Intra-orbital malignant melanoma: role of MR imaging (a case report and literature review).

Magnetic resonance imaging is a non-invasive modern imaging tool that can definitely diagnose malignant melanoma despite its anatomic localisations. This is borne out of tumour paramagnetic melanin pigment content. Melanin is known to shorten T1 and T2 relaxation times of protons thereby exhibiting hyperintense T1W and hypointense T2W signals, hence conferring some histiological diagnosis. This is unlike Amelanotic melanoma, other intra-orbital tumours and tumours in general that show usual hypointense T1W and hyperintense T2W signals. However a few mimics of signal characteristics of malignant melanoma like sub-retinal serous collection exist. This therefore needs additional MRI sequences like fat suppression with Gado-pentetate Dimeglumine enhancement for differentiations.