Solitary Fibrous Tumor of the Soft Tissues

Solitary fibrous tumors are rare spindle cell neoplasms that were first described in the pleural space, but which can occur anywhere in the body, including the retroperitoneum, deep soft tissues of the proximal extremities, abdominal cavity, and head and neck.

Solitary fibrous tumors are a distinctive mesenchymal neoplasm that have hemangiopericytoma-like microscopic features. Indeed, many tumors previously classified as hemangiopericytomas are now called solitary fibrous tumors.

Unlike thoracic tumors, solitary fibrous tumors elsewhere tend to be symptomatic. Like their thoracic cousins, solitary fibrous tumors of the soft tissues are benign tumors that are cured by surgical resection in almost all cases. Lipomatous hemangiopericytoma, a rare variant of the solitary fibrous tumor, contains mature adipose tissue, and will be discussed at a later date.

On CT and MRI, solitary fibrous tumors have well-defined margins and usually lobulated contours. Solitary fibrous tumors can exert mass effect on and displace adjacent structures, but local invasion is rare. Post-contrast images reveal avid contrast enhancement in the majority of cases, usually with a heterogeneous pattern. Calcification is uncommon.

MRI reveals nonspecific features: high signal intensity on T2-weighted images and intermediate signal intensity on T1-weighted images. Large collateral feeding vessels can be seen as perilesional flow voids.

Differential considerations include highly vascular soft-tissue lesions such as high-grade sarcomas, angiosarcoma, and a solitary vascular metastasis.

References

• Gengler C, Guillou L. Solitary fibrous tumour and haemangiopericytoma: evolution of a concept. Histopathology. 2006 Jan;48(1):63-74.
• Wignall OJ, Moskovic EC, Thway K, Thomas JM. Solitary fibrous tumors of the soft tissues: review of the imaging and clinical features with histopathologic correlation. AJR Am J Roentgenol. 2010 Jul;195(1):W55-62.