PERINEURAL TUMORS

Perineural invasion consists of tumor growth along, around, or in a nerve. The tumor must follow a nerve path to be considered perineural. Simply having a nerve incidentally sitting within a tumor mass does not qualify as perineural invasion. Perineural invasion generally begins in the small cutaneous nerves. Consequently, it most commonly occurs where there is a dense network of cutaneous nerves such as on the head and neck.

Incidence

The incidence of perineural invasion is somewhat difficult to quantify, as most studies on perineural invasion have been done by Mohs surgeons and/or in referral centers on select, high-risk population groups. The overall incidence of perineural invasion has been quoted as 5%. Note that published incidences of perineural invasion are typically calculated from a select Mohs surgical or referral center patient population base. Consequently, the incidence values seem inflated, given that the majority of skin cancers are not treated with Mohs surgery and are therefore not included as part of the denominator when the incidence of perineural invasion is computed. A large population study from Australia calculated an incidence of perineural involvement of 2.7% of basal cell carcinomas (BCCs) in patients treated by Mohs surgery. Others have determined an incidence of less than 1% to as high as 10%.

Significance of Perineural Invasion

Why is perineural invasion important to recognize and treat appropriately? Subclinical perineural invasion can create a broader and deeper tumor burden than anticipated. This can result in greater surgical morbidity and reconstructive challenges.