Arachnoid Cyst of the Fourth Ventricle

Abstract

A 65-year-old female was admitted because of progressive vertigo, truncal ataxia, and unsteadiness of gait for the past 6 years. Computed tomography (CT) and magnetic resonance imaging revealed a non-enhanced, large midline cyst in the posterior fossa and slightly dilated lateral and third ventricles. Metrizamide CT cisternography showed no communication between the cyst and the subarachnoid space. Suboccipital craniectomy, laminectomy of the atlas, and membranectomy of the cyst were performed. On light microscopic examination, the cyst wall was composed of arachnoid cells and connective tissues. Thus, this lesion was not an epithelial cyst but an arachnoid cyst occupying the fourth ventricle. An arachnoid cyst of the fourth ventricle is extremely rare, and only two cases were previously reported.

Intraepithelial carcinoma arising in an endodermal cyst of the posterior fossa

“…Other benign epithelial cysts derived from the leptomeninges are referred to as arachnoid cysts (AC). A differential diagnosis with endodermal cysts is not difficult because AC, histologically, show a delicate fibrous capsule lined by a very attenuated epithelium of meningothelium type 52 …”

“…A differential diagnosis with endodermal cysts is not difficult because AC, histologically, show a delicate fibrous capsule lined by a very attenuated epithelium of meningothelium type. 52 The cysts, lined by keratinizing squamous epithelium with or without skin appendages, are readily recognized as dermoid and epidermoid cysts, respectively. 1 A cystic secondary tumor is also easily excluded by clinical, radiologic and histologic studies.…”

Fourth ventricle arachnoid cyst

“…8,9 There are isolated case reports in the literature discussing the presence of lateral ventricular 10,11 and fourth ventricular arachnoid cyst. [1][2][3][4][5][6][7] We identified reports of seven fourth ventricle arachnoid cysts. [1][2][3][4][5][6][7] One case included in the present series was reported by us previously.…”

“…[1][2][3][4][5][6][7] We identified reports of seven fourth ventricle arachnoid cysts. [1][2][3][4][5][6][7] One case included in the present series was reported by us previously. 5 Fourth ventricular arachnoid cysts can present a diagnostic dilemma, posing as a dilated fourth ventricle secondary to fourthventricular outlet obstruction.…”

“…[1][2][3][4][5][6][7] Identification of an arachnoid cyst within the fourth ventricle is crucial as these are entirely benign lesions, which can often be mistaken as a dilated fourth ventricle (Fig. 1).…”