Extra-abdominal desmoid fibromatosis

Case contributed by Ammar Ashraf
Diagnosis certain


Right lower back swelling for a few months. Not increasing in size. Getting painful after activity for a few weeks.

Patient Data

Age: 30 years
Gender: Female

Findings: A spiculated soft tissue mass lesion, measuring 3.1 x 2.5 cm is seen in right lower back deep subcutaneous soft tissues. There is strong suggestion of involvement of the underlying oblique muscles. The lesion is of low signal intensity on T1 and T2 weighted images and shows moderate enhancement on post contrast study. 

Impression: Spiculated soft tissue lesion in deep subcutaneous soft tissues of the right lower back. Imaging differential diagnosis includes fibromatosis, desmoid, or less likely soft tissue sarcoma. 


A well-defined, predominantly hypoechoic solid lesion with mildly lobulated borders is seen in deep subcutaneous tissues in the right lower back region. No significant internal vascularity or calcifications are seen in it. No signs of inflammation in the adjacent soft tissues.

Case Discussion

Procedure: Excision.

Diagnosis: Histological features, consistent with extra-abdominal desmoid fibromatosis.

The immunostain antibody anti-Beta-Catenin showed intense positivity and accumulation of Beta-Catenin in the nucleus and cytoplasm.  The immunostain antibody anti-smooth muscle actin also showed diffuse intense positivity of tumor cells.  However, the immunostain antibody anti-estrogen receptor (ER) and progesteron receptor (PR) is negative.

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