Arachnoid cyst of the brain is a formation filled with cerebrospinal fluid located between the duplication of the arachnoid membrane. It may have an innate and secondary nature. It often proceeds latently, without clinical manifestations. With an increase in volume, the cyst debuts with symptoms of intracranial hypertension, convulsive paroxysms and focal neurological deficit. It is diagnosed mainly according to MRI of the brain. With an increase in clinical symptoms, surgical treatment is required — drainage of the cyst, its fenestration, excision or bypass surgery.
G93.0 Arachnoid cyst
Arachnoid cyst is a limited accumulation of cerebrospinal fluid (CSF) in the thickness of the membranes covering the brain. The cyst got its name in connection with localization in the arachnoid cerebral membrane. At the site of cyst formation, the arachnoid membrane is thickened and has a duplication, i.e. it is divided into two leaves, between which cerebrospinal fluid accumulates. As a rule, cysts have a small volume, but when a large amount of cerebrospinal fluid accumulates in them, they have a compression effect on the underlying cerebral cortex. This leads to the manifestation of clinical manifestations of intracranial (intracranial) volume formation.
Arachnoid cyst can have a different location. Most often, such cysts are located in the area of the cerebellar angle, the Sylvian furrow and above the Turkish saddle (suprasellar). According to available data, about 4% of the population have arachnoid cysts, but not all of them give any clinical manifestations. Male persons are more susceptible to the occurrence of cysts.
The etiological classification takes into account the origin of arachnoid cerebral cysts. By their origin, they can be primary, or congenital, and secondary, or acquired. Primary cysts refer to abnormalities in the development of the brain, secondary cysts arise as a result of traumatic injuries, inflammatory processes or bleeding occurring in the cerebral membranes.
Morphologically, simple and complex arachnoid cyst are distinguished. In the first case, the cyst cavity is expelled by arachnoid membrane cells that have the ability to produce cerebrospinal fluid. In the second case, the structure of the cyst includes other tissues, for example, glial elements. The morphological classification of arachnoid cysts has no actual significance in practical neurology, while the etiological classification is necessarily taken into account when making a detailed diagnosis.
Clinically, arachnoid cysts are divided into progressive and frozen. Progressive cysts are characterized by an increase in neurological symptoms due to an increase in the volume of the cyst. Frozen cysts do not increase in size and usually have a latent course. Determining the type of arachnoid cyst in accordance with this classification is of paramount importance for choosing an adequate treatment strategy.
Congenital arachnoid cysts are formed due to disorders in the process of intrauterine development of the brain. The factors that cause their formation include various harmful effects on the fetus that occur during pregnancy. These can be intrauterine infections (toxoplasmosis, rubella, herpes, cytomegaly, etc.), intoxication (occupational hazards, alcoholism, smoking, drug addiction, taking pharmaceuticals with a teratogenic effect), radiation exposure, overheating (visiting a sauna or bathhouse by a pregnant woman, excessive insolation, the habit of taking hot baths). Cysts localized in the arachnoid membrane are often noted in patients with Marfan syndrome and hypogenesis of the corpus callosum.
Acquired arachnoid cysts occur after traumatic brain injuries (concussion, brain injury), and may also be a consequence of brain surgery. The formation of a secondary cyst is possible after meningitis, arachnoiditis or meningoencephalitis. The formation of an arachnoid cyst may occur after resolution of a subarachnoid hemorrhage or subdural hematoma. Factors that can provoke the formation of an arachnoid cyst can also cause a progressive increase in the volume of a small subclinical cystic formation previously existing in the arachnoid membrane due to hyperproduction and accumulation of cerebrospinal fluid in it.
In most cases, an arachnoid cyst of the brain has an insignificant volume and does not manifest itself clinically in any way. A congenital cyst may be an accidental finding when performing neurosonography through a fontanel or brain MRI in connection with another intracranial pathology. Its clinical debut is possible with infectious, vascular or traumatic brain damage.
With an increase in the amount of cerebrospinal fluid inside the cyst and, accordingly, the size of the cyst itself, symptoms of increased intracranial pressure and focal neurological manifestations appear, the nature of which depends on the location of the cyst. The patient is worried about headaches (cephalgia), periodic dizziness, tinnitus, a feeling of a “heavy head”, sometimes a feeling of pulsation in the head, unsteadiness of walking.
With the increase in the volume of the cyst, the aggravation of these symptoms occurs. Cephalgia becomes permanent and intense, accompanied by nausea, pressure on the eyeballs, vomiting. Possible development of hearing loss (hearing loss), decreased visual acuity, double vision or the appearance of “spots” in the fields of vision, numbness of certain limbs, vestibular ataxia, dysarthria. Hemiparesis may occur — a decrease in muscle strength in the arm and leg of one half of the body. Episodes of convulsive seizures and syncopal states (fainting) are not uncommon. In some cases, there is a hallucinatory syndrome. Children develop mental retardation.
The aggravation of neurological symptoms indicates a further increase in the size of the arachnoid cyst and progressive compression of the brain. A significant increase in the volume of the cyst is dangerous with the possibility of its rupture, resulting in the death of the patient. The long-term existence of cerebral compression leads to irreversible degenerative processes in brain tissues with the formation of persistent neurological deficits.
The clinic of an arachnoid cyst has no specific manifestations and corresponds to the clinical picture common to most volumetric formations of the brain. The latter include intracerebral and sheathed hematomas, primary and metastatic brain tumors, brain abscess, intracerebral cyst. Neurologist’s examination and primary neurological examination (electroencephalography, rheoencephalography and echo-encephalography) allow to establish the presence of intracranial formation with intracranial hypertension and the existing convulsive activity of the brain. To clarify the nature of the volume formation and its localization, it is necessary to conduct an MRI, CT scan of the brain or CT.
The optimal diagnostic method for recognizing arachnoid cysts is MRI of the brain with contrast. The use of contrast agents makes it possible to differentiate a cyst from a brain tumor. The main criterion of an arachnoid cyst that distinguishes it from a tumor is the lack of the ability to accumulate contrast. With the help of MRI, differential diagnosis is performed with subdural hematoma, subarachnoid hemorrhage, subdural hygroma, abscess, stroke, encephalitis, and other cerebral diseases.
Frozen arachnoid cysts with a subclinical course do not need therapy. Patients are recommended to be monitored by a neurologist and undergo annual MRI for dynamic control of cyst size. Progressive arachnoid cysts, cysts accompanied by epilepsy and /or a significant increase in intracranial pressure, which cannot be stopped by conservative methods of therapy, are subject to surgical treatment. To resolve the issue of the expediency of surgical treatment of an arachnoid cyst and the choice of the optimal method of its implementation, a consultation of a neurosurgeon is conducted.
In the presence of hemorrhage in the area of the arachnoid cyst and with its rupture, complete excision of the cyst is shown. However, this method of treatment is highly traumatic and requires a long recovery period. Therefore, in the absence of complications, preference is given to endoscopic intervention with the so-called fenestration of the cyst. The operation is performed through a milling hole and consists in aspiration of the cyst contents, followed by the creation of holes connecting the cyst cavity with the ventricle of the brain and / or subarachnoid space. In some cases, bypass surgery is used – cystoperitoneal bypass surgery, as a result of which the cerebrospinal fluid from the cyst cavity flows into the abdominal cavity, where it is absorbed. The disadvantage of such operations is the probability of violation of the patency of the shunt.
Arachnoid cyst of the brain can have a very different course. In many cases, it is asymptomatic throughout the patient’s life. Progressive arachnoid cysts are dangerous. With delayed diagnosis, they can cause disabling neurological deficits and even death. Timely surgical treatment of a cyst, as a rule, leads to recovery. A complication may be a recurrence of the cyst.
Prevention of congenital arachnoid cysts, as well as the prevention of other malformations of intrauterine development, includes the correct management of pregnancy and the observance of a special protective regime by the pregnant woman, excluding harmful effects on the fetus. Prevention of acquired arachnoid cysts is the correct and timely treatment of injuries, inflammatory and vascular cerebral diseases.