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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