Fat-forming solitary fibrous tumor (SFT) is a rare variant of solitary fibrous tumor, a mesenchymal fibroblastic neoplasia with a particular branching hypervascular pattern. This tumor is usually classified as benign and only very few fat-forming SFTs with malignant histologic features have been reported. We report a histologically malignant fat-forming solitary fibrous tumor in a 61-year-old man, located in his neck. Ultrasonography examination was first performed showing a heterogeneous lesion, predominantly hyperechoic, with sound beam attenuation, containing two hypoechoic solid nodules. Magnetic resonance imaging and computed tomography examinations demonstrated a heterogeneous and predominantly adipose mass, containing post contrast enhancing solid nodules and thin septations. Treatment consisted of total removal of the lesion. Histologically, the tumor showed hypercellularity, numerous mitoses and cytological atypia, fulfilling the criteria for malignancy. The patient had no metastasis. This rare tumor may be confused with other fat-containing lesions on imaging examinations, mainly liposarcoma.
Keywords: MRI; fat-forming; helical computed tomography; lipomatous hemangiopericytoma; magnetic resonance imaging; malignant solitary fibrous tumor; ultrasonography.