In this article, the authors review pathologies of dermoid and epidermoid tumors in the brain and spine. Epidermoid and dermoid cysts arise from ectopic ectodermal cells that are retained within the neural groove during early gestation. These tumors have varying presentations that depend on location of the mass. Symptoms range from isolated cranial neuropathy to aseptic meningitis after cyst rupture. Imaging findings are typically diagnostic, with CT and MRI findings appearing similar to arachnoid cysts, but with restricted diffusion on diffusion-weighted MRI. With complete resection, recurrence is atypical. Incompletely resected masses are prone to recurrence as the cyst wall continues to produce keratin. However, as these are slow growing lesions, they are occasionally treated with debulking alone to avoid injury to the surrounding structures, including nerves and blood vessels. Extensive resections are associated with high rates of early or delayed postoperative deficits. Total resection is possible only in 50% to 70% of cases. Malignant transformation to squamous cell carcinoma occurs rarely.
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• Most epidermoids and dermoids are developmental in origin, forming between the third and fifth week of embryonic development.
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• The MRI characteristics of epidermoids and dermoids are usually diagnostic, but 5% have atypical appearance.
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• Epidermoids and dermoids are potentially curable with surgery. However, due to adhesions of cyst membrane to critical neurovascular structures, subtotal resections are frequently performed in order to preserve neurologic function.
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• Malignant transformation can be seen rarely.
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• Aseptic meningitis and ventriculitis may occur postoperatively if there is leaking of cholesterol crystals.
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• Perioperative morbidity (20%) and mortality (7%) remains high, particularly if total resection is attempted as epidermoids often grow along nerves and blood vessels.
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• Lesions are slow-growing, and late recurrence is common with incompletely resected tumors.
Historical note and terminology
The first description of an epidermoid has been attributed to Pinson, an artist in the School of Medicine in Paris, who created a wax model of a smooth cyst located at the cerebellopontine angle in 1807 (72). It was not until 1829 that Jean Cruveilheir, a French pathologist, first recognized epidermoids as a specific entity and gave them the name "tumeur perleé" (23). Dr. Müller described these masses as well, calling them "cholesteatomas" as they were seen to contain cholesterol (100). Walter Dandy described epidermoid tumors as “the most beautiful tumor in the body” given their pearly appearance; whereas dermoid tumors have less of this appearance, containing hair and fat (26). Epidermoid and dermoid tumors are no longer included amongst the tumors of the 2016 edition of the World Health Organization Classification of Tumors of the Central Nervous System (67). Medical literature uses the terms "cysts" or "tumors" interchangeably to describe "epidermoids" and "dermoids."
Intracranial dermoid and epidermoid cysts are usually considered to be 2 different entities in the literature. Both of these cysts are epidermoid inclusion cysts, lined by stratified squamous epithelium, similar to skin. Dermoid cysts, in addition, have skin appendages, including apocrine, eccrine, and sebaceous glands as well as other exodermal structures such as hair follicles and teeth (91). CNS epidermoid or dermoid cysts are benign, slow-growing lesions and can be congenital or acquired (60). However, they rarely undergo malignant transformation into squamous cell carcinoma (44; 24).