Pigmented villonodular synovitis of the ankle presenting as a persisting ankle effusion.

A 38-year-old woman was referred to our department with persisting pain and swelling of the right ankle, 10 months following an inversion trauma. Initial standard radiographs were unremarkable. Conservative treatment with physiotherapy and local infiltration was unsuccessful. Three month later, repeated plain radiographs revealed a slightly radiodense mass at the anterior aspect of the talocrural joint (Fig. A, white arrow). An MRI was performed for further characterization. These images show an intra-articular nodular mass within the anterior ankle joint recess. The lesion was of intermediate to low signal intensity on axial T1-weighted (WI) images (Fig. B, star). On sagittal fatsuppressed T2-WI, the lesion contained multiple intralesional areas of low signal intensity interspersed with areas of high signal (Fig. C, star). A peripheral low signal intensity rim was seen, in keeping with hemosiderin deposition within the synovium (Fig. C, black arrow). Blooming artefact was seen on gradient echo imaging (not shown). Based on the imaging findings, the diagnosis of Pigmented VilloNodular Synovitis (PVNS) was made, which was confirmed on surgery (Fig. D, surgical view showing a lesion with black pigment within the synovium) and subsequent histological examination. The postoperative course was uneventful.