Malignant melanotic nerve sheath tumor

The patient went on to have a resection. 

Histology

The sections show a tumour with mixed architecture including dyscohesive cells in sheets and small nests partially bounded by reticulin positive type IV collagen fibres. In some areas, there is a mature network of capillaries and mildly hyalinised small vessels. The tumour cells are epithelioid and feature some pleomorphic and hyperchromatic nuclei with red nucleoli and abundant pink cytoplasm with abundant intracytoplasmic melanin pigment granules. No mitoses are seen. A nerve lies in close approximation to the tumour. 

Immunostains for Sox10, MelanA and HMB45 are positive. No PAS-positive psammoma bodies are present. The BRAF V600E stain is uninterpretable.

Ki67 index = ~15%.

FINAL DIAGNOSIS: malignant melanotic schwannomanerve sheath tumour.

Comment: The behaviour of melanotic schwannoma is difficult to predict. Some cases behave aggressively and metastasise without overt malignant features on histology.

A dumbbell-shaped mass on the left at C1/C2 has a component anterior to the cord, which it displaces posteriorly with a subtle increase in T2 signal, and a component within the foramen. 

The mass has intrinsically high T1 signal, low T2 signal and probably enhances somewhat although this is difficult to confirm given the prominent intrinsic high T1 signal. 

Conclusion: 

Morphology of the mass suggests a diagnosis of schwannoma, although occasionally meningiomas can also be dumbbell-shaped. The presence of intrinsic high T1 signal suggests melanin. Both meningiomas and schwannomas have melanotic variants and meningeal melanocytoma is an additional differential diagnosis to consider. A melanoma metastasis is less likely given the extra-axial location. 

Overall a malignant melanotic schwannomanerve sheath tumour is is favoured given the morphology.