Mixed cranial neuropathies due to occult perineural invasion of basal cell carcinoma

PURPOSE: To report a diagnostically challenging case of cranial neuropathy due to perineural invasion by a basal cell carcinoma presenting 7.5 years after treatment of the primary tumor with Mohs micrographic surgery. OBSERVATIONS: A 62-year-old male with a history of Mohs micrographic surgery for basal cell carcinoma (BCC) of the left brow presented with insidious onset of diplopia and paresthesia localizing to the ipsilateral cranial nerves V(1), V(2), and VI. He had no evidence of recurrent cutaneous BCC. Magnetic resonance imaging of the orbits and skull base identified equivocal, subtle abnormalities in the ipsilateral superior orbital fissure and cavernous sinus, with normal appearance of the clinically involved nerve branches. A radiographically normal branch of cranial nerve V was biopsied and histopathology identified perineural invasion by recurrent basal cell carcinoma. CONCLUSIONS AND IMPORTANCE: The diagnosis of perineural invasion by BCC can pose several challenges, including subtle to absent imaging findings of clinically involved nerves and a lengthy latent period following primary tumor treatment. This case represents, to our knowledge, the longest reported interval between primary treatment and biopsy-proven recurrence with perineural invasion by BCC.