Introduction
Background
Epidermoid cysts (sebaceous cysts) are benign congenital lesions of ectodermal origin. They account for approximately 1% of all intracranial tumors. Although these lesions are congenital, patients are usually not symptomatic until they are aged 20-40 years.
Epidermoid, brain. CT scans show a large mass with predominantly decreased attenuation, located in the middle cranial fossa with extension into the suprasellar cistern. Note the areas of heterogeneity within the mass.
Presentation
Demographics
- Epidermoids are congenital. Because of their slow growth, patients usually are not symptomatic until they are aged 20-40 years.
- Epidermoids occur with equal frequency in men and women.
- Epidermoids rarely rupture. Dermoids more commonly rupture. The spillage of the contents of dermoids into the subarachnoid space may cause chemical meningitis.
- Epidermoid cysts are estimated to represent 1% of all intracranial masses.
Epidermoids arise from ectopic ectodermal cells that are retained within the neural groove at the time of closure at 3-5 weeks' gestation. They are well-circumscribed, smooth or lobulated, encapsulated lesions. Histologically, they appear as an internal layer of stratified squamous epithelium with a whitish fibrous capsule; these features account for the term "pearly tumor." They tend to slowly enlarge as epithelial cells desquamate, with the formation of keratin and cholesterol crystals in the center of the lesion.
Although the vast majority of epidermoids are intradural, they can be extradural. The most common locations are within the cerebellopontine (CP) angle, parasellar region, and middle cranial fossa. The CP angle is the most common site for epidermoids. Of all CP angle masses, epidermoids are the third most common after vestibular schwannomas and meningiomas. Occurrences within the ventricular system, brain parenchyma, and even the spinal cord, have been reported.
At diagnosis, epidermoids usually insinuate within the sulci and cisterns, and they may engulf cranial nerves and blood vessels.
Epidermoids should be distinguished from dermoids, which also are a result of congenital ectodermal inclusion. Dermoid inclusion cysts 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 (CNS) dermoids should be distinguished from abdominal (ovarian) dermoids that are actually well-differentiated teratomas.
The clinical presentation of patients with epidermoids depends on the location of the mass. Common presentations for CP angle masses include headache, diplopia, trigeminal neuralgia, hypoacusia, and gait ataxia.
Treatment
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.1,2
Preferred Examination
CT and MRI are both helpful in diagnosing epidermoids. Although CT findings may be nonspecific, MRI findings are reliable in diagnosis.
Limitations of Techniques
With CT scans, the differentiation between arachnoid cyst and epidermoid may be difficult.
Differential Diagnoses
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References
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Roy K, Bhattacharyya AK, Tripathy P, Bhattacharyya MK, Das B. Intracranial epidermoid--a 10-year study. J Indian Med Assoc. Jul 2008;106(7):450-3. [Medline].
Ikushima I, Korogi Y, Hirai T. MR of epidermoids with a variety of pulse sequences. AJNR Am J Neuroradiol. Aug 1997;18(7):1359-63. [Medline].
Kallmes DF, Provenzale JM, Cloft HJ. Typical and atypical MR imaging features of intracranial epidermoid tumors. AJR Am J Roentgenol. Sep 1997;169(3):883-7. [Medline].
Jolapara M, Kesavadas C, Radhakrishnan VV, Saini J, Patro SN, Gupta AK, et al. Diffusion tensor mode in imaging of intracranial epidermoid cysts: one step ahead of fractional anisotropy. Neuroradiology. Feb 2009;51(2):123-9. [Medline].
Hu XY, Hu CH, Fang XM, Cui L, Zhang QH. Intraparenchymal epidermoid cysts in the brain: diagnostic value of MR diffusion-weighted imaging. Clin Radiol. Jul 2008;63(7):813-8. [Medline].
Atlas SW. Magnetic Resonance Imaging of the Brain and Spine. 1996.
Gao PY, Osborn AG, Smirniotopoulos JG. Radiologic-pathologic correlation. Epidermoid tumor of the cerebellopontine angle. AJNR Am J Neuroradiol. May-Jun 1992;13(3):863-72. [Medline].
Osborne AG. Diagnostic Neuroradiology. 1994.
Ziyal IM, Bilginer B, Bozkurt G, Cataltepe O, Tezel GG, Akalan N. Epidermoid cyst of the brain stem symptomatic in childhood. Childs Nerv Syst. Dec 2005;21(12):1025-9. [Medline].
Further Reading
Keywords
brain epidermoid, pilar cyst, sebaceous cyst, epidermoid, epidermoid tumors, epidermoid cyst, congenital cholesteatoma, pearly tumor
