Background: Intracranial arachnoid cysts are a common incidental finding. Most of these remain asymptomatic with surgical intervention being reserved for those cysts causing symptoms from mass effect or hydrocephalus. It is not properly understood why cysts enlarge nor is it possible to predict in which cysts this will occur. The aim of this study is to review the natural history of incidental arachnoid cysts.
Methods: A retrospective case review was conducted of all patients diagnosed with an arachnoid cyst between 2007 and 2016. Case notes and radiology reports were reviewed for demographics, symptoms, and changes in cyst sizes.
Results: Four hundred and eighty-five patients were diagnosed with an arachnoid cyst during this time period; of these, 425 (87.6%) were asymptomatic. Patients with symptomatic cysts were significantly younger and more likely to have associated hydrocephalus. The most common indications for imaging which resulted in the diagnosis of the cyst were headaches (n = 106), stroke (n = 51), and seizures (n = 41). The cyst size remained stable or reduced in 147 patients (99.3%) with follow-up imaging (n = 148), and the enlarging cyst remained asymptomatic.
Conclusions: Asymptomatic arachnoid cysts have a low rate of cyst enlargement on follow-up imaging, which supports not routinely imaging these patients. However, serial imaging and surgery may still be indicated in asymptomatic patients at risk of obstructive hydrocephalus which, in this series, was only seen in the pediatric population. A better understanding of the natural history of intracranial arachnoid cysts allows for more efficient follow-up planning.
Keywords: Arachnoid cyst; Congenital abnormality.
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