Peripheral trigeminal nerve branch lesions: CT and MRI findings in a pathologically confirmed case series

The peripheral branches of the trigeminal nerve (V1, V2, and V3) follow an intricate and tortuous course through various skull base foramina and soft tissue spaces. Due to the rarity of lesions specifically involving these distal segments, radiological diagnosis remains a significant challenge. This study aims to summarize the characteristic imaging patterns of diverse pathologically confirmed lesions affecting the peripheral trigeminal branches using CT and MRI.

We retrospectively reviewed 18 patients (2008-2022) with pathologically proven peripheral trigeminal lesions. The cohort included schwannoma (n = 10), neurofibroma (n = 3), adenoid cystic carcinoma (n = 1), intraneural perineurioma (n = 1), malignant peripheral nerve sheath tumor (n = 1), lymphoid hyperplasia (n = 1), and IgG4-related disease (n = 1). All patients underwent comprehensive multi-planar CT and contrast-enhanced MRI.

V1, V2, and V3 divisions were involved in 5, 6, and 5 cases, respectively. We identified three descriptive imaging groupings: Benign Neurogenic Grouping: Characterized by fusiform or nodular thickening with "smooth expansile remodeling" of bony foramina (e.g., foramen rotundum and ovale). Malignant Infiltrative Grouping: Exemplified by adenoid cystic carcinoma, showing aggressive "creeping" spread along neural pathways, often involving the pterygopalatine fossa hub and traversing multiple anatomical compartments. Diffuse/Symmetric Grouping: Observed in intraneural perineurioma and lymphoproliferative disease/IgG4-related disease, manifesting as long-segment, uniform, and often bilateral nerve thickening without focal mass formation.

Accurate diagnosis of peripheral trigeminal lesions requires a segmental anatomical approach. While MRI is superior for evaluating neural architecture and signal changes, CT provides critical surrogate markers via bone remodeling patterns. Recognizing these descriptive imaging groupings as observed in our series-ranging from indolent remodeling to aggressive perineural spread-is helpful for differentiating rare neural pathologies and guiding clinical management.