Leptomeningeal carcinomatosis (LMC) is a rare, frequently fatal complication of cranial nerve invasion by a primary cutaneous carcinoma.

Complete absence of nerve tissue was observed in retrospect in a Mohs surgery case that had subsequently proceeded to LMC. We theorized that the cancer invaded the perineural space and spread contiguously until meeting a point of resistance, in this case the mental foramen. Pressure on the nerve resulted in Wallerian degeneration of the peripheral nerve, causing progressive anesthesia and obscuring the presence of perineural invasion (PNI). Our objective was to find out if this was an isolated phenomenon or an important sign of PNI progressing to LMC.

We report and describe a case and review similar case reports in the literature.

Twenty-two case reports fit our criteria. In only two cases was carcinomatous PNI reported in initial surgical specimens.

There are relatively few similar case reports in the literature. In many reports, histopathologic findings are not detailed enough to be helpful. Absence of peripheral nerves, although inferred, is not specifically stated in any other case report.

The absence of nerve tissue in a Mohs surgery specimen, coupled with signs of cranial nerve involvement, could be important early indicators of PNI progressing to LMC.