What are arachnoid cysts?
An arachnoid cyst is a fluid-filled sac that develops between the brain or spinal cord and the arachnoid membrane, one of the three protective layers surrounding the central nervous system. These cysts are typically filled with cerebrospinal fluid (CSF).
Types of arachnoid cysts:
- Primary (congenital): present at birth due to developmental abnormalities.
- Secondary (acquired): develop later as a result of trauma, infection, surgery or bleeding.
Prognosis of arachnoid cysts
Most arachnoid cysts are benign and remain stable throughout life without causing symptoms. They are often discovered incidentally on brain imaging. When symptomatic, outcomes are generally very good with appropriate treatment.
Rarely, complications may occur if the cyst enlarges, causes mass effect, or leads to hydrocephalus.
Symptoms of arachnoid cysts
Many individuals remain asymptomatic. When symptoms occur, they depend on the cyst’s size and location and may include:
- Persistent or worsening headaches.
- Nausea and vomiting (especially with raised intracranial pressure).
- Seizures.
- Dizziness or balance difficulties.
- Visual disturbances.
- Cognitive or developmental delay in children.
- Focal neurological deficits (weakness or sensory changes).
Diagnosis of arachnoid cysts
Arachnoid cysts are diagnosed using neuroimaging:
- Magnetic resonance imaging (MRI): the gold standard, providing detailed assessment.
- Computed tomography (CT) scan: useful in initial detection.
Imaging helps determine the cyst’s size, location, and whether there is pressure on adjacent brain or spinal structures. In most cases, no further tests are required.
What causes arachnoid cysts?
Arachnoid cysts may occur as a result of:
- Congenital malformation during development (most common).
- Head trauma.
- Central nervous system infections (meningitis).
- Previous neurosurgery.
- Subarachnoid haemorrhage.
Can arachnoid cysts be prevented?
Primary arachnoid cysts cannot be prevented. The risk of secondary cysts may be reduced by preventing head injuries and ensuring prompt treatment of neurological infections.
Treatments for arachnoid cysts
Conservative management involves regular clinical and radiological monitoring of the cyst without active intervention when it is asymptomatic and stable, typically using periodic MRI scans.
Surgical treatment
Surgical treatment is indicated for symptomatic cysts or those causing mass effect.
- Endoscopic fenestration: first-line in many cases.
- Microsurgical (open) fenestration or excision: for complex or inaccessible cysts.
- Cystoperitoneal shunt: used when fenestration is not suitable or has failed.
Medications for arachnoid cysts
There is no medication to treat the cyst itself. However, medication may be prescribed to control symptoms, including:
- Anti-epileptic drugs for seizure management.
- Analgesics for headache relief.
All medications must be prescribed and monitored by a doctor.
Which specialist treats arachnoid cysts?
Arachnoid cysts are managed by neurologists for assessment and ongoing symptom control, and by neurosurgeons when surgical evaluation or intervention is required.
Referral to a neurosurgeon is recommended if the cyst is symptomatic, increasing in size, or causing neurological deficits.
