perineural spread
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.
Terminology
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.
Pathology
Perineural tumor spread is more frequently associated with :
- mucosal/cutaneous squamous cell carcinoma
- oral cavity/laryngeal (2-30%) > cutaneous (3-8%)
- most common overall
- salivary gland carcinoma
- adenoid cystic carcinoma (highest incidence per individual tumor )
- mucoepidermoid carcinoma
- mucosal/cutaneous basal cell carcinoma (2-5% demonstrate perineural tumor spread)
- melanoma
- lymphoma
- sarcoma
- meningioma (rare)
Radiographic features
MRI
Signs on MRI suggesting perineural tumor spread are:
- nerve thickening
- widening of the neural foramen
- loss of the fat surrounding the nerve
- abnormal perineural contrast enhancement