- Epidermoids (AKA epidermoid inclusion cysts) are benign congenital lesions.
- Account for approximately 1% of all intracranial tumors.
- Patients are usually not symptomatic until they are aged 20-40 years.
- Epidermoids should be distinguished from dermoids, which also are a result of congenital ectodermal inclusion.
- Dermoids also result from ectodermal inclusions, but they have a lining that has further differentiated to include dermal appendage structures such as hair follicles, sebaceous glands, and sweat glands.
- Central nervous system dermoids should be distinguished from abdominal (ovarian) dermoids that are actually well-differentiated teratomas.
- Epidermoids rarely rupture. Dermoids more commonly rupture (spillage of the contents of dermoids into the subarachnoid space may cause chemical meningitis).
- Epidermoids occur with equal frequency in men and women.
- Although the vast majority of epidermoids are intradural, they can be extradural.
- The most common locations are within the cerebellopontine angle (CP), parasellar region, and middle cranial fossa.
- Total removal is the goal of surgery.
- Aggressive resection might not be undertaken when lesions are adherent to vital structures such as the cranial nerves or brainstem.
 Imaging Findings
- At diagnosis, epidermoids usually insinuate within the sulci and cisterns, and they may engulf cranial nerves and blood vessels.
- Preferred Examination: CT and MRI are both helpful in diagnosing epidermoids. Although CT findings may be nonspecific, MRI findings are reliable in diagnosis.
- Epidermoids usually have the same attenuation as that of cerebrospinal fluid; this characteristic makes their differentiation from arachnoid cysts difficult. Enhancement is rare, but can sometimes be seen around the margin of the tumor. Calcification occurs in only 15-20% of cases.
- On T1-weighted images these lesions are generally slightly hyperintense or isointense relative to gray matter.
- The lesions are usually isointense relative to CSF on T2-weighted images, but they may be slightly hyperintense.
- Enhancement of portions of the rim may be seen after the administration of contrast material. The remainder of the lesion does not enhance.
- Fluid-attenuated inversion recovery (FLAIR) images demonstrate epidermoids as being hyperintense relative to CSF.
- Diffusion-weighted imaging can be used to differentiate from arachnoid cysts, because epidermoids have markedly restricted diffusion and, therefore, high signal intensity on the diffusion-weighted trace images.
 See Also
 External Links
- E-medicine epidermoid article