What Are Arachnoid Cysts?

Arachnoid cysts can be classified into congenital and secondary (traumatic and post-infection) categories according to their etiology. Congenital arachnoid cyst is a bag-like structure formed by cerebrospinal fluid enclosed in the arachnoid, and it is not connected with the subarachnoid space. Secondary cases due to arachnoid adhesions form cysts in the subarachnoid space containing cerebrospinal fluid.

Sun Liyong	(Resident)	Department of Neurosurgery, Xuanwu Hospital, Capital Medical University
Wu Hao	(Deputy Chief Physician)	Department of Neurosurgery, Xuanwu Hospital, Capital Medical University

Arachnoid cysts are congenital benign brain cysts and are caused by abnormal arachnoid division during development. The wall of the capsule is mostly arachnoid, glial and pia mater, and there is cerebrospinal fluid-like cystic fluid in the capsule. The cyst is located on the surface of the brain, the cleft of the brain, and the cistern, and does not involve the parenchyma of the brain. Most are single shots and a few are multiple shots. The disease is mostly asymptomatic, and those with large volume can simultaneously compress the brain tissue and skull, which can produce neurological symptoms and changes in skull development. This disease is more common in children and adolescents, more men, more common on the left than on the right.

Western Medicine Name: Arachnoid cyst
Affiliated Department: Surgery-Neurosurgery

Disease site: Brain
Multiple groups: Children and adolescents
Contagious: Non-contagious

Arachnoid cyst disease classification

It can be divided into intracranial type and spinal type according to different parts. The intracranial type is mostly located in the relevant cistern of the brain surface. The spinal cord type can be located in the epidural, intradural or nerve sheath, and cause related nerve root symptoms and signs. ^[1]

Etiology and Pathology of Arachnoid Cyst

Intracranial arachnoid cysts can be classified into three types: congenital, traumatic and arachnoid cysts after infection.

Arachnoid cyst

Congenital arachnoid cysts are a common type, and the pathogenesis is not fully understood. There are the following speculations: The cause of this disease may be that during the development of the embryo, a small piece of arachnoid falls into the subarachnoid space and develops. That is, the cyst is located in the arachnoid. Microscopically, the arachnoid is divided into two layers around the cyst. The outer layer forms the surface part of the cyst and the inner layer forms the bottom of the cyst. There is still a subarachnoid space between the pia mater and the bottom of the cyst. Some people believe that during the development of the embryo, due to the choroid plexus pulse, it acts as a pump on the cerebrospinal fluid, which can separate the loose perimedullary network around the nerve tissue to form a subarachnoid space. If the early cerebrospinal fluid flows abnormally, it can Cysts formed within the mesh. Because the disease is often accompanied by other congenital abnormalities, such as ectopic choroid plexus in the cyst, local loss of the cerebral sickle, and loss of the orbital plate, temporal lobe, and internal carotid artery, etc., it is confirmed that the basic cause of the disease is brain dysplasia. To. The reason for the continuous increase of arachnoid cysts is currently no unified opinion. It may be: There are small holes in the wall of the cyst that communicate with the subarachnoid space. From this hole, the cerebrospinal fluid continuously flows into the sac. The small holes function as a valve. Pulsing makes the cyst gradually increase. There may also be some factors that cause the foramen to be blocked and cause increased intracranial pressure. There is an ectopic choroid plexus in the sac that secretes too much cerebrospinal fluid and cannot be absorbed. In some cases, the cyst is not connected with the subarachnoid space, the protein in the cyst fluid is increased, and the difference between the osmotic pressure inside and outside the cyst causes the cyst to gradually increase. Venous bleeding in the sac or the sac wall makes the sac cavity rapidly enlarge.

Arachnoid cyst after arachnoid cyst infection

After meningitis, cysts are formed due to local adhesions of the arachnoid, and the cysts are filled with cerebrospinal fluid. Mostly multiple. More common in children. Common in the optic cross pool, basal pool, cerebellum bulbar pool, ring pool and so on. Cerebrospinal fluid circulation is blocked.

Arachnoid cyst after arachnoid cyst injury

Pia mater cyst. The mechanism is a linear fracture of the skull caused by injury, with a dural tear defect. There is hemorrhage in the subarachnoid space below or adhesion around the arachnoid border, causing local cerebrospinal fluid circulation disturbance, causing local arachnoid process to the dura mater and fracture. In the line, cysts are gradually formed under the continuous impact of the brain pulse, which continuously expands the edge of the fracture, which is called growth fracture. Cysts can protrude below the scalp and can also compress the underlying cerebral cortex. The capsule is filled with clear liquid and there is scar tissue around it. If the pia mater is damaged during trauma, the brain tissue can also hernia into the fracture, and the ipsilateral ventricle is enlarged, and even a perforation of the brain is formed. This disease is more common in infants and young children. ^[2]

Clinical manifestations of arachnoid cyst

Arachnoid cyst symptoms

The onset of this disease is hidden and mostly asymptomatic. Some large arachnoid cysts can have clinical manifestations similar to those of intracranial masses.

Skull abnormalities or giant skull deformities, especially in children;

Pediatric saddle pool cysts can be manifested as head-up and head-down movements, i.e. doll-like symptoms;

The left middle cranial fossa cyst can be combined with inattention (ADHD);

headache, but not all patients with arachnoid cysts;

epilepsy;

Hydrocephalus (excessive accumulation of cerebrospinal fluid);

increased intracranial pressure;

stunting;

behavioral changes;

nausea;

Hemiplegia (weakness or paralysis of one limb);

Ataxia (muscle movement disorder);

Hearing;

Alzheimer's disease, mostly with Alzheimer's disease.

(>65 ) Arachnoid cysts in elderly patients (> 65 years)

Elderly patients (> 65 years) have symptoms similar to chronic subdural hematoma or normal pressure hydrocephalus:

dementia;

Urinary incontinence;

Hemiplegia;

headache;

Epilepsy.

Arachnoid cyst site related symptoms

Superficial cysts may resemble Meniere's disease;

Depression in frontal cysts;

The left temporal lobe cyst may have mental symptoms. Left frontotemporal cysts are more manifested as alexithymia;

Cysts in the right fissure area can cause new schizophrenia to appear around the age of 61;

The left middle cranial fossa cyst may have auditory hallucinations, migraines, and episodic illusions;

Most neurosurgeons believe that arachnoid cysts are associated with mental illness. ^[3]

Arachnoid cyst diagnosis

Routine application of CT and MRI can generally confirm the diagnosis. In a few cases, the cerebrospinal fluid contrast agent or flow measurement examination is applied to the midline saddle and posterior cranial foci. Cognitive function can also be evaluated by the Mini Mental Scoring Scale (MMSE). ^[4]

Arachnoid cyst disease treatment

Most scholars believe that asymptomatic patients do not need surgery. For those with symptoms, surgical treatment is required to decompress the cyst and remove the cyst wall.

1.Draining cyst:

The sac fluid is drained internally to the subdural space.

Cyst-Abdominal shunt to drain cyst fluid into the abdominal cavity.

2. Sacral wall incision:

The cyst was removed by craniotomy.

Various endoscopic techniques and laser-assisted techniques remove the cyst.

3. Drill holes or acupuncture to suck fluid.

4. Medication for symptoms of epilepsy or pain. ^[5]