SAN FRANCISCO Nearly half of congenital dermoid cysts on infant heads may have risky intracranial connections that link the outside world to the brain, said Dr. Brandie J. Metz.
Tracts that expose the brain put a child "at higher risk for meningitis and abscess formation," Dr. Metz said at a meeting sponsored by Skin Disease Education Foundation. Fortunately, dermoid cysts in the most common locationthe lateral third of an eyebrowhave 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 of the cysts 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 to an MRI 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.
"If it's a teenager with a dermoid cyst in a very classic location, and you're not looking for an intracranial connection but rather to determine if there's any bony defect, CT might be useful," she explained.
If it is found that there is intracranial connection to the cyst, the patient should be referred to a neurosurgeon for surgical removal of the connection, Dr. Metz said.
In a 1988 study, 70 children had a solitary nontraumatic lump on the scalp, of which 26 had intracranial extensions.
Forty-one (59%) of these lumps were determined to be dermoid cysts. Other causes of the lumps included cephalhematoma deformans, eosinophilic granuloma, or occult meningoceles or encephaloceles.
The lumps that were determined to be dermoid cysts were the most likely to have intracranial extensions, in 15 of the 41 cases (37%).
Most of the dermoid cysts with extensions were on the posterior fontanelle or occipital scalp, "where we would have done preoperative imaging" to look for intracranial connections, Dr. Metz said.
A different infant scalp lesion that often gets confused with dermoid cysts also can have a rudimentary stalk that opens intracranial communicationheterotopic neural nodules of the scalp.
"The ones that are heterotopic neural nodules are more likely to have some other signs than do dermoids," noted Dr. Metz.
In a 2005 study of 12 heterotopic neural nodules of the scalp, 10 had a hair collar sign, 9 had capillary stain overlying the nodule, and 5 had calvarial defects in the bone that were identified with preoperative imaging.
SDEF and this news organization are wholly owned subsidiaries of Elsevier.
Dr. Brandie J. Metz: Dermoid cysts located on the lateral third of the eyebrow do not require radiologic imaging.
This MRI of a midline nasal dermoid cyst on a child confirms an intracranial connection to the cyst. Photos courtesy Dr. Brandie J. Metz