Neuritis ossificans is an extremely rare pathologic condition consisting in an idiopathic heterotopic formation of bone in the context of peripheral nerves, histologically similar to the far more common myositis ossificans. Only a few cases of neuritis ossificans have been previously reported in the literature. In this paper, we describe the ultrasound (US) and MR imaging appearance neuritis ossificans in three cases.

Three patients with neuritis ossificans (one 16 year-old woman; two 39 and 60 year-old men) of the sciatic, tibial and peroneal nerve at the knee were examined with high resolution US and 1.5T MR imaging. CT and radiography were also performed in two cases. Presentation symptoms included pain, functional impairment with loss of knee extension and tenderness on palpation along the course of the affected nerve.

In the affected nerves, US and MR imaging revealed a focal lesion characterized by a peripheral calcified rim encasing the nerve fascicles. In the early phase, the affected nerve appeared focally swollen with partial loss of the fascicular echotexture and the perineural tissues showed extensive inflammatory changes with diffuse hyperemia on Doppler imaging and soft-tissue edema on fluid-sensitive sequences. On MR imaging, the nerve fascicles initially appeared hyperintense on T2-signal. All three patients were treated conservatively and, in follow-up examination, the lesion shrank with improvement...

Ultrasound is able to identify the ossification process of neuritis ossificans at an early stage. MR imaging can be used to confirm the diagnosis and better depict the perineural edema and the perineural soft-tissue involvement.

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