Malignant melanotic nerve sheath tumour (MMNSTs), earlier known as melanotic schwannoma, is an extremely rare variant of peripheral nerve sheath tumour arising from Schwann cells which is characterised by its ability to produce abundant melanin pigment. The melanotic schwannoma is a very rare neoplasm, accounting for less than 1% of all nerve sheath tumours. These tumours are usually seen in young females with average age of 38 years. We report a 45 years old female with a history of headache and vomiting since 2 years which was worsening since 2 months with imbalance in walking since 1 year. She had cerebellar signs such as dysdiadochokinesia and ataxic gait with features of raised intracranial pressure and grade 2 papilledema on fundoscopic examination. A provisional diagnosis of ependymomawas suggested on radiology. She underwent a midline sub occipital craniotomy and posterior fossa tumour excision.
A final diagnosis of melanotic Schwanomma was made based on histomorphology, histochemistry, immunohistochemistry along with a history of recurrence.
Definitive criteria of malignancy in melanotic Schwanomma are not well established, although a combination of histologic features like large, pleomorphic cells with prominent nucleoliand necrosis, raises concern for aggressive behaviour. The Posterior fossa MS involving floor of fourth ventricle are uncommon and becomes challenging on preoperative diagnosis. Correct diagnosis is extremely important because of its high predilection to recur locally and to metastasize, which emphasizes the importance of diagnostic recognition and close clinical follow-up of patients with melanotic Schwanomma.
Keywords: Malignant melanocytic nerve sheath tumour, Melanotic schwannoma, Nerves, Recurrence, Metastasis.
