Diagnostic Dilemma and Management of a Rapidly Enlarging Thigh Mass: A Case Report of Fibromatosis Mimicking Soft-tissue Sarcoma.
Digvijay Jaideepsingh Jadhav, Shreya Reddy Nagula, Virendra S Athavale et al.
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Case in brief
A 27-year-old woman presented with a painless, firm, immobile left-thigh mass that enlarged from 2 cm × 2 cm to 10 cm × 10 cm over 9 months. MRI of the thigh and pelvis suggested soft-tissue sarcoma. Trucut biopsy instead showed hypocellular spindle-cell proliferation, thick collagen deposition, and no nuclear atypia; immunohistochemistry was positive for β-catenin and negative for desmin, S-100, and CD-34, supporting fibromatosis. Wide local excision achieved R0 margins, and postoperative histopathology confirmed the diagnosis. MRI follow-up was advised because of recurrence risk; no recurrence was evident at 6 months.
What made this case unusual
The rapidly enlarging mass and MRI appearance suggested sarcoma, but biopsy and immunohistochemistry established fibromatosis, illustrating a clinically and radiologically misleading presentation.
Diagnostic / clinical pearl
When imaging suggests soft-tissue sarcoma, tissue diagnosis can distinguish fibromatosis; hypocellular spindle cells with abundant collagen and β-catenin positivity supported the diagnosis in this case.