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.
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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 1,2,5:
- mucosal/cutaneous squamous cell carcinoma
- oral cavity/laryngeal (2-30%) > cutaneous (3-8%)
- most common overall 5
-
salivary gland carcinoma
- adenoid cystic carcinoma (highest incidence per individual tumor 5)
- mucoepidermoid carcinoma
- mucosal/cutaneous basal cell carcinoma (2-5% demonstrate perineural tumor spread) 4
-
melanoma
- 0.8 - 2.6% demonstrate perineural spread8
- 65% are desmoplastic subtype
- 0.8 - 2.6% demonstrate perineural spread8
- lymphoma
- sarcoma
- meningioma (rare) 6
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
MRI can depict perineural tumor spread with a sensitivity of 95%, that falls to 63% regarding the entire spread's map. The presence of perineural tumor spread can be determined but for deducing its extent, cautious analysis and patterns of enhancement may be needed 9.