Perineural spread of tumour is a form of local invasion in which primary tumours cells spread along the tissues of the nerve sheath. It is a well-recognised 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 tumour cell infiltration or associated with small nerves that cannot be radiologically imaged, while the latter is macroscopic tumour involvement along a nerve extending away from the primary tumour; this can be radiologically apparent. A third term, neurotropism, simply means that a tumour has an affinity for growth along nerves.
Perineural tumour 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 tumour spread) 4
- meningioma (rare) 6
Perineural tumour spread could be characterised as nerve thickening, widening of the neural foramen, loss of the fat surrounding the nerve and enhancement of the nerve following contrast administration.
Radiation-induced neuritis is the main differential diagnosis in the appropriate clinical setting (i.e. following radiotherapy treatment) 7. PET-scan might be helpful as tumours are usually FDG avid whereas radiation-induced neuritis is not.
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