Chondromyxoid Fibroma Arising in Craniofacial Sites: A Clinicopathologic Analysis of 25 Cases.

Chondromyxoid fibroma (CMF) is a rare benign tumor, usually arising in the metaphysis of long bones in young adults. Occurrence in craniofacial bones presents a particular diagnostic challenge given its unusual location and resemblance to malignant mimics. We describe the clinicopathologic features of 25 cases of craniofacial CMF identified between 1999 and 2017. Patients were 14 men and 11 women, with median age of 44 years (range, 5 to 83 y). Sites of involvement were sphenoid (7), ethmoid (5), maxilla (3), occipital (2), nasal septum (2), palatine (2), temporal (2), orbit (1), and undisclosed skull (1). Tumor size ranged from 0.8 to 6.0 cm (median, 2.0 cm). Of the 21 tumors with available radiology, 15 arose on the bone surface with expansion into adjacent sinuses; 6 were intraosseous. Bony erosion/destruction was present in most (13/16) cases, and 7/12 showed calcification on imaging. Microscopically, most tumors showed a lobulated growth pattern with hypocellular central chondromyxoid areas and peripheral hypercellularity, though many samples were fragmented. Tumor cells had ovoid to tapered nuclei and abundant palely eosinophilic cytoplasm, frequently with stellate cell processes. Mitoses ranged from 0 to 2 per 10 high-power fields (median count, 0). None showed necrosis. Significant atypia was present in 2 cases, 1 of which was a previously radiated recurrence. Bone infiltration was present in 6 cases. Thirteen tumors had focal calcification, and 2 had foci of hyaline cartilage. All tumors were negative for keratin and GFAP (0/24), with frequent positivity for SMA (7/7) and occasional staining for EMA (5/24) and S-100 (2/24). Most patients underwent piecemeal excision or curettage (5/5 positive margins when reported). Follow-up data were available for 15 patients, and 5 suffered local recurrence. Craniofacial CMF poses diagnostic pitfalls including frequent aggressive radiologic features and lack of a specific immunophenotype. Tumors may recur, largely due to the difficulty of obtaining clear surgical margins in this anatomic region. Furthermore, propensity for local destruction and invasion can create significant morbidity.