Beyond hernias: a multimodality review of abdominal wall pathology

The diagnosis of abdominal wall pathology is often obvious on clinical physical examination; however, multimodality imaging often yields incidental, and occasionally important, findings aiding in assessing the overall clinical picture. While various hernias are common, there are numerous other causes of abdominal wall pathology. Knowledge of these entities is crucial to avoid misinterpretation and assure proper radiological judgment.

The anterior abdominal wall is composed of muscle and fascial layers that serve many functions including containment, support and protection for the intraperitoneal contents and involvement in movement and breathing (Figure 1). While hernias are often encountered and well reviewed in the literature, less commonly seen abdominal wall pathology can be confusing when encountered or a pitfall when overlooked on imaging. This pictorial review briefly discusses the anatomy of the anterior abdominal wall and presents a multimodality pictorial review of a variety of abdominal wall abnormalities beyond hernias. Congenital Urachal anomalies arise from incomplete obliteration of the embryonic connection between the urinary bladder and the allantoic duct (Figure 2).1 Failure of this process in utero results in a spectrum of anomalies including: patent urachus, urachal cyst, urachal sinus and urachal diverticulum.2 A patent urachus is often easily diagnosed at birth with ectopic urine leakage through the abdominal wall at the umbilicus. Acquired urachal infection and urachal adenocarcinoma are two feared sequela of urachal remnant disease that remain more difficult to diagnosis without the benefit of diagnostic imaging. Vascular/trauma Rectus sheath haematoma presents with acute abdominal pain and a palpable mass after trauma, muscular strain or in the setting of anticoagulation (Figure 3). The majority result from the rupture of epigastric vessels or tearing of the rectus abdominis muscle fibres.3 The natural course is typically self-limited, as the bleeding eventually tamponades itself. Vascular shunts are often clinically evident from prominence of vessels in the abdominal wall (Figure 4). Abdominal wall venous collateral vessels may occur in the setting of systemic venous occlusion or portal hypertension. Under extreme pressure, the recanalized paraumbilical vein within the round ligament can reopen to allow the passage of blood and is highly specific for portal hypertension. These vessels present an additional risk during paracentesis or other similar procedures that penetrate the abdominal wall. Inflammatory Cellulitis/abscess of the abdominal wall classically presents with focal tenderness, overlying erythema, fever and/or leukocytosis (Figure 5). This acute infection of the dermis and subcutaneous tissues occurs following disruption of the skin and invasion from either indigenous flora or exogenous bacteria. Abdominal wall abscesses can occur in patients who are post-operative or post-traumatic and can occasionally arise spontaneously as extension of an intra-abdominal process such as in Crohn disease. Necrotizing fasciitis is a rare and rapidly aggressive soft-tissue infection most commonly seen in diabetics (Figure 6). It is usually caused by underlying infection of the lower genitourinary tract or soft tissues of the perianal region. While difficult to clinically differentiate in the early stages of disease, diagnosis and treatment is paramount with mortality rates as high as 70–80%.4 Scar endometriosis typically results in a palpable abdominal wall mass with cyclical pain during menses in females with a history of caesarean delivery (Figure 7). Endometrial stem cells can be ectopically implanted along the course of the surgical incision within the abdominal wall skin, subcutaneous tissue or rectus sheath.5 Neoplastic Lipomas are benign mesenchymal tumours that resemble normal fat. They are most often found within soft tissues and skeletal muscle, but can arise in any region of the body that contains fat (Figure 8).6 Desmoid tumours are benign non-inflammatory fibroblastic tumours often associated with Gardner syndrome, previous trauma or surgical incision and have a strong prevalence among reproductive-age females (Figure 9).7 They tend to locally invade and recur without metastasis. Condyloma acuminatum is pink- or flesh-coloured macules or verrucous papillomas and is a clinically evident manifestation of the sexually transmitted human papilloma virus (Figure 10). Patients who are immunosuppressed are at the greatest risk of transmission and development of malignant transformation into invasive squamous cell carcinoma. Neurofibromas are benign neoplasms composed of schwann cells and a network of collagen fibres presenting most commonly in neurofibromatosis Type 1 (NF1) or 2 (Figure 11). Localized neurofibromas are usually solitary and sporadic; however, plexiform neurofibromas are associated with (NF1). Multiple neurofibromas are virtually diagnostic of NF1. Lesions not associated with NF1 are usually surgically excised, whereas lesions associated with NF1 are often non-surgical owing to multiplicity of lesions. Metastatic deposits are usually clinically evident, but may be overlooked, particularly in the patient with obesity (Figure 12). Typical primary lesions that cause subcutaneous metastases include melanoma, lung, renal and ovarian cancer.8 Direct spread of a variety of intra-abdominal malignancies to the abdominal wall is also common. Rarely, percutaneous biopsy can seed subcutaneous metastasis most commonly in breast cancer and hepatocellular carcinoma. Iatrogenic Seroma formation usually occurs as a complication of surgery, but can also be seen following trauma (Figure 13). Serous fluid is a proteinaceous fluid that accumulates with local haemorrhage and is thought to be due to disruption of lymphatic and vascular channels. Most resolve within 30 days; however, drainage is indicated if symptomatic or unresolved after 6 weeks. Foreign body granulomas represent a benign granulomatous proliferation in response to a retained foreign body (Figure 14). The most common culprits are surgical sutures, surgical sponges, teflon or activated charcoal. Superficial injections are an incidental clinically insignificant finding (Figure 15). Any recent subcutaneous injection may result in subcutaneous air. Subcutaneous (intralipomatous) rather than intramuscular injection of drugs can cause localized fat necrosis, scar formation and dystrophic calcification. Heparin products can incite delayed hypersensitivity reactions at the injection site, resulting in skin necrosis, skin nodule and inflammatory plaques. Lipohypertrophy is focal subcutaneous fat proliferation most commonly occurring in Type I diabetics, who inject insulin into the subcutaneous tissue (Figure 16). Local pain sensation decreases as lipohypertrophy develops, resulting in preferential injection of insulin at that site. It is important to recognize, as insulin absorption is impaired in these areas. The transplantation of a transverse rectus abdominis myocutaneous flap is a commonly used surgical procedure for breast reconstruction following mastectomy (Figure 17). It consists of an autologous myocutaneous flap comprised of abdominal skin, subcutaneous fat, the rectus abdominis muscle and adjoining vasculature. The transverse rectus abdominis myocutaneous flap is based on the superior epigastric vessels and uses the contralateral rectus abdominis muscle in its entirety for unilateral reconstruction. Complications include ventral abdominal bulging or hernia at the donor site related to diminished abdominal wall integrity. Several medical devices can be implanted within the abdominal wall (Figure 18). Unless the device was recently placed, the presence of gas or fluid around the implant should raise suspicion of infection.9 Liposuction is a cosmetic procedure commonly performed on the trunk to reduce “target fat” leaving a desired body contour. Currently, there are many surgical techniques for liposuction including powered liposuction, laser-assisted lipolysis, chemical lipolysis and ultrasound-assisted liposuction.10 While powered liposuction usually achieves the goal of a reduction in adipose tissue, this method also leaves behind characteristic concentric fibrous scars encircling the abdominal wall (Figure 19).

The abdominal wall, comprised of skin, subcutaneous tissues, muscular and fascial layers, serves important containment and supportive functions. Attention to the abdominal wall should be included in every search pattern and familiarity with a variety of processes affecting the abdominal wall will enable the astute radiologist to efficiently diagnose pathology and assist in patient management. Contributor Information Brady S Davis, Email: [email protected]. Dell P Dunn, Email: [email protected]. Valerie C Hostetler, Email: [email protected].

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