Meningo (encephalo) cele refers to herniation of the meninges, CSF, and/or brain through an osseous defect in the cranium. Meningoencephaloceles are more common than meningoceles. Congenital encephaloceles are due to an abnormality in the process of invagination of the neural plate.58,59 During embryogenesis, the dura around the brain contacts the dermis in the facial/nasion region as the neural plate regresses. Failure of dermal regression may lead to an encephalocele, dermoid cyst, sinus tract, or nasal glioma. “Nasal glioma” is a misnomer, as it is not a true neoplasm. With nasal gliomas, there is a fibrous connection with the intracranial compartment. Dermoid sinus tracts may have an intracranial connection in up to 25% of cases, and may be complicated by infection (osteomyelitis, meningitis, and abscess). Nasofrontal and sphenoethmoidal encephaloceles are frequently clinically occult, and the differential diagnosis is broad when seen through the endoscope. Anterior basal encephaloceles have an association with other developmental anomalies ( Fig. 3.12 ), including migrational abnormalities, agenesis of the corpus callosum, and cleft lip and palate.60–63
In the setting of trauma or surgery, most acquired meningoencephaloceles involve the sinonasal cavity or the temporal bone. Patients may present with rhinorrhea.
A combination of imaging modalities, including nuclear scintigraphy, CT, and/or MRI, can be used to assess CSF leaks and meningoencephaloceles. It is important to determine whether the CSF leak is due to a dural laceration or a meningo (encephalo) cele. Following the placement of pledgets in the nasal cavity, intrathecal instillation of indium-diethylene triamine pentaacetic acid (DTPA) may be used to confirm the CSF leak. Once a leak is established, coronal CT may be performed for anatomic localization. In the hands of skilled otolaryngologists and radiologists, iodinated contrast CT cisternography is rarely necessary. If an encephalocele is suspected, multiplanar MRI easily establishes the diagnosis by showing direct continuity of the tissue in the sinonasal cavity with the intracranial brain ( Fig. 3.7 ). Although imaging may be useful in detecting CSF leaks, fluorescein injected intrathecally followed by an endoscopic evaluation may allow for direct visualization of an active leak.