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Perineural Spread of Tumour

Summary

fleuron

  • Perineural spread (PNS) involves tumour cells invading and spreading along nerve sheaths
  • Commonly seen in head and neck cancers, particularly squamous cell carcinoma
  • Imaging plays a crucial role in detection and staging, with MRI being the modality of choice

Pathophysiology

  • Tumour cells infiltrate nerve sheaths, typically along the path of least resistance
  • Spread occurs bidirectionally along nerves, both proximally and distally
  • Mechanisms involve:
    • Direct invasion of nerves by tumour cells
    • Lymphatic spread within nerve sheaths
    • Haeatogenous spread to nerves

Demographics

  • Most common in head and neck cancers:
    • Squamous cell carcinoma (50-80% of cases)
    • Adenoid cystic carcinoma
    • Mucoepidermoid carcinoma
  • Other tumours with PNS include:
    • Melanoma
    • Lymphoma
    • Prostate cancer
  • Incidence increases with:
    • Advanced tumour stage
    • Poor differentiation
    • Larger tumour size

Diagnosis

  • Clinical presentation:
    • Often asymptomatic in early stages
    • Neurological symptoms (e.g., pain, numbness, weakness) when advanced
  • Histopathological examination:
    • Gold standard for definitive diagnosis
    • Challenging due to skip lesions and discontinuous spread
  • Imaging:
    • Essential for early detection and accurate staging

Imaging

  • MRI:
    • Modality of choice for detecting PNS
    • High-resolution T1-weighted sequences with fat suppression
    • Gadolinium enhancement improves detection
    • Key findings:
    • Nerve enlargement and enhancement
    • Loss of perineural fat plane
    • Muscular denervation changes
  • CT:
    • Useful for bony involvement and skull base erosion
    • Less sensitive than MRI for soft tissue involvement
  • PET/CT:
    • Helpful in detecting distant metastases
    • Limited sensitivity for early PNS

panels-1

  • A 70-year-old patient underwent an MRI as part of surveillance for following radical parotidectomy and radiotherapy.
  • On the first scan, there was pathological enhancement filling the left internal auditory canal and along the length on the facial nerve down to its mastoid section (red arrows).
  • 6 months later, the intracranial component of the tumour has enlarged and there was extension of the facial nerve thickening and enhancement.
  • The CT showed remodelling of bone around the facial geniculate ganglion (blue arrow).

Treatment

  • Multidisciplinary approach:
    • Surgery
    • Radiotherapy
    • Chemotherapy
  • Surgical management:
    • Wide local excision with clear margins
    • Nerve sacrifice may be necessary in extensive PNS
  • Radiotherapy:
    • Often used as adjuvant treatment
    • Extended fields to cover potential areas of spread
  • Chemotherapy:
    • Role in advanced or recurrent disease
    • Often combined with radiotherapy
  • Prognosis:
    • Presence of PNS associated with poorer outcomes
    • Early detection and appropriate treatment crucial for improved survival

Differential diagnosis

Differential Diagnosis Differentiating Feature
Bell's palsy Enhancement of facial nerve without discrete perineural thickening; no skull base foramen enlargement
Schwannoma Well-defined, encapsulated enhancing mass along a single nerve; does not involve multiple branches
Neurofibroma Fusiform nerve expansion; may involve multiple nerves in NF1; "target sign" on T2-weighted MRI
Lymphoma Diffuse nerve infiltration; associated cervical lymphadenopathy; lacks discrete skip lesions
Sarcoidosis Cranial nerve enhancement with associated leptomeningeal enhancement; hilar lymphadenopathy on chest imaging
Leptomeningeal carcinomatosis Diffuse leptomeningeal enhancement; multiple cranial nerve involvement simultaneously; hydrocephalus