Epidermoid cyst (intracranial)

FACTS

  • Pathology: Congenital, benign inclusion cyst derived from ectodermal epithelial rests trapped during neural tube closure.
  • Contents: Keratin, cholesterol, and desquamated epithelial debris—creates a pearly white lesion at surgery.
  • Growth: Slow, by desquamation (not mitosis).
  • Typical locations:
    • Cerebellopontine angle (CPA) – most common
    • Parasellar/suprasellar cisterns
    • Fourth ventricle, quadrigeminal cistern, or cisternal spaces around the brainstem
  • Behavior: Benign but may cause cranial nerve or brainstem compression; can recur if capsule incompletely removed.
  • Malignant transformation (rare): to squamous cell carcinoma.

HPI

universal ROS
  • Symptoms evolve slowly over years due to mass effect on nearby structures.
  • Common presentations by location:
    • CPA lesions: Progressive hearing loss, facial numbness or weakness, dysphagia, imbalance.
    • Suprasellar/parasellar: Visual loss, endocrine changes, headache.
    • Brainstem/ventricular: Hydrocephalus, ataxia, cranial nerve palsies.
  • Ask:
    • Onset and duration of symptoms (often gradual).
    • Headaches—positional or chronic pressure-type.
    • Any prior aseptic meningitis episodes (can occur if cyst ruptures).
    • Hearing, facial, or visual changes specifically.

PHYSICAL EXAM

universal exam
  • Cranial nerve exam:
    • V–VIII deficits for CPA lesions (trigeminal numbness, facial weakness, hearing loss).
    • II, III, VI for suprasellar lesions (field cuts, diplopia).
  • Cerebellar testing: Dysmetria, ataxia, nystagmus if posterior fossa.
  • Long tract signs: Contralateral weakness or sensory change in large/brainstem lesions.
  • Signs of raised ICP: Papilledema, nausea, vomiting if hydrocephalus.

IMAGING

  • MRI Brain w/wo contrast
Sequence
Findings
T1
Hypointense (similar to CSF)
T2
Hyperintense (similar to CSF)
FLAIR
Partially hyperintense relative to CSF (distinguishes from arachnoid cyst)
DWI
Bright diffusion restriction (key distinguishing feature) due to keratin content
ADC map
Low signal confirming restricted diffusion
Post-contrast
No enhancement, though thin rim enhancement possible if inflamed
CT
Hypodense, nonenhancing lesion; may show irregular margins or calcifications

A/P

  • Asymptomatic/incidental lesions can be observed with interval MRI (q6–12 months).
  • Symptomatic lesions: surgical planning for resection.
  • Surgical Management
    • Goal: Microsurgical total resection — remove cyst contents and capsule.
    • Approach:
      • CPA → retrosigmoid or translabyrinthine (if hearing nonfunctional).
      • Suprasellar → pterional or endonasal (if feasible).
    • Challenge: Capsule often adherent to cranial nerves and vessels; sometimes subtotal resection safer.
    • Intra-op pearls: Capsule dissection under high magnification; avoid rupture (can cause aseptic meningitis).
  • Long-Term Management (counseling)
    • Recurrence risk: ~5–15% if subtotal resection.
    • Reoperation for symptomatic recurrence.
    • Rarely, malignant transformation to squamous carcinoma → new enhancement or rapid regrowth = red flag.

Notes

Post-op complications

  • Aseptic meningitis is a common complication because caustic and irritative effects of the cyst contents on surrounding tissue and CSF

Differential Diagnosis

  • Arachnoid cyst (follows CSF on all sequences, no restriction).
  • Dermoid cyst (T1 hyperintense from fat).
  • Cystic neoplasm (enhances, may have mural nodule).