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

Abstract

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.

Figure 1. Imaging

Postgadolinium T1-weighted brain MRI reveals thickened patchy and nodular contrast enhancement most pronounced along the right anterolateral pons (arrow) (A), extending into the interpeduncular cistern (arrow) (B), without diffusion restriction on diffusion-weighted imaging (DWI) (C), and apparent diffusion coefficient map (D). DWI signal is isointense to the gray matter. Postcontrast thin sections on skull base MRI demonstrate (arrows) leptomeningeal enhancement in the right internal auditory canal along the right cranial nerve (CN) VII and VIII complex (E), bilateral CN V (F), and bilateral CN III (G). The right CN V is inseparable from the mass-like lesion at the root entry zone, as seen on constructive interference in steady state (CISS) sequence (H). Brain ¹⁸F-FDG-PET shows (arrows) increased uptake along the right anterolateral surface of the pons and the interpeduncular cistern (I, J). Maximal standard uptake value (SUVmax) was 7.9 (normal <2.5). Follow-up skull base MRI demonstrates disease extension (arrows) with new leptomeningeal enhancement along the right cerebellar folia (K), which represented the biopsy target, and increased enhancement of the right CN VII and VIII complex (L).

Figure 2. Histopathology

Hematoxylin and eosin stain show cellular glial neoplasm (A), with frequent (arrows) mitotic activity (B, C). Tumor cells are immunoreactive for GFAP (D) and OLIG2 (E), indicative of relatively preserved glial differentiation, while Ki-67 proliferation index is moderate (F). Tumor cells are negative for IDH1-R132H (G) and H3K27M protein (H). SOX-10 (I) labels scattered tumor cells. Panels A, D–I are ×10 magnification; panels B and C are ×100 magnification.