Inflammatory pseudotumor of the peroneal nerve: case report and literature review

Inflammatory pseudotumors (IPTs) are a group of lesions of obscure etiology. Although they are presumably reactive, their exact pathogenesis is unknown. Inflammatory pseudotumors are identified in different organs; however, IPTs of the peripheral nerves have been rarely reported in the English literature. We report a 44-year-old woman who presented with left foot drop. Examination revealed a thickening in the posterolateral aspect of the popliteal fossa and features consistent with peroneal nerve palsy. Magnetic resonance imaging revealed a mass that may represent a Baker cyst or perineural sheath mass that was excised. After pathological examination, the case was diagnosed as IPT of peroneal nerve, and the patient received no further therapy. Inflammatory pseudotumors of the peripheral nerves, although rare, should always be of consideration in the differential diagnosis of peripheral nerve nodular mass lesions. They can mimic neoplastic nerve sheath lesions, clinically and radiologically. However, they are amenable to surgical cure with nerve-sparing surgery. Thus, despite their rarity, on dealing with neural S100 negative lesion, their inclusion is mandatory to avoid an unnecessary and a rather aggressive surgery.