====== Posterior fossa neuroglial cyst ====== Posterior fossa [[neuroglial cyst]] also known as [[Posterior fossa glioependymal cyst]] are uncommon. The origin is not understood, but possibilities include [[neuroglial heterotopia]], persistent [[Blake's pouch]] (diverticulum of the roof of fourth ventricle), and remnants of a [[tela chorioidea]]. The location of the cyst and the presence of myelinated axons in the cyst wall may be best explained by an origin from neuroglial heterotopia ((Tsuchida T, Kawamoto K, Sakai N, Tsutsumi A. Glioependymal cyst in the posterior fossa. Clin Neuropathol. 1997 Jan-Feb;16(1):13-6. PMID: 9020388.)). see [[Pontine Neuroglial cyst]]. see also [[Cerebellopontine angle neuroglial cyst]]. ===== Differential diagnosis ===== [[Posterior fossa arachnoid cyst]]. ===== Case reports ===== A previously healthy elderly [[woman]] suffered intermittent attacks of [[headache]] and vomiting associated with [[gait abnormality]]. MRI documented a large cystic lesion occupying all the [[fourth ventricle]]. An endoscope-assisted fenestration of the lesion through a [[telovelar approach]] determined only temporary improvement, hence a second surgery with [[gross total resection]] of the cyst was performed, with successful long-term clinical and radiological resolution. Histology revealed CPC. Fourth ventricle symptomatic CPCs are extremely rare lesion, especially in the elderly. Their presence must be carefully evaluated as a possible rare cause of intermittent [[obstructive hydrocephalus]]. Even though [[cyst]] [[fenestration]] with restoration of [[cerebrospinal fluid]] [[pathway]] represents the best treatment in the majority of cases, a more aggressive resection is sometimes necessary ((Draghi R, Mongardi L, Panzacchi R, et al. [[Choroid Plexus Cyst]] of the Fourth Ventricle associated with Intermittent Obstructive Hydrocephalus: Case Report [published online ahead of print, 2020 Jul 31]. World Neurosurg. 2020;S1878-8750(20)31686-7. doi:10.1016/j.wneu.2020.07.164)). ---- A [[glioneuronal heterotopia]] in the [[cerebellomedullary cistern]] in association with salivary gland and adipose tissue in a 56-year-old woman. The patient presented with persistent pain of the posterior neck and was diagnosed with a snow-man shaped cystic solid mass in the cerebellomedullary cistern of the posterior fossa on brain MRI. Surgical exploration revealed a tan to gray solid mass with a cystic portion that was ruptured during surgery. Histologically, the mass consisted of [[glioneuronal]] [[cell]]s in the gliofibrillary or neuropil matrix and was diagnosed as glioneuronal heterotopia. This heterotopic glioneuronal mass contained CD34-positive neuroglial cells and pericellular stroma. In addition, an island of normal-appearing salivary gland and adipose tissue was found in close relationship with the mass. The cystic portion of the mass was a duct cyst of the salivary gland. The pathogenesis of this case with heterotopic glioneuronal, salivary and adipose tissues remains unclear ((Oh SJ, Lee D, Suh YL, Lee JI. Heterotopic glioneuronal mass of the cerebellomedullary cistern with duct cyst formation of ectopic salivary gland tissue. Neuropathology. 2013 Apr;33(2):179-84. doi: 10.1111/j.1440-1789.2012.01334.x. Epub 2012 Jun 21. PMID: 22716318.)). ---- Frazier et al. discussed the [[clinical presentation]], pathological features, and treatment options for this lesion. A 55-year-old woman with a 10-year history of a recurrent cytic lesion in the left cerebellar hemisphere, which required two operations, presented with [[diplopia]], [[dizziness]], and [[ataxia]]. Magnetic resonance imaging revealed a multiloculted cytic lesion in the left cerebellar hemisphere. Resection, through a [[suboccipital craniectomy]], resulted in improvement of the patient's neurologic status. Microscopic examination of a surgical specimen revealed complex cysts lined by a single layer of ependyma-like cells and underlying gliotic parenchyma with florid reactive changes. [[Glioependymal cyst]]s of the posterior fossa may present with symptoms of increased [[intracranial pressure]] and compression of local structures. Recurrence in this case may be partly explained by [[subtotal resection]] in the previous two operations and may also be associated with a florid, proliferative ependymal element. Definitive diagnosis is by microscopic examination of surgically resected specimens. Total extirpation of these cystic lesions is recommended ((Frazier J, Garonzik I, Tihan T, Olivi A. Recurrent glioependymal cyst of the posterior fossa: an unusual entity containing mixed glial elements. Case report. J Neurooncol. 2004 May;68(1):13-7. doi: 10.1023/b:neon.0000024660.91021.2a. PMID: 15174516.)). ---- A large cyst filled with clear fluid was resected from the cerebellum of a 29-year-old man. By light microscopy the cyst was lined by flat epithelial cells. These epithelial cells abutted on a glial layer and immunohistochemical staining revealed that some of them expressed glial fibrillary acidic protein. Corpora amylacea were noted within the glial layer. Ultrastructurally, 2 types of cells lining the cyst were identified. One was characterized by electron-dense cytoplasm, cytoplasmic vacuoles, microvilli without surface-coated material, cilia, and basal bodies. The other was a cell with a smooth cytoplasmic membrane, round nucleus, and clear cytoplasm. Zonulae adherentes was observed between cyst lining cells and the cyst lining cells were shown to rest directly on the glial layer. Surprisingly, myelinated axons were identified in the glial layer, although nerve cells were not identified. These findings are compatible with those of a glioependymal cyst. The origin of glioependymal cysts of the posterior fossa is not understood, but possibilities include neuroglial heterotopia, persistent Blake's pouch (diverticulum of the roof of fourth ventricle), and remnants of a tela chorioidea. The location of the cyst and the presence of myelinated axons in the cyst wall may be best explained by an origin from neuroglial heterotopia ((Tsuchida T, Kawamoto K, Sakai N, Tsutsumi A. Glioependymal cyst in the posterior fossa. Clin Neuropathol. 1997 Jan-Feb;16(1):13-6. PMID: 9020388.)). ---- The clinical, radiologic and pathological findings in two cases of [[neuroepithelial cyst]] of the posterior fossa are described. The first patient was a 43-year-old woman who presented with clumsiness of the hands, gait disturbance and slurring of speech. Magnetic resonance imaging (MRI) revealed a large cystic structure between the cerebellum and the brain stem on the left side, accompanied by compression of the medulla oblongata and displacement of the forth ventricle to the right. The second patient was an 11-month-old boy who presented with progressive bulbar dysfunction. He had previously undergone surgery for myelomeningocele and hydrocephalus associated with Arnold-Chiari type 2 malformation. MRI revealed a large cystic mass isointense with cerebrospinal fluid between the cerebellum and the midbrain, compressing the fourth ventricle and displacing the brain stem to the right. The cases were pathologically similar, the cyst containing a single layer of cuboidal epithelium and rims of neuroglial cells. Immunohistochemical staining was consistent with neuroepithelial cyst. It is important to distinguish this type of cyst from a malignant mass to ensure appropriate treatment and determine the prognosis. In addition, even though neuroepithelial cysts of the posterior fossa are benign, they are often symptomatic because of their mass effect. The second case was unusual because the cyst developed over a period of 2 months, which shows that this type of cyst can develop rapidly. To the authors' knowledge, the association with Arnold-Chiari type 2 malformation has not previously been reported ((Goh RH, Maguire J. Neuroepithelial cyst of the posterior fossa: two case reports with radiologic-pathologic correlation. Can Assoc Radiol J. 1996 Apr;47(2):126-31. PMID: 8612085.)). ===== References =====