Intracranial Extracerebral Glioneuronal Heterotopia with Adipose Tissue and a Glioependymal Cyst: A Case Report and Review of the Literature

The presence of central nervous system (CNS) tissue outside the cranium is often referred to as " heterotopia, " although technically this should be termed " ectopia, " according to the dictionary definition. Glioneuronal heterotopia (GH) is a rare, mass-forming, malformative lesion. Ectopic glioneuronal tissue of the head and neck has been detected in the nasopharynx, oro-pharynx, tongue, palate, tonsils, soft tissue, eye, and orbit, and intracranial extracerebral glioneuronal heterotopia (IEGH) has also been reported, although less frequently. Since the first description of neuroglial heterotopia in the dorsal meninges of the cervical spinal cord by Wolbach in 1907, 3 fewer than 20 cases of IEGH have been reported. Glioependymal cysts are rare, epen-dyma-lined, cystic lesions of the subarachnoid space, which have been referred to as epithelial or ependymal cysts. Histopatholog-ically, they are lined with ependymal cells abutted on the glial layer and are commonly detected in the posterior fossa. The origin of glioependymal cysts of the posterior fossa is not clear, but these cysts may represent neuroglial heterotopia, persistent Blake's pouch (diverticulum of the roof of the fourth ventricle), or remnants of a tela chorioidea. We report here a case of IEGH that was predominantly composed of cerebellar tissue with some fat tissue and a large glioependymal cyst, and was initially mis-diagnosed as a teratoma with a glioependymal cyst. The patient was a 4-month-old female infant who was delivered spontaneously at 37 weeks of gestation. An atrial septal defect and patent foramen ovale of the heart were detected after birth. The patient also showed a low nasal bridge, a right-sided deviated nasal septum, ptosis of the left eye, and limited extra-ocular movement of the left eye. Brain magnetic resonance imaging (MRI) revealed a 5-cm mass in the left frontotemporal and suprasellar areas, with cys-tic changes at both the center and on the left side of the mass (Fig. 1). The peripheral portion of the mass had a component of fat tissue. A 5.6-cm arachnoid cyst was observed in the left middle cranial fossa (MCF). In addition, through the anterior skull base defect, we observed left paramedian herniation of the mass into 3 areas: the left nasal cavity, ethmoid sinus, and left medial extraconal orbital space. Following left temporal craniotomy and dural incision, an arachnoid cyst was found in the left sphenoid ridge. This arach-noid cyst was penetrated during surgery, and another cyst was detected under this arachnoid cyst. This second …