Why do central arachnoid pouches expand?

Abstract

SYNOPSIS Three cases of progressive hydrocephalus, two occurring in infants and one in a 12 year old girl who also exhibited precocious puberty, were found to be associated with large arachnoid pouches originating within the posterior fossa. The pathogenesis of such cysts is discussed with special reference to the possibility that their progressive distension results from CSF pulsations of venous origin. Both a direct method of treatment (opening the cyst into the adjacent subarachnoid space) and an indirect one (insertion of a ventriculo-atrial shunt) have been used with success.

Symptomatic Isolated Lumbar Interdural Arachnoid Cyst -Case Report-

“…10,19) According to both theories, the interdural cyst may have arisen as a result of a congenital microscopic defect in the mesenchymal cell lining of the dura mater. Like dural ectasia, which may lead to thecal sac dilatation, meningeal cyst formation may be derived from defective mesenchymal development of the thecal sac.…”

Middle Fossa Arachnoid Cyst: Clinical, Neuroradiological, and Surgical Features

“…As was reported by Robinson [27], some middle fossa arachnoid cysts may be asso ciated with congenital dysgenetic brain and such a lesion may well be cate gorized as an arachnoid pouch, as Williams and Guthkelch [44] and Danziger and Block [7] have described.…”

“…Since the arachnoid cysts in our series were histologically defined, the probability of secretion of fluid from the cells lining the cyst wall as in ependymal cysts [4] or choroidal epithelial cyst [22] seems unlikely. A ball valve or a one-way valve theory may describe the inflow mechanism of the cerebrospinal fluid into the cyst, but this theory alone cannot properly account for the outflow of the intracystic fluid [33,39], Increased colloid osmotic pressure of the intracystic fluid compared to the cerebrospinal fluid may be considered one possible mechanism of cyst expansion only when complicated by intracystic bleeding or excessive transudation of serous fluid from vessels into the cyst [42,43], Furthermore, pulsations of the intracystic fluid, regardless of the presence or absence of its direct communications to the cerebrospinal fluid space, are considered to be an important factor in a possible mechanism of cyst expansion [35,44].…”

“…We also believe that establishment of free communication between the cystic cavity and the basal cistern alone is inadequate [10], Under this condition the cystic cavity may remain as a semiblind pouch. Since the direction of cerebrospinal fluid flow is physio logically from the basal cistern to the Sylvian fissure, the cyst cavity which has been given a wide communication with the basal cistern may merely collect the cerebrospinal fluid without improving its circulation [44]. Based on these considerations, all of our cases were treated by the same method, namely craniotomy and removal of the outer cyst membrane followed by a cystoperitoneal shunt.…”

Subdural Hygroma: Results of Treatment by Ventriculo-Abdominal Shunt

“…Communications between hygroma and subarachnoid spaces have been demonstrated by Stroobrandt et al [27] [24], often observed more or less marked ventricular dilata tion in subdural hygroma cases, and ascribed this to blockade of the circu lation or absorption of cerebral CSF as a result of the hygroma. The con gested CSF, they held, not only tried to escape to the subdural space but also gave rise to subarachnoid cystic dilatations between the sulci, which are not infrequently interpreted as cortical atrophy [29],…”