Massive abdominal wall desmoid tumor

Case contributed by Dr Michael P Hartung

Presentation

Slowly growing abdominal mass.

Patient Data

Age: 20 years
Gender: Female

Massive extraperitoneal mass measuring 13 x 21 x 23 cm (AP X TR X CC). Appears to be arising from the left rectus abdominis muscle. There are several internal blood vessels. Several collateral vessels coursing along the rightward aspect of the mass.

Case Discussion

Pathology report (following surgical excision where it was arising from abdominal wall musculature and also adhered to the bladder wall):  Cores consist of a spindle cell lesion characterized by bland spindle cells infiltrating into skeletal muscle fibers. Mitotic activity is rare. No evidence of necrosis.  Tumor cells are positive for B-Catenin and negative for ASMA.

Final diagnosis: Desmoid tumor 

Desmoid tumor should be considered when evaluating an unknown rounded abdominal wall or mesenteric mass, particularly if it is a younger patient, slowly growing, and associated with childbirth (usually after). Despite the large size, there isn't really a long differential for such a mass without metastases. The lower curved margin with the abdominal wall on sagittal images (at the level of the Space of Retzius) indicates that it is extraperitoneal and arising from the abdominal wall, as well as the relatively indistinguishable plane with the musculature on axial images where it appears that the tumor extends to the subcutaneous fat fascial plane. 

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