Teaching NeuroImages: Sonographic detection of intraneural perineurioma in therapy-refractory carpal tunnel syndrome

A 55-year-old man with typical clinical and electrodiagnostic findings of carpal tunnel syndrome complained of progression of his symptoms. Since repeated surgical interventions did not provide any relief, sonographic examination was performed and depicted a massive median nerve enlargement with hyperechoic perineurial tissue (figure, A). Beyond postoperative perineural fibrosis, the findings were suspicious for an underlying tumor. MRI revealed a tumorous nerve swelling and surgical neurolysis of hypertrophic fascicles followed (figure, B and C). Histopathology confirmed the diagnosis of intraneural perineurioma, a rare, benign, slow-growing peripheral nerve sheath tumor of perineurial cell origin (figure, D and E).1 Nerve sonography is recommended in therapy-refractory cases, as it might uncover unusual causes of entrapment syndromes.2