BASICS
DESCRIPTION
- Histologically benign, CSF-filled, space-occupying lesion of the central nervous system
- May be intracranial (most are supratentorial), spinal, or perineuronal
- Classification (1)
- Primary (congenital)
- Intra- or extradural, found around the brain or spine
- Often no communication with the subarachnoid space
- Contains clear CSF-like fluid
- Cyst walls are meningothelial cells often capable of secreting CSF.
- Secondary (acquired)
- CSF sequestration due to inflammatory or traumatic processes
- Surrounded by arachnoid scarring
- Contain CSF and possibly hemosiderin-stained or inflammatory cells
- Usually communicates with the subarachnoid space
- System(s) affected: central nervous; peripheral nervous
- Synonym(s): leptomeningeal cysts
EPIDEMIOLOGY
- Diagnosed most frequently in the first 2 decades of life (1)
- 2:1 male predominance
- Middle cranial fossa cysts are most common, with an increased incidence on the left side (2,3).
Prevalence
0.2-1.7%, although as imaging becomes more common, a prevalence up to 2.9% is suggested, with peaks at age 1 and 5 years (3)
ETIOLOGY AND PATHOPHYSIOLOGY
- Several theories of arachnoid cyst formation (4).
- Agenesis of part of the brain
- Defect in the arachnoid development, leading to membrane splitting or duplication creating diverticula
- Failure of temporal embryonic meninges to merge as the sylvian fissure forms
- Defect in condensation of the mesenchyme from abnormal CSF flow
- Arachnoid adhesions due to trauma, meningitis, mastoiditis, subarachnoid hemorrhage, or iatrogenic causes
- Cyst growth also has many suggested causes (4):
- One-way ball-valve allowing CSF to enter but not exit the cyst (cerebrospinal fluid obstruction and vent mechanism) (5)[A]
- Distribution of arachnoid trabeculae leading to trapping of fluid in the cyst
- Fluid production by cells lining the walls of the cyst
- Osmotic gradients due to higher protein content of cyst fluid (6)
- Symptoms are due to compression and mass effect on adjacent brain or spinal cord structures, interruption of CSF flow, or intracyst/ subdural hemorrhage.
- Primary arachnoid cysts are congenital.
- Secondary arachnoid cysts are associated with inflammation and trauma.
Genetics
No specific genetic association with arachnoid cysts, although bilateral cysts may occur in Hurler syndrome.
RISK FACTORS
- Primary arachnoid cysts are congenital.
- Risks for secondary arachnoid cysts
- Inflammation from infection, hemorrhage, or iatrogenic causes
- Trauma from lumbar puncture, anesthetic procedures, or intradural surgery
COMMONLY ASSOCIATED CONDITIONS
Rarely, associated with the following:
- Hydrocephalus
- Chronic subdural hematoma
- Dysgenesis of the corpus callosum
- Malformation of the cerebral venous system
- Glutaric aciduria type I
- Trisomy chromosome 12
- Neurofibromatosis
- Autosomal dominant polycystic kidney disease
DIAGNOSIS
HISTORY
- Most cases are asymptomatic, and the cyst is an incidental finding.
- Presenting symptoms depend on the size and location of the cyst and are often nonspecific (1,4):
- Intracranial arachnoid cysts (1,6,7)
- Hydrocephalus
- Seizures
- Headaches
- Hemiparesis
- Signs and symptoms of increased intracranial pressure (altered mental status, headache, nausea, emesis)
- Craniomegaly and cranial deformities
- Cranial nerve dysfunction
- Developmental delay
- Visual loss
- Hypothalamic-pituitary dysfunction (e.g., precocious puberty, growth retardation, diabetes insipidus)
- Psychomotor retardation
- Spinal arachnoid cysts (4,6)[B]
- Waxing and waning pain
- Bilateral lower extremity weakness
- Bowel and bladder dysfunction
- Ataxia
- Progressive spastic or flaccid paraparesis that may be exacerbated by Valsalva maneuvers.
- Symptoms of isolated radiculopathy
- Less commonly: noncardiac chest pain
PHYSICAL EXAM
Depends on location and size of cyst
- Vital signs: bradycardia and hypertension
- Rare findings of endocrine deficiencies or precocious puberty
- Funduscopic exam for papilledema due to possibility of increased intracranial pressure
- Neurologic
- Cranial nerve deficits, including vision loss and upgaze palsy
- Focal findings of paraparesis, hemiparesis, or radiculopathy
- Craniomegaly, cranial deformities, and developmental delay in children
DIFFERENTIAL DIAGNOSIS
- Tumors; metastasis
- Abscesses; parasitic infections
- Tarlov or colloid cysts; craniopharyngioma
- Holoprosencephaly; agenesis of the corpus callosum
- Dandy-Walker syndrome
DIAGNOSTIC TESTS & INTERPRETATION
Initial Tests (lab, imaging)
Imaging identifies cyst and evaluates mass effect, hydrocephalus, and communication between the cyst and subarachnoid space:
- MRI (4)[B]
- Most sensitive and specific imaging modality
- Allows evaluation of the walls, contents, and extent of the cyst (1)
- IV gadolinium helps differentiate between cystic tumors, synovial cysts, and arachnoid cysts.
- Diffusion-weighted MRI allows differentiation from an epidermoid cyst, abscess, and tumor, which lack CSF signal and evaluation of spinal cord atrophy, inflammatory changes, and nerve root compression (4).
- CT
- Used to assess communication between intraspinal subarachnoid space and spinal arachnoid space (4)
- Valuable in evaluation of patients for whom an MRI is contraindicated (4).
Follow-Up Tests & Special Considerations
- Cine MRI may localize dural defects to facilitate minimally invasive treatment (1),(4)[B].
- No more than yearly imaging to assess change in cyst size and development of new abnormalities for asymptomatic cysts
- Immediate reimaging is recommended if the patient develops new or worsening symptoms.
- CSF contrast or flow studies (i.e., cisternogram) may be used in the diagnosis of suprasellar and posterior fossa cysts.
Test Interpretation
- Primary cysts contain clear CSF-like fluid. Secondary cysts may contain inflammatory or hemosiderin-stained cells.
- Hematoxylin and eosin staining of an arachnoid cyst wall illustrates fibrous tissue lined by meningothelial cells (4).
- Meningothelial cells lining the cyst wall often positive for epithelial membrane antigen and negative for carcinoembryonic antigen
TREATMENT
Most patients are asymptomatic or have symptoms that are best managed by observation. Treatment is indicated when cysts cause mass effect or become symptomatic-often regardless of size or location.
SURGERY/OTHER PROCEDURES
Surgery should be considered primarily based on presenting symptoms, although location and size of the cyst should also be considered:
- Spinal arachnoid cysts:
- Consider surgery if significant focal paraparesis or radiculopathy.
- Extradural cysts tend to be resected, intradural cysts are commonly fenestrated (6)[B].
- Complete surgical resection is often preferred to reduce recurrence.
- Intracranial arachnoid cysts (8)[B]
- Surgery is appropriate for the following:
- Large and expanding middle cranial fossa cysts
- Cysts causing increased intracranial pressure
- Cysts leading to seizures
- Cysts causing significant mass effect
- Cysts leading to obstruction of CSF flow and hydrocephalus
- Surgical intervention is not indicated for the following:
- Asymptomatic cysts
- Chronic headaches
- Disordered pituitary function associated with midline supratentorial cysts
- The goal of surgery is to create a connection into a space where the cystic fluid can be absorbed (1,7).
- Treatment options include the following:
- Needle drainage
- Burr hole evacuation
- Craniotomy with wall fenestration draining cyst into basal cisterns
- Endoscopic cyst fenestration
- Cystoventriculostomy
- Cystoperitoneal shunting
- The recommended method is under debate; aspiration and endoscopic fenestration are often preferred due to the simplicity and speed of the procedures, although recurrence rates are high.
INPATIENT CONSIDERATIONS
Most patients do not require preoperative hospitalization, although this depends on the presenting symptoms.
Admission Criteria/Initial Stabilization
- If presenting with increased intracranial pressure
- Establish adequate ventilation.
- Maintain peripheral vascular circulation.
- Neuroimaging to assess the cause
- Establish hyperventilation.
- Mannitol if the patient is euvolemic
- Placement of an intracranial pressure monitor or external ventricular drain
- Surgical decompression
- If presenting with seizures
- Stabilize vital signs.
- Ensure adequate oxygenation.
- If seizure activity persists
- Benzodiazepine as initial treatment
- Further seizure prophylaxis with levetiracetam or phenytoin
- Arterial blood gas monitoring
- ECG monitoring
- Electroencephalogram (EEG) and imaging to assess cause of seizures
- If presenting with neurologic abnormalities: imaging to assess the cause
- The patient should be admitted if found to have the following:
- New-onset or worsening seizures
- New or worsening neurologic findings
- Evidence of increased intracranial pressure
IV Fluids
For increased intracranial pressure, isotonic and depending on the etiology, hypertonic fluids may be used to maintain peripheral vascular perfusion and limit cerebral edema.
Nursing
- Ensure patient comfort and adherence to medications.
- Monitor patient for seizure activity, vital signs abnormalities, and signs of increased intracranial pressure.
- Postsurgical: Change and monitor incision and drain sites.
Discharge Criteria
- A patient does not need to remain hospitalized due to an asymptomatic arachnoid cyst.
- Symptomatic patients may be discharged when symptoms due to the arachnoid cyst have abated or resolved.
- Postoperatively, the patient's pain should be controlled; ensure surgical incision healing and symptoms (particularly seizures and increased intracranial pressure) controlled with oral medications.
ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
Patient Monitoring
- Repeat CTs or MRIs are recommended, no more than yearly, for patients being managed by clinical observation.
- For incidentally discovered arachnoid cysts in adults for whom surgery is not indicated, a single follow-up imaging study in 6 months is usually adequate.
- Patients should present for further evaluation if any new or worsening symptoms develop.
- Follow-up with a neurosurgeon accordingly.
PATIENT EDUCATION
Subdural hemorrhage is a rare complication of intracranial arachnoid cysts that may occur spontaneously or after minor head trauma. Patients do not need to avoid contact sports but should have a low threshold for hospital referral if not recovering from what seems to be minor head trauma (8).
PROGNOSIS
- Most arachnoid cysts do not cause symptoms and do not change in size.
- There are excellent neurologic outcomes following surgical interventions for spinal arachnoid cysts (4).
- After surgery, 45-70% of patient with spinal arachnoid cysts have improvement (6)[B].
- Resolution of symptoms has been reported between 20% and 30% and as high as 68% (6)[B].
- Complications are reported in 15-28% of cases after surgery.
- The best outcomes are seen when the defect correlates with clinical presentation (4).
COMPLICATIONS
- Precocious puberty is reported in 10-40% of patients with suprasellar arachnoid cysts (7).
- Hydrocephalus is present in 30-60% of patients with cranial arachnoid cysts (1).
- Remodeling of adjacent skull (1)
- Acute and chronic subdural hemorrhages are rare complications and may occur spontaneously or after minor head trauma.
REFERENCES
11 Cincu R, Agrawal A, Eiras J. Intracranial arachnoid cysts: current concepts and treatment alternatives. Clin Neurol Neurosurg. 2007;109(10):837-843.22 Helland CA, Lund-Johansen M, Wester K. Location, sidedness, and sex distribution of intracranial arachnoid cysts in a population-based sample. J Neurosurg. 2010;113(5):934-939.33 Al-Holou WN, Yew AY, Boomsaad ZE, et al. Prevalence and natural history of arachnoid cysts in children. J Neurosurg Pediatr. 2010;5(6):578-585.44 Hughes G, Ugokwe K, Benzel EC. A review of spinal arachnoid cysts. Cleve Clin J Med. 2008;75(4):311-315.55 Evangelou P, Meixensberger J, Bernhard M, et al. Operative management of idiopathic spinal intradural arachnoid cysts in children: a systematic review. Childs Nerv Syst. 2013;29(4):657-664.66 Bond AE, Zada G, Bowen I, et al. Spinal arachnoid cysts in the pediatric population: report of 31 cases and a review of the literature. J Neurosurg Pediatr. 2012;9(4):432-441.77 G ¼zel A, Trippel M, Ostertage CB. Suprasellar arachnoid cyst: a 20-year follow-up after stereotactic internal drainage: case report and review of the literature. Turk Neurosurg. 2007;17(3):211-218.88 Hayward R. Postnatal management and outcome for fetal-diagnosed intra-cerebral cystic masses and tumours. Prenat Diagn. 2009;29(4):396-401.
CODES
ICD10
- G93.0 Cerebral cysts
- Q04.6 Congenital cerebral cysts
ICD9
- 348.0 Cerebral cysts
- 742.4 Other specified congenital anomalies of brain
SNOMED
- arachnoid cyst (disorder)
- congenital cerebral cyst (disorder)
- Cerebral arachnoid cyst
- spinal arachnoid cyst (disorder)
- Traumatic arachnoid cyst
CLINICAL PEARLS
- Most arachnoid cysts are asymptomatic and do not require treatment.
- The degree of symptoms produced by an arachnoid cyst, not the cyst's location or size, is the most important factor in surgical decision making.
- Spinal arachnoid cysts can be percutaneously aspirated/fenestrated or treated with open surgical resection.