Can arachnoid cysts enlarge over time and cause imbalance?

Arachnoid Cysts: Growth Potential and Imbalance

Yes, arachnoid cysts can enlarge over time, but most remain stable or decrease in size, and while they can theoretically cause imbalance through mass effect or hydrocephalus, the vast majority remain asymptomatic throughout life. 1, 2

Growth Characteristics

The majority of arachnoid cysts do not grow. A large retrospective volumetric study tracking 166 arachnoid cysts over a mean of 2.5 years found that most cysts remained constant in size or became smaller, with only larger temporal pole cysts (Galassi II type) showing growth at a rate of 0.3 ml per year—and even these remained clinically silent. 1

• In a series of 485 patients, cyst size remained stable or reduced in 99.3% of cases with follow-up imaging, and the single enlarging cyst remained asymptomatic. 2
• Arachnoid cysts have a high rate of change and can undergo spontaneous growth, reduction, or complete disappearance. 3
• These cysts are thin-walled sacs filled with clear CSF fluid that appears isointense to CSF on all MRI sequences. 4, 5

Mechanism of Symptoms Including Imbalance

When arachnoid cysts do cause symptoms, the mechanism is through mass effect on adjacent neural structures or obstruction of CSF flow leading to hydrocephalus—both of which can produce imbalance. 3, 6

Direct Mass Effect

• Large cysts can compress and displace neurovascular structures, potentially affecting cerebellar or vestibular pathways that control balance. 3
• "Giant" cysts (>50mm diameter) are occasionally found in locations like the Sylvian fissure. 4
• Small cysts are often asymptomatic, while larger cysts produce mass effect leading to compression of neural tissue. 3

Hydrocephalus-Related Symptoms

• Cysts can cause hydrocephalus through mechanical obstruction of ventricles or basal cisterns. 7
• CSF circulation disturbances from brain mass displacement with occlusion of the foramen of Monro or aqueduct cause obstructive hydrocephalus, increasing intracranial pressure. 8
• Increased intracranial pressure manifests as headaches, dizziness, nausea, vomiting, and ataxia (imbalance). 3, 8

Clinical Presentation

Symptoms depend critically on cyst size and location. 3, 6

• Headaches and seizures are the most common symptoms of middle cranial fossa cysts. 6
• Ataxia (imbalance), hearing loss, mental status changes, and worsening mood can occur with symptomatic cysts. 3
• In adults and older children, headaches are usually the first clinical symptom. 8
• 87.6% of arachnoid cysts remain asymptomatic. 2

Management Implications

Asymptomatic Cysts

• Simple asymptomatic arachnoid cysts not causing CSF obstruction should be managed conservatively with patient counseling and reassurance. 5
• Asymptomatic cysts have a low rate of enlargement, supporting the practice of not routinely imaging these patients. 2
• Once stability is confirmed with 2 sequential scans approximately 1 year apart, long-term imaging follow-up is not necessary unless concerning symptoms develop. 5

Symptomatic Cysts

• Definitive treatment for symptomatic arachnoid cysts is surgery, with indications including progressive hydrocephalus or intracranial hypertension. 6
• Seizures refractory to medical management or visual disturbances from compression may require surgical intervention. 5
• The primary surgical goal is establishing communication between CSF and cyst content to effect pressure equalization. 8

Important Caveats

• Serial imaging and surgery may still be indicated in asymptomatic patients at risk of obstructive hydrocephalus, which is primarily seen in the pediatric population. 2
• Patients with symptomatic cysts are significantly younger and more likely to have associated hydrocephalus. 2
• Nonspecific headaches unrelated to hydrocephalus are not well-accepted indications for surgical intervention. 5