Fibrocartilaginous mesenchymoma of the rib with atypical imaging features

Fibrocartilaginous mesenchymoma is a locally aggressive intraosseous lesion first described in 1984, which most commonly presents in the long bones of children and young adults. It is rare-less than 40 cases have been reported to date. The typical radiological features are those of an expansile lytic lesion with chondroid calcification, cortical destruction and frequent extraosseous extension, suggesting an aggressive benign or low-grade malignant tumour. On MRI the lesion returns low T1 and high T2 signal and usually shows intense contrast enhancement. Histologically the lesion is characterised by a spindle cell proliferation, areas of ossification and benign cartilage nodules resembling the epiphyseal plate, the latter considered the hallmark of this tumour. We present a case of fibrocartilaginous mesenchymoma in the rib of a 28-year-old female, a very uncommon location for this tumour. The case is also exceptional because of the age of the patient and its unusual imaging appearances: the lesion showed no evidence of chondral-type matrix mineralisation, displayed profound T2 hypointensity and only minimal enhancement following intravenous Gadolinium administration.