Clinical Reasoning: A 63-Year-Old Man With Progressive Multicranial Neuropathy and Leptomeningeal Enhancement.

A 63-year-old man, with a history of melanoma and basal cell carcinoma, presented with progressive right-sided facial numbness, vertical diplopia, and headache. Brain MRI revealed leptomeningeal enhancement of multiple cranial nerves and an enhancing mass-like lesion along the anterolateral surface of the pons and midbrain. Subsequent brain biopsy demonstrated the final diagnosis. This case highlights the broad differential diagnosis of leptomeningeal disease, emphasizing the role of specific clinical, laboratory, and imaging cues in guiding clinical reasoning.