Last Updated: September 14, 2020
- Benign ectodermal inclusion cysts of congenital or acquired etiology
- Most common congenital intracranial tumor (~1%)
- Congenital: arise from ectodermal epithelium in the third to fifth weeks of embryogenesis during the process of neural tube closure
- May be seen in association with dermal sinus tracts or vertebral anomalies
- Rare acquired lesions are thought to have a post-traumatic 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
- Patient age of 20–60 years most common
- No gender predilection
- Presenting signs and symptoms depend on tumor size and location
- Headache, cranial neuropathies (cranial nerves V [trigeminal nerve], VII [facial nerve], and VIII [vestibulocochlear nerve] most common)
- Cyst rupture can 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
- 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
- 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
- Signal intensity typically greater than that of CSF but less than that of brain parenchyma
- Highest signal often seen at the margin of the tumor
- Signal intensity greater than that of 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
- Isointense 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 might be seen; significant enhancement might suggest malignant degeneration
- MRI with FLAIR and DWI/ADC
For more information, please see the corresponding chapter in Radiopaedia.
Contributor: Rachel Seltman, MD
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