Malignant Melanotic Schwannoma of the Spine

A 34-year-old woman complained about backache of one-year duration. She had progressive left lower extremity weakness for the last three months. There was no trauma history. She was referred to the radiological department for further evaluation.

The patient initially underwent the plain radiography, which was unremarkable. Magnetic resonance imaging (MRI) was performed considering the clinical findings. MRI demonstrated an intramedullary lesion at the level of T11-T12 disc. The lesion was hyperintense on the T1-weighted sequence (T1W) and hypointense on the T2-weighted sequence (T2W) (figure 1, 4). It showed prominent contrast enhancement on post-contrast T1W (figure 2). There were perilesional spinal cord edema and expansion on T2W images (figure 3). Adjacent dural enhancement and additional lesions were not evident.

Schwannomas are peripheral nerve sheaths tumours of neural crest origin. They are encapsulated, solitary, and slow-growing neoplasms. Melanotic schwannoma composes of neoplastic Schwann cells, which synthesize melanin. The intramedullary location and melanotic nature of them are exceedingly rare. This tumour accounts for <1% of peripheral nerve sheath tumours [1, 2].

Melanotic schwannoma usually occurs in posterior spinal nerve roots and sympathetic ganglia. It presents in younger patients than conventional schwannoma and affects 30-40 years old patients. The clinical presentation is pain, sensory abnormality, muscle weakness, and paralysis. Melanotic schwannoma is encapsulated tumour and has a more aggressive nature, unlike conventional schwannoma. Malignant potential is approximately 10% of cases, and the local recurrence rate is up to 35% [2, 3].

Psammomatous melanotic schwannoma is a variant of melanotic schwannoma that contains psammoma bodies. This tumour is associated with the Carney complex, an autosomal dominant disorder involving pigmentary skin abnormalities, myxomas, and endocrine tumours [4].

Melanotic schwannoma has distinct imaging findings on MRI scans. It demonstrates a high signal on T1W and a low signal on T2W since the paramagnetic effect of melanin. Conventional schwannoma shows hypointense on T1W and hyperintense on T2W. Early subacute hematoma has a similar imaging appearance on precontrast MRI sequences. Contrast enhancement of schwannoma is a characteristic feature of schwannoma when differentiating it from spinal cord hematoma and oedema [4].

They appear black-coloured macroscopically. Histopathological examination reveals high melanin deposition, spindle morphology, nuclear pleomorphism, and low mitotic rate with or without psammoma bodies. It is considered malignant when nuclear atypia, necrosis,

mitosis, and metastasis are evident [2, 3].

Total surgical excision of the intramedullary medullary schwannoma is recommended treatment. Careful follow-up should be performed due to the high risk of recurrence, malignant transformation, and metastasis. Radiotherapy is highly recommended after subtotal resection. The role of adjuvant chemotherapy is unclear [2].

Our patient underwent surgery. Intraoperatively, a black-coloured, hemorrhagic, intramedullary tumour was encountered. Subtotal resection of the tumour was achieved. Postoperative imaging demonstrated excision of most of the lesion and the residual enhancing lesion. Fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT), brain, and spinal MRI scans did not detect metastatic implants. Histopathological study revealed the diagnosis of malignant intramedullary melanotic schwannoma. Our patient underwent adjuvant radiotherapy following surgery.

MRI is the preferred imaging for clarifying spinal cord lesions. The preoperative imaging findings should suggest the diagnosis of melanotic schwannoma. Thus, the radiological study could influence the surgical strategy.