Mesenchymal chondrosarcoma: three cases of the jaws and skull, each with variant histopathology; all confirmed with identification of the Hey1::NCOA2 fusion

Introduction

Mesenchymal chondrosarcoma is a high grade biphasic primitive tumor with foci of hyaline cartilage. The tumors may occur in bone or soft tissue and are common in the craniofacial region. Microscopically this neoplasm can be difficult to diagnosis. Identification of the Hey1::NCOA2 fusion confirms the diagnosis. Two cases involving the jaws and one of the skull are reported.

Case Findings

Case 1: A 44-year-old male with right jaw pain and facial asymmetry presented for evaluation. Imaging revealed a 7 cm destructive intraosseous mixed radiolucent-radiopaque lesion. Case 2: An 11-year-old male presented with swelling of left temporal region of two weeks duration. Imaging revealed a 5 cm destructive lesion with a mixed radiographic appearance. Case 3: An 11-year-old male presented with a 2 month post-traumatic unresolved reddish-blue soft tissue swelling of upper anterior labial mucosa. Imaging revealed minimal bony surface destruction of the anterior maxilla.

Results

Microscopic variability characterized the three cases. Case 1 exhibited classic histopathological presentation of nodules of cartilage surrounded by spindle cells. Case 2 predominately exhibited spindle cells with a pericytomatous vascular growth pattern without a cartilage component. Osseous components were identified; it was unclear whether the bone was native or neoplastic. Case 3 exhibited a monotonous spindle cell lesion suggestive of monophasic synovial sarcoma, but minute osteochondroid foci led to molecular interrogation. Molecular analysis in all three cases identified a Hey1::NCOA2, confirming the mesenchymal chondrosarcoma diagnoses.

Conclusion

Aggressive clinical behavior characterized all three cases. Histologically, the biphasic presentation was best represented in Case 1. Case 2 and 3 showed the characteristic primitive cells with minimal to no atypia; a minimal cartilaginous component was noted on extensive sampling of case 3. Mesenchymal chondrosarcoma was confirmed in each case by identifying the Hey1::NCOA2 fusion.