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 have an outer connective tissue capsule and are lined with stratified squamous epithelium that also contains hair follicles, sebaceous glands, and sweat glands. Centrally,  contain desquamated epithelial keratin and some lipid material. The external surface 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.

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.

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.

Dermoid tumors are often located at the cranial midline within the posterior cranial fossa, suprasellar cistern, and subfrontal areas. 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.

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 . 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.

A 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. 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.

Most 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 .

The treatment goal for dermoid  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, if its contents spill into the subarachnoid or ventricular spaces.

Chemotherapy and radiation therapy are not useful in the management of these tumors.