Arachnoid Cyst: Causes, Symptoms and Treatment
An arachnoid cyst is a benign, fluid-filled sac that forms between the layers of the brain membranes. Most are congenital and cause no symptoms.
Things worth knowing about "Arachnoid Cyst"
An arachnoid cyst is a benign, fluid-filled sac that forms between the layers of the brain membranes. Most are congenital and cause no symptoms.
What Is an Arachnoid Cyst?
An arachnoid cyst is a benign, fluid-filled sac that develops within the arachnoid membrane, the middle layer of the three protective membranes (meninges) surrounding the brain and spinal cord. The cyst is filled with cerebrospinal fluid (CSF), the same fluid that surrounds and cushions the brain. The name derives from the Greek word for spider web, reflecting the delicate, web-like structure of the arachnoid membrane. In most cases, arachnoid cysts are harmless and do not cause symptoms.
Causes
Arachnoid cysts are most commonly congenital, meaning they form during fetal development when the arachnoid membrane splits or duplicates abnormally. Less frequently, they may develop as a result of secondary causes, including:
- Head trauma or skull injuries
- Inflammation of the meninges (meningitis)
- Brain surgery or neurosurgical procedures
- Brain tumors or other space-occupying lesions
Primary (congenital) arachnoid cysts are far more common than secondary (acquired) forms and are often found in the middle cranial fossa, near the temporal lobe, cerebellum, or brain poles.
Symptoms
The majority of arachnoid cysts are discovered incidentally during brain imaging and produce no symptoms. However, if a cyst enlarges and compresses adjacent brain structures, the following symptoms may occur:
- Persistent headaches
- Nausea and vomiting
- Visual disturbances or double vision
- Balance problems and dizziness
- Seizures (epilepsy)
- Cognitive difficulties or problems with concentration
- In infants: abnormal enlargement of the head (macrocephaly)
The severity of symptoms depends on the size and location of the cyst within the skull.
Diagnosis
Arachnoid cysts are typically identified through neuroimaging:
- Magnetic Resonance Imaging (MRI): The gold standard for diagnosis; provides detailed information about the size, location, and relationship of the cyst to surrounding structures.
- Computed Tomography (CT): Often the first imaging study performed in acute situations; shows the cyst as a hypodense (dark) lesion.
- Ultrasound: Can be used in newborns and infants through the open fontanelle to visualize intracranial cysts.
A neurological examination and, where seizures are suspected, an EEG (electroencephalogram) may complement the diagnostic workup.
Treatment
Since most arachnoid cysts remain asymptomatic, no treatment is required in many cases. A watch-and-wait approach with periodic imaging follow-up is recommended to monitor for any growth or change in the cyst.
Treatment is indicated when the cyst causes symptoms, shows significant growth, or leads to elevated intracranial pressure. Surgical options include:
- Craniotomy with cyst fenestration: A neurosurgical procedure in which the cyst wall is opened and partially removed to relieve pressure.
- Endoscopic fenestration: A minimally invasive technique using an endoscope to create a communication between the cyst and adjacent CSF spaces.
- Shunt placement: A catheter is inserted to drain the cyst fluid into another body cavity (e.g., the abdominal cavity). This option carries a higher risk of long-term complications.
The choice of procedure depends on the location and size of the cyst, the nature and severity of symptoms, and the age and general health of the patient.
Prognosis
The overall prognosis for arachnoid cysts is excellent. Most cysts remain stable and never require treatment. Following surgery, outcomes are generally favorable, although complete resolution of all symptoms cannot always be guaranteed. Rare complications include cyst-related hemorrhage or recurrence after surgical treatment.
References
- Westermaier T., Schweitzer T., Ernestus R. I. (2012): Arachnoid cysts. Advances and Technical Standards in Neurosurgery, 37, 1-58. DOI: 10.1007/978-3-7091-0673-0_1
- Strahle J. et al. (2011): Arachnoid cysts: Natural history and management. Journal of Neurosurgery: Pediatrics, 8(6), 578-586. DOI: 10.3171/2011.9.PEDS11272
- National Institute of Neurological Disorders and Stroke (NINDS): Arachnoid Cysts Information Page. www.ninds.nih.gov
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