Malignant fat-forming solitary fibrous tumor (lipomatous hemangiopericytoma) in the neck: Imaging and histopathological findings of a case

Abstract

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.

Malignant Fat-Forming Solitary Fibrous Tumor of the Thigh

“…Fat-forming SFTs usually occur in older adults, predominantly in males, and have a broad anatomical distribution 1. Although fat-forming SFTs are typically nonrecurring and nonmetastasizing benign tumors, they can show malignant histologic features and malignant behavior 2-5. Reported cases of malignant fat-forming SFTs revealed that men and women are equally affected, that the age of patients ranged from 20 to 93 years, and that the maximal size of a malignant tumor was 20 cm (range, 3.4 to 20 cm).…”

“…Reported cases of malignant fat-forming SFTs revealed that men and women are equally affected, that the age of patients ranged from 20 to 93 years, and that the maximal size of a malignant tumor was 20 cm (range, 3.4 to 20 cm). These tumors commonly involve the thigh and could also affect variable anatomical sites including the calf, neck, scalp, posterior thoracic cavity, ligamentum teres of the liver, arm, pelvis, lower back, vulva, and retroperitoneum 2-5. All of the reported malignant fat-forming SFTs were well emarcated and encapsulated.…”

“…The histological features suggestive of malignancy were increased cellularity, pleomorphism, mitotic count over 4 in 10 HPF, hemorrhage, necrosis, and infiltrative margin 1,4. The mitotic count ranged from 2 to 37 in 10 HPF 2-5. However, definitive criteria for malignancy in fat-forming SFTs have yet to be established.…”

“…The fat-forming variant of SFT exhibits benign biological behavior; however, in rare case, it can have malignant histologic features. Fewer than 20 malignant cases have been reported in the English literature 2-5. Herein, we present a case of fat-forming SFT with malignant histologic features arising in the thigh, in addition to a review of the literature.…”

“…Fewer than 20 malignant cases have been reported in the English literature. 2 - 5 Herein, we present a case of fat-forming SFT with malignant histologic features arising in the thigh, in addition to a review of the literature.…”