US images may depict both fetal and postnatal presacral masses, the information derived from US is not sufficient for surgical planning. CT and MR imaging are both reasonable alternatives. The superior depiction of soft tissue (including small areas of fat) and of bone that is afforded by MR imaging makes this the preferred modality both for initial diagnosis and for surveillance for local recurrence.

Benign teratomas are predominantly cystic; have attenuation similar to that of fluid on CT scans; and may include bone, fat, and calcification (Figs 2, 3). Cystic areas typically have the appearance of fluid on T1-weighted and T2-weighted MR images (Fig 4). Areas of fatty tissue demonstrate high signal intensity on T1-weighted images (Fig 5), while calcification and bone are depicted as areas of signal void. The coccyx is always involved, even in benign sacrococcygeal teratoma, and must be resected with the tumor (Fig 5) (6,13–15). Malignant teratomas have a predominant solid component (Fig 5), and hemorrhage and necrosis are common. Approximately 50% of benign teratomas contain calcification, whereas this feature is seldom observed in malignant tumors. Malignant teratomas may metastasize (Fig 6) or extend into adjacent structures such as the spine or gluteal muscle. Such extension is also best depicted with MR imaging. In summary, a predominant cystic component, fat, and calcification are features of a mature benign sacrococcygeal teratoma, whereas the predominant solidity of a germ cell tumor is suggestive of malignancy.

View larger version (121K): [in this window] [in a new window] [Download PPT slide]   Figure 2a.  Mature (benign) sacrococcygeal teratoma in an 11-day-old girl with a perineal mass. (a) Frontal pelvic radiograph reveals ischiopubic separation due to a presacral mass. (b) Axial unenhanced CT scan through the upper portion of the lesion shows attenuation similar to that of water, a finding indicative of a predominant cystic component. (Reprinted, with permission, from reference 6.)

View larger version (119K): [in this window] [in a new window] [Download PPT slide]   Figure 2b.  Mature (benign) sacrococcygeal teratoma in an 11-day-old girl with a perineal mass. (a) Frontal pelvic radiograph reveals ischiopubic separation due to a presacral mass. (b) Axial unenhanced CT scan through the upper portion of the lesion shows attenuation similar to that of water, a finding indicative of a predominant cystic component. (Reprinted, with permission, from reference 6.)

View larger version (149K): [in this window] [in a new window] [Download PPT slide]   Figure 3.  Benign sacrococcygeal teratoma in an infant boy. Axial unenhanced CT scan at the level of the coccyx shows a presacral mass with multilocular cystic (C) and solid (S) components. The rectosigmoid (R) segment of the colon is displaced anteriorly.

View larger version (151K): [in this window] [in a new window] [Download PPT slide]   Figure 4a.  Recurrent sacrococcygeal teratoma in a 2-year-old girl. Axial T1-weighted (repetition time msec/echo time msec, 600/17) spin-echo MR image (a) and axial T2-weighted (5500/132) fat-saturated turbo spin-echo image (b) show two well-defined round cystic masses with predominantly intermediate signal intensity in a and high signal intensity in b. High-signal-intensity areas in a represent fat. The rectum (R) was displaced anterolaterally. The coccyx previously was removed.

View larger version (159K): [in this window] [in a new window] [Download PPT slide]   Figure 4b.  Recurrent sacrococcygeal teratoma in a 2-year-old girl. Axial T1-weighted (repetition time msec/echo time msec, 600/17) spin-echo MR image (a) and axial T2-weighted (5500/132) fat-saturated turbo spin-echo image (b) show two well-defined round cystic masses with predominantly intermediate signal intensity in a and high signal intensity in b. High-signal-intensity areas in a represent fat. The rectum (R) was displaced anterolaterally. The coccyx previously was removed.

View larger version (149K): [in this window] [in a new window] [Download PPT slide]   Figure 5a.  Malignant sacrococcygeal teratoma with an abdominopelvic component in an 18-month-old girl. Sagittal MR images show a midline region of fat with high signal intensity on the T1-weighted image (arrows in a) and intermediate to low signal intensity on the T2-weighted fat-saturated image (b). Also visible are involvement of the distal sacrum and coccyx (arrowheads in b), anterior displacement of the vagina and uterus (arrows in b), and superior and anterior displacement of the bladder (B). (Reprinted, with permission, from reference 6.)

View larger version (139K): [in this window] [in a new window] [Download PPT slide]   Figure 5b.  Malignant sacrococcygeal teratoma with an abdominopelvic component in an 18-month-old girl. Sagittal MR images show a midline region of fat with high signal intensity on the T1-weighted image (arrows in a) and intermediate to low signal intensity on the T2-weighted fat-saturated image (b). Also visible are involvement of the distal sacrum and coccyx (arrowheads in b), anterior displacement of the vagina and uterus (arrows in b), and superior and anterior displacement of the bladder (B). (Reprinted, with permission, from reference 6.)

View larger version (140K): [in this window] [in a new window] [Download PPT slide]   Figure 6a.  Malignant sacrococcygeal teratoma in a 2-year-old girl. (a, b) Axial unenhanced T1-weighted (540/12) MR image (a) and axial T2-weighted (4333/99) fat-saturated turbo spin-echo image (b) at the level of the pelvis demonstrate a well-defined lobular cystic mass with multiple septa that has displaced the rectum (R), uterus (U), and bladder (B) anteriorly. The images also show a subcutaneous left inguinal soft-tissue mass (arrow). (c) Axial T1-weighted fat-saturated image obtained with intravenous contrast material shows contrast enhancement of the septa and rim of the cystic mass and the left inguinal soft-tissue mass (arrow). The latter was diagnosed as metastatic adenopathy.

View larger version (130K): [in this window] [in a new window] [Download PPT slide]   Figure 6b.  Malignant sacrococcygeal teratoma in a 2-year-old girl. (a, b) Axial unenhanced T1-weighted (540/12) MR image (a) and axial T2-weighted (4333/99) fat-saturated turbo spin-echo image (b) at the level of the pelvis demonstrate a well-defined lobular cystic mass with multiple septa that has displaced the rectum (R), uterus (U), and bladder (B) anteriorly. The images also show a subcutaneous left inguinal soft-tissue mass (arrow). (c) Axial T1-weighted fat-saturated image obtained with intravenous contrast material shows contrast enhancement of the septa and rim of the cystic mass and the left inguinal soft-tissue mass (arrow). The latter was diagnosed as metastatic adenopathy.

View larger version (159K): [in this window] [in a new window] [Download PPT slide]   Figure 6c.  Malignant sacrococcygeal teratoma in a 2-year-old girl. (a, b) Axial unenhanced T1-weighted (540/12) MR image (a) and axial T2-weighted (4333/99) fat-saturated turbo spin-echo image (b) at the level of the pelvis demonstrate a well-defined lobular cystic mass with multiple septa that has displaced the rectum (R), uterus (U), and bladder (B) anteriorly. The images also show a subcutaneous left inguinal soft-tissue mass (arrow). (c) Axial T1-weighted fat-saturated image obtained with intravenous contrast material shows contrast enhancement of the septa and rim of the cystic mass and the left inguinal soft-tissue mass (arrow). The latter was diagnosed as metastatic adenopathy.

Up to 18% of sacrococcygeal teratomas are associated with other anomalies, including the Currarino triad (6), a syndrome that is discussed in greater detail in the next section.

Anterior Sacral Meningocele
An anterior sacral meningocele is a congenital abnormality that arises from herniation of the cerebrospinal fluid–filled dura mater through a sacral foramen or a defect in the sacral bone. It may be accompanied by symptoms, but it is usually asymptomatic in older children. Eighty percent of anterior meningoceles are manifested in the first decade of life. Anterior sacral meningocele is rare; it occurs in one of 40,000 individuals. When symptoms are present, they are usually due to mass effect, neurologic compromise, meningitis, or rupture of the meningocele (3,6,20). Early recognition of anterior sacral meningoceles may help reduce morbidity and mortality due to meningitis.

An anterior sacral meningocele may include nerve roots, and the visualization of any neural elements within the hernial sac is important for surgical planning. Various osseous defects also may be seen, such as vertebral scalloping, hypoplasia, and aplasia. Scimitar sacrum is highly suggestive of this condition and is easily recognized on conventional radiographs. Pelvic US images may demonstrate a presacral cystic mass but are not sufficient for surgical planning. Osseous abnormalities are better evaluated with CT, which also can depict the neck of the meningocele. However, MR imaging is the modality of choice for the assessment of anterior sacral meningoceles because of its excellent depiction of neural elements, especially with the multiplanar reformatting of image data. Sacral defects, neck, hernial sac, nerve roots (which appear as areas of intermediate signal intensity on T2-weighted images), and dysraphism are best assessed with MR imaging (6,21–23).

An anterior sacral meningocele may be accompanied by other anomalies or syndromes, including uterine, anorectal, renal, and bladder malformations; Marfan syndrome; and type 1 neurofibromatosis. Alternatively, the lesion may occur as an isolated abnormality.

In addition, an anterior sacral meningocele may occur as part of the Currarino triad, also known as ASP triad (anorectal malformation, sacrococcygeal osseous defect, and presacral mass), a rare syndrome characterized by autosomal dominant genetic inheritance in more than 50% of cases. The presacral mass in those affected by this syndrome may be a teratoma, anterior sacral meningocele, dermoid cyst, hamartoma, or enteric duplication cyst, or more than one of these types of masses may be present (21,22) (Fig 7). Incomplete forms of this syndrome exist, especially in relatives of patients with ASP syndrome (20,24,25). In ASP syndrome, meningocele and teratoma are the most common presacral masses. Radiography may demonstrate the sacral anomaly; however, MR imaging is necessary for adequate preoperative evaluation. Large meningoceles may displace bowel gas, and anterior or lateral displacement of the rectum and sigmoid colon may be depicted on images obtained with luminal contrast enhancement. Approximately 80% of cases of ASP syndrome are diagnosed in patients who are younger than 16 years and who typically have symptoms of constipation. Most investigators of this syndrome have suggested that sacral bone abnormalities are an unequivocal finding of ASP triad. However, presacral masses without sacral bone defects have been reported in relatives of patients with ASP syndrome (6,25–27).

View larger version (127K): [in this window] [in a new window] [Download PPT slide]   Figure 7a.  Currarino triad (ASP complex) in a 7-year-old girl with urinary incontinence and a history of anal atresia repair. (a) Pelvic radiograph shows a scimitar sacrum with osseous defect on the right side (arrows). (b) Axial unenhanced CT scan demonstrates a well-defined mass (arrow) with attenuation slightly lower than that of fluid, a feature that represents fatty tissue in a dermoid, and leftward displacement of the rectum. B = bladder. (c) Image from a barium enema study performed after atresia repair also shows the dermoid at the low presacral level and anterior displacement of the rectum (arrow). (Reprinted, with permission, from reference 6.)

View larger version (160K): [in this window] [in a new window] [Download PPT slide]   Figure 7b.  Currarino triad (ASP complex) in a 7-year-old girl with urinary incontinence and a history of anal atresia repair. (a) Pelvic radiograph shows a scimitar sacrum with osseous defect on the right side (arrows). (b) Axial unenhanced CT scan demonstrates a well-defined mass (arrow) with attenuation slightly lower than that of fluid, a feature that represents fatty tissue in a dermoid, and leftward displacement of the rectum. B = bladder. (c) Image from a barium enema study performed after atresia repair also shows the dermoid at the low presacral level and anterior displacement of the rectum (arrow). (Reprinted, with permission, from reference 6.)

View larger version (136K): [in this window] [in a new window] [Download PPT slide]   Figure 7c.  Currarino triad (ASP complex) in a 7-year-old girl with urinary incontinence and a history of anal atresia repair. (a) Pelvic radiograph shows a scimitar sacrum with osseous defect on the right side (arrows). (b) Axial unenhanced CT scan demonstrates a well-defined mass (arrow) with attenuation slightly lower than that of fluid, a feature that represents fatty tissue in a dermoid, and leftward displacement of the rectum. B = bladder. (c) Image from a barium enema study performed after atresia repair also shows the dermoid at the low presacral level and anterior displacement of the rectum (arrow). (Reprinted, with permission, from reference 6.)

Enteric Cysts
Enteric cysts are rare developmental abnormalities that may arise in locations between the rectum and sacrum. They are defined and classified according to their histologic basis as either tailgut cysts (also referred to as retrorectal cystic hamartomas, mucin-secreting cysts, tailgut vestiges, and myoepithelial hamartomas of the rectum) or rectal duplication cysts (30). Although they are frequently asymptomatic, infection, bleeding, and malignant degeneration can occur. To avoid such occurrences, surgical resection of enteric cysts is recommended.

Tailgut cysts are rare congenital abnormalities in the presacral space and may be manifested in childhood or adulthood. The cysts may be uni- or multilocular and are lined with various epithelia, usually in combination. Mucin-secreting cells are responsible for the mucoid contents of the cysts (31). Tailgut cysts, which differ histologically from teratomas and dermoids, are believed to be persistent remnants of embryonic gut that include normal fetal gastrointestinal tract tissue (31,32).

By definition, a rectal duplication cyst is characterized by three histologic criteria: (a) the presence of two layers of smooth muscle, (b) continuity with the rectum, and (c) a mucosal lining that is similar to rectal mucosa and that may contain ectopic tissues, including gastric mucosa, urothelial mucosa, and pancreatic tissue. Unlike rectal duplication cysts, tailgut cysts do not have a smooth muscle layer (31).

Overall, alimentary tract duplications are rare; the most common site is the ileum. A rectal location of duplication is particularly rare (5% of duplications). Rectal duplications generally are cystic and are encountered in the presacral region. Rectal duplication cysts may communicate internally with the anorectal lumen or externally with the skin surface. The most frequent form of duplication is a spherical cystic lesion with a muscular wall and usually with its own mucosa and sub-mucosa (31,33,34).

Enteric cysts may cause a widening of the retrorectal space, an effect that is visible on lateral radiographs. Communication between the cyst and the intestinal lumen may be observed during a barium enema study (Fig 8) (35). US demonstrates uni- or multilocular presacral cystic masses that may contain areas of echogenicity representing mucoid content and inflammatory debris (35,36). US images also may show the bowel signature, areas of hypoechogenicity in the musculature of the cyst wall. On CT scans, the cysts appear as well-defined thin-walled uni- or multilocular presacral lesions with low attenuation and without contrast enhancement. The cyst wall may be thickened as a result of infection (37). MR imaging demonstrates well-marginated thin-walled lesions with low signal intensity on T1-weighted images and high signal intensity on T2-weighted images (Fig 9). Mucoid contents of tail-gut cysts cause them to have high signal intensity on T1-weighted images. Malignant degeneration, if present, appears as asymmetric and irregular wall thickening with heterogeneous contrast enhancement (35).

View larger version (142K): [in this window] [in a new window] [Download PPT slide]   Figure 8.  Rectal duplication cyst in a 6-month-old girl with recurrent infection. Oblique radiograph of the pelvis, obtained during a barium enema examination, demonstrates a well-defined retrorectal tubular communication (arrowheads) with the rectum.

View larger version (144K): [in this window] [in a new window] [Download PPT slide]   Figure 9a.  Tailgut cyst in a 17-year-old boy with rectal fullness. (a) Axial CT scan obtained with oral and intravenous contrast material at the level of the symphysis pubis demonstrates a lobular well-defined fluid-attenuation mass that compresses the barium-filled rectum (R) anterolaterally. (b) Axial T2-weighted (3500/80) fat-saturated MR image shows high signal intensity in the mass. The intermediate attenuation seen in the mass in a reflects its mucoid content. R = rectum.

View larger version (147K): [in this window] [in a new window] [Download PPT slide]   Figure 9b.  Tailgut cyst in a 17-year-old boy with rectal fullness. (a) Axial CT scan obtained with oral and intravenous contrast material at the level of the symphysis pubis demonstrates a lobular well-defined fluid-attenuation mass that compresses the barium-filled rectum (R) anterolaterally. (b) Axial T2-weighted (3500/80) fat-saturated MR image shows high signal intensity in the mass. The intermediate attenuation seen in the mass in a reflects its mucoid content. R = rectum.

Retroperitoneal cystic lymphatic malformations are usually detected incidentally, but they may be complicated by infection, hemorrhage, rupture, or mass effect (40). US images typically show a sharply marginated uni- or multilocular cystic lesion with internally increased echogenicity in the presence of infection or hemorrhage (40). CT scans better demonstrate the anatomic extent of the lesion. On CT scans, cystic lymphatic malformations appear as masses with attenuation similar to that of water and with thin, often contrast-enhanced walls and septa (38,40). MR imaging also can depict the extent of the malformation and is superior to other imaging methods because of its excellent display of soft-tissue contrast information. On MR images, cystic lymphatic malformations appear as areas of homogeneous high signal intensity on T2-weighted images and have the signal intensity of fluid on T1-weighted images (41). A fluid-fluid level can be seen in the setting of acute hemorrhage.

	Neurogenic Masses

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Congenital and Developmental... Neurogenic Masses Inflammatory Masses Mesenchymal Masses Lymphomatous Masses Sacral Masses with Presacral... Other Masses Conclusions References

 
Ganglion Cell or Neuroblastic Tumors
Neuroblastoma, ganglioneuroblastoma, and ganglioneuroma originate from neural crest cells. This lesion group is also referred to as ganglion cell tumors or neuroblastic tumors. The tumors originate along the sympathetic chain, from the neck to the pelvis, as well as in the adrenal medulla (42,43). Primordial neural crest cells may undergo differentiation into mature ganglion or Schwann cells or may remain undifferentiated and immature neuroblastic cells. Neuroblastomas consist of neuroblasts, and mature ganglion cells constitute ganglioneuromas. Ganglioneuroblastoma is composed of both differentiated and undifferentiated tumor cells (43). Ganglioneuroma is considered benign, but neuroblastoma and ganglioneuroblastoma are malignancies and are usually classified together with regard to treatment.

Neuroblastoma.— Neuroblastoma accounts for about 10% of all pediatric cancers and is the most common malignancy in infancy (the 1st year of life). Neuroblastoma is, overall, the fourth most common malignancy in childhood, after leukemia, lymphoma, and central nervous system tumors (44). The median age at diagnosis is 22 months. About 95% of cases are diagnosed within the first decade of life; more than 80% of these are diagnosed at or before 5 years of age. Neuroblastoma can be detected at prenatal US (44,45). Approximately 70% of neuroblastomas and ganglioneuroblastomas are found in the abdomen (adrenal gland and retroperitoneal area), 20% in the posterior mediastinum, 5% in the neck region, and only 2%–3% in the pelvis (46).

The clinical manifestations of neuroblastoma are nonspecific and may include constitutional symptoms such as fever, weight loss, malaise, and failure to thrive. Symptoms secondary to mass effect also are common and may include pain, urinary retention or frequency of evacuation, and constipation. Other symptoms are related to the effects of hormonal secretion, such as diarrhea due to vasoactive intestinal peptides, or opsomyoclonus, a nonmetastatic paraneoplastic condition. In patients with a presacral tumor, the pelvic mass also may be detected during physical examination.

Primary tumor size and status with regard to local invasion and metastasis help to determine the clinical stage (47). Detection and staging of neuroblastoma can be accomplished with CT, MR imaging, and nuclear medicine. Bone scintigraphy with technetium 99m, and skeletal radiography, are used to determine the areas of involvement. Both false-positive and false-negative results of metaiodobenzylguanidine studies have been reported (48,49), but this technique is sufficiently sensitive to have become a mainstay for assessment of the entire body, including the skeletal system.

Radiographic findings are nonspecific and include calcification, which has been observed in 30% of cases. Presacral tumors may extend into the spinal space through the neural foramina and cause erosion and remodeling of bone. In addition, indirect indicators of the presence of a presacral tumor, such as displacement of the bowel or urinary bladder, can be seen radiographically (50). Neuroblastomas may include areas of hemorrhage or necrosis, but they do not contain fat.

Neuroblastomas with hemorrhagic and necrotic contents have a heterogeneous appearance at US. Calcifications are seen as focal or diffuse hyperechoic areas with or without posterior acoustic shadowing (Fig 10). US may or may not demonstrate the origin of the mass. Doppler US may help determine the relation of the mass to regional vessels (50,51). CT demonstrates the location of the tumor, its boundaries, and any extension, including involvement of neural foramina. Calcifications are seen in more than 80% of neuroblastomas at CT (Fig 11). Small tumors are usually homogeneous in appearance. Larger tumors show heterogeneous attenuation because of the presence of hemorrhage and necrosis (Fig 12) (51). Neuroblastoma and ganglioneuroblastoma have heterogeneous signal intensity at MR imaging, with low signal intensity and variable contrast enhancement on T1-weighted images and with high signal intensity on T2-weighted images (Fig 12) (51,52). Hemorrhagic areas may have high signal intensity on T1-weighted images. Cystic and necrotic areas may be seen as hyperintense on T2-weighted images, while areas of calcification are devoid of signal (52). Soft-tissue contrast resolution and marrow information are better with MR imaging than with CT, as is characterization of the primary tumor and any local invasion, including spinal involvement (51).

View larger version (151K): [in this window] [in a new window] [Download PPT slide]   Figure 10a.  Neuroblastoma detected incidentally at US in a 9-week-old girl with a urinary tract infection. (a) Axial US image of the upper pelvis demonstrates a large, well-defined, solid mass that contains a small cystic area (curved arrow); multiple smaller areas of high echogenicity representing calcifications; the right iliac bone (straight arrow); and the sacral vertebrae (arrowhead). (b) Axial CT scan of the pelvis, obtained with intravenous contrast material, demonstrates a well-defined and heterogeneously enhanced presacral mass that contains scattered foci of calcifications. The mass has encroached on the neural foramen (arrow) in the left side and has displaced the rectosigmoid (R) colon segment anterolaterally.

View larger version (118K): [in this window] [in a new window] [Download PPT slide]   Figure 10b.  Neuroblastoma detected incidentally at US in a 9-week-old girl with a urinary tract infection. (a) Axial US image of the upper pelvis demonstrates a large, well-defined, solid mass that contains a small cystic area (curved arrow); multiple smaller areas of high echogenicity representing calcifications; the right iliac bone (straight arrow); and the sacral vertebrae (arrowhead). (b) Axial CT scan of the pelvis, obtained with intravenous contrast material, demonstrates a well-defined and heterogeneously enhanced presacral mass that contains scattered foci of calcifications. The mass has encroached on the neural foramen (arrow) in the left side and has displaced the rectosigmoid (R) colon segment anterolaterally.

View larger version (100K): [in this window] [in a new window] [Download PPT slide]   Figure 11a.  Stage 1 presacral neuroblastoma detected incidentally in a 3-year-old boy at routine physical examination. (a) Axial unenhanced CT scan of the pelvis reveals a low-attenuation presacral mass that has displaced the rectosigmoid (R) colon segment leftward and that contains subtle punctate calcifications (arrows). (b) Axial CT scan obtained with intravenous contrast material shows heterogeneous enhancement in the mass but no pelvic vessel involvement. (Reprinted, with permission, from reference 6.)

View larger version (130K): [in this window] [in a new window] [Download PPT slide]   Figure 11b.  Stage 1 presacral neuroblastoma detected incidentally in a 3-year-old boy at routine physical examination. (a) Axial unenhanced CT scan of the pelvis reveals a low-attenuation presacral mass that has displaced the rectosigmoid (R) colon segment leftward and that contains subtle punctate calcifications (arrows). (b) Axial CT scan obtained with intravenous contrast material shows heterogeneous enhancement in the mass but no pelvic vessel involvement. (Reprinted, with permission, from reference 6.)

View larger version (141K): [in this window] [in a new window] [Download PPT slide]   Figure 12a.  Neuroblastoma in a 2-year-old boy with constipation. (a) Axial pelvic CT scan obtained with intravenous contrast material shows a large mass that contains areas of low attenuation consistent with necrosis. The mass extends to the right S1 vertebral foramen (arrow) and has displaced the rectum to the right side and the bladder (arrowhead) anteriorly. (b) Sagittal T1-weighted MR image of the pelvis demonstrates a large presacral mass that extends to the neural foramen (arrow). The mass has predominant intermediate signal intensity and multiple rimlike areas of high signal intensity (arrowheads) that are presumably due to hemorrhage. (c) Sagittal T2-weighted fat-saturated MR image shows heterogeneous, predominantly high signal intensity in the mass (arrowheads).

View larger version (158K): [in this window] [in a new window] [Download PPT slide]   Figure 12b.  Neuroblastoma in a 2-year-old boy with constipation. (a) Axial pelvic CT scan obtained with intravenous contrast material shows a large mass that contains areas of low attenuation consistent with necrosis. The mass extends to the right S1 vertebral foramen (arrow) and has displaced the rectum to the right side and the bladder (arrowhead) anteriorly. (b) Sagittal T1-weighted MR image of the pelvis demonstrates a large presacral mass that extends to the neural foramen (arrow). The mass has predominant intermediate signal intensity and multiple rimlike areas of high signal intensity (arrowheads) that are presumably due to hemorrhage. (c) Sagittal T2-weighted fat-saturated MR image shows heterogeneous, predominantly high signal intensity in the mass (arrowheads).

View larger version (197K): [in this window] [in a new window] [Download PPT slide]   Figure 12c.  Neuroblastoma in a 2-year-old boy with constipation. (a) Axial pelvic CT scan obtained with intravenous contrast material shows a large mass that contains areas of low attenuation consistent with necrosis. The mass extends to the right S1 vertebral foramen (arrow) and has displaced the rectum to the right side and the bladder (arrowhead) anteriorly. (b) Sagittal T1-weighted MR image of the pelvis demonstrates a large presacral mass that extends to the neural foramen (arrow). The mass has predominant intermediate signal intensity and multiple rimlike areas of high signal intensity (arrowheads) that are presumably due to hemorrhage. (c) Sagittal T2-weighted fat-saturated MR image shows heterogeneous, predominantly high signal intensity in the mass (arrowheads).

The imaging characteristics of ganglioneuroma do not differ consistently from those of neuroblastoma and ganglioneuroblastoma (Fig 13). However, the imaging appearance of a ganglioneuroma tends to be more homogeneous. CT shows calcifications in two-thirds of cases (54,55). As with imaging of neuroblastomas and ganglioneuroblastomas, MR imaging is superior to CT in its depiction of involvement of ganglioneuroma in the spine or neural foramen.

View larger version (151K): [in this window] [in a new window] [Download PPT slide]   Figure 13.  Ganglioneuroma in a 14-year-old boy. Sagittal T2-weighted MR image shows a high-signal-intensity presacral ganglioneuroma that distorts the distal sacrum (arrow) and has displaced the bladder (B) anteriorly.

Neurofibroma.— Neurofibromas may occur singly, or they may occur in multiples as in type 1 neurofibromatosis, a common autosomal dominant disease that affects one person in 2000–4000. Approximately 90% of those affected receive the diagnosis of neurofibroma during childhood. Abdominal involvement in type 1 neurofibromatosis is most likely to affect the retroperitoneal, mesenteric, and paraspinal regions and may be manifested as a large mass (58,59). At CT, a neurofibroma may resemble lymphadenopathy and may have attenuation lower than that of soft tissue (Fig 14). On T1-weighted MR images, the lesion appears as an area with homogeneously isointense or mildly hyperintense signal in comparison with the signal intensity of muscle. On T2-weighted images, the lesion has a targetlike appearance, with a hyperintense rim of myxoid material and a central zone of low signal intensity that indicates a fibrous core (Figs 15, 16). The targetlike MR imaging appearance of a benign neurofibroma is characteristic and helps to differentiate it from a malignant neurofibroma (58,59).

View larger version (142K): [in this window] [in a new window] [Download PPT slide]   Figure 14.  Type 1 neurofibromatosis in a 17-year-old boy. Axial pelvic CT scan obtained with intravenous contrast material shows well-circumscribed bilateral masses with soft-tissue attenuation, anterior to the sacrum, that have compressed the rectosigmoid colon segment and displaced the bladder. Neurofibromas also are visible in the inguinal regions.

View larger version (149K): [in this window] [in a new window] [Download PPT slide]   Figure 15.  Type 1 neurofibromatosis. Axial T2-weighted (4500/120) fat-saturated MR image of the middle pelvis in an 18-year-old male patient shows multiple bilateral target signs indicative of intrapelvic neurofibromas, which extend into the inguinal regions. A subcutaneous lesion also is visible in the left buttock.

View larger version (112K): [in this window] [in a new window] [Download PPT slide]   Figure 16.  Type 1 neurofibromatosis. Axial T2-weighted MR image in an 11-year-old girl with spasticity of the lower extremities shows multiple lesions with the characteristic target sign: a large central region of hypointense signal representing a fibrous core, surrounded by a rim of hyperintense signal indicative of myxoid material. Abnormal soft tissue has filled and expanded the spinal canal. The mass effect of the pelvic lesions has caused lateral displacement of the rectosigmoid (R) colon segment and anterosuperior displacement of the bladder (B).

	Inflammatory Masses

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Conventional radiographs may show intralesional air, including air-fluid levels. At US, abscesses may have complex fluid contents; may appear homogeneously echogenic, mimicking a soft-tissue mass; or may have multiple septa. However, CT is more helpful than radiography or US for the detection and localization of an isolated area of infection in the abdomen or pelvis (Fig 17). The role of radionuclide studies in this application is limited; although an accumulation of radiolabeled leukocytes in an abscess would aid in its detection, scintigraphy is usually reserved for use in whole-body surveys for occult infection undetected on images obtained with other modalities.

View larger version (157K): [in this window] [in a new window] [Download PPT slide]   Figure 17.  Abscess in a 17-year-old girl with fever and pelvic discomfort after bladder augmentation surgery. Axial pelvic CT scan obtained with oral and intravenous contrast material demonstrates multiple fluid collections with peripheral enhancement that represent a postoperative abscess. The rectosigmoid colon segment (arrow) has been displaced laterally. U = uterus.

	Mesenchymal Masses

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Two histologic types account for the majority of pediatric rhabdomyosarcomas: the embryonal type, which includes botryoid and spindle cell variants; and the alveolar or adolescent type (66,67). Pleomorphic, anaplastic, and undifferentiated sarcomas are rarer types. The embryonal type accounts for 80% of all rhabdomyosarcomas (66,67). Rhabdomyosarcoma is one of the small round blue cell tumors that typically are found in children, a group that also includes neuroblastoma, Ewing sarcoma–primitive neuroectodermal tumor (the Ewing sarcoma family of tumors, described later), lymphoma, and desmoplastic small round blue cell tumor.

Imaging findings of rhabdomyosarcoma are, in general, nonspecific (65,67–69). A rational approach to differential diagnosis must integrate the anatomic site of the lesion with the child’s age, clinical and laboratory data, and evidence of local spread or metastatic disease. Characteristics of rhabdomyosarcoma as depicted on radiographs and images from barium studies include a soft-tissue mass with displacement or invasion of normal pelvic structures. US, CT, and MR imaging can be used to accurately characterize the mass; however, CT and MR imaging better depict local extension and metastatic disease, whereas the US features are variable and nonspecific. The solid component of the lesion has been described as heterogeneous in appearance and may include necrosis or hemorrhage (67,68). At CT, pelvic rhabdomyosarcoma is seen as a heterogeneous mass that only very rarely contains calcifications and that shows variable enhancement (Figs 18, 19). Because rhabdomyosarcomas are typically large and extensive at the time of diagnosis, it may be difficult or impossible to determine the site of origin. CT is helpful for detecting inguinal and retroperitoneal lymphadenopathy and lung metastases (65,67,71). MR imaging features are nonspecific, with low signal intensity on T1-weighted images and heterogeneous high signal intensity on T2-weighted images. On contrast-enhanced MR images, rhabdomyosarcoma usually shows heterogeneous enhancement (65,69).

View larger version (113K): [in this window] [in a new window] [Download PPT slide]   Figure 18.  Rhabdomyosarcoma. Axial pelvic CT scan obtained with intravenous contrast material in a 15-year-old boy initially treated for proctitis depicts a presacral mass that has displaced the bladder (B) anteriorly and the rectosigmoid colon segment (arrow) to the left. The mass, which is predominantly necrotic, shows peripheral enhancement and some linear central enhancement. (Reprinted, with permission, from reference 6.)

View larger version (137K): [in this window] [in a new window] [Download PPT slide]   Figure 19.  Rhabdomyosarcoma. Axial pelvic CT scan obtained with oral and intravenous contrast material in an 8-month-old boy demonstrates an infiltrative soft-tissue mass that extends anteriorly, causing deviation of the urinary bladder (B), and posteriorly into both sciatic notch regions. The mass contains punctate calcifications. The spinal canal is abnormally wide and shows increased soft-tissue attenuation (arrow). A bladder catheter (F) also is visible.

View larger version (134K): [in this window] [in a new window] [Download PPT slide]   Figure 20a.  Undifferentiated sarcoma in a 15-year-old girl with intermittent left thigh pain. (a) Sagittal T1-weighted MR image shows a low-signal-intensity presacral soft-tissue mass that has displaced the rectum (R) anteriorly and has infiltrated the upper sacral vertebrae, which have an irregular appearance. Intermediate-signal-intensity soft tissue also is visible in the sacral spinal canal (arrows). (b) Sagittal T2-weighted MR image more clearly depicts involvement of the sacrococcygeal vertebrae (arrow) as well as the spinal canal soft-tissue mass (arrowheads).

View larger version (169K): [in this window] [in a new window] [Download PPT slide]   Figure 20b.  Undifferentiated sarcoma in a 15-year-old girl with intermittent left thigh pain. (a) Sagittal T1-weighted MR image shows a low-signal-intensity presacral soft-tissue mass that has displaced the rectum (R) anteriorly and has infiltrated the upper sacral vertebrae, which have an irregular appearance. Intermediate-signal-intensity soft tissue also is visible in the sacral spinal canal (arrows). (b) Sagittal T2-weighted MR image more clearly depicts involvement of the sacrococcygeal vertebrae (arrow) as well as the spinal canal soft-tissue mass (arrowheads).

	Lymphomatous Masses

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Symptoms can be systemic or caused by a local mass effect and may include abdominal pain, diarrhea, vomiting, peritonitis, and ascites. Lymphoma often is first assessed with US and then with CT of the abdomen and pelvis (Fig 21) for evaluation of the primary site and for staging (71,75). US demonstrates a solid hypoechoic mass. At MR imaging, the mass appears heterogeneous, with low signal intensity on T1-weighted images and high signal intensity on T2-weighted images (Fig 22). The appearance of posttransplantation lymphoma is indistinguishable from that of lymphoma unrelated to transplantation (Fig 23).

View larger version (103K): [in this window] [in a new window] [Download PPT slide]   Figure 21.  Burkitt lymphoma in a 3-year-old boy. Axial pelvic CT scan obtained with oral and intravenous contrast material shows a large heterogeneous mass with soft-tissue attenuation that extends to the presacral space and superior pelvis and encases the rectosigmoid colon segment (arrows).

View larger version (147K): [in this window] [in a new window] [Download PPT slide]   Figure 22a.  Burkitt lymphoma in a 16-year-old boy. Axial (a, b) and sagittal (c) T2-weighted (3500/80) turbo spin-echo MR images obtained with (a) and without (b, c) fat saturation reveal a large heterogeneous pelvic mass with high signal intensity that has surrounded the rectum (arrow in a and c) and displaced the small-bowel loops superiorly. In b, note the left inguinal lymphadenopathy (arrowhead) and left acetabular involvement.

View larger version (150K): [in this window] [in a new window] [Download PPT slide]   Figure 22b.  Burkitt lymphoma in a 16-year-old boy. Axial (a, b) and sagittal (c) T2-weighted (3500/80) turbo spin-echo MR images obtained with (a) and without (b, c) fat saturation reveal a large heterogeneous pelvic mass with high signal intensity that has surrounded the rectum (arrow in a and c) and displaced the small-bowel loops superiorly. In b, note the left inguinal lymphadenopathy (arrowhead) and left acetabular involvement.

View larger version (162K): [in this window] [in a new window] [Download PPT slide]   Figure 22c.  Burkitt lymphoma in a 16-year-old boy. Axial (a, b) and sagittal (c) T2-weighted (3500/80) turbo spin-echo MR images obtained with (a) and without (b, c) fat saturation reveal a large heterogeneous pelvic mass with high signal intensity that has surrounded the rectum (arrow in a and c) and displaced the small-bowel loops superiorly. In b, note the left inguinal lymphadenopathy (arrowhead) and left acetabular involvement.

View larger version (127K): [in this window] [in a new window] [Download PPT slide]   Figure 23.  Lymphoproliferative disease related to Epstein-Barr virus in a 7-year-old girl after a cord blood transplant for metachromatic leukodystrophy. Axial CT scan obtained with oral and intravenous contrast material shows a minimally heterogeneous presacral mass.

View larger version (139K): [in this window] [in a new window] [Download PPT slide]   Figure 24.  Vascular malformation in an infant girl. Axial T2-weighted MR image demonstrates a mixed-signal-intensity mass (arrows) that involves the posterior sacrum as well as the presacral space.

	Sacral Masses with Presacral Extension

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Benign Primary Tumors of the Sacrum
Giant Cell Tumor.— Giant cell tumor of the spine is rare, and only 3%–7% of all giant cell tumors occur in the vertebrae. Most giant cell tumors of the spine occur in the sacrum. Overall, this bone tumor is the second most common neoplasm of the sacrum, after chordoma, and most commonly manifests in the second through the fourth decades of life (78). Sacral lesions are usually eccentric and may extend across the sacroiliac joint. Giant cell tumors are frequently lytic and destructive and do not contain calcifications or septa. Because of their subchondral location, these tumors can cross articular surfaces (79).

Giant cell tumors generally appear heterogeneous on CT and MR images (Fig 25). Low-attenuation areas on CT scans represent necrosis. Hemorrhage is present when there is high signal intensity on both T1- and T2-weighted images. Fibrotic tissue appears as an area of low signal intensity on both T1- and T2-weighted images. Both CT and MR images show contrast enhancement of the tumor (3,79).

View larger version (132K): [in this window] [in a new window] [Download PPT slide]   Figure 25a.  Giant cell tumor in a 15-year-old girl with hip pain. (a) Axial pelvic CT scan obtained with intravenous contrast material shows a large and expansile osteolytic mass (arrow) in the upper sacrum, with involvement of the sacral neural foramina and spinal canal and extension into the presacral space. (b) Axial T1-weighted MR image shows an area of low signal intensity in the mass, a finding that indicates penetration into the bone marrow. The spinal canal is markedly narrowed, and the left sacroiliac joint is irregular.

View larger version (101K): [in this window] [in a new window] [Download PPT slide]   Figure 25b.  Giant cell tumor in a 15-year-old girl with hip pain. (a) Axial pelvic CT scan obtained with intravenous contrast material shows a large and expansile osteolytic mass (arrow) in the upper sacrum, with involvement of the sacral neural foramina and spinal canal and extension into the presacral space. (b) Axial T1-weighted MR image shows an area of low signal intensity in the mass, a finding that indicates penetration into the bone marrow. The spinal canal is markedly narrowed, and the left sacroiliac joint is irregular.

The classic aneurysmal bone cyst consists of multiple blood-filled spaces separated by septa. In contrast to giant cell tumors, aneurysmal bone cysts are delimited by a thin rim of bone. Both CT and MR imaging are useful for depicting the lesion (Fig 26). These modalities also can display multiple fluid-fluid levels representing hemorrhage, which is characteristic of but not specific to this lesion type (78,79,81).

View larger version (153K): [in this window] [in a new window] [Download PPT slide]   Figure 26a.  Aneurysmal bone cyst in a 15-year-old boy with back pain, lower extremity pain, paresthesia, and a palpable mass in the buttock. (a) Anteroposterior pelvic radiograph demonstrates distortion of the sacrum (arrows). (b) Axial CT scan obtained with intravenous contrast material at the level of the inferior sacrum shows an expansile osteolytic mass (arrows) with cortical destruction, involvement of the sacral spinal canal, and disruption of the left sacroiliac joint.

View larger version (132K): [in this window] [in a new window] [Download PPT slide]   Figure 26b.  Aneurysmal bone cyst in a 15-year-old boy with back pain, lower extremity pain, paresthesia, and a palpable mass in the buttock. (a) Anteroposterior pelvic radiograph demonstrates distortion of the sacrum (arrows). (b) Axial CT scan obtained with intravenous contrast material at the level of the inferior sacrum shows an expansile osteolytic mass (arrows) with cortical destruction, involvement of the sacral spinal canal, and disruption of the left sacroiliac joint.

View larger version (185K): [in this window] [in a new window] [Download PPT slide]   Figure 27.  Osteoblastoma in a 16-year-old girl. Sagittal T2-weighted (4790/122) MR image of the pelvis shows the origin of the heterogeneous presacral mass in the distal sacrum.

View larger version (149K): [in this window] [in a new window] [Download PPT slide]   Figure 28.  Chordoma in a 14-year-old girl with hip and back pain. Axial CT scan obtained with intravenous contrast material at the level of the middle sacrum shows an expansile soft-tissue mass with calcifications (arrows), cortical destruction, extension into the presacral space, and involvement of the epidural space of the sacral spinal canal. (Reprinted, with permission, from reference 6.)

Osteogenic Sarcoma.— Osteogenic sarcoma, or osteosarcoma, is the most frequent primary malignant bone tumor. Spinal involvement is very rare; less than 3% of all osteosarcomas are seen in the spine (82). Involvement of the lumbosacral spine accounts for two-thirds of those cases. In addition, osteosarcoma represents only 5% of all primary malignant tumors of the spine. Spinal osteosarcoma may occur after radiation therapy. Osteosarcoma appears as a lytic, osteoblastic, or mixed lesion on radiographs and CT scans. CT can depict extension into the paravertebral tissues and spinal canal (Fig 29). At MR imaging, the mass demonstrates low signal intensity on T1-weighted images and high signal intensity on T2-weighted images (79–82).

View larger version (131K): [in this window] [in a new window] [Download PPT slide]   Figure 29a.  Osteogenic sarcoma of the sacrum in a 16-year-old boy with back and right hip pain. (a) Axial unenhanced CT scan shows a predominantly sclerotic sacrum with indistinct anterior margins. (b) Axial T1-weighted MR image at the level of the middle sacrum shows replacement of the bone marrow of the right sacral ala and body by a low-signal-intensity mass. The tumor extends anteriorly to efface the fat plane adjacent to the right psoas muscle and presacral space (arrows). The right sacroiliac joint is indistinct, but there is no evident involvement of the right iliac bone or spinal canal.

View larger version (158K): [in this window] [in a new window] [Download PPT slide]   Figure 29b.  Osteogenic sarcoma of the sacrum in a 16-year-old boy with back and right hip pain. (a) Axial unenhanced CT scan shows a predominantly sclerotic sacrum with indistinct anterior margins. (b) Axial T1-weighted MR image at the level of the middle sacrum shows replacement of the bone marrow of the right sacral ala and body by a low-signal-intensity mass. The tumor extends anteriorly to efface the fat plane adjacent to the right psoas muscle and presacral space (arrows). The right sacroiliac joint is indistinct, but there is no evident involvement of the right iliac bone or spinal canal.

Radiography and CT show lytic, sclerotic, or mixed features in the tumor. CT depicts the soft-tissue component and the bone lesions better than radiography, and MR imaging clearly depicts both intra- and extraosseous components of the tumor, including paraspinal, extradural, and presacral involvement (Figs 30, 31) (79,80). The extraosseous component is usually the predominant part of the tumor and may include thin fibrous septa.

View larger version (148K): [in this window] [in a new window] [Download PPT slide]   Figure 30.  Ewing sarcoma. Axial pelvic CT scan obtained with intravenous contrast material in a 15-year-old girl with back and bilateral hip pain shows destruction of the lower sacrum by a mass with a significant soft-tissue component. The mass has extended into the presacral space dorsal to the sacrum, displaced the uterus (U) and bladder (B) anteriorly, and obliterated the neural foramina.

View larger version (146K): [in this window] [in a new window] [Download PPT slide]   Figure 31a.  Ewing sarcoma. Axial pelvic CT scan obtained with intravenous contrast material in a 14-year-old girl with hip pain shows an enhanced soft-tissue mass that has displaced the rectum (white arrow) and invaded a sacral foramen (black arrow). Sagittal T2-weighted MR image demonstrates a heterogeneous presacral mass with extension posterior to the sacrum (arrow).

View larger version (165K): [in this window] [in a new window] [Download PPT slide]   Figure 31b.  Ewing sarcoma. Axial pelvic CT scan obtained with intravenous contrast material in a 14-year-old girl with hip pain shows an enhanced soft-tissue mass that has displaced the rectum (white arrow) and invaded a sacral foramen (black arrow). Sagittal T2-weighted MR image demonstrates a heterogeneous presacral mass with extension posterior to the sacrum (arrow).

	Other Masses

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View larger version (184K): [in this window] [in a new window] [Download PPT slide]   Figure 32a.  Presacral mass in a male neonate after ostomy placement for anal atresia. Sagittal unenhanced T2-weighted MR image (a) and sagittal contrast-enhanced T1-weighted fat-saturated MR image (b) show a homogeneous presacral mass (arrows) with persistent high signal intensity despite fat saturation in b, a finding indicative of a hematoma.

View larger version (129K): [in this window] [in a new window] [Download PPT slide]   Figure 32b.  Presacral mass in a male neonate after ostomy placement for anal atresia. Sagittal unenhanced T2-weighted MR image (a) and sagittal contrast-enhanced T1-weighted fat-saturated MR image (b) show a homogeneous presacral mass (arrows) with persistent high signal intensity despite fat saturation in b, a finding indicative of a hematoma.

	Conclusions

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	Footnotes

 

Abbreviations: ASP = anorectal malformation, sacrococcygeal osseous defect, and presacral mass

	References

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