Fibromatosis with aggressive demeanor: Benign impersonator of malignancy

Fibromatosis or desmoid fibromatosis is a rare benign neoplasm and develops commonly in the abdominal wall, abdominal cavity, or extra-abdominal sites. The mainstay of treatment is surgery. Chemotherapy and radiotherapy are preferred in cases of inoperable/relapse or a multifocal disease. Hereby, we report a case of fibromatosis arising in the left popliteal fossa, proven by histopathology and immunohistochemistry. Local excision of the mass was performed. The patient was asymptomatic for 6 months, after which she complained of difficulty in walking. Clinical evaluation elicited recurrence in the surgical bed. In spite of the surgical excision with tumor-free margins, recurrence was seen within a span of 6 months. ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET/CT) was done to rule out multifocal disease and to define the extent of relapse. Although magnetic resonance imaging provides an excellent soft-tissue resolution to delineate the disease, ¹⁸F-FDG PET/CT is an important and supplementary tool which aids in the management of fibromatosis.