Intradural extramedullary meningeal melanocytoma: a case report and literature review

Abstract

Primary meningeal melanocytomas are extremely rare, benign tumours arising from the leptomeninges. While they are considered to be benign lesions, there is potential for their growth and transformation into malignant melanomas. They are commonly found in the cervical spine, with a decreased incidence in the thoracic and lumbar regions. We present a case report of a 56-year-old man who presented to our unit with a 4-month history of lower limb weakness and a sensory level at T6. Magnetic resonance imaging shows an intradural extramedullary tumour. The patient underwent a thoracic debulking of the lesion with neurophysiological monitoring. Histopathology confirmed the diagnosis of melanocytoma of meningeal origin, with a low mitotic count. Our patient recovered well post-operatively with no complications. Surgical resection is an effective method to manage this tumour; however, adjuvant radiotherapy is advised due to the risk of recurrence and malignant transformation.

Keywords: extradural intramedullary lesion; meningeal melanocytoma; spinal melanocytoma; thoracic melanocytoma.

Figure 1

MRI on initial presentation; T1 (A) sagittal view sowing mild high signal changes alongside a T2 sequence transverse view (B) which shows the intermediate signal change; when compared with post-contrast T1 sagittal and transverse imaging (C) and (D), showing there is no significant enhancement post-contrast. MRI revealed an intramedullary spinal cord lesion at the level of T6 measuring 24 mm in craniocaudal dimension.

Figure 2

Repeat contrasted MRI whole spine; demonstrates findings consistent with spinal cord meningioma at the level of T6; this can be clearly visualized by comparing the T1 sagittal pre-contrast (A) with a T1 sagittal post-contrast (B), where a clearly demarcated lesion can be seen at the level of T6; this is supported further by the sagittal T2 image (C) shown where an ~24 mm lesion can be seen at T6.

Figure 3

19 days post operative MRI; T1 pre-contrast sagittal (A) and T1 pre-contrast axial (B) show evidence of surgery at T6. Post-contrast T1 sagittal (C) and axial (D) show evidence of a small ‘fleck’ of dural enhancement, however, provide no evidence of any definite residual lesion.

Figure 4

Histopathological examination with haematoxylin and eosin staining reveals a tumour with a storiform pattern (A) and widespread melanin pigment deposition (B). Immunostaining for HMB45 is positive in the tumour cells (C); the Ki67 proliferative index is estimated at 5% (D); the scale bar corresponds to 100 μm (A, C) and 50 μm (B, D); copy number assay derived from the methylation array suggests a gain of Chromosome 6p (E).