SAN FRANCISCO – Nearly half of congenital dermoid cysts on infant heads may have risky intracranial connections that link the brain to the outside world.
Tracts that expose the brain put a child “at higher risk for meningitis and abscess formation,” Dr. Brandie J. Metz said at a meeting sponsored by Skin Disease Education Foundation. Fortunately, dermoid cysts in the most common location–the lateral third of an eyebrow–have never been reported to contain intracranial connections.
Dermoid cysts also can occur on the midline nasal bridge, the scalp, the anterior lateral neck, or postauricular areas, and may need imaging to check for intracranial connections, said Dr. Metz, chief of pediatric dermatology at the University of California, Irvine.
Congenital dermoid cysts are epithelial-lined cysts containing epidermal appendages such as hair, sebum, and sebaceous and apocrine glands. They are formed as the embryonic fusion lines of the skull close and structures get sequestered into the skin. In some reports, almost half are associated with intracranial connections.
Dermoid cysts in the nasal or midline scalp regions are more likely to have intracranial extensions. Dr. Metz recommended getting MRI exams of all congenital dermoid cysts on the scalp, especially if there's an overlying hair collar sign (longer, courser, darker hair surround the scalp nodule) or capillary stain, or if the cyst is in an atypical location. All midline dermoid cysts deserve imaging as well, especially if there are sinus pits or hairs projecting from the cyst, she said.
Most dermoid cysts appear at birth, and 70% are visible by age 5 years. They present as soft, rubbery, mobile subcutaneous tumors. Dermoid cysts on the nose can appear anywhere from the glabella down to the tip of the nose, and may present with a subtle appearance–“just a kind of yellow broadening of the tip of the nose or the nasal bridge,” Dr. Metz said. An MRI will show the extent and nature of the lesion and can rule out intracranial connection.
The one scenario in which a CT scan may be preferable is in an older child with a very long, thin lesion in a classic location. Dermoid cysts that have been present for a long time can cause bony erosions.
“[In] a teenager with a dermoid cyst in a very classic location, you're not looking for an intracranial connection but rather to determine if there's any bony defect, CT might be useful,” she said. If it is found that there is intracranial connection, the patient should be referred to a neurosurgeon for surgical removal of the connection.
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Dermoid cysts at the lateral third of the eyebrow don't need radiologic imaging.
Here, an MRI of a midline nasal dermoid confirms an intracranial connection. Photos courtesy Dr. Brandie J. Metz