= (MALIGNANT) ANGIOBLASTOMA

= rare locally aggressive / low-grade malignancy of bone

Risk factors for malignant course:

• male sex, young age at presentation, short duration of symptoms, pain at initial presentation, local recurrence

Histo: zonal architecture of neoplastic epithelial cells (reactive to cytokeratins) concentrated centrally in osteofibrous stroma that forms peripherally columnar cells in a palisade pattern; prominent vascularity; resembles ameloblastoma of the jaw

Age: 25–50 (range, 3–74) years, commonest in 2^nd–3^rd decade

Prevalence: <0.5% of malignant bone tumors

• frequently history of trauma; local swelling ± pain

Location: middle ⅓ of tibia (90%), fibula, ulna, carpals, metacarpals, humerus, shaft of femur

Size: average length of 10 cm

• eccentric round osteolytic lesion with sclerotic margin
• multiple additional foci (= multicentricity) in continuity with major lesion (CHARACTERISTIC) in 27%
• longitudinally oriented along anterior tibial diaphysis
• narrow zone of transition, may show mottled density
• slight bone expansion (frequent)
• cortical breakthrough in 15%
• synchronous fibular involvement in 5–10%

MR:

• intermediate signal intensity relative to muscle on T1WI
• intensity similar to fat on T2WI
• marked homogeneous enhancement

Prognosis: tendency to recur after local excision (19%); after several recurrences pulmonary metastases may develop; 13% mortality rate

DDx: fibrous dysplasia (in child <10 years of age, painless enlargement of tibia, anterior bowing, pathologic fracture, eccentric bubbly cortical lucency and expansion with spontaneous regression)