Teaching Case

A 42-year-old female patient suffering from a painful “lump” at the anterior abdominal wall in the left lower quadrant. Medical history included laparoscopically treated pelvic endometriosis and a successful pregnancy after assisted reproduction, respectively 6 years and 3 years earlier.
Physical examination revealed local tenderness, circumscribed hard-consistency nodule fixed at abdominal wall planes.

Ultrasound (Fig.1) showed a sizeable (4x3x2.5 cm) hypoechoic mass with lobulated contour, which extended ventrally from the aponeurosis of the left rectus abdominis muscle into the subcutaneous fat.
Further investigation with MRI (Fig.2) confirmed a complex abdominal wall mass which infiltrated the superficial portion of the rectus muscle, and included a central portion showing intermediate-to-high T2-weighted signal intensity and several tiny cyst-like structures at the periphery. The latter structures showed pre-contrast T1-hyperintensity consistent with recent blood and a fluid-fluid level. Additionally, several linear bands were seen radiating into the adjacent fat, configurating the characteristic "Gorgon sign". After intravenous gadolinium (Fig.3) both the mass and radiating strands showed marked contrast enhancement.
Fine-needle aspiration biopsy and histopathology after en-bloc surgical resection (including the anterior fascia of the rectus abdominis muscle) showed bloody specimen including stromal fragments and endometrial epithelium, thus confirming the radiologic diagnosis of abdominal wall endometriosis.

Endometriosis refers to functioning endometrium outside the uterine cavity. The most common extrapelvic form, abdominal wall endometriosis (AWE) generally develops secondary to transportation of endometrial tissue during surgical manipulation. The majority (65-81%) of cases occur at Caesarean section (CS) scars, with incidence approaching 0.1-0.8% in women with risk factors (parity, body mass index, previous laparotomy). Alternatively, AWE occurs at other gynaecological incisions or laparoscopic access ports, particularly in women with treated peritoneal and ovarian endometriosis. Occasionally AWE develops without surgical history, from presumed haematogenous or lymphatic dissemination [1-3].
A rare but well-described condition, AWE should be considered when faced with abdominal wall lumps, in young adult women (mean age 35.2±5.9 years) with history of CS or other surgery, developing after a variable time delay from the most recent relevant surgery (median 4 years). AWE generally manifests as a focal, tender rubbery nodule located in proximity to a surgical incision, associated with acute or recurrent pelvic pain, which is often cyclic and synchronous with menses [1, 2].
Ultrasound shows AWE as unspecific round or oval-shaped, more or less heterogeneous hypoechoic nodules (measuring 2-5 cm) compared to the abdominal wall fat, with ill-defined, sometimes spiculated margins which may be easily confused with infiltrative malignancies. The key differential diagnosis is desmoid tumour, often occurring in young women after childbirth and characterised by similar locally invasive behaviour [4-7].
At CT, AWE shows soft-tissue attenuation, similar or mildly hyperdense (median 45 Hounsfield units) compared to muscles, mild to moderate enhancement [7, 8]. As this case exemplifies, MRI better demonstrates the depth of infiltration, structure and morphology. AWE arises in the superficial layers of the abdomino-pelvic wall, develops ventrally to and sometimes infiltrates the rectus or oblique muscles. The characteristic “Gorgon sign” corresponds to linear infiltration strands irradiating peripherally from the central soft-tissue nodule. AWE has low signal intensity, mostly isointense or slightly hyperintense to muscle on both T1- and T2-weighted images. Small foci of T1-hypersignal correspond to recent bleeding within endometriotic crypts, best appreciated with fat suppression. Contrast enhancement is often marked. Chronic lesions show lower signal intensity from fibrosis and haemosiderin [7, 9, 10].
Preoperative fine-needle biopsy may be helpful to exclude malignancy. The optimal treatment is wide surgical excision with or without mesh placement. Pharmacological therapy with hormonal suppression agents may alleviate symptoms but AWE recurs after cessation. Histological confirmation relies on presence of benign endometrial glands and stroma [2, 6]. Malignant transformation has been occasionally reported [11].