Figure 8.

Indirect perineural invasion of the skull base by a previously surgically resected parotid adenoid cystic carcinoma. (A,B) Axial T2W image shows asymmetric infiltration of the inferior aspect of the right cavernous sinus, Meckel’s cave, and inferior orbital fissure by a hypointense soft tissue lesion (white arrows) extending into the right prepontine cistern along the trigeminal nerve cisternal segment (black arrows). (C) Coronal postcontrast T1W image demonstrates infiltrative heterogeneous enhancement in the right masticator and parapharyngeal spaces and a thickened enhancing right mandibular nerve (blue arrow), which provides a pathway for the perineural intracranial spread of the tumor. (D–F) Axial postcontrast T1W images show heterogenous enhancement of the perineural tumoral infiltration in the foramen ovale (blue arrow), inferior orbital fissure, Meckel’s cave, and right trigeminal nerve cisternal segment (white arrows).