The Common Vein Copyright 2010
A dermoid is considered a congenital lesion and like epidermoids are thought be caused by abnormal location of surface ectoderm which may be a result of abnormal migration during neural tube closure. They are usually located in the midline and when they are intracranial they are frequently within the posterior fossa in the cisterna magna, fourth ventricle and prepontine cistern. They may also be located in a supratentorial location, usually in the suprasellar region. They are a common cause of orbital lesions in young patients as well.
They may grow slowly over time due to the accumulation of desquamated debris and gland products. Dermoids may also rupture which can result in chemical meningitis or other conditions such as seizure or hydrocephalus. Rarely they may degenerate into squamous cell carcinoma.
Pathologically, dermoids are made up of ectodermal elements including squamous epithelium in combination with dermal appendage structures such as apocrine, sweat and sebaceous glands in addition to hair follicles. They are characterized by a thick lined unilocular cystic structure which may contain lipid or proteinaceous debris
Presenting symptoms includes headache and seizure. Suprasellar lesions may also result in visual disturbances.
On imaging, dermoids appear as unilocular cystic lesions. On CT the internal cyst contents may match fat attenuation on CT. The wall may be slightly thick, contain calcification and enhance. On MRI, the cyst contents may be hyperintense on T1 in regions due to high lipid content of the sebaceous material within the cyst. Fat-fluid levels may also be seen. Alternatively, some dermoids can look exactly like epidermoids.
Total surgical resection is the only effective treatment. Incomplete resection may result in recurrence.
Image Courtesy Elisa Flower MD and Asim Mian MD 97640c01.8
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