What is the appropriate evaluation and management for an arachnoid cyst?

Arachnoid Cyst: Evaluation and Management

For asymptomatic arachnoid cysts discovered incidentally, conservative management with observation is appropriate, while symptomatic cysts causing hydrocephalus, seizures refractory to medical management, or progressive neurological deficits require surgical intervention.

Initial Diagnostic Evaluation

MRI is the imaging modality of choice for identifying and characterizing arachnoid cysts. 1, 2

• Standard MRI protocol should include T1-weighted, T2-weighted, and fluid-attenuated inversion recovery (FLAIR) sequences 1, 2
• Arachnoid cysts appear isointense to CSF on all MRI sequences with no enhancement after gadolinium administration 1, 2, 3
• MRI with 3D volumetric sequencing (FIESTA, CISS, or BFFE) provides enhanced resolution and is particularly useful when hydrocephalus is present 1, 3
• The cyst wall is typically not visible on imaging, as these are thin-walled sacs filled with clear CSF 1

For thoracic spine arachnoid cysts specifically, CT myelography is useful for differentiating cysts from arachnoid webs or ventral cord herniation and for presurgical planning 2

Clinical Assessment and Risk Stratification

Determine whether the cyst is symptomatic or asymptomatic, as this fundamentally guides management.

Symptomatic Presentations Requiring Intervention:

• Obstructive hydrocephalus or elevated intracranial pressure 1, 4
• Seizures refractory to medical management 1, 4
• Progressive neurological deficits or focal neurological signs 5, 6
• Visual disturbances from tectal compression 1
• Hemiparesis or cranial nerve dysfunction 7

Asymptomatic or Minimally Symptomatic:

• Nonspecific headaches unrelated to hydrocephalus are not well-accepted indications for surgical intervention 1
• Most arachnoid cysts (>80%) remain stable in size over time 1, 8
• The natural history is benign, with only 2.3% of cysts increasing in size during follow-up 8

Management Algorithm

For Asymptomatic Incidental Cysts:

Conservative management with surveillance imaging is the appropriate approach. 1, 2, 5

• Provide patient counseling and reassurance 1
• For patients with nonspecific symptoms like headache or fatigue, obtain 2 sequential scans separated by approximately 1 year to demonstrate stability 1
• Long-term imaging follow-up is not necessary once stability is confirmed, unless concerning symptoms develop 1
• The majority of arachnoid cysts remain asymptomatic throughout life 1, 8

For Symptomatic Cysts:

Surgical intervention is indicated for symptomatic cysts. 1, 5, 7

Surgical Options by Location:

For lateral and third ventricle cysts:

• Removal via minimally invasive neuroendoscopy is recommended when technically feasible 1
• Endoscopic fenestration offers a less invasive option but carries higher recurrence risk 5

For fourth ventricle cysts:

• Surgical removal is recommended over medical therapy or shunt surgery 1

For adherent ventricular cysts:

• Shunt surgery is preferred when surgical removal is technically difficult 1
• Attempted removal of inflamed or adherent ventricular cysts carries increased risk of complications 1

For supratentorial cysts:

• Excision and marsupialization provides good results, with 65% of cysts reducing in size and 17% resolving completely 7
• Cystoperitoneal shunting should be considered when other approaches are not feasible 1, 7

For thoracic spinal cysts:

• Microsurgical fenestration, complete cyst resection, and dural repair are surgical options 2

Perioperative Management:

• Corticosteroids should be administered in the perioperative period to decrease brain/cord edema 1, 2
• Avoid preoperative antiparasitic drugs as they may cause cyst disruption 1

Follow-Up Protocol

MRI should be repeated at least every 6 months until resolution of cystic lesions in surgically treated patients. 1, 3

• Monitor for potential complications including shunt failure, recurrence of symptoms, and development of arachnoiditis 3
• The overall recurrence rate after surgical intervention is approximately 29% 7
• Good outcomes are achieved in 72% of surgically managed cases 7

Common Pitfalls and Critical Considerations

• Do not confuse arachnoid cysts with other cystic lesions: Arachnoid cysts are distinguished by their CSF-isointense signal on all sequences and lack of enhancement, unlike epidermoid cysts (which restrict on DWI) or neurocysticercosis (which may enhance) 9
• Sellar and suprasellar cysts are more likely to be symptomatic and require intervention 8
• Middle fossa cysts are less likely to be symptomatic and are predominantly left-sided (70%) 8
• Emergency surgical intervention is required for cysts causing uncal herniation or acute neurological deterioration 6

Special Population: Pregnancy

For pregnant patients with elevated intracranial pressure due to arachnoid cysts, aggressive management is needed even during pregnancy, with corticosteroids used when necessary 3