Perineural spread of tumor
Perineural spread of tumor is a form of local invasion in which primary tumors cells spread along the tissues of the nerve sheath. It is a well-recognized phenomenon in head and neck cancers.
An important distinction has to be made between perineural invasion (PNI) and perineural spread (PNS). The former is a histological finding of tumor cell infiltration or associated with small nerves that cannot be radiologically imaged, while the latter is macroscopic tumor involvement along a nerve extending away from the primary tumor; this can be radiologically apparent. A third term, neurotropism, simply means that a tumor has an affinity for growth along nerves.
The exact prevalence of perineural spread is unknown. The overall incidence is estimated to be between 2.5 and 5% but it will depend on the tumor, reaching as much as 82% in squamous cell carcinoma 1 and almost 90% in adenoid cystic carcinoma 2. It’s more common in males.
The perineural invasion is often asymptomatic (40%). Patients may experience pain, paresthesia, numbness and formication. Sometimes, in advanced cases, complete denervation may induce muscle atrophy. The Vth and VIIth facial nerves being the most frequently affected, the clinical presentation may include weakness of the muscles of mastication or facial expression. Loss of masseter muscle bulk may be observed.
Perineural tumor spread is more frequently associated with 1,2,5:
- mucosal/cutaneous squamous cell carcinoma
- oral cavity/laryngeal (2-30%) > cutaneous (3-8%)
- most common overall 5
- salivary gland carcinoma
- mucosal/cutaneous basal cell carcinoma (2-5% demonstrate perineural tumor spread) 4
- meningioma (rare) 6
Perineural tumor spread could be characterized as nerve thickening, widening of the neural foramen, loss of the fat surrounding the nerve and enhancement of the nerve following contrast administration.