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Epidermoid Cyst

Summary

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  • Benign, slow-growing congenital lesion containing keratin and cholesterol
  • Typically in the cerebellopontine angle or parasellar region, insinuating around and encasing vessels and nerves
  • Follows CSF signal but shows characteristic restricted diffusion and incomplete FLAIR suppression1

Pathophysiology

  • Derived from ectoderm trapped during neural tube closure (3rd-5th week of embryogenesis)
  • Lined by stratified squamous epithelium producing keratin debris
  • Slow growth rate (1-2 mm/year) due to desquamation of epithelial cells

Demographics

  • Accounts for 0.2-1.8% of all intracranial tumours
  • Male to female ratio: 1.3:1
  • Peak incidence: 20-40 years of age
  • Rare in children (<5% of cases)

Diagnosis

  • Often asymptomatic and discovered incidentally
  • When symptomatic:
    • Headache (most common)
    • Cranial nerve deficits (especially CN V, VII, VIII)
    • Cerebellar signs
    • Seizures (if supratentorial)
  • Rarely, can rupture causing chemical meningitis

Imaging

  • CT:
    • Hypodense, well-circumscribed lesion
    • No enhancement with contrast
    • Calcifications in 10-25% of cases
  • MRI:
    • T1: Hypointense to isointense
    • T2: Hyperintense
    • FLAIR: incomplete/heterogeneous suppression ("dirty CSF"), unlike an arachnoid cyst
    • DWI: marked restriction — the key diagnostic feature
    • No enhancement with gadolinium
    • Insinuates through cisterns and encases vessels/nerves rather than displacing them

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  • 25-year-old patient presented with headache.
  • MRI showed a diffusion-restricting non-enhancing suprasellar lesion that encased arteries and the infundibular stalk.

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  • 60-year-old patient present with ataxia and poor left-sided hearing.
  • MRI showed a T2-hyperintense non-enhancing lobulated lesion with low ADC values in the left side of the posterior fossa, encasing the 7th and 8th nerve complexes.
  • There was significant mass effect on the cerebellum (presumably relevant to the ataxia) but there was no oedema, indicating that this lesion has grown slowly.

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  • 40-year-old patient presented with facial weakness and paraesthesia.
  • MRI showed a 2.2 cm lesion in the left cerebellopontine angle cistern that caused diffusion restriction.
  • The lesion displaced the trigeminal nerve (red arrow) and facial nerve (blue arrow).

Treatment

  • Observation for asymptomatic lesions
  • Surgical resection for symptomatic cases:
    • Goal: maximal safe resection
    • Complete resection challenging due to adherence to neurovascular structures
    • Subtotal resection acceptable to preserve neurological function
  • Gamma Knife radiosurgery:
    • Alternative for residual or recurrent tumours
    • Limited effectiveness due to slow growth rate
  • Regular follow-up with MRI recommended due to potential for recurrence

Differential diagnosis

Differential Diagnosis Differentiating Feature
Dermoid cyst Contains T1-hyperintense fat
Arachnoid cyst No diffusion restriction on MRI
Neurenteric cyst Typically located ventral to the brainstem or spinal cord; T1 hyperintense
Abscess Surrounding oedema and contrast enhancement
Cholesteatoma Typically found in the middle ear or mastoid

  1. Spinato et al. Giant Epidermoid Cyst of Posterior Fossa-Our Experience and Literature Review. 2021. Dose-response : a publication of International Hormesis Society - Open in new tab. ↩