Answer to Dermacase continued from page 31
2. Dermoid cyst
Dermoid cysts are true hamartomas derived from both ectoderm and mesoderm. There are 3 types: acquired epidermal cysts, which result from traumatic implantation of part of the skin into its deeper layers; congenital teratomas, arising from embryonic epithelium and containing bone, cartilage, teeth, and other structures, which typically develop in the ovaries and testes; and congenital inclusion dermoid cysts, which form along the lines of embryologic fusion1 and include dermoid cysts of the head and neck.
Dermoid cysts might be seen at birth but often present in childhood. Sudden changes in size make diagnosis more challenging. Approximately 7% of dermoid cysts occur on the head and neck, with the orbit most commonly affected.2 They also occur in the floor of the mouth, nasal, submental, and substernal areas.3 Pathologic confirmation is required to establish diagnosis. Histologically, a dermoid cyst must contain 2 germ cell layers. A keratinizing squamous epithelium is typically present, as are adnexal structures such as hair follicles and sebaceous glands. The contents of a dermoid cyst vary and might also include cartilage and teeth.1–3
The differential diagnosis includes epidermal inclusion cysts, glioma, meningoencephalocele, and nevus sebaceus.2,4 An epidermal inclusion cyst is a benign cutaneous skin-coloured or red inflamed papule or nodule, commonly on the face or trunk. Glioma, a neoplasm arising from glial cells, most commonly occurs in the brain. A meningoencephalocele is a protrusion of the meninges or brain tissue as a result of a congenital cranial defect. Nevus sebaceus, a hamartomatous lesion usually noted at birth or in early childhood, usually manifests as a solitary hairless patch on the scalp. Dermoid cysts can be easily differentiated based on their peculiar histologic features. In our case, after a computed tomography scan of the head revealed no evidence of intracranial communication, punch biopsy results revealed the typical histologic features of a dermoid cyst.
A high index of suspicion is required to detect dermoid cysts. A sinus dimple or abnormal hair distribution on a congenital lesion at a typical location should raise suspicion of intracranial extension.5 Medical imaging helps rule out this possibility and must be performed before surgical intervention. Intracranial extension is rare—it is mostly reported with midline lesions over the scalp and nose.6 After complete excision of dermoid cysts, recurrence is unusual.
Footnotes
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Competing interests
None declared
- Copyright© the College of Family Physicians of Canada
References
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