Desmoid Fibromatosis Involving the Retropharyngeal and Danger Spaces: A Case Report

Desmoid fibromatosis (DF) is a rare, non-metastasizing but locally aggressive mesenchymal tumor arising from fibroblasts or myofibroblasts. We report a solitary case of DF involving the retropharyngeal and danger spaces, a location rarely documented. The patient, a woman in her 70s, presented with progressive pharyngeal discomfort over six months. Imaging studies revealed a soft-tissue mass consistent with DF, and the diagnosis was confirmed pathologically. The tumor demonstrated unique imaging findings, including band-like hypointense areas on T2-weighted imaging on magnetic resonance imaging and moderate 2-deoxy-2-[¹⁸F]fluoro-D-glucose uptake on positron emission tomography/computed tomography (PET/CT), which may aid in differentiating DF from malignant tumors in atypical locations. Furthermore, this case highlights the effectiveness of radiotherapy in achieving significant tumor reduction, offering insights into the management of DF in rare and challenging locations. These findings not only aid in refining the differential diagnosis but also provide evidence supporting radiotherapy as a viable treatment option in cases where surgical resection is unfeasible.