L3 rootlet recurrent melanocytic schwannoma – case report and literature review

Abstract

First described by Miller in 1932, melanocytic schwannoma (MS) (melanotic schwannoma, pigmented schwannoma) is a rare variation of peripheral nerve sheet tumours with ectodermal origin occurring predominantly in somatic, but also in the autonomic peripheral system with around two hundred cases in the literature. Predominantly benign tumours, MS are still imaging and pathological challenge and can be easily misdiagnosed with more aggressive peripheral nerve tumours. We report a case of melanocytic schwannoma on L3 sensory rootlet with systematic literature review of nearly 200 cases presented in intracranial, paraspinal region, thoracic, abdominal or pelvic cavities and skin. Two-thirds of cases are part of Carney complex. We present a case of a 61-year-old male with a 3-month history of low back pain, progressive numbness and stiffness in the right thigh, shin and knee, tibial and peroneal paresis causing gait disturbance and neurological claudication. MRI findings present “sand clock” type intradural extramedullary tumour formation with extension to the L3 rootlet through right L3-L4 foramen, hypointense on T2 and hyperintense on T1. Pathological diagnosis of sporadic type melanocytic schwannoma was made via immunohistological and ultrastructural analysis. Thirteen months after total resection there was clinical and MRI evidence of recurrence of the tumour. Total resection and radiosurgery was performed with a recurrence free period of 14 months.A gold standard for melanocytic schwannoma treatment is gross total surgical resection. Despite being considered benign tumours, MS have a local or metastatic recurrence of around 13%. MRI imaging in most of the cases is insufficient and only exhaustive pathological and immunohistological examination is the key to diagnosis. Need of postoperative radiation therapy is still controversial. For the first time, a criterion for postoperative adjuvant therapy was established.