What is the management and treatment of arachnoid cysts?

Arachnoid Cyst Management

Definition and Imaging Characteristics

Arachnoid cysts are CSF-filled sacs within the arachnoid membrane that appear isointense to CSF on all MRI sequences without gadolinium enhancement, and MRI with 3D volumetric sequencing is the gold standard for diagnosis. 1, 2

• The cyst wall is typically not visible on imaging, and these are thin-walled sacs filled with clear CSF fluid 1
• Standard T1- and T2-weighted sequences, along with fluid-attenuated inversion recovery (FLAIR) sequences, should be included in the imaging protocol 1, 2
• Arachnoid cysts may exhibit mass effect on adjacent brain tissue 2
• Diffusion-weighted imaging and cine phase-contrast MRI help differentiate communicating versus non-communicating cyst types and assess CSF dynamics 3

Epidemiology and Location

• Prevalence is approximately 1-2% of the population, with male predominance 3
• Most commonly occur in the Sylvian fissure (50% of cases) and posterior fossa 3, 4
• "Giant" cysts (>50mm diameter) are occasionally found in the Sylvian fissure/opercular region 2
• In patients with autosomal dominant polycystic kidney disease (ADPKD), prevalence is 8-15% 1

Conservative Management for Asymptomatic Cysts

The majority of arachnoid cysts remain asymptomatic throughout life and should be managed conservatively with patient counseling and reassurance. 1

• Simple pineal and other asymptomatic arachnoid cysts not causing CSF obstruction or visual problems require only conservative management 1
• Most pineal cysts (>80%) remain stable in size over time 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 or there is elevation in tumor markers 1
• Nonspecific headaches unrelated to hydrocephalus are not well-accepted indications for surgical intervention 1

Surgical Indications

Surgery is reserved for symptomatic cases, particularly those associated with hydrocephalus, seizures refractory to medical management, or focal neurological deficits. 1, 3, 4

• Progressive hydrocephalus or intracranial hypertension are definitive indications for surgery 4
• Seizures refractory to medical management require surgical intervention 1
• Visual disturbances from tectal compression necessitate surgery 1
• Presence of progressive neurological deficits warrants intervention 3

Surgical Treatment Algorithm by Location

Lateral and Third Ventricle Cysts

For lateral and third ventricle cysts, removal via minimally invasive neuroendoscopy is recommended when technically feasible. 1

• Avoid preoperative antiparasitic drugs as they may cause cyst disruption 1
• Careful preoperative assessment of cyst location and presence of ependymitis is essential for surgical planning 5

Fourth Ventricle Cysts

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

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

Spinal Arachnoid Cysts

The aim of surgical treatment for spinal cysts is neural decompression and prevention of refilling, best accomplished by complete resection and closure of communication between cyst and subarachnoid space. 6

• MRI is the diagnostic procedure of first choice to demonstrate exact localization, extent, and relationship to the spinal cord 6
• Myelography and CT-myelography demonstrate communication between subarachnoid space and cyst, important for surgical planning 6
• Cord atrophy secondary to compression can be visualized and used for prediction of neurological outcome 6

Surgical Technique Options and Outcomes

Fenestration (Craniotomy)

Fenestration achieves favorable outcomes in approximately 76% of cases and should be considered first-line surgical treatment to avoid shunt dependency. 7

• Mean cyst volume reduction is 58% after fenestration 8
• 22 of 29 cysts (76%) treated with initial fenestration required no additional treatment 7
• Endoscopic fenestration offers a less invasive option but carries higher recurrence risk compared to microsurgical fenestration 3

Cystoperitoneal Shunting

• Mean cyst volume reduction is 74% after shunting 8
• Favorable outcomes achieved in 6 of 9 patients (67%) treated with shunting 8
• Should be considered when fenestration is not feasible or has failed 1
• Shunt failure is common in patients with hydrocephalus secondary to arachnoid cysts, often requiring multiple revisions 5
• Of 12 cystoperitoneal shunts, 5 required revisions on one or more occasions 7

Outcome Predictors

• Degree of cyst volume reduction correlates significantly with clinical outcome 8
• Patients with infratentorial cysts have more favorable outcomes 8
• Headache as the only symptom does not influence outcome 8
• Postoperative outcome is favorable in patients without preoperative cord damage 6

Perioperative Management

• Corticosteroids should be administered in the perioperative period to decrease brain edema 1

Follow-up Recommendations

MRI should be repeated at least every 6 months until resolution of cystic lesions following surgical intervention. 1

Special Clinical Scenarios

Third Ventricle Cysts and Normal Pressure Hydrocephalus

• Large third ventricle arachnoid cysts can cause NPH through disruption of CSF dynamics and ventricular obstruction 5
• NPH typically presents with the classic triad: gait disturbance, urinary incontinence, and cognitive decline/dementia 5
• Without treatment, progressive ventricular dilation can lead to worsening neurodegeneration and cognitive decline 5
• Patients with moderate to severe neurodegenerative changes prior to treatment may have limited improvement despite successful CSF diversion 5

Pregnancy

• For pregnant patients with elevated intracranial pressure due to arachnoid cysts, aggressive management is needed even during pregnancy 1

Common Pitfalls and Caveats

• CT myelography can be performed for further evaluation when MRI shows findings suspicious for arachnoid cyst/arachnoid web or ventral cord herniation 9
• In cases of clinical concern for positional myelopathy, MRI with flexion/extension can be performed as follow-up 9
• Both fenestration and shunting are equally effective for treatment, with surgery resulting in favorable outcomes in two-thirds of patients 8
• Shunt independence should be a major goal of therapy, making fenestration preferable when feasible 7