DOI: 10.1148/rg.256055018
RadioGraphics 2005;25:1501-1520
© RSNA, 2005
Abdominal Wall Hernias: Imaging Features, Complications, and Diagnostic Pitfalls at Multi–Detector Row CT1
Diego A. Aguirre, MD,
Agnes C. Santosa, MD,
Giovanna Casola, MD and
Claude B. Sirlin, MD
1 From the Department of Radiology, University of California, San Diego, 200 W Arbor Dr, San Diego, CA 92103-8756 (D.A.A., A.C.S., G.C., C.B.S.); and the Fundación Sante Fe de Bogotá, University Hospital, Bogotá, Colombia (D.A.A.). Presented as an education exhibit at the 2004 RSNA Annual Meeting. Received February 3, 2005; revision requested March 7 and received April 5; accepted April 11. All authors have no financial relationships to disclose.
Address correspondence to D.A.A. (e-mail: daguirre{at}ucsd.edu).
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Abstract
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Abdominal wall hernias are a common imaging finding in the abdomen and may be complicated by strangulation, incarceration, or trauma. Because of the risk of developing complications, most abdominal wall hernias are surgically repaired, even if asymptomatic. However, post-surgical complications are also common and include hernia recurrence, infected and noninfected fluid collections, and complications related to prosthetic material. Multi–detector row computed tomography (CT) with its multiplanar capabilities is particularly useful for the evaluation of unrepaired and surgically repaired abdominal wall hernias. Multi–detector row CT provides exquisite anatomic detail of the abdominal wall, thereby allowing accurate identification of wall hernias and their contents, differentiation of hernias from other abdominal masses (tumors, hematomas, abscesses), and detection of pre- or postoperative complications. These findings improve the communication of imaging results to clinicians and help optimize treatment planning. Knowledge of multi–detector row CT findings in unrepaired and surgically repaired abdominal wall hernias and their complications is essential for making the correct diagnosis and may help guide clinical management.
© RSNA, 2005
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LEARNING OBJECTIVES FOR TEST 2
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After reading this article and taking the test, the reader will be able to:- Describe the role and technique of multi–detector row CT in diagnosing complications of abdominal wall hernias and hernia repairs.
- Recognize multi–detector row CT findings in abdominal wall hernias and hernia repairs and in related complications.
- Discuss the differential diagnosis and potential pitfalls of abdominal wall hernias at multi–detector row CT.
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Introduction
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Abdominal wall hernias are a frequent imaging finding in the abdomen. Although most abdominal wall hernias are asymptomatic, they may develop acute complications that necessitate emergent surgery. In the United States, complications related to external hernias represent one of the most common reasons for emergent surgery performed in patients over 50 years old (1,2). Prompt diagnosis is desirable because delay is associated with greater morbidity (3,4).
To prevent acute complications, external hernias are usually repaired electively (5); surgical correction of hernias is currently the major operation most frequently performed by general surgeons in the United States and the second most common abdominopelvic surgery after cesarean section (6). Over 1 million hernia repairs are performed annually (1,2), about 5% more frequently than cholecystectomy (6). Unfortunately, complications from surgical repair such as hernia recurrence, postoperative fluid collections, and complications related to prosthetic material occur in up to 20% of cases (7,8). Prompt diagnosis and management of these complications is crucial, but clinical evaluation is of limited value; therefore, imaging studies have become important for the detection and diagnosis of these complications.
Different imaging modalities have been used to confirm suspected complications of abdominal wall hernias and hernia repairs (9,10); adequate visualization of intraabdominal organs and the abdominal wall, fast imaging acquisition, three-dimensional data sets, and multiplanar reformation capabilities are important advantages of multi–detector row computed tomography (CT) compared with other modalities (11–15). In addition, because of its superior anatomic detail, multi–detector row CT may help detect subtle signs of complication within the hernia sac, including bowel obstruction, incarceration, strangulation, and traumatic wall hernias. A few studies suggest that magnetic resonance (MR) imaging may permit detection of abdominal wall hernias (16–19). To our knowledge, however, there has been no clinical study on MR imaging of abdominal wall hernia complications, and MR imaging is not discussed further in this article. Instead, we describe multi–detector row CT technique and review the various types of abdominal wall hernias (eg, groin, ventral, lumbar, and incisional hernias). We also discuss and illustrate the most common complications of abdominal wall hernias (eg, bowel obstruction, incarceration, strangulation, trauma) and the characteristic imaging findings in these hernias and their complications. In addition, we discuss surgical repair procedures, post-surgical complications (eg, hernia recurrence, fluid collections, infection, mesh-related complications), and diagnostic pitfalls at multi–detector row CT (eg, abdominal wall tumors, rectus sheath hematomas).
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Multi–Detector Row CT Technique
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Different multi–detector row CT techniques have been described for the evaluation of abdominal wall hernias (11,20). Because most of these hernias are unsuspected findings, axial imaging performed with the patient supine is typical. If hernias are seen, we recommend thin reconstruction (
2.5-mm sections) to improve multiplanar reformation.
If multi–detector row CT is performed for the evaluation of known or suspected hernias, postural maneuvers (eg, prone or lateral decubitus patient positioning) and maneuvers to increase intraabdominal pressure (eg, straining, Valsalva maneuver) can help depict subtle hernias that would otherwise be missed (Fig 1 ) (20).
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Figure 1a. (a) Axial contrast material–enhanced reformatted CT image of the abdomen obtained with the patient at rest shows an umbilical hernia containing omental fat (arrows). (b) Axial contrast-enhanced reformatted CT image obtained during a Valsalva maneuver reveals that the hernia contains small bowel loops (arrowhead). Increased intra-abdominal pressure may improve the detection of small abdominal wall defects.
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Figure 1b. (a) Axial contrast material–enhanced reformatted CT image of the abdomen obtained with the patient at rest shows an umbilical hernia containing omental fat (arrows). (b) Axial contrast-enhanced reformatted CT image obtained during a Valsalva maneuver reveals that the hernia contains small bowel loops (arrowhead). Increased intra-abdominal pressure may improve the detection of small abdominal wall defects.
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Intravenous administration of contrast material is necessary for characterization of the vascular supply. Positive oral contrast material or water may be used to better visualize bowel loops.
At our institution, we acquire supine images during a single breath hold with a four–detector row scanner (Light Speed; GE Medical Systems, Milwaukee, Wis) after bolus injection of 125 mL of iodinated contrast material (Optiray 320; Mallinckrodt, St Louis, Mo) with a power injector (LF CT 9000; Liebel-Flarsheim, Cincinnati, Ohio). Table speed is 10 mm/sec, and collimation is 2.5 mm. Thin (2.5-mm) reformatted images are routinely obtained in all cases.
Multiplanar reformatted (MPR) images provide important information in addition to that provided by axial images in that they may better delineate the size and shape of the hernia sac and associated complications. Moreover, displaying the anatomy in a manner more familiar to clinicians may enhance the communication of imaging findings.
For these reasons, we recommend routine use of MPR images in patients with suspected disease of the abdominal wall.
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Types of Abdominal Wall Hernias
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Multi–detector row CT findings in various types of abdominal wall hernias are reviewed in detail elsewhere (11). We present an abridged review in this article.
Groin Hernias
Inguinal Hernias.—
Inguinal hernias are the most common type of abdominal wall hernia. They may occur in children (most commonly indirect type hernias) or adults (both direct and indirect types), manifesting medial (direct type) or lateral (indirect type) to the inferior epigastric vessels (Fig 2). Regardless of patient age, inguinal hernias are more common in males than in females. In boys, most inguinal hernias develop because the peritoneal extension accompanying the testis fails to obliterate. In adults, inguinal hernias are caused by acquired weakness and dilatation of the internal inguinal ring (12).
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Figure 2. Direct inguinal hernia in a 57-year-old man. Axial unenhanced reformatted CT image of the abdomen shows a direct inguinal hernia (arrow) medial to the inferior epigastric vessels on the right side of the groin. Note the presence of bowel loops in the hernia sac.
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Femoral Hernias.—
Femoral hernias are less common than inguinal hernias. They occur medial to the femoral vein and posterior to the inguinal ligament, usually on the right side. Unlike inguinal hernias, they are more common in females.
Ventral Hernias
Ventral hernias include all hernias in the anterior and lateral abdominal wall. Midline defects include umbilical, paraumbilical, epigastric, and hypogastric hernias. Umbilical hernias are by far the most common type of ventral hernia; they are usually small and are particularly common in women. Paraumbilical hernias are large abdominal defects through the linea alba in the region of the umbilicus and are usually related to diastasis of the rectus abdominis muscles. Epigastric hernias (Fig 3) and hypogastric hernias occur in the linea alba above and below the umbilicus, respectively.
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Figure 3. Epigastric hernia in a 65-year-old man. Axial contrast-enhanced reformatted CT image of the abdomen shows an epigastric hernia (arrows) containing the transverse colon and small bowel loops. Note also the interparietal hernia through the right lateral aspect of the abdominal wall (arrowhead) containing the hepatic flexure of the colon.
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Strangulation (ischemia caused by a compromised blood supply) and incarceration (irreducible sac) are common in all midline hernias (Fig 4). Clinical diagnosis is difficult: Physical examination is limited, especially in obese patients, and symptoms are nonspecific.
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Figure 4. Incarcerated umbilical hernia in a 56-year-old woman. Axial contrast-enhanced reformatted CT image of the abdomen shows herniation of omental fat through the umbilical orifice (arrow). Associated stranding of herniated fat is also seen. The narrow neck of the hernia sac and the fat stranding suggest incarceration. The hernia was irreducible at physical examination, and an incarcerated hernia was confirmed at surgery.
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Paramedian or lateral defects may also occur, although they are less common. Typically, omentum and short segments of bowel protrude through the defect. These entities have a high prevalence of incarceration.
Lumbar Hernias
Lumbar hernias occur through defects in the lumbar muscles or the posterior fascia, below the 12th rib and above the iliac crest. They usually occur after surgery or trauma. Herniation may occur through the superior (Grynflett-Lesshaft) (Fig 5) or, less commonly, the inferior (petit) lumbar triangle. The superior lumbar triangle is bordered by the internal oblique muscle anteriorly, the 12th rib superiorly, and the erector spinal muscle posteriorly. The inferior lumbar triangle is bordered by the external oblique muscle anteriorly, the iliac crest inferiorly, and the latissimus dorsi muscle posteriorly. Diffuse lumbar hernias may also occur, usually after flank incisions in kidney surgery, and may contain bowel loops, retroperitoneal fat, kidneys, or other viscera (Fig 6).
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Figure 5. Superior lumbar hernia in a 63-year-old man who had undergone right nephrectomy for renal cell carcinoma. Axial contrast-enhanced reformatted CT image of the abdomen shows a superior lumbar hernia (incisional type) (arrows). Note the protrusion of the ascending colon into the subcutaneous tissue. The left kidney has an extrarenal pelvis, a finding that was discovered incidentally.
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Figure 6. Diffuse lumbar hernia in a 58-year-old man who had undergone left nephrectomy for renal cell carcinoma. Axial unenhanced reformatted CT image of the abdomen shows a diffuse lumbar hernia (incisional type). Note the extensive herniation of the mesentery and bowel loops through the wall defect (arrows).
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Incisional Hernias
Incisional hernias are delayed complications of abdominal surgery. They may manifest anywhere in the abdominal wall and are more commonly encountered in association with vertical than with transverse incisions. Incisional hernias usually manifest during the first few months after surgery. Their reported prevalence ranges from 0.5% to 13.9% for most abdominal surgeries but may be as high as 41% after aortic surgery (13,21).
Parastomal hernias are considered a subtype of incisional hernia. They occur adjacent to a stoma and are particularly difficult to detect at physical examination.
Other Hernias
Less common hernias include (a) interparietal, Richter, and Littre hernias of the abdominal wall; and (b) sciatic, obturator, and perineal hernias in the pelvis.
Interparietal (interstitial) hernia refers to a hernia sac located in the fascial planes between the abdominal wall muscles that does not exit into the subcutaneous tissue. This type of hernia occurs most frequently in the inguinal region. Richter hernia refers to herniation of the antimesenteric wall of the bowel that does not compromise the entire wall circumference. It most frequently occurs in association with femoral hernias. Littre hernia refers to an inguinal hernia that contains a Meckel diverticulum. All of these uncommon abdominal hernias are particularly prone to incarceration and strangulation.
Pelvic hernias most frequently occur in elderly women and are secondary to acquired weakness of the pelvic floor. Sciatic and obturator hernias are rare and usually manifest as herniation of small bowel loops or a ureter through the sciatic or obturator foramen, respectively. Perineal hernias are more common than sciatic or obturator hernias and occur adjacent to the anus or labia majora or in the gluteal region.
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Complications of Abdominal Wall Hernias
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The most common complications of abdominal wall hernias are bowel obstruction secondary to the hernia, incarceration, and strangulation. These complications can often be detected at clinical evaluation. Presenting symptoms may include abdominal pain, vomiting, and distention. Physical examination may reveal a firm, tender abdominal wall mass. Abdominal distention, dehydration, or peritoneal signs eventually become manifest (22).
Imaging studies are required when the clinical manifestation is misleading or inconclusive or preoperative assessment of the hernia or secondary obstruction is required (23). Moreover, early diagnosis of hernia complications is feasible with multi–detector row CT, potentially improving patient outcome by preserving bowel viability (3). Therefore, knowledge of imaging findings that suggest hernia complications is important.
Bowel Obstruction
After adhesions, abdominal wall hernias are the second leading cause of small bowel obstruction (10%–15% of cases) (24). Colonic obstruction caused by abdominal wall hernia is uncommon.
Most cases of bowel obstruction secondary to abdominal wall hernia occur after incarceration and strangulation (discussed later). In these cases, bowel obstruction occurs with the transition point at the level of the hernia. Key CT findings (25–29) include (a) dilated bowel proximal to the hernia and (b) normal-caliber, reduced-caliber, or collapsed bowel distal to the obstruction. The degree of change in caliber helps predict the grade of obstruction. Other findings may include tapering of the afferent and efferent limbs at the hernia defect, dilatation of the herniated bowel loops, and fecalization of small bowel contents proximal to the obstruction. Findings of strangulation may also be observed.
Incarceration
Incarceration refers to an irreducible hernia and is diagnosed clinically when a hernia cannot be reduced or pushed back manually. The diagnosis of incarceration cannot be made with imaging alone but can be suggested when herniation occurs through a small defect and the hernia sac has a narrow neck. Detection is important because incarceration predisposes to complications such as obstruction (Fig 7), inflammation, or ischemia. Axial and MPR images are important (Fig 8), since they improve visualization of the hernia defect and permit assessment of size and content (11). Impending strangulation of these hernias should be suspected when there is free fluid within the hernia sac, bowel wall thickening, or luminal dilatation (23,30).
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Figure 7a. Incarcerated hernia in a 78-year-old man. (a) Axial contrast-enhanced reformatted CT image of the abdomen shows herniation of stool-filled, thin-walled colon (arrow) through a narrow abdominal wall defect. The patient was asymptomatic but presented with acute abdomen 1 month later. (b) Axial contrast-enhanced reformatted CT image shows multiple ventral hernias (arrowheads). The sac of the hernia shown in a now contains extraluminal fluid and fluid-filled, mildly thickened colon and causes colonic obstruction. Incarceration with colonic obstruction was confirmed at surgery.
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Figure 7b. Incarcerated hernia in a 78-year-old man. (a) Axial contrast-enhanced reformatted CT image of the abdomen shows herniation of stool-filled, thin-walled colon (arrow) through a narrow abdominal wall defect. The patient was asymptomatic but presented with acute abdomen 1 month later. (b) Axial contrast-enhanced reformatted CT image shows multiple ventral hernias (arrowheads). The sac of the hernia shown in a now contains extraluminal fluid and fluid-filled, mildly thickened colon and causes colonic obstruction. Incarceration with colonic obstruction was confirmed at surgery.
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Figure 8a. Incarcerated hypogastric hernia in a 55-year-old woman who presented with abdominal distention. (a) Axial unenhanced reformatted CT image of the abdomen shows the herniation of small bowel loops through a narrow defect in the abdominal wall (arrow). Fat stranding is seen in the hernia sac. (b) Coronal unenhanced reformatted CT image better depicts proximal small bowel obstruction (arrowheads). Arrow indicates an abdominal wall defect. Incarcerated hypogastric hernia was confirmed at surgery.
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Figure 8b. Incarcerated hypogastric hernia in a 55-year-old woman who presented with abdominal distention. (a) Axial unenhanced reformatted CT image of the abdomen shows the herniation of small bowel loops through a narrow defect in the abdominal wall (arrow). Fat stranding is seen in the hernia sac. (b) Coronal unenhanced reformatted CT image better depicts proximal small bowel obstruction (arrowheads). Arrow indicates an abdominal wall defect. Incarcerated hypogastric hernia was confirmed at surgery.
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If fatty tissue or fluid but no bowel is present in an incarcerated hernia, time is not a limiting factor in preparing the patient for surgery. In contrast, incarcerated bowel requires immediate surgery to prevent bowel necrosis and subsequent resection of the affected bowel loop (23).
Strangulation
Strangulation refers to ischemia caused by a compromised blood supply. It usually occurs when the hernia defect obstructs the afferent and efferent bowel loops, creating a closed loop within the herniated bowel. Multi–detector row CT findings include closed loop obstruction and ischemia (Fig 9) (3). Findings in closed loop obstruction include dilated, fluid-filled U- or C-shaped loops of bowel entrapped within the hernia sac and proximal obstruction (Fig 10). Findings in ischemia include wall thickening, abnormal mural hypo- or hyperattenuation and enhancement, mesenteric vessel engorgement, fat obliteration, mesenteric haziness, and ascites. The afferent and efferent limbs may have a "serrated beak" appearance at the transition point.
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Figure 9a. Strangulated hernia in a 56-year-old man. (a) Axial contrast-enhanced reformatted CT image of the abdomen shows a strangulated left inguinal hernia with a C-shaped con-figuration (arrows). Note the bowel wall thickening, severe fat stranding, mesenteric engorgement, and extraluminal fluid confined to the hernia sac, findings that suggest strangulation. (b) Sagittal contrast-enhanced reformatted CT image of the abdomen more clearly shows a hernia defect (arrowhead). In this case, mural enhancement of herniated bowel is normal (similar to that of intraabdominal bowel loops). Normal mural enhancement does not exclude strangulation, whereas abnormal enhancement strongly suggests it.
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Figure 9b. Strangulated hernia in a 56-year-old man. (a) Axial contrast-enhanced reformatted CT image of the abdomen shows a strangulated left inguinal hernia with a C-shaped con-figuration (arrows). Note the bowel wall thickening, severe fat stranding, mesenteric engorgement, and extraluminal fluid confined to the hernia sac, findings that suggest strangulation. (b) Sagittal contrast-enhanced reformatted CT image of the abdomen more clearly shows a hernia defect (arrowhead). In this case, mural enhancement of herniated bowel is normal (similar to that of intraabdominal bowel loops). Normal mural enhancement does not exclude strangulation, whereas abnormal enhancement strongly suggests it.
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Figure 10a. Strangulated hernia in a 44-year-old man. (a) Axial contrast-enhanced reformatted CT image of the abdomen shows a strangulated umbilical hernia (arrows) causing small bowel obstruction (arrowheads). A herniated bowel loop with a C-shaped configuration, discrete mesenteric engorgement, and ascitic fluid within the hernia sac are also seen. (b) Sagittal contrast-enhanced reformatted CT image of the abdomen more clearly demonstrates the amplitude of the umbilical defect (thin arrows), air-fluid levels in herniated bowel loops, and dilatation of intraabdominal bowel loops secondary to small bowel obstruction (arrowhead). Note the ascitic fluid within the scrotum (thick arrow), a finding that is characteristic of inguinoscrotal hernia.
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Figure 10b. Strangulated hernia in a 44-year-old man. (a) Axial contrast-enhanced reformatted CT image of the abdomen shows a strangulated umbilical hernia (arrows) causing small bowel obstruction (arrowheads). A herniated bowel loop with a C-shaped configuration, discrete mesenteric engorgement, and ascitic fluid within the hernia sac are also seen. (b) Sagittal contrast-enhanced reformatted CT image of the abdomen more clearly demonstrates the amplitude of the umbilical defect (thin arrows), air-fluid levels in herniated bowel loops, and dilatation of intraabdominal bowel loops secondary to small bowel obstruction (arrowhead). Note the ascitic fluid within the scrotum (thick arrow), a finding that is characteristic of inguinoscrotal hernia.
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Strangulated abdominal wall hernias are associated with a high surgical fatality rate (6%–23%) secondary to the strangulated viscus (8).
Trauma
Hernias may be complicated by trauma in two ways: A hernia may be caused by trauma (traumatic hernia), or there may be trauma to a preexisting hernia.
Traumatic Hernia.—
Abdominal trauma can result in a wide variety of abdominal wall hernias ranging from small defects caused by direct injury to more extensive defects resulting from compression injury to the abdomen (4).
Most traumatic hernias are associated with high-impact blunt trauma (eg, high-velocity motor vehicle accidents), which produces increased intraabdominal pressure sufficient to disrupt the abdominal wall musculature. Seat belt use, which exposes the wall musculature to full deceleration forces, increases the risk for traumatic hernias. No association exists between the site of impact and the location of the defect. The most common locations are areas of relative anatomic weakness: the lumbar region (Fig 11) and the lower abdomen (4). In more severe cases, diaphragmatic rupture may occur, and herniation of abdominal contents into the chest may be seen (Fig 12).
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Figure 11. Lumbar hernia in a 33-year-old man who had sustained injury in a high-impact motor vehicle accident. The patient was a front-seat passenger and was wearing a seat belt at the time of the accident. Axial contrast-enhanced CT scan of the abdomen shows a trauma-related lumbar hernia. Note the protrusion of colon (arrow), the mild mesenteric haziness, and the traumatic disruption of the abdominal wall musculature (arrowheads). Traumatic abdominal wall hernia is usually an indication for emergent laparotomy in the setting of acute trauma.
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Figure 12a. Diaphragmatic hernia in a 33-year-old man who had sustained injury in a motor vehicle accident. (a, b) Axial contrast-enhanced reformatted CT images of the chest and abdomen show an acute diaphragmatic hernia, along with small bowel loops (arrows in a) and mesenteric fat (arrowheads in b) in the chest. Note the collapse of the left lung and the presence of chest tubes. (c) Coronal thick-slab reformatted image shows the herniation of bowel loops into the chest (straight arrow). Note the diminished mural enhancement of the herniated loops in the chest (arrowheads) compared with the nonherniated loops in the abdomen (curved arrows). The diminished enhancement suggests strangulation, a finding that was confirmed at surgery.
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Figure 12b. Diaphragmatic hernia in a 33-year-old man who had sustained injury in a motor vehicle accident. (a, b) Axial contrast-enhanced reformatted CT images of the chest and abdomen show an acute diaphragmatic hernia, along with small bowel loops (arrows in a) and mesenteric fat (arrowheads in b) in the chest. Note the collapse of the left lung and the presence of chest tubes. (c) Coronal thick-slab reformatted image shows the herniation of bowel loops into the chest (straight arrow). Note the diminished mural enhancement of the herniated loops in the chest (arrowheads) compared with the nonherniated loops in the abdomen (curved arrows). The diminished enhancement suggests strangulation, a finding that was confirmed at surgery.
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Figure 12c. Diaphragmatic hernia in a 33-year-old man who had sustained injury in a motor vehicle accident. (a, b) Axial contrast-enhanced reformatted CT images of the chest and abdomen show an acute diaphragmatic hernia, along with small bowel loops (arrows in a) and mesenteric fat (arrowheads in b) in the chest. Note the collapse of the left lung and the presence of chest tubes. (c) Coronal thick-slab reformatted image shows the herniation of bowel loops into the chest (straight arrow). Note the diminished mural enhancement of the herniated loops in the chest (arrowheads) compared with the nonherniated loops in the abdomen (curved arrows). The diminished enhancement suggests strangulation, a finding that was confirmed at surgery.
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Traumatic abdominal wall hernias are easily overlooked at physical examination performed at initial presentation and are associated with intra-abdominal injuries in up to 60% of cases (4). Incarceration and strangulation of hernia contents are also common (31). For these reasons, traumatic abdominal wall hernias usually require emergent laparotomy, even in the absence of other imaging findings (31).
Multi–detector row CT permits reliable diagnosis and assessment of traumatic hernias, including characterization of hernia contents, visualization of disrupted abdominal muscle layers, and identification of associated intraabdominal injuries.
Trauma to Preexisting Hernia.—
Patients with known abdominal wall hernia who present following high-impact trauma should be scrutinized for the presence of fluid within the hernia sac, bowel wall thickening, asymmetric bowel wall enhancement, vessel engorgement, and fat stranding within the hernia sac or in surrounding soft tissues. These findings should alert the radiologist to traumatic injury of a preexisting abdominal wall hernia, which usually requires surgical management.
Other Complications
Less severe complications include herniation of intraabdominal organs, whether solid (eg, liver, kidneys) (Fig 13) or nonsolid (eg, stomach, bladder, neobladder) (Fig 14). In rare cases, intraabdominal tumors may herniate through weak portions of the abdominal wall (Fig 15) or may be contained within the hernia sac (Fig 16). Finally, extension of intraabdominal inflammatory conditions into the hernia sac may occur, exacerbating symptomatology (Fig 17).
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Figure 13. Incisional hernia in a 64-year-old man who had undergone midline abdominal incision for gallbladder resection several years earlier. Axial contrast-enhanced CT scan of the abdomen shows post-surgical changes anterior to the liver and an incisional (epigastric) hernia containing the left hepatic lobe (arrows).
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Figure 14a. Inguinal hernia in a 64-year-old man. Axial contrast-enhanced CT scan (a) and sagittal reformatted CT image (b) of the lower abdomen show herniation of the bladder through a right inguinal hernia (arrows). The bladder herniation is more clearly delineated on the sagittal image.
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Figure 14b. Inguinal hernia in a 64-year-old man. Axial contrast-enhanced CT scan (a) and sagittal reformatted CT image (b) of the lower abdomen show herniation of the bladder through a right inguinal hernia (arrows). The bladder herniation is more clearly delineated on the sagittal image.
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Figure 15a. Inguinal hernia in a 67-year-old man with retro-peritoneal liposarcoma. (a) Axial contrast-enhanced reformatted CT image of the abdomen shows a large, soft-tissue retro-peritoneal mass (arrows). (b) Axial contrast-enhanced reformatted CT image obtained inferior to a shows herniation of the mass through the right inguinal canal (arrows). (c) Sagittal contrast-enhanced reformatted CT image helps confirm herniation of the mass through the inguinal canal (arrows) and more clearly delineates the hernia defect.
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Figure 15b. Inguinal hernia in a 67-year-old man with retro-peritoneal liposarcoma. (a) Axial contrast-enhanced reformatted CT image of the abdomen shows a large, soft-tissue retro-peritoneal mass (arrows). (b) Axial contrast-enhanced reformatted CT image obtained inferior to a shows herniation of the mass through the right inguinal canal (arrows). (c) Sagittal contrast-enhanced reformatted CT image helps confirm herniation of the mass through the inguinal canal (arrows) and more clearly delineates the hernia defect.
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Figure 15c. Inguinal hernia in a 67-year-old man with retro-peritoneal liposarcoma. (a) Axial contrast-enhanced reformatted CT image of the abdomen shows a large, soft-tissue retro-peritoneal mass (arrows). (b) Axial contrast-enhanced reformatted CT image obtained inferior to a shows herniation of the mass through the right inguinal canal (arrows). (c) Sagittal contrast-enhanced reformatted CT image helps confirm herniation of the mass through the inguinal canal (arrows) and more clearly delineates the hernia defect.
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Figure 16. Lumbar hernia containing peritoneal metastases in a 55-year-old man with known gastric carcinoma. Axial contrast-enhanced CT scan of the abdomen shows malignant ascites and multiple peritoneal metastases (black arrowheads). There is also a small lumbar hernia (arrow) containing ascites and a peritoneal metastasis (white arrowhead). Increased intraabdominal pressure, caused in this case by malignant ascites, increases the risk for abdominal wall hernias. These hernias tend to occur in the lumbar region and the lower abdomen, which are considered to be areas of relative anatomic weakness.
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Figure 17a. Omental infarction extending to an inguinal hernia in a 48-year-old man. (a) Axial contrast-enhanced CT scan of the abdomen shows a severe inflammatory process in the right lower quadrant. Note the mesenteric fluid and fat stranding (arrows), which cause mass effect. (b) Sagittal contrast-enhanced reformatted CT image shows extension of the inflammatory process (arrow) into a right inguinal hernia sac (arrowhead). Extensive omental infarction was demonstrated at surgery.
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Figure 17b. Omental infarction extending to an inguinal hernia in a 48-year-old man. (a) Axial contrast-enhanced CT scan of the abdomen shows a severe inflammatory process in the right lower quadrant. Note the mesenteric fluid and fat stranding (arrows), which cause mass effect. (b) Sagittal contrast-enhanced reformatted CT image shows extension of the inflammatory process (arrow) into a right inguinal hernia sac (arrowhead). Extensive omental infarction was demonstrated at surgery.
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Surgical Repair Procedures
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Several different surgical procedures are used to repair abdominal wall hernias, ranging from open or laparoscopic suture repair to the use of mesh. To date, tension-free mesh repair has been accepted as the standard surgical technique for the majority of abdominal wall hernias, regardless of defect size (5,32), and is most commonly used.
Meshes come in different sizes and shapes and may be three-dimensional or flat. Depending on the type of abdominal defect, the mesh may be placed in the preperitoneal space, close to the posterior surface of the fascia transversalis, or within the muscular aponeurotic layer. Moreover, the surgical approach may be open or laparoscopic (7,33). The mesh material is porous so as to facilitate ingrowth of fibrous tissue and gradual encapsulation for wound healing. Two main types of mesh with different principal components are used: polypropylene mesh and expanded polytetrafluoroethylene (PTFE) mesh.
Polypropylene mesh (Marlex [Phillips Sumika, Houston, Tex], Prolene [Ethicon, Somerville, NJ], Trelex [Boston Scientific, Natick, Mass]) is most commonly used and consists of an inert, 0.44-mm-thick sterile nonabsorbable monofilament that shows rapid incorporation into the tissues. It is not visible at CT because it is isoattenuating relative to surrounding tissues (7,8).
Expanded PTFE mesh (Teflon [DuPont, Wilmington, Del], Gore-Tex [Gore, Newark, Del]) is a strong, inert, 1-mm-thick macrofilament that rapidly becomes fixated within the tissues. Its thickness and high attenuation allow visualization at CT as a linear hyperattenuating structure (Fig 18) (7,8).
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Figure 18a. Hernia repair with PTFE mesh in a 54-year-old man. (a) Axial contrast-enhanced CT scan of the abdomen shows a large, incisional type lateral hernia containing small bowel loops (arrows). The patient subsequently underwent surgical correction of the hernia. (b) Axial maximum-intensity-projection image obtained after surgical repair shows hyperattenuating PTFE mesh in the abdominal wall (arrowheads).
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Figure 18b. Hernia repair with PTFE mesh in a 54-year-old man. (a) Axial contrast-enhanced CT scan of the abdomen shows a large, incisional type lateral hernia containing small bowel loops (arrows). The patient subsequently underwent surgical correction of the hernia. (b) Axial maximum-intensity-projection image obtained after surgical repair shows hyperattenuating PTFE mesh in the abdominal wall (arrowheads).
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Tissue expanders are crescent-shaped reservoirs of saline solution that are placed subcutaneously adjacent to large abdominal wall defects several weeks to months prior to surgery to facilitate subsequent surgical repair of the defects. They provide more tissue coverage for primary closure by stretching the skin and subcutaneous tissue (34,35) prior to the attempted repair (Fig 19 ). These crescent-shaped reservoirs are connected to a subcutaneous saline solution port to regulate volume and applied pressure, allowing periodic injection to ensure adequate tissue expansion. The duration of implantation is variable and depends on the size of the wall defect (34,35).
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Figure 19a. Hernia repair with use of tissue expanders in a 49-year-old man with an incisional hernia. Axial contrast-enhanced reformatted CT images of the abdomen obtained 2 weeks (a), 8 weeks (b), and 12 weeks (c) after the implantation of tissue expanders show a large incisional hernia (arrowheads in a and b) and demonstrate the progression of treatment with the expanders (arrows in a and b). Note the progressive stretching of the skin and subcutaneous tissue, allowing hernia repair with mesh (arrows in c) and closure of the wall defect. A small fluid collection (arrowhead in c) is present at the previous site of an expander.
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Figure 19b. Hernia repair with use of tissue expanders in a 49-year-old man with an incisional hernia. Axial contrast-enhanced reformatted CT images of the abdomen obtained 2 weeks (a), 8 weeks (b), and 12 weeks (c) after the implantation of tissue expanders show a large incisional hernia (arrowheads in a and b) and demonstrate the progression of treatment with the expanders (arrows in a and b). Note the progressive stretching of the skin and subcutaneous tissue, allowing hernia repair with mesh (arrows in c) and closure of the wall defect. A small fluid collection (arrowhead in c) is present at the previous site of an expander.
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Figure 19c. Hernia repair with use of tissue expanders in a 49-year-old man with an incisional hernia. Axial contrast-enhanced reformatted CT images of the abdomen obtained 2 weeks (a), 8 weeks (b), and 12 weeks (c) after the implantation of tissue expanders show a large incisional hernia (arrowheads in a and b) and demonstrate the progression of treatment with the expanders (arrows in a and b). Note the progressive stretching of the skin and subcutaneous tissue, allowing hernia repair with mesh (arrows in c) and closure of the wall defect. A small fluid collection (arrowhead in c) is present at the previous site of an expander.
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Postsurgical Complications
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Complications after surgical hernia repair may occur in up to 50% of cases, depending on surgical technique and the status of the hernia sac vasculature. Approximately one-half of these complications may require surgical reintervention, and accurate diagnosis at multi–detector row CT is necessary for optimal patient treatment (8,32,36).
Hernia Recurrence
Hernia recurrence constitutes the most common complication after hernia repair, usually occurring 2–3 years after surgery (8,32). The prevalence of hernia recurrence varies with the type of repair: It may be seen in up to 30% of cases after open surgery without mesh placement, up to 10% after open surgery with mesh placement, and up to 7.5% after laparoscopic surgery (8,36). A small proportion of recurrent hernias occur 5 or more years after surgery, usually related to the aging of tissues and the weakening of muscles (32).
Clinical evaluation of recurrent hernias is usually limited due to the existence of nonabsorbable mesh and accompanying fibrosis or to obesity, abdominal distention, or spontaneous contraction of the abdominal wall. Under these circumstances, multi–detector row CT allows the correct diagnosis of recurrent hernia (Fig 20) (8,32,37).
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Figure 20a. Recurrent paraumbilical hernia in a 48-year-old man who had undergone surgical correction of the hernia with PTFE mesh 3 months earlier. (a) Axial contrast-enhanced reformatted CT image of the abdomen shows a recurrent paraumbilical hernia (arrows). (b) Sagittal reformatted CT image shows the protrusion of mesenteric fat inferior to the lower edge of the mesh (arrowheads). Recurrent hernia was confirmed at surgery.
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Figure 20b. Recurrent paraumbilical hernia in a 48-year-old man who had undergone surgical correction of the hernia with PTFE mesh 3 months earlier. (a) Axial contrast-enhanced reformatted CT image of the abdomen shows a recurrent paraumbilical hernia (arrows). (b) Sagittal reformatted CT image shows the protrusion of mesenteric fat inferior to the lower edge of the mesh (arrowheads). Recurrent hernia was confirmed at surgery.
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Fluid Collections
Fluid collections occur frequently in the immediate postoperative period after hernia repair (up to 17% of cases) (8). These collections usually contain serous fluid (seromas) or blood products (hematomas), and their formation is related to both the surgical technique and the properties of the mesh used for hernia repair (38).
Most seromas resolve without manipulation within 30 days; aspiration may be indicated if the collection persists for more than 6 weeks, steadily grows, produces symptoms, or is suspected to be infected (8,36). Imaging-guided aspiration or drainage may be problematic for large collections located under the mesh due to infolding of the mesh layers. In such cases, an oblique approach with use of small-diameter catheters may be necessary.
CT helps identify fluid collections, differentiate them from hernia recurrence (which may be difficult at physical examination, especially in obese patients), and confirm their resolution. At CT, postoperative fluid collections can have a globular, tubular, or multilobular appearance. Some collections may be loculated with enhancing rims, reflecting recent surgical intervention (Fig 21) (36), whereas others may contain air-fluid levels, resemble bowel loops, or be mistaken for recurrent hernias.
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Figure 21a. Seroma in a 50-year-old woman who had undergone surgical correction of a paraumbilical hernia. Axial contrast-enhanced reformatted CT images of the abdomen obtained immediately (a) and 4 weeks (b) after surgery demonstrate a seroma (arrows) subjacent to PTFE mesh (arrowheads). Note the interval enlargement of the seroma despite the regression of postoperative changes. Immediately after surgery, fluid collections at the surgical bed may be heterogeneous due to the presence of peritoneal fluid and blood secondary to surgical trauma.
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Figure 21b. Seroma in a 50-year-old woman who had undergone surgical correction of a paraumbilical hernia. Axial contrast-enhanced reformatted CT images of the abdomen obtained immediately (a) and 4 weeks (b) after surgery demonstrate a seroma (arrows) subjacent to PTFE mesh (arrowheads). Note the interval enlargement of the seroma despite the regression of postoperative changes. Immediately after surgery, fluid collections at the surgical bed may be heterogeneous due to the presence of peritoneal fluid and blood secondary to surgical trauma.
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Infection
Infected postoperative fluid collections occur in 1%–5% of patients after hernia repair (32), depending on the surgical technique used and whether the surgery was delayed. These complications tend to occur more frequently in older female patients, especially after surgical repair of strangulated and incarcerated hernias (8). Moreover, they tend to manifest early in the postoperative period (<2 weeks after surgery) and constitute an important risk factor for hernia recurrence (7).
Infected fluid collections may involve subcutaneous (superficial) or mesh-surrounding (deep) tissues. Differentiation is important because superficial infections are managed conservatively, whereas deep infections require intervention such as percutaneous drainage or prosthesis removal.
Diagnosis is usually based on clinical criteria such as the presence of fever or leukocytosis and the amount of time elapsed since surgery (38). Imaging is used to confirm the presence and de-fine the location and volume of collections, to guide aspiration, and to monitor treatment.
Findings that are suspicious for infected fluid collections vary and include the development of gas or thick septa in a previously "simple" collection, an enhancing rim, fat stranding in surrounding tissues (Fig 22), or the development of a new collection 1 or more weeks after surgical repair. Imaging findings alone do not adequately help predict the nature of a fluid collection, and imaging-guided aspiration is often necessary to establish the diagnosis.
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Figure 22. Infected fluid collection in a 55-year-old woman who had undergone surgical correction of an umbilical hernia. Axial contrast-enhanced CT scan of the abdomen obtained 6 weeks after surgery shows a fluid collection (arrows). Note the presence of gas within the collection (arrowhead) and the fat stranding around the collection, findings that are suspicious for infection. Infection was confirmed at microbiologic analysis of fluid obtained with imaging-guided aspiration.
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Mesh-related Complications
Inflammatory reactions may lead to fibrosis of tissues surrounding the mesh. This condition may be suspected if the mesh has an asymmetric or irregular shape at CT (Fig 23). Mesh shrinkage may also occur (8). Intraperitoneal adhesions may develop, predisposing to small bowel obstruction (8). Less frequently, meshes may detach from supporting tissues and migrate within the abdominal wall (7).
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Figure 23. Fluid collection related to collapsed mesh in a 55-year-old woman who had undergone surgical correction of an interparietal hernia. Axial contrast-enhanced reformatted CT image of the abdomen obtained 12 weeks after surgery shows collapsed PTFE mesh (arrowheads) with an associated fluid collection (arrows). In some mesh-related complications, the mesh may have atypical morphologic features, especially if there are associated fluid collections.
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Other Complications
Testicular complications may occur after the repair of inguinal hernias and include ischemia with testicular atrophy and thickening of the spermatic cord (7,8). Other complications include transection or disruption of the vas deferens, hydrocele, osteitis pubis, bowel laceration, and erosion and thrombosis of adjacent vessels (5,8).
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Diagnostic Pitfalls
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Several abdominal wall diseases may be misdiagnosed as hernias at physical examination; fortunately, differentiation between these diseases and hernias is usually straightforward at multi–detector row CT because hernias are associated with abdominal wall defects, have necks, contain herniated intraabdominal contents, and may respond to provocative maneuvers.
Abdominal Wall Tumors
Benign tumors of the abdominal wall (eg, lipomas, hemangiomas, fibromas) are quite common. Malignant tumors of the abdominal wall are less common and are usually metastases, although primary sarcomas may also develop. Metastases are a result of either direct invasion by intraabdominal lesions or vascular dissemination. The two most common primary tumors that metastasize to the abdominal wall are lung tumors and pancreatic tumors. Solid nodules of the abdominal wall that do not clearly represent hernias should arouse suspicion for occult malignancy (Fig 24) (39).
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Figure 24. Abdominal wall metastasis in a 54-year-old cirrhotic man with a large hepatocellular carcinoma (not shown). Axial contrast-enhanced CT scan of the abdomen demonstrates an enhancing subcutaneous nodule (arrow) adjacent to the left rectus abdominis muscle. Histopathologic analysis revealed metastatic hepatocellular carcinoma. Such a metastasis could conceivably simulate an epigastric hernia at physical examination.
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Desmoid tumors (musculoaponeurotic fibromatoses) are a group of nonmetastasizing, locally invasive dysplastic lesions of connective tissue that involve skeletal muscle and fascial layers (Fig 25). These tumors most frequently occur in women during or following pregnancy, occasionally arising in surgical scars or in the mesentery. A familial form is associated with Gardner syndrome (40–42). Aggressive surgery is usually required but is rarely curative, and local recurrence is characteristic.
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Figure 25. Desmoid tumor in a 34-year-old woman. Axial contrast-enhanced reformatted CT image of the abdomen shows a desmoid tumor (arrows) invading the left rectus abdominis muscle. Although desmoid tumors are histologically benign, they demonstrate locally aggressive features.
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Rectus Sheath Hematomas
Rectus sheath hematomas may occur as a result of trauma to the abdominal wall or secondary to disorders of coagulation, blood dyscrasia, or degenerative vascular diseases. CT demonstrates that the hematoma is confined to the abdominal wall. Although hematomas are usually treated nonsurgically, a residual mass may persist for several weeks. Rectus sheath hematomas are usually easy to differentiate from hernias at multi–detector row CT. High attenuation on unenhanced images, lack of enhancement, and resolution on follow-up studies help confirm the diagnosis (Fig 26) (43,44).
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Figure 26. Rectus sheath hematoma in a 33-year-old hemophilic patient. Axial unenhanced CT scan of the abdomen shows a hematoma of the left rectus abdominis muscle (arrows). The lesion simulated an abdominal wall hernia at physical examination. A hyperattenuating blood collection and extensive subcutaneous edema are also seen.
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Other Diseases
Other diseases that may mimic abdominal wall hernias at physical examination include eventration (Fig 27); gas collections within the abdominal wall, which may mimic bowel loops at palpation (Fig 28); enlarged inguinal lymph nodes (Fig 29); an undescended testis; and enlarged vessels in the abdominal wall (Fig 30).
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Figure 27. Eventration in a 65-year-old woman. Axial contrast-enhanced reformatted CT image shows bulging of the abdominal wall (arrowheads) and severe atrophy of the wall muscles. These findings mimic a large ventral hernia, but absence of a full-thickness defect or hernia sac permits the correct diagnosis of abdominal wall eventration.
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Figure 28a. Gas collection within the abdominal wall in an 83-year-old woman with acute colonic perforation from colonic ischemia. (a) Axial contrast-enhanced CT scan of the lower abdomen shows free gas dissecting into the abdominal wall (arrowheads), a finding that could conceivably simulate a ventral wall hernia at physical examination. (b) Axial contrast-enhanced CT scan obtained at a higher level than a shows pneumatosis intestinalis in the ascending and transverse colon (arrows). Extensive pneumoperitoneum is also seen (arrowheads).
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Figure 28b. Gas collection within the abdominal wall in an 83-year-old woman with acute colonic perforation from colonic ischemia. (a) Axial contrast-enhanced CT scan of the lower abdomen shows free gas dissecting into the abdominal wall (arrowheads), a finding that could conceivably simulate a ventral wall hernia at physical examination. (b) Axial contrast-enhanced CT scan obtained at a higher level than a shows pneumatosis intestinalis in the ascending and transverse colon (arrows). Extensive pneumoperitoneum is also seen (arrowheads).
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Figure 29. Mycobacterium avium-intracellulare in a 25-year-old immunodeficient man who presented with a painful inguinal mass. Findings at physical examination were nonspecific. Axial contrast-enhanced CT scan of the lower abdomen shows a low-attenuation lymph node in the right inguinal region (arrow). Innumerable low-attenuation lymph nodes were seen in the abdomen. These findings suggested mycobacterial infection. M avium-intracellulare was confirmed at microbiologic analysis.
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Figure 30a. Varicocele in a 45-year-old man. (a) Axial contrast-enhanced reformatted CT image through the inguinal regions shows a right-sided varicocele (arrow) simulating an inguinal hernia. (b) Coronal thick-section MPR image delineates the course of the varicocele (arrows) to the level of a renal cell carcinoma (arrowheads) arising from the right kidney.
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Figure 30b. Varicocele in a 45-year-old man. (a) Axial contrast-enhanced reformatted CT image through the inguinal regions shows a right-sided varicocele (arrow) simulating an inguinal hernia. (b) Coronal thick-section MPR image delineates the course of the varicocele (arrows) to the level of a renal cell carcinoma (arrowheads) arising from the right kidney.
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Special attention should be given to cirrhotic patients, in whom enlarged abdominal wall vessels may simulate wall hernias (Fig 31). In such cases, careful imaging assessment is warranted for adequate treatment planning.
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Figure 31a. Enlarged abdominal wall vasculature in a 55-year-old cirrhotic man with portal hypertension. Axial (a) and sagittal (b) contrast-enhanced maximum-intensity-projection images show a recanalized paraumbilical vein (arrows) simulating an umbilical hernia. Innumerable subcutaneous varices are also seen (arrowheads), particularly in the area surrounding the umbilicus. The sagittal image more clearly delineates portosystemic collateral vessels extending into the chest than does the axial image.
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Figure 31b. Enlarged abdominal wall vasculature in a 55-year-old cirrhotic man with portal hypertension. Axial (a) and sagittal (b) contrast-enhanced maximum-intensity-projection images show a recanalized paraumbilical vein (arrows) simulating an umbilical hernia. Innumerable subcutaneous varices are also seen (arrowheads), particularly in the area surrounding the umbilicus. The sagittal image more clearly delineates portosystemic collateral vessels extending into the chest than does the axial image.
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Conclusions
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Abdominal wall hernias are the most common indication for major surgery in the Unites States and are a common finding at abdominal imaging. They are well evaluated with multi–detector row CT, which allows assessment of unrepaired and surgically repaired hernias and of related complications. The multiplanar capabilities of multi–detector row CT are especially important, since they allow excellent anatomic delineation, enhancement of the communication of imaging findings, and optimal treatment planning.
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Footnotes
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Abbreviations: MPR = multiplanar reformatted, PTFE = polytetrafluoroethylene
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Abstract
LEARNING OBJECTIVES FOR TEST...
