Dermoid cyst is a rare, benign, congenital intracranial tumor arising from ectodermal inclusion during embryonic development. Unlike epidermoid cyst, it contains both ectodermal and mesodermal elements (hair follicles, sebaceous glands, sweat glands) and is filled with fat-like material. It most commonly occurs in the posterior fossa midline and anterior fontanelle/nasal dermal sinus region. T1 hyperintense signal and signal loss on fat suppression on MRI are pathognomonic. Rupture may lead to chemical meningitis with fat droplets visible in the subarachnoid space.
Age Range
20-50
Peak Age
30
Gender
Male predominant
Prevalence
Rare
Dermoid cysts form during the 3rd-5th weeks of embryonic development when surface ectodermal elements become trapped within neural tissue during neural tube closure. These ectodermal islands contain both the epidermal layer (keratinized squamous epithelium) and dermal appendages (sebaceous glands, sweat glands, hair follicles) — this is the fundamental difference from epidermoid cyst. Sebaceous material (lipid-rich), cholesterol crystals, and keratin debris produced by the cyst wall accumulate in the cyst lumen, causing slow growth. The fat content produces T1 hyperintense signal on MRI because the short-chain fatty acids of triglycerides markedly shorten T1 relaxation time. Signal loss on fat suppression sequences is explained by chemical shift-selective frequency suppression targeting the resonance frequency of fat protons. Cyst rupture is a critical complication: when fatty contents spread into the subarachnoid space, aseptic meningitis develops due to chemical irritation, and subarachnoid fat droplets appear as hyperintense foci on FLAIR.
Pathognomonic combination for dermoid cyst: cystic lesion with markedly hyperintense T1 signal showing signal loss on fat suppression. Most reliable finding distinguishing dermoid among intracranial fat-containing lesions.
Dermoid cyst demonstrates markedly hyperintense signal on T1-weighted images. Signal intensity is similar to or even brighter than subcutaneous fat. Cyst contents are generally homogeneously hyperintense but hair, keratin, and calcification areas may create heterogeneous foci.
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A cystic lesion demonstrating markedly hyperintense signal isointense to subcutaneous fat is observed on T1-weighted images.
On fat suppression sequences, marked signal loss is observed in dermoid cyst contents. The bright signal on T1 is nearly completely suppressed. This finding confirms T1 hyperintensity is due to fat and provides definitive differentiation from subacute hemorrhage.
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Marked signal loss is observed in the lesion on fat suppression sequences, confirming that T1 hyperintensity is attributable to fat content.
Dermoid cyst shows variable signal on T2-weighted images; generally hyperintense due to lipid content, but chemical shift artifact may be visible along the margin. Solid elements such as keratin debris and hair may create low signal foci.
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The lesion demonstrates variable signal intensity on T2-weighted images with hyperintense areas consistent with lipid content and chemical shift artifact.
On CT, dermoid cyst appears as a hypodense mass at fat density; Hounsfield values range from -20 to -100 HU. Calcifications may be detected as hyperdense foci in the cyst wall. A fat-fluid level may be visible — hypodense fat layer on top, denser layer below.
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A hypodense intracranial cystic lesion at fat density (-20 to -100 HU) is observed on CT.
In case of rupture, fat droplets in the subarachnoid space appear as hyperintense foci on FLAIR. They are visible as bright spots within sulci that are normally dark on FLAIR due to CSF suppression. Without rupture, the cyst shows variable FLAIR signal.
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Hyperintense fat droplets are observed along the sulci on FLAIR, findings suggestive of dermoid cyst rupture.
Dermoid cyst generally does not show diffusion restriction on DWI — no restriction on ADC maps. This is critically important in differentiating from epidermoid cyst which shows markedly hyperintense DWI signal. T1 shine-through effect may create false-positive high signal — ADC map is mandatory for verification.
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Increased signal is observed on DWI with T1 shine-through effect; however, no true diffusion restriction is detected on ADC maps.
In intact dermoid cyst, no enhancement after gadolinium. In case of rupture, enhancement may be seen in cyst wall and surrounding meningeal structures (inflammation from chemical irritation). Leptomeningeal enhancement is important indicator of rupture.
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No enhancement in cyst wall after contrast / Leptomeningeal enhancement noted in setting of rupture.
Criteria
Midline cyst in vermis, fourth ventricle, or cerebellopontine angle. Most common location.
Distinct Features
Midline location, fat content, obstructive hydrocephalus risk. Fat droplets in posterior fossa cisterns upon rupture.
Criteria
Congenital dermoid in nasal dorsum, glabella, or anterior cranial fossa floor. May be associated with nasal dermal sinus. More common in childhood.
Distinct Features
Externally visible nasal mass, may have intracranial extension via dermal sinus tract. CT may show bony defect. Infection risk (meningitis) is important complication.
Criteria
Spontaneous or traumatic rupture with cyst content spread into subarachnoid space. Chemical meningitis. Subarachnoid fat droplets and leptomeningeal enhancement.
Distinct Features
Acute headache, meningismus, fever. Hyperintense fat droplets in sulci on FLAIR — pathognomonic. Fat suppression signal loss confirms diagnosis. Hydrocephalus may develop.
Distinguishing Feature
Epidermoid shows hypointense signal isointense to CSF on T1 (dermoid T1 hyperintense), marked DWI restriction (dermoid does not), no signal loss on fat suppression.
Distinguishing Feature
Craniopharyngioma is sellar/suprasellar, cystic component may be T1 hyperintense but no signal loss on fat suppression. Solid enhancement and calcification triad is characteristic.
Distinguishing Feature
Arachnoid cyst shows CSF-isointense signal on all sequences (T1 hypointense, T2 hyperintense, FLAIR suppressed). No fat content.
Distinguishing Feature
Colloid cyst specifically locates at foramen of Monro of third ventricle. T1 hyperintensity due to mucoid/proteinaceous content, no signal loss on fat suppression.
Urgency
routineManagement
surgicalBiopsy
Not NeededFollow-up
Asemptomatik olgularda yıllık MR takip. Semptomatik veya büyüme gösteren olgularda cerrahi planlama. Rüptür durumunda acil nöroşirürji konsültasyonu.Dermoid cyst is slow-growing benign lesion; conservative follow-up may be applied in asymptomatic cases. Surgical resection is indicated in symptomatic cases or upon rupture. Prevention of cyst content spillage into subarachnoid space during surgery is critical. Total resection is curative but subtotal resection may be preferred when cyst wall is adherent to critical neurovascular structures. Ruptured dermoid may require emergency surgery; steroid therapy for chemical meningitis. Malignant transformation is extremely rare.
Dermoid cysts are usually asymptomatic but may cause mass effect and neurological symptoms as they grow. The most serious complication is spontaneous rupture — fat droplets disseminating into CSF spaces can lead to chemical meningitis, vasospasm, and hydrocephalus. Surgical excision is indicated for symptomatic or growing lesions.