You are in: eMedicine Specialties > Radiology > BRAIN/SPINE Dermoid Tumor, CNSArticle Last Updated: Jul 2, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 11
  Author: Conway Lien, MD, Consulting Staff, Department of Radiology, Santa Clara Valley Medical Center Conway Lien is a member of the following medical societies: Radiological Society of North America Coauthor(s): Mahesh R Patel, MD, Chief of MRI, Department of Radiology, Santa Clara Valley Medical Center Editors: Hugh J Robertson, MD, DMR, FRCPC, FRCR, FACR, Professor Emeritus, Department of Radiology, Section of Neuroradiology, Louisiana State University School of Medicine; Clinical Professor, Department of Radiology, Tulane University School of Medicine, Consulting Staff, Department of Radiology, University Hospital; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; James G Smirniotopoulos, MD, Professor of Radiology, Neurology, and Biomedical Informatics, Chairman, Department of Radiology and Radiological Sciences, Uniformed Services University of the Health Sciences Author and Editor Disclosure Synonyms and related keywords: dermoids, dermoid cysts, inclusion cysts, congenital epidermoid tumors, acquired epidermoid tumors, brain tumor, spinal dermoid tumors INTRODUCTIONSection 2 of 11
  BackgroundDermoid 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. PathophysiologyDermoid 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. 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. FrequencyUnited StatesDermoid tumors account for approximately 0.3% of brain tumors and occur 4-10 times less frequently than do epidermoid tumors. Mortality/Morbidity
RaceNo known racial predilection exists. SexThere is a slight male predominance of dermoid tumors. Epidermoid tumors occur with similar frequency in male and female patients. AgeIntracranial 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. AnatomyDermoid tumors are often located at the cranial midline 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. 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. Clinical DetailsDermoid 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 (see Image 7). 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. Preferred ExaminationDermoid 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. DIFFERENTIALSSection 3 of 11
Arachnoid Cyst Craniopharyngioma Epidermoid, Brain Other Problems to Be ConsideredEpendymoma
RADIOGRAPHSection 4 of 11
FindingsFocal erosion of the calvarial bone may be present adjacent to a dermoid tumor of the scalp or orbit. In particular, epidermoid tumors of the skull can cause local bone expansion or erosion and round, intradiploic, lytic lesions with a thin, sclerotic margin. Deformity of the sella may occur from parasellar dermoid tumors. Spinal dermoid tumors can cause focal vertebral bone erosion, widening of the vertebral spinal canal, and flattening of the pedicles and laminae. Degree of ConfidenceLarge, calvarial dermoid tumors can be visualized on plain skull radiographs, but radiographs have low sensitivity in depicting intracranial dermoid tumors. CT scanning and MRI demonstrate the location and imaging features of intracranial lesions. CT SCANSection 5 of 11
FindingsA dermoid tumor appears as a well-circumscribed, predominantly cystic mass on a CT scan, with decreased attenuation in the range of -20 to -40 HU because of its fat content (see Image 1, Image 5). The tumor may appear slightly heterogeneous due to additional ectodermal elements, including hair follicles, sebaceous glands, and sweat glands. Calcifications are frequent in the wall of the tumor. Contrast enhancement is uncommon, but some enhancement may be seen in the wall. If enhancement is present in a suprasellar tumor, other diagnoses should be considered, including craniopharyngioma, teratoma, or germinoma. Fat droplets in the ventricular or subarachnoid spaces strongly suggest rupture of a dermoid tumor. Dermoid tumors located in the fourth ventricle do not often cause obstructive hydrocephalus. The differential diagnoses include tumors that do commonly cause hydrocephalus, such as ependymomas, medulloblastomas, hemangioblastomas, or cystic astrocytomas of the fourth ventricle. Epidermoid tumors often have attenuation similar to CSF, but they may have hyperattenuation on nonenhanced images because of high tumoral protein content, hemorrhage, or cellular debris. The wall of epidermoid tumors may sometimes enhance after intravenous administration of contrast medium. Degree of ConfidenceCT scanning is useful in the initial diagnosis of CNS dermoid tumors if the typical findings are present. A fat-fluid level in the ventricles or fat droplets in the subarachnoid spaces due to dermoid tumor rupture adds additional confidence to the diagnosis. MRI may be performed to further localize the lesion and to identify any involvement of adjacent structures. MRISection 6 of 11
FindingsMost dermoid tumors have signal intensity characteristics similar to fat—that is, they are hyperintense on T1-weighted images and hypointense on T2-weighted images. Fat-suppression techniques may be helpful in confirming the presence of fat in the lesion. Centrally, dermoid tumors may appear inhomogeneous due to the presence of hair follicles, calcifications, and cellular debris. Rupture of a dermoid tumor can result in fat droplets in the subarachnoid spaces or ventricles, with T1 high signal intensity. Fat-fluid levels may be found anteriorly in the lateral ventricles. A chemical-shift artifact is often present on T2-weighted images as a markedly hypointense band posterior at the fat-fluid interface (see Images 7-8). Vascular displacement or encasement by the dermoid tumor may be demonstrated by means of magnetic resonance angiography (MRA) or CT angiography (CTA). Epidermoid tumors are usually hypointense on T1-weighted images and hyperintense on T2-weighted images (ie, epidermoid tumors are slightly more hyperintense with a heterogeneous signal relative to CSF on both T1 and T2 sequences) (see Image 10, Image 12). Fast fluid-attenuated inversion recovery (FLAIR) sequences demonstrate slightly higher signal intensity than do fast spin-echo T2-weighted sequences in epidermoid tumors. Echo-planar diffusion-weighted imaging shows a hyperintense signal within epidermoid tumors. The calculated apparent diffusion coefficient (ADC) exceeds that of CSF, but it is less than that of the brain substance. Magnetic resonance spectroscopy in epidermoid tumors has a lactate peak at 1.3 ppm. Additional protein metabolites, when present, can simulate brain abscess. Epidermoid tumors and arachnoid cysts have similar fluid attenuation on CT scans. They often have similar signal intensities on T1- and T2-weighted magnetic resonance images. FLAIR sequences frequently demonstrate a heterogeneously increased signal intensity in epidermoid tumors as compared with that in arachnoid cysts. Diffusion-weighted imaging shows definitive high signal intensity (whiteness) in epidermoid tumors and low signal intensity (blackness) in arachnoid cysts. Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. As of late December 2006, the Food and Drug Administration (FDA) had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape. Degree of ConfidenceA unilocular cystic mass located at or near the cranial midline, with signal intensity similar to that of fat, is highly suggestive of a dermoid tumor. Epidermoid tumors are rarely hyperintense on T1-weighted images and may simulate a dermoid tumor. Definitive diagnosis then requires histologic correlation. ULTRASOUNDSection 7 of 11
FindingsSonography has a limited role in the evaluation of CNS dermoid tumors. In young children, subgaleal dermoid cyst of the anterior fontanelle has been assessed by sonography. ANGIOGRAPHYSection 8 of 11
FindingsAngiography is seldom used in the study of dermoid and epidermoid tumors. A dermoid tumor is an avascular mass on angiography. Displacement or encasement of blood vessels adjacent to the tumor may be well demonstrated by angiography. INTERVENTIONSection 9 of 11
The treatment goal for dermoid and epidermoid tumors is complete surgical excision. Resectability depends on the location of the tumor, as well as on the extent of the tumor's encroachment and on its inflammatory attachment to adjacent blood vessels and nerves. Scalp tumors and intradiploic tumors of the skull are easier to excise completely than are intracranial tumors. Chemical meningitis may occur during removal of the dermoid or epidermoid tumor if its contents spill into the subarachnoid or ventricular spaces. Chemotherapy and radiation therapy are not useful in the management of these tumors. Patient Education: For excellent patient education resources, visit eMedicine's Procedures Center. See also eMedicine's patient education article Dermoid Cyst Removal. MULTIMEDIASection 10 of 11
REFERENCESSection 11 of 11
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