The Benign Side of the Abdominal Wall: A Pictorial Review of Non-Neoplastic Diseases

Abstract

The abdominal wall is the location of a wide spectrum of pathological conditions, from benign to malignant ones. Imaging is often recommended for the evaluation of known palpable abdominal masses. However, abdominal wall pathologies are often incidentally discovered and represent a clinical and diagnostic challenge. Knowledge of the possible etiologies and complications, combined with clinical history and laboratory findings, is crucial for the correct management of these conditions. Specific imaging clues can help the radiologist narrow the differential diagnosis and distinguish between malignant and benign processes. In this pictorial review, we will focus on the non-neoplastic benign masses and processes that can be encountered on the abdominal wall on cross-sectional imaging, with a particular focus on their management. Distinctive sonographic imaging clues, compared with computed tomography (CT) and magnetic resonance (MR) findings will be highlighted, together with clinical and practical tips for reaching the diagnosis and guiding patient management, to provide a complete diagnostic guide for the radiologist.

Keywords: abdominal wall; computed tomography; diagnosis; differential; incidentalomas; magnetic resonance imaging; ultrasonography.

Figure 1

Abscesses on US and CT in a 69-year-old woman with myelofibrosis, presenting with pain along the surgical scar and persistent fever two weeks after splenectomy. B-mode US (first picture, arrow) demonstrates a fluid collection, with no significant vascularization on color Doppler (CD, lower picture). On portal-phase CT (third picture), the abscess is easily distinguishable (arrowhead).

Figure 2

CT appearance of necrotizing fasciitis in a 58-year-old woman with a recent left lower limb open wound who arrived at the ER in septic shock. Arterial phase axial CT scan reveals the presence of free air in the fascial planes of the left lateral and posterior abdominal wall, with fascial thickening and lack of muscular enhancement, as compared to its counterpart (arrows). These elements are suggestive of necrotizing fasciitis. The patient was promptly referred to surgery, but she died on the operatory table.

Figure 3

Granuloma occurring along a surgical mesh for an inguinal hernia repair. Axial CT on unenhanced (image on the left) and delayed phase at 10 min (image on the right) shows the formation of a nodular, fibrotic mass, with uptake contrast in delayed phases around a surgical mesh (circle).

Figure 4

A 22-year-old man with reactivation of Crohn’s disease, presenting as a new enterocutaneous fistula. B-mode US with linear transducer (first picture) shows the presence of a fistulous trait between the skin and a superficial collection (arrows). Axial not-enhanced CT scan (second picture) revealed the course of the fistula, demonstrating communication between the bowel loops and the skin, together with a small collection (circle).

Figure 5

Urachal cysts are found along the superficial planes. On B-mode US, urachal anomalies appear as fluid-filled nodularity close to or in the context of the abdominal wall, incidentally found (arrow). As seen in axial, not-enhanced CT, small parietal calcification can also be seen (short arrow).

Figure 6

Axial, not-enhanced CT scan shows the congenital absence of the right rectus muscle (arrows).

Figure 7

A 23-year-old patient with Duchenne’s syndrome. Axial, not-enhanced CT scan demonstrates complete fat replacement of all abdominal wall muscles with obligated decubitus, as commonly seen in cases of Duchenne’s syndrome patients reaching the ages of 20–30.

Figure 8

CT appearance of “caput medusae” on axial, contrast-enhanced CT scan on portal venous phase in two cirrhotic patients, as a result of the recanalization of the umbilical vein due to portal hypertension. This appearance is due to tortuous vessels (arrows) reaching the abdominal wall at the level of the navel.

Figure 9

A 37-year-old man presenting with a pulsatile mass with trauma history. Volume rendering cutaneous reconstruction (A) and axial, contrast-enhanced portal-phase CT (B) showed the presence of a large post-traumatic pseudoaneurysm of the inferior right epigastric artery, with thrombotic apposition. B-mode US and CDUS (C–E) demonstrate the presence of an anechoic part, corresponding to the contrast-enhanced part on CT, and the heterogeneity of the thrombus. CDUS (D,E) shows the “yin–yang sign”. The pseudoaneurysm was promptly treated with thrombin injection.

Figure 10

CT and US post-traumatic rectus sheath hematoma above the arcuate line. CT scan shows a well-defined mass, hyperintense on basal scan, in the context of the left rectus sheath (short white arrows). In the second picture, the delayed phase acquired 10 min after the injection of intravenous contrast demonstrates active bleeding (yellow arrow). The third picture shows the same lesion (*), studied some days later on US.

Figure 11

Hematoma below the arcuate line in a 75-year-old woman, with acute myeloid leukemia and low platelet count. After a cough, she started complaining of strong abdominal pain and a mass started growing. Coronal and axial, pre- and post-contrast injection images showed the presence of a large left rectus sheath hematoma (thick arrow) with active arterial bleeding, as demonstrated by the subsequent spreading of contrast in all phases acquired (thin arrows). Since the hematoma was below the arcuate line, bleeding into the prevesical space is also noted (arrow, last picture, bottom row).

Figure 12

Progression of metastatic disease vs. injection granulomas. Axial, contrast-enhanced arterial and portal-phase CT scans of a 50-year-old woman with NEC of the small bowel. Three months after the surgery, some lesions on the subcutaneous fat of the lower back are noted (arrowheads). Four months later, these nodules are the same size, while along the surgical scar, new enhancing nodules appear (circle). In October 2020, these latter lesions become confluent and bigger, and other lesions appear (*), all compatible with metastatic nodules, while the nodules on the posterior abdominal wall are simple granulomas.

Figure 13

Non-enhanced sagittal and axial CT scan demonstrates free silicon material scattered with an infiltrative appearance, expanding all along the subcutaneous fat of the posterior abdominal wall (arrows). Strand-like lesions coexist with nodular and plaque-like areas, making the differential diagnosis with neoplastic conditions difficult.

Figure 14

Heparin vs. insulin treatment nodules in two 70-year-old patients. Axial not-enhanced CT in the first patient shows some collections with parenchymatous density, which indicate bleeding, and small air bubbles. In the second patient, instead, lipodystrophies with peripheral calcifications are seen.

Figure 15

Woman with long-standing dermatomyositis. Axial and sagittal not-enhanced CT scan reveals diffuse, multiple calcifications on the subcutaneous abdominal tissue, representing the evolution of non-controlled dermatomyositis. Large peritoneal effusion is also seen.

Figure 16

A 59-year-old woman who underwent splenectomy some years prior. During a CT scan, new, rounded masses (circles) were found along the peritoneum and the left rectus abdominis muscle. These formations show parenchymal attenuation on CT (pictures 1 and 2) and share the same T2 intensity as the spleen. These lesions were later characterized as splenosis.

Figure 17

Endometrioma of the abdominal wall on US: heterogeneously hypoechoic, round, or oval-shaped nodule, with scattered internal echoes.

Figure 18

MR study of an endometriotic nodule (arrows) in the left rectus abdominis muscles and subcutaneous tissue. Endometriotic implants inside muscle are well characterized on MR. They show heterogeneously low signal on T1 (A) and T2 images (images B,C) and strong enhancement after the injection of contrast agent (D). Sagittal reconstruction (C) shows the extension of the endometriotic nodule into fat tissue, fascia, and intramuscular location.