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Neoplastic and Non-neoplastic Conditions of the Abdominal Wall
Cross-sectional imaging modalities including ultrasonography, computed tomography (CT), and magnetic resonancy imaging (MRI) provide good anatomic detail of the abdominal wall and allow evaluation of pathologic processes in this area. Ultrasonography is frequently used as the first imaging modality to explore a palpable abdominal mass.
Non-neoplastic Conditions
Abdominal Wall InflamMation, Infection, and Fluid Collection
Etiology
Inflammatory processes involving the abdominal wall include diffuse edema ( Figure 83-1 ), infections such as cellulitis or abscess, and sterile collections (seroma or liquefying hematoma) ( Figure 83-2 ).
Fluid collections of the abdominal wall commonly result from trauma, postsurgical wound complication, or extension from an intra-abdominal source ( Figures 83-3 and 83-4 ).
Abdominal wall infections also can manifest as necrotizing fasciitis. This condition is considered a true surgical emergency.
Prevalence and Epidemiology
Spontaneous infection of the abdominal wall is infrequent in the general population. It is more commonly seen in patients with diabetes mellitus, immunosuppressant therapy, sepsis, surgery, trauma, atherosclerosis, alcoholism, obesity, and malnutrition.
Clinical Presentation
Clinical recognition of fluid collections or inflammatory processes can be difficult, and patients may present with fever, pain, and skin changes.
Pathology
Pathologic and laboratory findings vary according to the specific type of infection.
Imaging
Infectious involvement of the abdominal wall may manifest as cellulitis with poorly defined inflammatory changes in the subcutaneous fat tissue or as a well-defined collection (abscess). CT and MRI provide key information regarding the nature and extent of the infection.
Radiography.
Conventional radiographs have no role in assessing infection and collections of the abdominal wall.
Computed Tomography.
On CT, abscesses appear as low-attenuation fluid collections, often with enhancing margins and gas or gas/fluid levels. Diffuse inflammatory stranding of adjacent structures also is seen. Necrotizing fasciitis can be seen as soft tissue gas dissecting fascial planes in a characteristic appearance. CT plays an important role in guiding percutaneous aspiration or drainage procedures.
Magnetic Resonance Imaging.
Abscesses are often heterogeneous but generally appear hypointense on T1-weighted sequences and hyperintense on T2-weighted sequences with peripheral enhancement and inflammatory changes in the adjacent tissues.
Ultrasonography.
Fluid collections complicated by infection or hemorrhage have a complex appearance on ultrasound with echoes and internal septa.
Imaging Algorithm.
Ultrasonography is the mainstay for diagnosis of abdominal wall abscesses; however, in obese or postoperative patients, in whom ultrasound evaluation is limited, multidetector CT (MDCT) or MRI should be considered ( Table 83-1 ).
Classic Signs
Abdominal Wall Inflammation, Infection, and Fluid Collections
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Cellulitis appears as diffuse inflammatory changes involving the skin and subcutaneous tissue.
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Abscesses appear as fluid collections, with enhancing margins and surrounding inflammatory changes.
TABLE 83-1
Accuracy, Limitations, and Pitfalls of the Modalities Used in Imaging of Abdominal Wall Inflammation, Infection, and Fluid Collections
| Modality | Accuracy | Limitations | Pitfalls |
|---|---|---|---|
| Radiography | Limited availability of source literature for comparing accuracy of different imaging modalities for detecting non-neoplastic pathology of the abdominal wall | Not useful | |
| CT | Ionizing radiation | ||
| MRI | Expensive and not widely available Limited spatial resolution Limited on postoperative patients Patient-limiting factors (e.g., claustrophobia, pacemaker) |
||
| Ultrasonography | Obesity, significant scarring, patients with acute abdominal pain Operator dependent Requires high-frequency transducer |
If near field is overlooked, abdominal wall pathologic process may be missed. |
CT, Computed tomography; MRI, magnetic resonance imaging.
Differential Diagnosis
Differential diagnosis of abdominal wall collections includes uninfected seroma, hematomas, and abscess. Image-guided aspiration with bacteriologic analysis may be needed to differentiate between these entities.
Treatment
Therapy includes antimicrobial therapy and percutaneous drainage. Surgical management is usually required in severe conditions or in cases of necrotizing fasciitis.
Traumatic Abnormalities, Including Abdominal Wall Hematoma
Etiology
Traumatic injuries include laceration, contusion, hematoma, and muscle tear. Abdominal wall hematomas may be associated with trauma, anticoagulation therapy, and blood dyscrasias. Abdominal wall hematomas commonly involve the anterior or anterolateral muscle groups.
Groin, or retroperitoneal hematoma may occur as a complication of arterial or venous catheterization.
Prevalence and Epidemiology
Trauma may result in abdominal wall abnormalities that can be detected on imaging studies, including abdominal wall laceration ( Figure 83-5 ), hematoma, contusion, and muscular tear ( Figure 83-6 ).
Clinical Presentation
Above the arcuate line, wall hematomas are confined within the rectus sheath, they are oval ( Figure 83-7 ), and they manifest with pain and tenderness. Below the arcuate line and because of the absence of the posterior rectus sheath, the hematoma is unconfined; it can leak and dissect posteriorly into the extraperitoneal spaces, across the midline in the prevesical space (Retzius's space), or laterally into the flank, predisposing to hypovolemic shock secondary to uncontained blood loss ( Figure 83-8 ).
Pathology
Trauma may affect skin, subcutaneous tissues, and muscles of the abdominal wall.
Imaging
Computed Tomography.
On CT, acute hematoma is hyperdense relative to muscle because of clot formation. Attenuation values decrease with time as breakdown of blood products occurs. Chronic hematoma may be isodense or hypodense relative to surrounding muscle.
A classification method for rectus sheath hematoma has been described on the basis of CT findings, as follows :
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Type 1: The hematoma is unilateral and intramuscular.
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Type 2: The hematoma is intramuscular, as it is in type 1, but blood is also present between the muscle and the transversalis fascia. It may be unilateral or bilateral. No blood is seen in the prevesical space.
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Type 3: The hematoma may or may not affect the muscle; blood products are seen between the muscle and the fascia transversalis, as well as in the prevesical space.
Magnetic Resonance Imaging.
MRI is very useful in the diagnosis of abdominal wall hematoma, especially when the CT findings are nonspecific. Acute hematomas appear isointense relative to muscle on T1-weighted images and hypointense on T2-weighted images. Subacute hematomas demonstrate high signal intensity on both T1- and T2-weighted images.
Ultrasonography.
Hematomas appear as a nonspecific complex fluid collection with internal echoes and septations.
Imaging Algorithm.
Ultrasonography is the mainstay for diagnosis of suspected abdominal wall hematoma; however, in obese or postoperative patients, in whom ultrasound evaluation is limited, MDCT should be considered (see Table 83-1 ). In the acute setting, MDCT provides key information regarding hematoma size and extension into the abdominal cavity.
Classic Signs
Traumatic Abnormalities, Including Abdominal Wall Hematoma
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Hematomas appear as heterogeneous fluid collections. Rectus sheath hematomas occurring above the arcuate line are contained within the muscular fascia. Below the arcuate line, hematoma may extend into the prevesical space, becoming uncontained ( Figure 83-9 ).
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CT and MRI show a heterogeneous fluid collection with fluid/fluid levels (hematocrit effect).
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Ultrasonography demonstrates a complex collection.
Differential Diagnosis
Abdominal wall hematoma may mimic other pathologic processes leading to acute abdomen. It may be confused with other fluid collections, such as infected or uninfected seroma ( Figure 83-10 ) or abscesses.
Treatment
In hemodynamically stable conditions, conservative measures are the mainstay of treatment. If the patient becomes unstable or cannot be controlled with conservative measures, surgical intervention or transcatheter embolization may be considered.
Endometriomas
Etiology
Endometriomas form when functional endometrial tissue is located outside the uterine cavity. This may occur after surgical procedures that disrupt the uterine cavity (e.g., cesarean section), allowing endometrial tissue to be seeding. In these cases, endometriomas may be located within the abdominal wall at the site of the surgical incision.
Prevalence and Epidemiology
In most cases, ectopic endometrial tissue is located within the pelvis, associated with the ovaries, uterine ligaments, and pelvic peritoneal folds.
Clinical Presentation
Most patients present with a palpable mass in the region of a surgical scar. A history of cyclic pain associated with menses may be present.
Pathophysiology
Two leading theories exist for endometriosis. One hypothesis suggests that mesenchymal cells with multipotential properties may undergo metaplasia into endometriosis. The other theory states that endometrial cells may be transported to ectopic sites, forming an endometrioma. When these cells are stimulated by estrogens, they may proliferate and become symptomatic.
Pathology
Extrapelvic endometriosis has been described in nearly all body cavities and organs, but the abdominal wall is the most frequent location, occurring in approximately 0.8% of patients with endometriosis.
Imaging
The ultrasound, CT, and MRI features of abdominal wall endometriosis are nonspecific. Endometriomas appear as a solid mass in the abdominal wall with hypervascular component.
Computed Tomography.
The major role of CT is to demonstrate a solid, enhancing mass in the abdominal wall.
Magnetic Resonance Imaging.
MRI may show high signal intensity on T1- and T2-weighted images resulting from hemorrhage. Nevertheless, abdominal wall endometrioma may be nonspecific—hypointense or isointense to muscle on T1-weighted images and hyperintense on T2-weighted images and enhance after contrast administration.
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