Perineural invasion progressing to leptomeningeal carcinomatosis: Is the absence of peripheral nerves an important sign?

Histopathological features of clinical perineural invasion of cutaneous squamous cell carcinoma of the head and neck and the potential implications for treatment

“…These issues are particularly important with cranial nerve VII within the parotid gland because of the nerve's diverging ramification pattern. 23 However, scarring of the nerve would be recognizable on histological sections. 51 Cottel 47 discussed perineural "skip areas" in Mohs chemosurgery cases.…”

“…Despite the fact that skip lesions were disputed previously, 23,[41][42][43] they are still frequently propagated in the literature as a cause for concern in regard to margin control. 3,9,20,25,31,40 PNI was initially thought to arise from perineural lymphatics.…”

“…It is plausible that complete regression of perineural tumor segments could occur after an intense inflammatory reaction, leaving a "skip" in the residual lesion. 23 However, scarring of the nerve would be recognizable on histological sections. Complete regression of perineural tumor was not observed here, even in cases with intense inflammatory infiltrate.…”

“…This process of tumor spread is distinct from metastasis via a lymphatic or hematogenous route, and often exists independently. 22,23 When radiological or clinical evidence of PNS is present (ie, facial palsy or trigeminal nerve distribution numbness, paresthesia, formication, or pain) this is termed "clinical PNI." 21 This is typically managed by complete surgical excision and consideration of postoperative radiotherapy.…”

“…2,3,8 PNS can progress to involve cranial nerves (particularly the facial [VII] and trigeminal [V] nerves) and ganglia, and eventually spread into the brainstem or cause leptomeningeal carcinomatosis (ie, central failure). 22,23 When radiological or clinical evidence of PNS is present (ie, facial palsy or trigeminal nerve distribution numbness, paresthesia, formication, or pain) this is termed "clinical PNI." Although clinical PNI is seen in approximately 30% to 40% of all PNI cases, it carries a significantly worse prognosis than incidental PNI necessitating a more aggressive treatment approach.…”