= borderline tumor with benign / locally aggressive / malignant behavior (counterpart of glomus tumor)

◊Clinical behavior + histopathologic features are similar to solitary fibrous tumor

Age: 4^th–5^th decade; M÷F = 1÷1

Path: large vessels predominantly in tumor periphery

Histo: cells packed around vascular channels containing cystic + necrotic areas closely resembling cellular areas of solitary fibrous tumor; arising from contractile cells that surround the walls of vessels (= Zimmermann pericytes)

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

• slow-growing mass ± local mass effect

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

• Soft tissue
  = deep-seated well-circumscribed lesion arising in muscle
  Location: lower extremity in 35% (thigh), pelvic cavity, retroperitoneum, head & neck (unlikely), meninges
  • painless slowly growing mass up to 20 cm
  • large lobulated well-circumscribed hypervascular mass
  • foci of calcification + areas of necrosis
  • displacement of kidney
• Breast (extremely rare)
• Bone (rare)
  Location: lower extremity, vertebrae, pelvis, skull (dura similar to meningioma)
  • osteolytic lesion in metaphysis of long / flat bone
  • subperiosteal large blowout lesion (similar to aneurysmal bone cyst)
  
  Angio:
  • displacement of main artery
  • pedicle of tumor feeder arteries
  • spider-shaped arrangement of vessels encircling tumor
  • small corkscrew arteries
  • dense tumor stain

Prognosis: 47–86% 10-year survival rate

DDx: hemangioendothelioma, angiosarcoma