A 7-year-old male neutered Labrador Retriever presents with a 3-week history of progressive tetraparesis. MRI of the cervical spine reveals a T2-hyperintense, T1-isointense intramedullary lesion at C4-C5 that does not enhance with gadolinium contrast. The lesion has a 'flame-shaped' appearance on sagittal sequences. Which diagnosis is MOST consistent with these imaging findings?

Remaining questions and full explanations are VIP-exclusive.