Arachnoid cyst overview

# Overview
Arachnoid cysts are cerebrospinal fluid cysts covered by arachnoidal cells and collagen. They develop between the arachnoid membrane and the surface of the brain.  Arachnoid cysts are mostly a congenital disorder.

# Historical Perspective
Arachnoid cysts were first described by Richard Bright in 1831.

# Pathophysiology
The exact pathophysiology of arachnoid cysts is not known.

# Classification
Arachnoid cysts may be classified according to cause into 2 subtypes/groups: primary or secondary, or according to symptoms into 3 groups.

# Causes
The exact cause of arachnoid cysts is not known. Researchers believe that most cases of arachnoid cysts are developmental malformations that arise from the unexplained splitting or tearing of the arachnoid membrane, being classified as primary. There are also arachnoid cysts that arise from secondary causes, such as trauma, surgery, intracranial hemorrhage and infection.

# Differentiating Arachnoid Cyst from Other Diseases
The main differential diagnosis of Arachnoid cysts are epidermoid cysts. They can be differentiated using MRIs.

# Epidemiology and Demographics
Arachnoid cysts occur in about 1.2% of the general population and are more frequently seen in men than in women.

# Risk Factors
There is no doccumented risk factor for the development of arachnoid cysts.

# Screening
There is insufficient evidence to recommend routine screening for arachnoid cysts.

# Natural History, Complications and Prognosis
Prognosis of arachnoid cyst is generally excellent and is usually associated with a benign disease course, despite being symptomatic in a few patients. Most are found incidentally, and a few may, rarely, enlarge and complicate with the symptoms previously described such as hydrocephalus, seizures, hearing loss, visual changes and cervical myelopathy.

# History and Symptoms
Patients with arachnoid cysts will most likely never show symptoms, even in cases where the cyst is large. Therefore, while the presence of symptoms may provoke further clinical investigation. Symptoms independent of further data cannot, and should not be, interpreted as evidence of a cyst's existence, size or location. These symptoms usually are:
- Headache;
- Nausea/Vomiting;
- Seizures;
- Skull/spine deformation;
- Developmental delays;
- Obstructive hydrocephalus;
- Hearing loss;
- Head bobbing;
- Visual changes.

# Diagnostic Study of Choice
The diagnostic study of choice are MRIs as they can differentiate arachnoid cysts from all other causes of cystic CNS lesions while also presenting details about the origins, and anatomy of the cyst.

# Physical Examination
Physical examination is generally not very useful as most cases of arachnoid cysts are diagnosed incidentally, but in larger cysts, depending of the affected region, there may be some findings such as:
- Ataxia;
- Hearing loss;
- Visual changes;
- Protrusions from the head or spine;
- Head bobbing;
- Endocrine issues, e.g. early onset of puberty.

# Laboratory Findings
There are no laboratory findings associated with arachnoid cysts.

# ECG Findings
There are no ECG findings associated with arachnoid cysts.

# X-ray Findings
There are no x-ray findings associated with arachnoid cysts.

# Echocardiographic and Ultrasonographic Findings
There are no ultrasonographic findings associated with arachnoid cysts.

# CT
On brain/spine CT scan, arachnoid cysts are characterized by cystic images with similar density to CSF and non-enhancing borders, mostly found in the middle cranial fossa while they only rarely occur in the spinal cord.

# MRI
On brain/spine MRI, arachnoid cysts are characterized by cystic images with similar density to CSF and non-enhancing borders, mostly found in the middle cranial fossa while they only rarely occur in the spinal cord. MRIs are more adequate than CT scans for evaluating arachnoid cysts.

# Other Imaging findings
There are no other imaging findings associated with arachnoid cysts.

# Other Diagnostic Studies
There are no other imaging findings associated with arachnoid cysts.

# Medical Therapy
There is no medical treatment for arachnoid cysts. Some medications may be used for treating its symptoms, such as analgesics for headache, sleep aids for insomnia and other medications for the dizziness/nausea.

# Surgery
There are a number of approaches in treating arachnoid cysts, the most common are:
- Endoscopic fenestration and removal of the cyst wall (advances in neurosurgical techniques favor fenestration over shunt insertion as the preferred method for initial management).
- Microsurgical fenestration;
- Craniotomy followed by shunting.

# Primary Prevention
There are no primary preventive measures available for arachnoid cysts.

# Secondary Prevention
There are no secondary preventive measures available for arachnoid cysts.

# Cost-effectivenes of Therapy
Most patients won't demand treatment. The very few who do must be assessed regarding cyst size, location and symptoms. If symptomatic, it may be a significant cause of morbidity and the costs of neurosurgical procedures, which are mostly safe and effective, may be high.

# Future Investigational Therapies
Advances in neurosurgical techniques continue to improve the safeness and efficacy of the neurosurgical procedures in treating arachnoid cysts.