What is the recommended treatment approach for a patient presenting with an arachnoid cyst?

Treatment of Arachnoid Cysts

For asymptomatic or mildly symptomatic arachnoid cysts, conservative management with clinical observation is strongly recommended, as over 80% remain stable over time and carry a benign natural history. 1, 2

Initial Diagnostic Evaluation

MRI is the diagnostic modality of choice for evaluating arachnoid cysts, as it demonstrates exact localization, extent, relationship to neural structures, and can identify cord atrophy from compression that predicts neurological outcome 3. For suspected cases, the following imaging approach is recommended:

• Brain MRI with and without contrast should be obtained initially to characterize the cyst and exclude other pathology 4
• MRI with 3D volumetric sequencing (FIESTA, CISS, or BFFE) provides superior visualization, particularly for intraventricular and subarachnoid locations 5
• CT myelography may be added when MRI suggests arachnoid web, ventral cord herniation, or to demonstrate communication between cyst and subarachnoid space for surgical planning 4, 3

Management Algorithm Based on Clinical Presentation

Asymptomatic or Incidentally Discovered Cysts

Conservative management is the standard of care for asymptomatic arachnoid cysts given their benign natural history 1, 2:

• Patient counseling and reassurance about the benign nature of the finding 1
• Single follow-up MRI at 1 year to demonstrate stability may be reasonable 1
• No routine long-term imaging surveillance is necessary for stable, asymptomatic cysts 1
• Clinical follow-up without mandatory imaging is appropriate, with repeat imaging only if clinical deterioration occurs 1

The evidence supporting conservative management is robust: in a large natural history study of 213 arachnoid cysts followed for mean 3.8 years, only 2.3% increased in size and only 2 patients developed new symptoms 2. The prevalence of arachnoid cysts in adults is 1.4%, with most remaining clinically silent 2.

Symptomatic Cysts Requiring Intervention

When arachnoid cysts cause symptoms (headaches, seizures, neurological deficits, hydrocephalus, or mass effect with herniation), surgical intervention is indicated 6, 7:

Location-Specific Surgical Approaches:

For intraventricular cysts (lateral and third ventricles):

• Minimally invasive neuroendoscopic removal is the preferred approach over other surgical or medical options 5
• When surgical removal is technically difficult due to inflammation or adherence, shunt surgery for hydrocephalus is recommended 5
• Perioperative corticosteroids should be administered to decrease brain edema 5

For suprasellar arachnoid cysts:

• Endoscopic ventriculocystocisternostomy produces superior results compared to ventriculocystostomy alone 8
• Adequate fenestration with flow through fenestration sites and reduction of cyst size are key radiological outcomes 8

For spinal arachnoid cysts with cord compression:

• Complete surgical resection with closure of communication between cyst and subarachnoid space is the treatment goal 3
• Corticosteroids are recommended for patients with spinal cord dysfunction (paraparesis or incontinence) 5
• Favorable outcomes occur in patients without preoperative cord damage; cord atrophy on MRI predicts poorer neurological recovery 3

For convexity and middle fossa cysts:

• Surgical excision and marsupialization provides good results in 72% of cases, with 65% showing cyst size reduction 7
• Recurrence rate is approximately 29% with this approach 7

Emergency Presentations

For arachnoid cysts presenting with acute herniation or rapid neurological decline:

• Emergency craniotomy with cyst excision is indicated for "tension" cysts causing uncal herniation 6
• Non-contrast CT is appropriate for rapid diagnosis in emergency settings 6
• Timely surgical intervention shows positive recovery outcomes even with significant herniation 6

Important Clinical Caveats

Key pitfalls to avoid:

• Do not routinely operate on asymptomatic cysts - the natural history is benign with only 2.3% showing size increase over years of follow-up 2
• Middle fossa cysts are less likely to be symptomatic (predominantly left-sided in 70% of cases) and should be managed conservatively unless clearly causing symptoms 2
• Sellar and suprasellar cysts are more likely to be symptomatic and warrant closer monitoring 2
• Attempted removal of inflamed or adherent ventricular cysts carries increased complication risk - shunt surgery is safer in these cases 5

Note: The provided evidence regarding neurocysticercosis 4 is not applicable to arachnoid cysts, which are developmental CSF-filled collections rather than parasitic infections. These represent entirely different pathological entities requiring distinct management approaches.