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Epidermoid Cyst

Last Updated: March 27, 2020

Figure 1: A low density lesion in the left cerebellopontine angle on CT (top row left) could represent a number of lesions including arachnoid cyst or epidermoid cyst. T2WI (top row right) and T1WI post contrast (middle row left) give little additional diagnostic information, with the lesion still matching CSF signal. FLAIR imaging (middle row right), as in this case, often demonstrates an epidermoid cyst to have different signal than CSF. Diffusion weighted imaging (bottom) is the most helpful sequence with these lesions, demonstrating often dramatic hyperintensity.

Figure 2: This large epidermoid cyst looks similar to CSF on T1 (top row left) and T2 (top row right), but its identity as a possible simple cyst should be questioned given the degree of heterogeneity that is often visible on FLAIR (middle row left). Diffusion restriction visible as bright signal on DWI (middle row right) and dark signal on ADC (bottom row left) is the hallmark of epidermoid cyst and can greatly help to differentiate from other simple cysts such as arachnoid cyst. This epidermoid cyst has a small amount of nodular contrast enhancement in the periphery (bottom row right), a finding that is only rarely present.

Basic Description

  • Benign ectodermal inclusion cysts of congenital or acquired etiology
  • Most common congenital intracranial tumor (~1%)


  • Congenital: Arise from ectodermal epithelium in the 3rd to 5th weeks of embryogenesis during the process of neural tube closure
    • Sporadic
    • May be seen in association with dermal sinus tracts or vertebral anomalies
  • Rare acquired lesions are thought to be post-traumatic in etiology, often spinal in location when secondary to lumbar punctures
  • Epidermoid cyst growth by desquamation and formation of cholesterol/keratin crystals
  • Gross pathologic features include shiny or “pearly” appearance within an outer connective tissue wall
  • Cyst contains solid cholesterol crystals and keratin

Clinical Features

  • Patient ages 20-60 years most common
  • No gender predilection
  • Presenting signs and symptoms depend on tumor size and location
    • Headache, cranial neuropathies (cranial nerves 5, 7, and 8 most common)
    • Cyst rupture may cause chemical meningitis
    • Often asymptomatic
  • Malignant degeneration into squamous cell carcinoma is rare
  • Treatment: microsurgical resection; gross total resection is often difficult because of involvement of adjacent structures and specifically attachment of the tumor pearls to the cerebrovascular structures
  • Prognosis: recurrence common with incomplete tumor resection or secondary to cerebrospinal spinal fluid (CSF) seeding; malignant degeneration into squamous cell carcinoma is rare


  • General
    • Most cases (90%) are intradural and located within the basal cisterns (cerebellopontine angle, fourth ventricle, parasellar)
    • Minority of cases (10%) are extradural and may arise within the bony calvarium (diploic space) or spine
  • Variable size, round or lobulated mass
  • Slow but insinuating or invaginating pattern of growth, often encases or surrounds adjacent nerves and vasculature
  • Computed Tomography (CT)

    • Well-defined, usually hypodense mass similar in density to CSF
    • <5% appear hyperdense, often due to proteinaceous, iron-rich, or hemorrhagic contents
    • Calcifications are common
    • Typically do not enhance on contrast enhanced CT
  • Magnetic Resonance Imaging (MRI)

    • T1WI
      • Signal intensity typically greater than CSF, but less than brain parenchyma
      • Highest signal often seen at the margin of the tumor
      • Signal intensity greater than brain parenchyma indicates a “white epidermoid,” brighter because of its higher degree of fatty components or blood products
      • Rare hypointense “black epidermoids” caused by low triglyceride and unsaturated fatty acid contents
    • T2WI

      • Iso- to hyperintense to CSF
      • Rare hypointense signal due to iron content or Ca++
    • FLAIR: intermediate to hyperintense due to incomplete dropout of fluid signal
    • DWI: demonstrates often markedly increased signal (restricts) with corresponding ADC value near that of brain parenchyma (in contrast to an arachnoid cyst which will not restrict)
    • T1WI+C: typically nonenhancing, although minimal enhancement at the margin of the tumor may be seen; significant enhancement may suggest malignant degeneration

Imaging Recommendations

  • MRI with FLAIR and DWI/ADC

For more information, please see the corresponding chapter in Radiopaedia.

Contributor: Rachel Seltman, MD

DOI: https://doi.org/10.18791/nsatlas.v1.03.01.15


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Mohanty A, Venkatrama SK, Rao BR, et al. Experience with cerebellopontine angle epidermoids. Neurosurgery. 1997; 40:24–30.

Osborn AG, Salzman KL, Jhaveri MD. Diagnostic Imaging (3rd ed). Philadelphia, PA: Elsevier, 2016.

Ren X, et al: Clinical, radiological, and pathological features of 24 atypical intracranial epidermoid cysts. J Neurosurg. 2012;116:611-621.

Tampieri D, Melanson D, Ethier R. MR imaging of epidermoid cysts. AJNR Am J Neuroradiol. 1989; 10:351–356.

Velamati R, et al: Meningitis secondary to ruptured epidermoid cyst: case-based review. Pediatr Ann. 2013;42:248-251.

Vellutini EA, et al: Malignant transformation of intracranial epidermoid cyst. Br J Neurosurg. 2014;28:507-509.

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