Introduction
Background
Dermoid tumors are not true neoplasms but are inclusion cysts composed of ectodermal elements. They are uncommon lesions, accounting for approximately 0.3% of all brain tumors. Dermoid tumors are often discussed with epidermoid tumors because of their similar appearance and developmental origin.
The dermoid tumor is hyperintense on this gadolinium-enhanced coronal T1-weighted image. Note the heterogeneity of the lesion posteriorly. The hyperintensity results not from the gadolinium contrast enhancement but instead from the short T1 of fat. Multiple hyperintense foci consistent with fat droplets are demonstrated in the subarachnoid spaces. A mild midline septal shift to the left is noted; this is due to compression of the right lateral ventricle by the dermoid tumor. A chemical-shift artifact is also noted at the superior marginal surface of the lesion.
Recent studies
Orakcioglu et al reviewed the charts of 5 men and 2 women with intracranial dermoid cysts and found that clinical presentations included focal neurologic deficits, epileptic seizures, persistent headache, mental changes, and psycho-organic syndromes. One patient underwent delayed ventriculo-peritoneal shunting after ruptured fatty particles caused obstructive hydrocephalus. In 3 patients, despite dermoid rupture into the subarachnoid space, hydrocephalus did not develop. In one patient, diffuse vascular supra-tentorial lesions occurred as a result of aseptic meningitis. The authors noted that diffusion-weighted imaging (DWI) hyperintensity in dermoid cysts is related to a decrease of water proton diffusion and should be used for both the diagnosis and follow-up of these lesions. In addition, they noted that although rupture does not necessarily cause hydrocephalus, radical removal of the tumor and close monitoring of ventricular size are necessary.1
A study by Jolapara et al indicated that diffusion tensor imaging (DTI) and diffusion tensor metrics (DTM) can together be used to analyze the microstructural anatomy of epidermoid tumors. Reporting on 10 patients with epidermoid tumors, the investigators measured directionally averaged mean diffusivity (Dav), exponential apparent diffusion coefficient (eADC), DTM-like fractional anisotropy (FA), diffusion tensor mode values, and linear (CL), planar (CP), and spherical (CS) anisotropy from the tumors, as well as from normal-appearing white matter. The authors found that the epidermoid tumors demonstrated high FA but, according to the Dav and eADC values, no indication of diffusion restriction. Diffusion tensor mode values were close to -1, and CP values within the tumor were high.2
Similar results were obtained by Santhosh et al in a DTI/DTM analysis in 3 patients with epidermoid cysts. FA, Dav, eADC, and DTM, such as CL, CP, and CS, were measured from the tumor core and normal-appearing white matter. Epidermoid cysts showed high FA, with Dav values similar to that of normal white matter. eADC maps did not show any restriction of diffusion. FA values were high, but not as high as that for the white matter. CP values were higher and CL values were lower than those obtained for the white matter in various regions.3
Handu et al analyzed the aspirates of epidermal inclusion cysts to identify cytologic features. The aspirates showed a clear background with high cellularity, along with nucleate and anucleate squames. In some cases, keratinous material was present but less than the cellular elements. In 31 cases, a diagnosis of infected EIC was made on the basis of dense inflammatory infiltrate in addition to the squames. Of 56 cases for which histopathology was available, 45 cases of EIC were diagnosed, 5 cases of dermoid cyst, 2 cases of branchial cyst, 2 cases of pilomatricoma, 1 case of sebaceous cyst, and 1 case of thyroglossal cyst.4
Pathophysiology
Dermoid and epidermoid tumors contain stratified squamous epithelium found in skin, but they also have histologic differences. Epidermoid tumors are lined with stratified squamous epithelium and have an outer connective tissue capsule. Dermoid tumors have an outer connective tissue capsule and are lined with stratified squamous epithelium that also contains hair follicles, sebaceous glands, and sweat glands. Centrally, both tumors contain desquamated epithelial keratin and some lipid material. The external surface of both tumors commonly has a smooth, lobulated, pearly appearance.5
Dermoid tumors are thought to arise from misplaced ectodermal elements during the third to fifth week of embryonic life, when the neural tube closes at the midline. This may explain the frequent midline location of dermoid tumors. In contrast, epidermoid tumors are often located lateral to the midline of the cranium. Dermoid tumors are more commonly associated with dermal sinus tracts and spinal abnormalities than are epidermoid tumors.
Congenital epidermoid tumors may develop from inclusion of ectodermal epithelial elements at the time of neural tube closure or during the formation of the secondary cerebral vesicles. Acquired epidermoid tumors are believed to form due to trauma, frequently lumbar puncture, with epithelial cells deposited within the lumbar spinal canal. Sites of epithelial deposition can occur anywhere between the neural tube and the overlying skin surface. This distribution may account for the presence of dermal sinus tracts or dimples, which are more commonly associated with dermoid tumors.
Dermoid tumors are solitary; they expand slowly over many years due to the central accumulation of epithelial debris and glandular secretions. Common intracranial sites of dermoid tumors include the posterior fossa (within the fourth ventricle or cerebellar vermis) and the suprasellar region.
A congenital lumbar dermal sinus may terminate in an epidermoid or, less frequently, dermoid tumor within or near the conus medullaris or cauda equina and is often associated with spinal dysraphism. A congenital nasal dermal sinus may be associated with dermoid or epidermoid tumors. Other dermoid tumor sites include the scalp, skull, and orbit. Epidermoid tumors are most commonly located near the cerebellopontine angle, but they may also occur in parasellar areas and may be intradiploic in cranial bones. Intracerebral epidermoid occurrence is very rare.
Frequency
United States
Dermoid tumors account for approximately 0.3% of brain tumors and occur 4-10 times less frequently than do epidermoid tumors.
Mortality/Morbidity
- Central nervous system (CNS) dermoid and epidermoid tumors are usually benign, slow-growing lesions that rarely undergo malignant transformation.
- Morbidity depends on the location of the tumor and on the involvement of adjacent structures. The rupture of a dermoid tumor can cause a granulomatous chemical meningitis that, in rare cases, produces infarction from arterial vasospasm.
Race
No known racial predilection exists.
Sex
There is a slight male predominance of dermoid tumors. Epidermoid tumors occur with similar frequency in male and female patients.
Age
Intracranial dermoid tumors are seen most frequently in patients up to 20 years of age. In contrast, epidermoid tumors are most often first diagnosed in patients aged 40-50 years.
Anatomy
Dermoid tumors are often located at the cranial midline (as seen in the images below) within the posterior cranial fossa, suprasellar cistern, and subfrontal areas. Epidermoid tumors are typically lateral and are most frequently located in the cerebellopontine angle; in the suprasellar and parasellar regions; in choroidal, sylvian, and interhemispheric fissures; or intraventricularly.
Elderly woman with chronic headaches. A nonenhanced computed tomography (CT) scan of the head demonstrates a well-circumscribed, cystic, low-attenuating lesion located at the cranial midline in the suprasellar region, posterior to the third ventricle. A small focus of calcification is noted at the posterior margin of the tumor.
The suprasellar lesion (same patient as in the image above) is hypointense on a subsequent axial T1-weighted image. The crescentic posterior rim of hyperintensity represents the fat chemical–shift artifact.
Gadolinium-enhanced axial T1-weighted image demonstrating nodular focus of enhancement in the right side of the suprasellar lesion (same patient as in the above 2 images).
Axial T2-weighted fast spin-echo magnetic resonance image demonstrating a hyperintense cystic component in the lesion (same patient as in the above 3 images).
Spinal dermoid tumors are most commonly situated near the thoracolumbar junction and tend to involve the conus medullaris and cauda equina. About 50% are intradural intramedullary, and 50% are intradural extramedullary. Extradural location is least common. Less common sites of dermoid tumors include the scalp (the most common location in childhood), skull, orbit, nasal and oral cavities, and neck.
Presentation
Dermoid tumors grow slowly. Symptoms and signs are associated with the location of the tumor and the mass/pressure effect on adjacent tissues. Suprasellar tumors can cause visual abnormalities from compression of the optic chiasm. Diabetes insipidus and hypopituitarism may occur. Parasellar tumors may be associated with seizures from mass effect or extension to the temporal lobe and sylvian fissure.
Intraventricular dermoid tumors are most frequently located in the fourth ventricle and sometimes cause hydrocephalus. It has been suggested that the cerebrospinal fluid (CSF) flow may occur through interstices on the surface of the tumor.
Dermoid tumors in the spinal canal may cause back or leg pain due to mass effect. Headache and meningitis may occur if an associated dermal sinus tract becomes infected. Vertebral abnormalities, such as diastematomyelia, hemivertebra, and scoliosis, are frequently associated with dermal sinuses, dermoid tumors, or epidermoid tumors.
Dermoid tumors can rupture, releasing lipid contents into the ventricular or subarachnoid spaces (as seen in the image below). This causes a chemical meningitis that can lead to recurrent symptoms, most commonly headache. The subsequent meningeal inflammation may result in arterial vasospasm and, rarely, stroke and death.
Axial gadolinium-enhanced T1-weighted image of a lesion demonstrating a hyperintense signal. In addition, multiple small foci of hyperintense signal are present along the sulci of the right temporal lobe. These represent fat droplets in the subarachnoid space, left by the focal rupture of the dermoid tumor.
Preferred Examination
Dermoid tumors are often first detected on computed tomography (CT) scans. Low attenuation values consistent with fat are suggestive of the diagnosis of dermoid tumor. Calcifications are frequent in dermoid tumors and are best seen through CT scanning.
Magnetic resonance imaging (MRI) is the preferred diagnostic procedure — not only because of its high spatial resolution, but also because of its multiplanar format — for optimal depiction of the location of dermoid tumors and the involvement of adjacent structures. The fat components that are characteristic of dermoid tumors are well demonstrated through MRI. Fat droplets located in the ventricles or subarachnoid spaces due to dermoid tumor rupture also are better appreciated with MRI than through other studies.
Differential Diagnoses
Arachnoid Cyst
Craniopharyngioma
Epidermoid, Brain
Other Problems to Be Considered
Ependymoma
Hemangioblastoma
Cystic astrocytoma
Germinoma
Cysticercosis
Teratoma
Lipoma
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References
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Keywords
dermoid tumor, dermoid, dermoid cyst, epidermoid, brain cyst, inclusion cyst, epidermoid cyst, dermoid cysts, dermoid cyst pictures, epidermoid tumor, inclusion cysts
