Desmoplastic fibroma

Case contributed by Dr Matt Skalski

Presentation

Forearm mass.

Patient Data

Age: Pediatric
X-ray

There is a well-defined, highly expansile, purely lytic lesion within the proximal ulna which extends to the distal third of the diaphysis, and demonstrates cortical destruction with a large associated soft-tissue mass. The soft tissue mass is observed circumferentially about the ulna and anterior to the elbow.  No periosteal reaction is appreciated, and there is no tumor matrix mineralization, however internal pseudotrabeculation is present. 

 

Pathology

Cut surface shows a lobulated mass. 

Pathology

There are spindle cells (fibroblasts/myofibroblasts)  within  an abundant, dense matrix of collagen.  The degree of cellularity is variable but cellular atypia and pleomorphism are minimal or absent. Mitoses are rare.

Case Discussion

Desmoplastic fibromas are extremely rare (~0.3%) primary benign bone tumors which are locally aggressive and affect a young age demographic with no sex predilection. 

This case is from pedorthpath.com, courtesy of Dr. Dariusz Borys, with permission. 

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