An 8-year-old male neutered Labrador presented with progressive multifocal forebrain signs noted over the previous 8 weeks. Relevant MR images are below.

The images below show multiple well-defined intra-axial lesions. The main feature is the T1 hyperintensity characteristic of these lesions. Only a few naturally occurring substances are known to reduce T1 relaxation times, including lipids, methaemoglobin, minerals (calcium, iron, copper, and manganese), proteins (including vasopressin-neurophysin II-copeptin complex), melanin, and gadolinium contrast agents. The majority of melanocytic tumours display characteristic signal patterns on MRI showing T1 and T2 shortening, resulting in T1W hyperintensity and T2W hypointensity. Please note that not all melanocytic tumors show T1 hyperintensity as amelanotic melanomas show low to intermediate intensity in T1 and intermediate to high intensity in T2. Primary melanocytic tumours (melanocytoma, melanoma, melanocytosis, and melanomatosis) of the CNS are rare, with metastatic melanocytic tumours being more frequent. This dog had toe amputation 6 months prior to presentation with melanoma confirmed histopathologically.

You can read more about metastatic melanoma in dogs by clicking on the link below.

Courtesy Mark Lowrie and Daphne Sivolapenko, Movement Referrals, Independent Veterinary Specialists, UK.