Intracranial epidermoid cysts are congenital lesions which account for about 1% of all intracranial tumours 2. They result from inclusion of ectodermal elements during neural tube closure.
Although congenital, epidermoid cysts are usually very slow growing and as such take many years to present. Typically patients are between 20 and 40 years of age 6. There may be increased prevalence in males, although this is not found in all series 5-6.
An uncommon association with anorectal anomalies, sacral anomalies and pre-sacral mass, and is known as the Currarino triad 5.
Signs and symptoms of epidermoid cysts are due to gradual mass effect, with presentation including 4:
- headaches : most common
- cranial nerve deficits
- cerebellar symptoms
- raised intracranial presure
Recurrent aseptic meningitis is uncommon but recognised, similar to the less common dermoid cyst 4.
They may be congenital (most common) or acquired (post surgical or post traumatic implantation. Pathologically intracranial epidermoid cysts are identical to the petrous apex and middle ear congenital cholesteatomas. They differ from dermoid cysts which have both epidermal and skin appendages such as hair and sebaceous cysts and mature teratomas which have all three layers.
They have a thin capsule which is made of a thin layer of squamous epithelium which macroscopically is white and pearly and may be smooth, lobulated or nodular. Internal cystic components are often filled with desquamated epithelial keratin and cholesterol crystals, grossly appearing as a creamy, waxy material. It should be noted that some authors contest that epidermoid cysts are along a spectrum which includes cystic (adamantinomatous) craniopharyngiomas, which have some histological similarities 7. Cholesterol and keratin components account for their distinct imaging characteristics 2.
- intra dural : 90%
- extra dural : 10 %
- most within skull
On CT intracranial epidermoid cysts appear as lobulated lesion that fills and expands CSF spaces and exerts gradual mass effect, insinuating between structures. A common feature of posterior fossa cysts is displacement of the basilar artery away from the pons.
The combination of cellular debris along with a high cholesterol content lower the density of epidermoids to approximately 0 HU, and can thus be identical in density to CSF, and look the same as an arachnoid cyst. Calcification is seen in a minority of cases, and rarely an epidermoid cyst may be hyperdense due to haemorrhage, saponification or high protein content.
They do not enhance, and only very rarely demonstrate any enhancement of the wall.
Appearances on MR are similar to those on CT, with epidermoids often being indistinguishable from arachnoid cysts or dilated CSF spaces on many sequences.
- usually iso intense to CSF
- higher signal compared to CSF around the periphery of the lesion is frequently seen
- rarely they can be of high signal and are known as white epidermoids
- rare intra-lesional haemorrhage can also result in intrinsic high signal
- thin enhancement around the periphery may sometimes be seen
- in the rare cases of malignant degeneration, enhancement becomes more pronounced
- usually iso intense to CSF (65%)
- slightly hyper intense (35%)
- rarely hypointense, usually in the setting of the so called white epidermoid (the term refers to the T1 appearance) 2
- often heterogeneous / dirty signal, higher than CSF
- beware of flow artefact from CSF pulsation which can mimic this appearance
- DWI : useful for differentiation from arachnoid cysts due to increased signal (due to a combination to true restricted diffusion and T2 shine through) which is not seen with arachnoid cysts
Treatment and prognosis
Surgical excision is the treatment of choice if symptomatic. Complete resection is however difficult as not all tissue can be removed, especially from around cranial nerves and vessels. Recurrence is therefore not uncommon, although growth is typically slow and many years can elapse without new symptoms.
The differential for an epidermoid cyst include:
CSF collections: e.g. arachnoid cyst or mega cisterna magna
- less lobulated
- follows CSF on all sequences, including FLAIR and DWI
- often fat density due to sebum
- inflammatory cyst: e.g. neurocysticercosis
- smaller, but may be multiple
- may enhance peripherally
- may have associated oedema
- usually no restricted disffusion
- cystic tumour: e.g. acoustic schwannoma or craniopharyngioma
- solid enhancing component is usually identifiable
- neurenteric cyst
- 1. Grossman RI, Yousem DM. Neuroradiology, the requisites. Mosby Inc. (2003) ISBN:032300508X. Read it at Google Books - Find it at Amazon
- 2. Chen CY, Wong JS, Hsieh SC et-al. Intracranial epidermoid cyst with hemorrhage: MR imaging findings. AJNR Am J Neuroradiol. 2006;27 (2): 427-9. AJNR Am J Neuroradiol (full text) - Pubmed citation
- 3. Swartz JD, Harnsberger HR. Imaging of the temporal bone. George Thieme Verlag. (1998) ISBN:0865777004. Read it at Google Books - Find it at Amazon
- 4. deSouza CE, deSouza R, da Costa S et-al. Cerebellopontine angle epidermoid cysts: a report on 30 cases. J. Neurol. Neurosurg. Psychiatr. 1989;52 (8): 986-90. doi:10.1136/jnnp.52.8.986 - Free text at pubmed - Pubmed citation
- 5. Albright AL, Adelson PD, Pollack IF. Principles and practice of pediatric neurosurgery. Thieme Medical Pub. (2007) ISBN:1588903958. Read it at Google Books - Find it at Amazon
- 6. DeMonte F, Gilbert MR, Mahajan A. Tumors of the Brain and Spine. Springer Verlag. (2007) ISBN:0387292012. Read it at Google Books - Find it at Amazon
- 7. Miller NR, Walsh FB, Hoyt WF. Walsh and Hoyt's Clinical Neuro-Ophthalmology. Philadelphia : Lippincott Williams & Wilkins, c2005. (2005) ISBN:0781748127. Read it at Google Books - Find it at Amazon
Synonyms & Alternative Spellings
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