Polyostotic Fibrous Dysplasia With Extensive Cartilaginous Differentiation: A Rare Case Clinically Mimicking Ollier Disease

Abstract Fibrous dysplasia is a dysplastic disorder of bone caused by missense mutations of the GNAS1 gene. Fibrocartilaginous dysplasia (also known as fibrochondrodysplasia or fibrous dysplasia with extensive cartilaginous differentiation) is a rare variant of fibrous dysplasia with extensive cartilaginous differentiation that shows a predilection for the lower extremities and can affect one or multiple bones. Although benign, this entity causes progressively expansile lesions that can lead to deformity and ultimately pathologic fracture. On imaging, this entity can show features consistent with a variety of benign and malignant cartilage-forming tumors. We present the case of a 16-year-old male patient who presented with clinical history of Ollier disease and multiple presumed enchondromas. He underwent below-the-knee amputation for progressive tibial deformity, pathologic fracture, and pain. Microscopic examination of multiple lower-extremity bones revealed a fibro-osseous lesion with massive cartilaginous differentiation consistent with fibrocartilaginous dysplasia.