Endometriosis - rectus abdominis

Case contributed by Dr Eid Kakish

Presentation

Previous cesarean section. Longstanding history of a growing lump in the lower anterior abdominal wall associated with cyclical abdominal pain and localized tenderness.

Patient Data

Age: 35 years
Gender: Female
Ultrasound

Transverse ultrasound images of the lower anterior abdominal wall show an irregular predominantly hypoechoic mass within the right rectus abdominis muscle, demonstrating minimal internal vascularity on color Doppler interrogation, with tiny intralesional cystic spaces.

There is an irregular heterogeneously enhancing soft-tissue lesion in the midline of the lower anterior abdominal wall, involving the linea alba and invading the rectus abdominis muscles, more to the right of the midline just proximal to the rectus abdominis origin at the pubic symphysis and tubercle. It demonstrates an isointense signal to the normal surrounding muscle on T2-weighted images, corresponding to a heterogenous bright signal on conventional and fat-suppressed T1-weighted images, consistent with intralesional hemorrhagic components, suggestive of ectopic endometrial tissue at the scar site of the previous cesarean section. It measures around 5.1 x 3.3 x 1.9 cm in length, width and thickness, respectively. No definite intraperitoneal or subcutaneous soft-tissue extension.

Photo

Resected abdominal wall mass showing tiny hemorrhagic foci and chocolate colored cystic lesions with a faint white background. 

Pathology:

Gross description:

Serial sectioning shows fibrous tissue with hemorrhagic spots in the middle portion of the specimen. The margins are free from hemorrhagic spots. 

Microscopic description:

Fibroskeletal tissue with dilated endometrial glands and stroma. 

Conclusion:

Anterior abdominal wall mass, consistent with endometrioma. Clear resection margins.

Case Discussion

Pathologically proven cesarean section scar endometrioma with full-thickness involvement of the anterior abdominal wall muscles.

Scar endometriosis can be easily overlooked on routine cross-sectional imaging. A previous cesarean section scar is one of the most common locations of endometriosis beyond the ovaries and uterus. 

The most plausible pathophysiological explanation is endometrial stem cell implantation at the surgical bed during uterine surgery. 

Scar endometriomas may show similar imaging features to pelvic endometriotic tissue on MRI, with high signal on fat-suppressed T1W images, representing ectopic endometrial glands. 

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