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  • Updated 12.17.2021
  • Released 09.13.1995
  • Expires For CME 12.17.2024

Arachnoid cyst

Introduction

Overview

Arachnoid cysts are one of the most common incidental findings on brain MRI. They are usually intracranial and supratentorial in location, but spinal and even intraneural cysts may be identified and possibly cause symptoms or confound medical decision-making. Most cysts are solitary, and the presence of multiple cysts should prompt an evaluation for glutaric aciduria type 1, which is present in 25% of bitemporal cases. Most asymptomatic cysts do not require active management or surveillance. The exceptions are discussed in this article. In the presence of symptoms, surgical evaluation and intervention are recommended. The indications, risks, and advantages of these approaches are discussed in detail herein.

Key points

• Be certain that the cyst is responsible for symptoms before considering intervention. Over 70% of pediatric and over 90% of adult cases have no attributable symptoms.

• Arachnoid cysts in children are more likely to present with hydrocephalus. Cyst resolution or shrinkage is more common than growth after the first year of life.

• For suprasellar arachnoid cysts, endocrinopathies, such as precocious puberty and GH deficiency, are common manifestations in children.

• There may be rupture of bridging veins or vessels in the cyst’s wall, which can result in a subdural hematoma or bleeding into the cyst.

• Endoscopic procedures for temporobasal arachnoid cysts have the lowest success rate (81%), highest recurrence (19%), and highest complication rate (24%).

• Cysts larger than 5 cm have a higher risk of rupture; however, a systematic review of published literature did not find evidence to support recommending against participation in sports for patients with arachnoid cysts.

Historical note and terminology

Although clear cysts along the neuraxis have been described on autopsies throughout the centuries (31), the earliest modern description of arachnoid cysts is ascribed to Bright in 1831 (10). Prior to the mid-20th century consolidation of the terminology, arachnoid cysts were referred to under a variety of terms, such as "meningitis serosa circumscripta," “chronic cystic arachnoiditis," "cerebral pseudotumor," or "leptomeningeal cyst” (64). Arachnoid cysts can be best described as non-neoplastic fluid collections that lie between two membranes of arachnoid matter--a thin inner and a collagen-reinforced outer membrane. Thus, arachnoid cysts would be most properly described as intra-arachnoid cysts.

Although there is no standard nomenclature, arachnoid cysts can be classified by symptoms, etiology (primary or developmental vs. secondary), embryological origin (eg, expansion of the roof plate of the brain vesicle), localization, or communication with CSF pathways.

There had been a historical debate whether arachnoid cysts are primary malformations of the arachnoid (64) or secondary to hypoplasia or agenesis of the underlying brain (54). The debate settled over the past half-century, when the diagnosis of arachnoid cysts shifted from an autopsy or surgical diagnosis to a radiographic diagnosis that is mostly made incidentally without concurrent hypoplasia noted.

One of the first successful surgical interventions for an arachnoid cyst was a partial removal by Placzek and Krause in 1907, resulting in clinical improvement (46). Traditional surgical resection of the cyst wall (38) was often complicated by damage to the surrounding brain and cyst recurrence. Over time, the successes with shunting the recurrent cysts led to shunt insertion becoming a primary treatment approach in the 1980s (65).

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