Nasal dermoid cyst and nasal glioma with intracranial extension.

These congenital midline nasal masses are the result of a failure of normal neural crest cell embryology. The ectodermal anterior neuropore (primitive frontonasal region) forms medial to the optic recess of the sphenoid sinus in the third week of gestation, and the frontal, nasal, and ethmoid structures form in the area immediately proximal to the anterior neuropore.3 Through the eighth week of gestation, the following occur. The fonticulus frontalis (gap between frontal and nasal bones) fuses with the foramen cecum (region between ethmoid and frontal bones connecting with the prenasal space) in the area of the future cribriform plate, separating intracranial contents from the nose and extracranial structures. Failure of closure here can lead to encephaloceles. Gliomas can form when faulty closure of the anterior neuropore leads to the development of rests of CNS tissue extracranially. Dermoids may develop after faulty closure of the fonticulus frontalis, which allows dermal elements to invaginate between the nasal bones and cartilage. Intracranial connections can be seen with all of these. None should be biopsied until radiographic imaging is obtained to determine intracranial extension, as this could be associated with CSF leak. Intracranial connection is also associated with an increased risk of meningitis.3