= mesenchymal tumor of fibroblastic / myofibroblastic origin and intermediate malignant potential

• Clinical behavior + histopathologic features are similar to hemangiopericytoma
• Most solitary fibrous tumors are benign!

Histo: patternless architecture characterized by alternating hypo- and hypercellular areas separated by thick bands of hyalinized collagen and branching vessels

Age: middle-aged adults

Location: anywhere; extrapleural >pleural site

• head & neck: nasal cavity, paranasal sinus, nasopharynx, parapharyngeal space, larynx
• meninges

May be associated with: hypoglycemia (← overproduction of insulinlike growth factor), arthralgia, osteoarthropathy, digital clubbing

• slow-growing mass ± local mass effect

CT:

• solitary well-circumscribed lobulated mass
• soft-tissue attenuation
• intense contrast enhancement
• heterogeneous texture if large ← hemorrhage, necrosis, cysts

MR:

• well-circumscribed solid mass
• low to intermediate SI on T1WI + T2WI
• heterogeneously high SI on T2WI ← myxoid / cystic degeneration
• low signal-intensity rim around lesion (= pseudocapsule) on T2WI
• hypervascularity with prominent enhancement + flow voids

DDx: hemangiopericytoma (overlapping histology)