Epidermoid and dermoid tumors are benign, congenital growths. They arise from misplaced germ cell islands during embryonic development, which become trapped in the neural tube. Epidermoids contain only epithelial cells, while dermoids also include other skin components such as hair, glands, or even teeth. These tumors grow linearly, not exponentially like malignant tumors, and can occur anywhere along the neuroaxis.

Epidemiology

Epidermoids account for about 1% of all intracranial tumors and 7% of masses in the cerebellopontine angle. Peak incidence is around age 40, affecting males and females equally. Dermoids are rarer (0.3% of brain tumors), peak earlier, and are more common in males.

Differences Between Epidermoid and Dermoid

Feature	Epidermoid	Dermoid
Incidence	0.5–1% of brain tumors	0.3% of brain tumors
Location	Often lateral (cerebellopontine)	Often midline or near midline
Cyst Content	Keratin, cholesterol, dead cells	Plus skin appendages (hair, glands, teeth)
Other	Usually isolated	50% associated with congenital anomalies
Meningitis	Mollaret meningitis	Bacterial meningitis

Clinical presentation

Symptoms depend on location. In the cerebellopontine angle, cranial nerve deficits (V, VII, VIII) are typical. Epidermoids may cause recurrent aseptic meningitis (Mollaret), while dermoids can cause bacterial meningitis.

Radiological findings

Common locations include the skull, suprasellar region, Sylvian fissure, cerebellopontine angle, basal/posterior fossa, or spine (mostly thoracic).
Epidermoids resemble arachnoid cysts on T1 & T2, but have irregular borders and do not enhance with contrast. They show diffusion restriction on DWI and are brighter than arachnoid cysts on FLAIR.

Imaging Differences: Arachnoid Cyst vs. Epidermoid

Characteristic	Arachnoid Cyst	Epidermoid
CT Density	Like CSF	Higher than CSF
Tumor Borders	Smooth	Irregular
Calcifications	None	In ~25% of cases
Neurovascular Effect	Displacing	Remodeling
MRI Contrast	Rare	None
MRI Diffusion	Dark	Bright
MRI ADC	Increased	Decreased
MRI FLAIR	Dark	Dark to bright

Differential diagnoses

• Craniopharyngioma
• Choroid plexus tumor
• Teratoma
• Lipoma
• Lymphoma

Special note

Cholesteatomas are histologically identical to epidermoids, but found extradurally in the middle ear, often in patients with chronic otitis media, and are not congenital.

Indication for surgery

Preferred treatment is complete surgical removal. The tissue is typically pearly. Care must be taken to prevent cyst contents from entering the ventricular system, which can cause chemical (aseptic) meningitis. Steroids and hydrocortisone irrigation may reduce this risk. Residual cyst wall may be left on vital structures to minimize complications. Postoperative, persistant displacement of surrounding structures is common.

Outcome

Epidermoid cyst surgery is generally considered safe with a good prognosis, especially if the cyst is located in a less complex area of the brain or spine. The majority of patients experience significant symptom relief after surgery, though recovery can vary. It’s essential to follow for regular monitoring to ensure the cyst has been fully removed and to address any potential complications early.

References

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