Dermoid and epidermoid tumours of the central nervous system are rare congenital cystic tumours arising from ectopic skin cells. When these embryonic dermal rests consist only of epithelial cells the resulting tumours are called epidermoid. Epidermoid tumours have a capsule of stratified squamous epithelium based on connective tissue. These squamous cells proliferate and desquamate, forming the central contents of this slowly growing cystic tumour. The contents are rich in keratin and lipids and appear as shiny white flakes giving rise to the term ‘tumeur perlée’.

When the embryonic dermal rests consist of multiple skin elements, including epithelial tissue, sweat glands, and hair follicles, the resulting tumours are called ‘dermoid’. In addition to desquamated epithelial cells, these tumours may contain large amounts of mucinous secretions and even hair.

In the skull or orbital roof, epidermoid tumours can manifest themselves as slowly growing masses scalloping bone and displacing the brain or orbit.

Intracranial epidermoid tumours in the parasellar and cerebellopontine angle regions present as cranial nerve deficits, with signs of brain-stem and cerebellar compression. Intracranial dermoid tumours usually occur in the midline, above or below the tentorium, and are often associated with a dermal sinus extending to the surface of the scalp. Intracranial epidermoid and dermoid tumours, although congenital, grow slowly, often coming to medical attention as large masses in adolescents and adults.

Epidermoid and dermoid tumours may occur in the spinal canal, and even within the substance of the spinal cord. They usually cause signs of spinal cord or cauda equina compression. Intraspinal dermoid tumours may have a cutaneous dermal sinus track presenting in the midline of the back. Rarely, spinal epidermoid tumours arise from epithelial cells implanted by a lumbar puncture.

Skull and orbital epidermoid tumours grow slowly; they have a typical appearance on plain radiographs, distinguishing them from most other cranial lesions, such as metastatic tumour, myeloma, haemangioma, and osteoma.

Intracranial epidermoid or dermoid tumours can now be diagnosed with virtual certainty by combining the clinical picture and the data from modern imaging studies. CT and MRI images show that these tumours are avascular and do not ‘enhance’; in addition, their high lipid content yields densities on CT scans lower than those of water, and produces characteristic signals on MRI scans.

Epidermoid or dermoid tumours in the spinal canal can also be diagnosed by combining the clinical, CT, and MRI data. An associated dermal sinus track is diagnostic. An intraspinal epidermoid tumour is difficult to differentiate from a lipoma.

Cranial and orbital lesions are usually excised for definitive diagnosis, for cosmesis, and for proptosis. A cranioplasty to repair the bony defect is usually desirable.

Intracranial epidermoid and dermoid tumours should be managed conservatively when they are causing minimal clinical symptoms, since they do not warrant the risks of intracranial surgery. Progressively symptomatic mass lesions should be reduced surgically; the intracapsular content of the tumours can be removed by current microneurosurgical techniques with a low risk to the patient. The capsule, of the epidermoid tumour, however, often grows into the interstices of the pia-arachnoid, cranial nerves, and blood vessels; this may make total removal of the capsule and tumour inappropriate, especially when the benign and slow-growing nature of the lesion is considered.

Epidermoid and dermoid tumours of the spinal cord are managed with the same plan as for intracranial tumours. In the spinal cord, however, conservative management probably carries a higher risk of morbidity. Presentation of a tumour with recurrent meningitis associated with a dermal sinus tract is a clear indication for surgery.

Epidermoid and dermoid tumours are not responsive to radiation or chemotherapy.

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