Arachnoid Cysts: Symptoms, Types, Causes and Treatment

Arachnoid cysts are fluid-filled sacs that develop between the brain or spinal cord and the arachnoid membrane, one of the three protective layers covering the central nervous system. While often discovered incidentally during imaging for unrelated issues, these cysts can sometimes cause significant symptoms and require medical intervention. Understanding their symptoms, types, causes, and available treatments is essential for patients, families, and healthcare providers. This article presents an in-depth review based on current clinical evidence.

Symptoms of Arachnoid Cysts

Arachnoid cysts are known for their clinical variability. Many are found by chance and never cause problems, but others can lead to diverse neurological symptoms depending on their size and location. Recognizing the symptoms is crucial for timely diagnosis and treatment.

Symptom	Prevalence/Notes	Typical Locations	Source(s)
Headache	Common presenting complaint	Cranial, Spinal	2 5 15 16
Weakness	Limb or general weakness	Cranial, Spinal	2 3 4 9
Seizures	Sometimes associated	Intracranial	2 16
Cognitive issues	Possible, controversial	Supratentorial	5 10
Dizziness	Sometimes reported	Cranial	1 16
Visual Loss	Rare, site-specific	Cranial	2
Gait Ataxia	Especially with spinal cysts	Spinal (Thoracic)	4 9
Sphincter dysfunction	Bowel/bladder issues	Spinal	3 4 9
Scoliosis	Occasionally with spinal cysts	Spinal	3

Table 1: Key Symptoms of Arachnoid Cysts

Symptom Variability and Incidental Findings

Most arachnoid cysts do not cause symptoms and are discovered incidentally during imaging for unrelated reasons. Large population studies reveal that the prevalence of arachnoid cysts is about 2–3%, with no significant difference between men and women. In these cases, common neurological symptoms such as headaches, dizziness, or cognitive impairment are not more frequent than in the general population, suggesting many cysts are asymptomatic and benign 1.

Symptomatic Presentations

When symptoms do arise, they depend heavily on the cyst’s size and location:

• Headache is the most frequently reported symptom, especially with cranial cysts that exert pressure on adjacent structures 2 15.
• Weakness and gait disturbance often occur with spinal cysts that compress the spinal cord or nerve roots 3 4 9.
• Seizures can be associated with intracranial cysts, particularly those near the temporal lobe 2 10 16.
• Cognitive dysfunction is controversial. Some studies suggest that select patients with supratentorial cysts experience cognitive and attention deficits, which may improve after surgical intervention 5 10.
• Visual disturbances and hydrocephalus may occur if cysts compress visual pathways or obstruct cerebrospinal fluid flow 2.
• For spinal arachnoid cysts, symptoms such as back pain, limb weakness, gait ataxia, and sphincter dysfunction are typical due to compression of neural tissues 3 4 9.

Subtle and Progressive Symptoms

• In children, subtle symptoms like learning difficulties or behavioral changes may be early indicators 10.
• Progressive neurological deficits, including worsening weakness, increased spasticity, or scoliosis, are red flags for spinal arachnoid cysts 3 4.

Types of Arachnoid Cysts

Arachnoid cysts can be classified based on their anatomical location, imaging characteristics, and underlying etiology. Understanding these distinctions is key for diagnosis and management.

Type/Location	Frequency/Notes	Distinguishing Features	Source(s)
Supratentorial	Most common, especially sylvian	Often in children; can be large	2 8 10 17
Infratentorial	Posterior fossa, rare	May cause cerebellar symptoms	2 6 8
Suprasellar	Near pituitary/optic chiasm	Visual/hormonal symptoms	2 7 8 14
Spinal	Extradural/intradural, thoracic common	Back pain, myelopathy	3 4 9 11
Primary	Congenital/developmental	Sporadic or familial	11 12 13
Secondary	Acquired (trauma, infection, surgery)	Often multiple, with adhesions	11 12

Table 2: Main Types of Arachnoid Cysts

Intracranial Arachnoid Cysts

• Supratentorial Cysts: These are most frequently located in the middle cranial fossa (sylvian fissure) and are common in children. They may be associated with maldevelopment of the temporal lobe and occasionally cause neurocognitive symptoms or seizures 2 8 10 17.
• Infratentorial Cysts: Found in the posterior fossa, these can compress the cerebellum or brainstem, causing ataxia or cranial nerve symptoms 2 6.
• Suprasellar Cysts: These lie near the pituitary gland and optic chiasm. They may present with visual disturbances, hormonal imbalances, or hydrocephalus due to obstruction of CSF pathways 2 7 8 14.
• Other Locations: Cysts can also occur in the quadrigeminal cistern, interhemispheric fissure, or along the convexity of the brain, each with their own unique clinical challenges 8.

Spinal Arachnoid Cysts

• Extradural Cysts: Located outside the dura mater, these are the most common spinal arachnoid cysts. They often occur in the thoracic spine and can cause back pain, weakness, and gait issues 4 9.
• Intradural Cysts: Situated within the dura but outside the spinal cord, these are less common but may cause more significant neurological deficits 3 4 9 11.
• Perineural Cysts: Also known as Tarlov cysts, these form around nerve roots and are usually asymptomatic 9.

Primary vs. Secondary Cysts

• Primary (Congenital) Cysts: Result from developmental anomalies in the arachnoid membrane. These are the most common and may be sporadic or familial 11 12 13.
• Secondary (Acquired) Cysts: Develop after trauma, infection (such as meningitis), bleeding, or previous surgery. These are less common and often present with multiple lesions and more extensive adhesions 11 12.

Classification by Communication

Some cysts are classified by their communication with the CSF pathways:

• Communicating Cysts: Cyst cavity is in open communication with CSF spaces.
• Non-communicating Cysts: Isolated from normal CSF pathways, often leading to progressive enlargement 7.

Causes of Arachnoid Cysts

The exact causes of arachnoid cyst formation remain under investigation, with several theories proposed. Both genetic and acquired factors play a role.

Cause/Mechanism	Description	Evidence/Notes	Source(s)
Developmental Anomaly	Splitting/duplication of arachnoid membrane	Most common, congenital	12 13 17
Genetic Factors	Familial cases, syndromic associations	Chudley-McCullough, others	13
Ball-valve Mechanism	CSF enters cyst via one-way valve	May explain expansion	12
Osmotic Gradient	Differences in fluid/osmotic pressure	Possible enlargement factor	12
Trauma/Infection	Injury or inflammation causes cyst formation	Secondary cysts	3 4 11 12
Fluid Hypersecretion	Overproduction by cyst lining cells	Rare, debated	12

Table 3: Causes and Pathogenesis of Arachnoid Cysts

Developmental and Congenital Origins

Most arachnoid cysts are believed to arise from developmental defects during embryogenesis, leading to duplication or splitting of the arachnoid membrane. This results in a pocket that gradually fills with cerebrospinal fluid (CSF) 12 17.

Genetic Factors

While most cases are sporadic, a subset of arachnoid cysts occurs in families or as part of genetic syndromes (e.g., Chudley-McCullough syndrome, acrocallosal syndrome). These associations underscore a genetic predisposition in some patients 13.

Theories of Cyst Expansion

Several mechanisms have been proposed to explain cyst enlargement over time:

• Ball-Valve Mechanism: CSF enters the cyst through a one-way valve, preventing exit and causing the cyst to enlarge 12.
• Osmotic Gradient: Differences in osmotic pressure between the cyst fluid and surrounding CSF may draw fluid into the cyst 12.
• Hypersecretion: Lining cells of the cyst may secrete excess fluid, though this is less well supported 12.

Secondary (Acquired) Cysts

Arachnoid cysts may also develop after:

• Trauma: Head injuries or spinal trauma can disrupt the arachnoid, leading to cyst formation 3 4 11 12.
• Infection: Meningitis and other inflammatory conditions may cause adhesions and cyst development (secondary cysts) 11 12.
• Hemorrhage or Surgery: Subarachnoid hemorrhage and prior neurosurgical procedures can also contribute 11.

Treatment of Arachnoid Cysts

Treatment decisions for arachnoid cysts depend on the presence and severity of symptoms, cyst size, and location. Many cysts require only observation, but others necessitate surgical intervention.

Treatment	Indication	Efficacy/Notes	Source(s)
Observation	Asymptomatic/minimal symptoms	Most cysts require no intervention	1 2 10 17
Endoscopic Fenestration	Symptomatic cysts	Minimally invasive, preferred initial option	[2,14-16]
Microsurgical Fenestration	Large/inaccessible cysts	Traditional approach, more invasive	2 14 16
Cystoperitoneal Shunt	Recurrent/persistent cysts	Effective, risk of shunt dependency	2 14 15
Marsupialization/Excision	Spinal cysts, recurrence	Complete removal may be required	4 9 11
Conservative Surgery	Selected cases	Partial resection often sufficient	17

Table 4: Treatment Options for Arachnoid Cysts

Observation and Monitoring

• Asymptomatic cysts are typically managed with periodic clinical and imaging follow-up. This conservative approach is supported by evidence showing no difference in symptoms or outcomes in most patients with incidentally discovered cysts 1 2 10 17.

Surgical Interventions

When cysts cause significant symptoms or show progressive enlargement:

• Endoscopic Fenestration: A minimally invasive technique where small openings are created in the cyst wall to allow CSF to flow into normal pathways 2 14 15 16. This is increasingly favored due to lower risk and quick recovery, especially for suprasellar and quadrigeminal cysts 14 15 16.
• Microsurgical Fenestration: Open surgery is sometimes required for large or complex cysts, or when endoscopic access is not feasible 2 14 16.
• Cystoperitoneal Shunting: A shunt diverts cyst fluid to the abdomen. While effective for rapid cyst reduction, it carries a risk of shunt dependency and complications, making it a second-line option 2 14 15.
• Marsupialization and Excision: Particularly for spinal arachnoid cysts, complete or partial removal through laminoplasty or laminectomy is performed to decompress neural structures 4 9 11.

Outcomes and Prognosis

• Most patients experience symptom improvement or resolution after successful surgery, especially when intervention is timely [2,4,5,14-16].
• There may be a risk of recurrence, particularly with endoscopic procedures; thus, long-term follow-up is recommended 15.
• In secondary (acquired) cysts, surgery may only offer temporary stabilization due to underlying scarring or inflammation 11.

Conclusion

Arachnoid cysts are a diverse group of CSF-filled lesions that are often benign but can occasionally cause significant neurological symptoms. Their diagnosis, classification, and management require a nuanced understanding of their natural history and clinical behavior. Advances in neuroimaging and minimally invasive surgery have improved outcomes for symptomatic patients.

Key Points:

• Most arachnoid cysts are asymptomatic and discovered incidentally 1 2.
• Symptoms, when present, depend on cyst size and location and can range from headaches to neurological deficits 2 3 4 5 15.
• Types include supratentorial, infratentorial, suprasellar, and spinal cysts, with further distinction between primary (congenital) and secondary (acquired) forms 2 3 4 6 7 8 9 10 11 12 13 14 15 16 17.
• Causes are mainly developmental but can involve genetic, traumatic, or infectious factors 12 13.
• Asymptomatic cysts require observation; symptomatic ones may be treated with minimally invasive surgery or shunting, depending on individual factors 2 14 15 16.

With individualized care and modern surgical techniques, patients with arachnoid cysts can expect excellent outcomes in most cases.