Imaging features of desmoid-type fibromatosis in the teres major muscle

Desmoid-type fibromatosis is a locally aggressive fibroblastic neoplasm with a tendency for local recurrence, despite adequate surgical resection. Its clinical presentation, biological behavior, and natural history can vary considerably. We present a unique case of desmoid-type fibromatosis arising in the left teres major muscle of a 62-year-old female. Physical examination showed a 7-cm, elastic-hard, immobile, tender mass. Magnetic resonance imaging (MRI) revealed a partially ill-defined mass, with intermediate signal intensity on T1-weighted sequences and heterogenous high signal intensity on T2-weighted sequences. Contrast-enhanced fat-suppressed T1-weighted sequences demonstrated intense and homogenous enhancement throughout the mass. Integrated positron-emission tomographic (PET)/computed tomographic (CT) images showed moderate focal ¹⁸F-fluorodeoxyglucose uptake corresponding to the clinically palpable and MRI-described soft tissue mass, with a maximal standardized uptake value of 4.85. The possibility of a malignant lesion was raised. Following an open biopsy, wide resection of the tumor was performed. Histological examination confirmed the diagnosis of desmoid-type fibromatosis. Finally, we discuss the imaging features of this peculiar neoplasm on MRI and PET/CT.