What is the treatment approach for an arachnoid cyst in the left cerebral hemisphere?

Treatment of Arachnoid Cyst in the Left Cerebral Hemisphere

For asymptomatic arachnoid cysts in the left cerebral hemisphere, conservative management with observation and serial MRI follow-up every 6 months until stability is confirmed is recommended, while symptomatic cysts causing mass effect, seizures, or neurological deficits require surgical intervention with endoscopic fenestration as the preferred first-line approach. 1, 2

Initial Diagnostic Evaluation

MRI with 3D volumetric sequencing is the gold standard for comprehensive evaluation of cerebral hemisphere arachnoid cysts, assessing location, size, relationship to surrounding structures, and presence of hydrocephalus. 1, 2

Key imaging characteristics to identify:

• Cysts appear isointense to CSF on all MRI sequences with no enhancement after gadolinium administration 2
• Diffusion-weighted imaging (DWI) is essential to differentiate arachnoid cysts from epidermoid cysts or other pathology 3, 4
• Standard T1, T2-weighted, and FLAIR sequences should be included 2
• Noncontrast CT scan provides complementary information about mass effect and midline shift 1

A critical pitfall is missing complications on CT alone - subacute hemorrhage within cysts may be isodense to brain on CT but clearly visible on MRI, potentially leading to delayed diagnosis of surgical emergencies. 5

Management Algorithm

For Asymptomatic or Minimally Symptomatic Cysts

Conservative observation is the standard of care for incidentally discovered arachnoid cysts without significant symptoms. 1, 2

• Follow-up MRI at 6-month intervals until stability is confirmed 1, 2
• Once stability is documented over 1-2 years, long-term imaging surveillance is not necessary unless new concerning symptoms develop 2
• Nonspecific headaches alone are not well-accepted indications for surgery unless associated with hydrocephalus or clear mass effect 2

The majority of arachnoid cysts remain asymptomatic throughout life, with over 80% remaining stable in size over time. 2

For Symptomatic Cysts Requiring Intervention

Surgical intervention is indicated when cysts cause:

• Seizures refractory to medical management 2
• Focal neurological deficits from mass effect 4, 6
• Hydrocephalus from CSF flow obstruction 4, 6
• Acute deterioration with herniation or hemorrhage 6

Surgical Treatment Options

Endoscopic fenestration is the preferred first-line surgical approach for most symptomatic cerebral hemisphere arachnoid cysts, offering less invasive treatment with good outcomes. 2, 4

Alternative surgical options include:

• Microsurgical fenestration with craniotomy for larger or complex cysts 4, 7, 8
• Cystoperitoneal shunting when fenestration is not feasible or has failed 2, 4

Important surgical considerations:

• Perioperative corticosteroids should be administered to decrease brain edema 2
• Communication between the cyst and subarachnoid space should be established during surgery 8
• Endoscopy carries higher recurrence risk compared to microsurgical approaches but has lower morbidity 4

Emergency Management

For acute presentation with uncal herniation or significant midline shift (>10mm), emergency craniotomy with cyst excision is life-saving. 6

Signs requiring emergency intervention:

• Sudden loss of consciousness 6
• Anisocoria indicating herniation 6
• Acute hemiparesis 6
• Rapid neurological decline 6

Rapid diagnosis with cranial CT is preferred in emergency settings, though MRI provides superior characterization once the patient is stabilized. 6, 5

Follow-Up After Treatment

MRI should be repeated at least every 6 months until resolution or confirmed stability of the cystic lesion post-intervention. 1, 2

Critical Pitfalls to Avoid

• Never perform unnecessary surgery on asymptomatic or minimally symptomatic benign cysts - this carries surgical risks without clear benefit 1
• Do not rely solely on CT imaging - subacute hemorrhage or subtle mass effect may be missed 5
• Avoid attributing all nonspecific symptoms to the cyst - obtain sequential imaging to demonstrate stability before considering intervention 2
• Do not assume all cysts are stable - initial 6-month follow-up imaging is essential even for asymptomatic cysts 1