Prevalence of Retrocerebellar (Posterior Fossa) Arachnoid Cysts
Retrocerebellar arachnoid cysts are relatively common, representing approximately 33% of all intracranial arachnoid cysts in adults, making them the second most frequent location after middle fossa cysts. 1
Overall Prevalence Data
- Arachnoid cysts occur in approximately 1.4% of adults undergoing brain MRI, based on a large retrospective study of 48,417 consecutive patients 1
- The overall prevalence ranges from 1-2% in the general population 2
- Men have a significantly higher prevalence than women (p < 0.0001) 1
Location-Specific Distribution
The distribution of arachnoid cysts by location shows:
- Middle fossa: 34% (most common location) 1
- Retrocerebellar/posterior fossa: 33% (second most common) 1
- Convexity: 14% 1
- Other locations (sellar, suprasellar, etc.) comprise the remainder 1
Clinical Context
Posterior fossa arachnoid cysts are considered "uncommon" in the posterior cranial fossa compared to other intracranial locations, though they still represent a substantial proportion of all arachnoid cysts 3, 4. These cysts constitute approximately 1% of all intracranial masses overall 3.
Important Clinical Characteristics
- Multiple arachnoid cysts can occur in the same patient (occurred in 30 of 661 patients, or 4.5%) 1
- Posterior fossa cysts generally remain asymptomatic or cause vague, non-specific symptoms 4
- When symptomatic, they may present with headaches, seizures, focal neurologic signs, or rarely isolated sensorineural hearing loss 3, 4
Natural History
The vast majority of posterior fossa arachnoid cysts remain stable over time, with only 2.3% increasing in size during follow-up (mean 3.8 years) 1. This benign natural history supports conservative management for asymptomatic cases 5, 1.