Arachnoid cyst

    Last updated date: 15-May-2023

    Originally Written in English

    Arachnoid cyst

    Arachnoid cyst


    On cross-sectional neuroimaging of the brain, arachnoid cysts are a common accidental discovery. They can be symptomatic and require therapy if they are present in the right place and are large enough. They can also cause symptoms when they arise in the spine. Due to mass effect or rupture, both spinal and intracranial arachnoid cysts develop.


    What are Arachnoid cysts?

    Arachnoid cysts

    Arachnoid cysts are sacs filled with cerebrospinal fluid (CSF). CSF is usually a naturally occurring protective fluid that surrounds the brain and spine. Because the walls of the arachnoid cyst prevent this fluid from flowing into the CSF system, it gradually builds up inside.

    Arachnoid cysts are often congenital, meaning they are present from birth in children. These cysts are referred to as primary arachnoid cysts. On the other hand, secondary arachnoid cysts are cysts that appear later in life. Primary arachnoid cysts, however, are more common.

    In most cases, arachnoid cysts form in the brain, although they can also occur around the spinal cord. Because it develops in the region between the brain or spine and the arachnoid membrane, it is called an arachnoid cyst. It is one of three layers of membranes that surround the brain and spinal cord. When you have an arachnoid cyst on your head, it grows between your skull and brain or in pockets (known as ventricles) in the brain.


    Causes of Arachnoid Cysts

    Causes of Arachnoid Cysts

    The cause of arachnoid cyst development is unknown, however they are thought to be caused by aberrant arachnoid splitting during embryogenesis. If inflammatory cells, excess collagen, or hemosiderin stains are present on histology, an inflammatory or traumatic origin is suspected. Due to mass effect, underlying gliosis is seldom observed in the nearby brain.

    Primary arachnoid cysts, also known as congenital arachnoid cysts, occur due to aberrant growth of the brain and spine while the baby is still in the womb. The cause of this growth is unknown. However, it may be genetic.

    Noncongenital arachnoid cysts, also known as secondary arachnoid cysts, can occur due to a variety of factors. In general, some of the risk factors that increase the chances of developing an arachnoid cyst include;

    • Meningitis, a type of infection or inflammation of the sacs around the spinal cord and brain
    • Brain or spinal cord tumors
    • Surgery on the brain or spinal cord
    • Head injury
    • Male gender


    Men are more likely to have arachnoid cysts than women. Cysts can appear at any age, while children and adults of various ethnicities and geographic areas are equally susceptible to the disorder. Typically, arachnoid cysts are the most common form of intracranial cysts. It is not possible to estimate the true prevalence of arachnoid cysts in the general population because many patients are asymptomatic.



    Meningitis is a life-threatening condition caused mostly by bacteria or viruses. The disease was always lethal before the advent of antibiotics. Despite considerable advances in healthcare, the illness still has a death rate of over 25%.


    Meningitis causes

    The inflammation of the meninges is known as meningitis. The dura mater, arachnoid mater, and pia mater are the three membranes that surround the vertebral canal and skull, encapsulating the brain and spinal cord. Encephalitis, on the other hand, is a kind of brain inflammation.

    Infectious and non-infectious causes of meningitis include autoimmune illnesses, cancer/paraneoplastic syndromes, and medication responses. Bacteria, viruses, fungi, and, less typically, parasites are the infectious etiologic agents of meningitis.


    Meningitis symptoms

    Meningitis can appear in a variety of ways, depending on the host's age and immunological condition. Fever, neck pain/stiffness, and photophobia are common symptoms. Headache, dizziness, disorientation, delirium, irritability, and nausea/vomiting are some of the more general symptoms. Increased intracranial pressure signals a bad prognosis.


    The following risk factors should increase clinical suspicion:

    • Close contact exposures (military barracks, college dorms)
    • Incomplete vaccinations
    • Immunosuppression
    • Children younger than five years and adults older than 65 years
    • Alcohol use disorder

    A history of exposures, sexual interaction, animal contact, past neurosurgical intervention, recent travel, and the season should all be considered. The majority of viral infections occur during the summer months.

    The physical exam in adults is focused on finding localized neurologic deficits, meningeal irritation (Brudzinski and Kernig symptoms), and, in meningococcal meningitis, specific skin lesions (petechiae and purpura). In 10% to 20% of individuals, there are anomalies in the cranial nerves.


    Meningitis diagnosis 

    White blood cell count, glucose, protein, culture, and, in certain situations, polymerase chain reaction are used to diagnose meningitis (PCR). A lumbar puncture (LP) is used to extract CSF, and the opening pressure can be monitored.

    Additional testing should be performed tailored on suspected etiology:

    • Viral: Multiplex and specific PCRs
    • Fungal: CSF fungal culture, India ink stain for Cryptococcus
    • Mycobacterial: CSF Acid-fast bacilli smear and culture

    The following are the predicted CSF results in bacterial, viral, and fungal meningitis: CSF abnormalities expected in bacterial, viral, and fungal meningitis. Before starting antimicrobials, the CSF sample should be acquired. When bacterial meningitis is suspected and the patient is critically unwell, antibiotics should be started before the LP.


    Meningitis treatment

    In all instances of bacterial meningitis, antibiotics and supportive treatment are essential. The basis of meningitis care includes managing the airway, preserving oxygenation, and administering enough intravenous fluids while controlling temperature.

    The antibiotic used is determined by the organism suspected of causing the illness. In order to offer the greatest antimicrobial coverage, the doctor must consider the patient's demographics and medical history.


    Brain Tumors

    Brain tumors have similar characteristics and obstacles in terms of diagnosis and treatment with tumors elsewhere in the body, but they also present unique challenges due to the organ they reside in. The blood–brain barrier (BBB), which separates most of the brain from the blood, has a considerably tighter control over chemicals that are permitted to pass (or may even be subject to promote transit) than most other organs.

    Many tracers that easily reach tumors elsewhere in the body would only reach brain tumors if the tumor disrupted the BBB, such as glioblastomas; if the tumor developed from intracranial tissues that do not have a BBB, such as meningioma (derived from the meninges); or if the tumor spread to the brain .

    As a result, the rupture of the BBB, which may be clearly identified on contrast-enhanced MRI and computed tomography (CT), is recognized as the key diagnostic signal for malignant gliomas, meningiomas, and brain metastases, as well as certain less common cancers without an intact BBB.

    There are brain tumors with an intact BBB, such as most low-grade gliomas (LGG), that may be overlooked on a contrast-enhanced CT scan but are easily spotted on MRI scans without contrast enhancement due to higher signal. Thus, nuclear imaging is rarely used to identify brain cancers, whereas MRI with and without contrast enhancement is the gold standard for practically all types of brain tumors, offering good sensitivity . Nuclear imaging is used to characterize the biological characteristics of brain tumors, particularly those that are important for treatment planning.

    Distinct degrees of anaplasia in different tumor areas are common in brain tumors. Surgical biopsies, particularly those performed stereotactically, may thereby miss the most aggressive tumor portion, resulting in an underestimation of tumor grade. To address this issue, positron emission tomography (PET) imaging can be used to focus biopsies to the most malignant tumor portion, which needs integration with operation planning and stereotactic neuronavigation.


    Spinal Tumors

    Primary tumors of the spine and its associated structures are studied, as are secondary (metastatic) cancers of distant organs that spread hematogenously and lymphatically and are found in the spine and its surrounding tissues. The spine is prone to metastasis because it is strongly vascularized and has a close association with regional lymphatic and venous drainage systems (particularly Batson's venous plexus).

    Metastatic tumors of the spine are the most prevalent (97 percent). Adenocarcinomas, which most commonly arise in the lung, breast, prostate, kidney, gastrointestinal system, and thyroid, are known to metastasis to the spine. It was shown that between 50 percent and 70 percent of cancer patients had experienced bone metastases before death, with the number rising to 85 percent in the case of breast cancer.

    Surgery can be used to treat up to 10% of individuals with symptomatic spine metastases. The thoracic and thoracolumbar spines are the most prevalent locations for spine metastasis (70 percent), with the lumbar spine and sacrum accounting for more than 20 percent of metastatic lesions. The cervical spine is a less common location for metastases.

    Because primary spine tumors are uncommon and most of these lesions are asymptomatic, the true prevalence is unclear. Hemangiomas, which were once thought to be the most prevalent primary tumors of the spine, are thought to occur between 11 and 14 percent of the time. This ratio has been discovered to be reliant on lesions discovered by chance when doing diagnostic procedures for other reasons. Correct diagnosis of these asymptomatic lesions, which are very common in the spine and do not require treatment, will prevent unnecessary diagnostic procedures from being performed.


    Clinical features

    Medical histories and physical examination results in patients with spine tumors are not always linked to the present condition. However, in order to provide the physician with any hints regarding the condition, these data must be thoroughly comprehended and assessed. Pain is the most prevalent and prominent symptom in people with spine tumors.

    Patients with spine tumors, like patients with virtually all skeletal system cancers, think that their pain is related to a recent traumatic incident. This situation can suggest a pathological fracture, which is caused by the vertebral body collapsing as a consequence of current degradation as a result of small trauma. The most common indicator of a spine tumor is discomfort that begins slowly, steadily worsens, is frequently persistent at night, and finally troubles the patient even when they are at rest.

    A pathological fracture is defined as acute pain that begins without any trauma in a patient who has had no previous symptoms. Pain in spinal tumors can be caused by a variety of factors. A tumor that develops inside the vertebral body and expands causes bone remodalization and cortical thinning at first, followed by pathologic fracture and invasion of paravertebral tissues. The major source of discomfort at the start of the disease is a stretched periosteum caused by cortical enlargement.


    Arachnoid Cysts and Genetics

    Most diagnoses of arachnoid cysts are sporadic. This means that they occur in children who do not have a family history of arachnoid cysts. However, in medical research, examples of the family of arachnoid cysts have been found. This suggests that hereditary predisposition may play a role for other patients.

    Arachnoid cysts, for example, have been recorded in at least three sets of unrelated siblings. Autosomal recessive inheritance is possible in familial cases. Arachnoid cysts can also develop as a result of other genetic diseases, such as Marfan syndrome.


    Arachnoid Cyst Signs and Symptoms

    Arachnoid Cyst Signs and Symptoms

    Arachnoid cysts do not show any symptoms in most cases. That is, they have a low tendency to cause symptoms. Unless a patient is referred to a referral clinic because of symptoms, the arachnoid cyst is usually discovered accidentally. The most common cyst placements in the middle cerebral fossa and retrocerebellar area, fortunately, are not linked with symptoms. Cysts located in unusual places are more likely to be symptomatic.

    When arachnoid cysts create symptoms, they usually do so through one of two processes. One is caused by mass effect, while the other is caused by rupture. Because arachnoid cysts are frequently accidental and unrelated to the reason the patient is being examined, they are identified in a variety of situations.

    Symptoms of arachnoid cyst may develop in other patients. Symptoms, however, vary depending on the location of the cyst as well as its size. When a cyst presses on a nerve or sensitive part of the brain or spinal cord, for example, symptoms may develop. Cysts can cause one or more of these symptoms if they are in the brain;

    • Delay in development
    • Dementia
    • Dizzy
    • Headache
    • Hearing, vision, or difficulty walking
    • Problems with balance
    • Lethargy
    • Seizures
    • Nausea and vomiting




    Even if a patient presents with a Headache, an arachnoid cyst is most likely unrelated to the headache and was discovered by chance. However, each instance must be carefully assessed. The arachnoid cyst can grow to be quite big, and it can be the source of severe Headaches and seizures. Larger cysts are more likely than tiny cysts to be symptomatic, and larger cysts are more likely to require surgery.

    Arachnoid cysts are seldom the source of serious neurological symptoms such hydrocephalus, ataxia, or cranial nerve impingement. Arachnoid cysts, however, induce a wide range of symptoms due to their relatively regular occurrence and the several places where they can be found. Vision loss, nausea/vomiting, macrocephaly, third nerve palsy, trochlear dysfunction, trigeminal neuropathy, hemifacial spasm, sensory neuronal hearing loss, facial palsy, vertigo, and eighth cranial neuropathy are only a few of the symptoms.

    The symptoms vary depending on where the cyst is located. Trochlear nerve dysfunction might develop from a quadrigeminal plate cistern arachnoid cyst compressing the trochlear nerves and quadrigeminal plate. An arachnoid cyst impinging on the optic nerve can induce a visual field loss in the ipsilateral eye, bitemporal hemianopsia from a cyst in the suprasellar cistern, and homonymous hemianopsia from a cyst in the occipital cortex.

    Arachnoid cysts have caused some strange symptomatology. The rhythmic movement of the head known as bobble-head doll syndrome has been linked to third ventricular dilatation and maybe cerebellar involvement. It has been shown that depression can be resolved by marsupialization of an arachnoid. The occurrence of an arachnoid cyst producing depression is unusual, but conceivable considering the cyst's location and significant mass influence on the brain.

    The spinal arachnoid cyst is a rather uncommon condition. Arachnoid cysts can be seen all throughout the spine, although they're most prevalent in the thoracic area. Backache and varying leg weakness are the most typical symptoms. Monoparesis, radicular discomfort, spastic quadriparesis, neurogenic claudication, sensory disturbance, monoplegia, incontinence, pain, paresthesia, and neurogenic bladder have all been linked to. The cysts are most usually seen posteriorly; however, they can also be found anteriorly.

    Arachnoid cyst rupture resulting in a subdural hygroma is uncommon. Trauma or spontaneous rupture of the arachnoid cyst are also possibilities. The ensuing subdural hygroma may usually be monitored without therapy, although surgical intervention may be required in some cases. Furthermore, violent rupture of an arachnoid cyst seldom results in arachnoid cyst hemorrhage or a subdural hematoma.


    Arachnoid Cyst Diagnosis

    Arachnoid Cyst Diagnosis

    Arachnoid cysts are usually discovered incidentally, mostly during examination of a child who has had seizures or symptoms of a brain injury. A pediatric neurosurgeon can suspect a diagnosis after a complete patient history, thorough medical examination, and a number of specialized tests. These tests primarily include advanced imaging techniques such as computed tomography (CT) scans and magnetic resonance imaging (MRI).

    Both an MRI and a CT scan can help diagnose or verify an arachnoid cyst in a suspected patient. Computer and x-ray techniques are useful in making films that show cross-sectional images of brain tissue structures during a CT scan. The brain is imaged in a cross-sectional view using a magnetic field and radio waves during an MRI.


    Arachnoid Cyst Treatment

    Arachnoid Cyst Treatment

    Treatment is not necessary for arachnoid cysts that do not cause symptoms or put pressure on the brain and spinal cord. The main goal of treating arachnoid cysts involves draining the fluid to reduce the pressure within the cyst.

    There are two treatment approaches available. They include;

    • Craniotomy

    This procedure involves making a small cut or incision around the arachnoid cyst and removing a small portion of the skull bone. The pediatric neurosurgeon will then insert an endoscope, a small, flexible tube, through the incision. The tiny light and tiny camera on the endoscope allow the neurosurgeon to visualize the cyst. An endoscope is also used to make an opening in the cyst and open it, a process known as fenestration.

    The fluid in the arachnoid cyst will flow out of the cyst into various parts of the brain that contain cerebrospinal fluid once it opens. The cyst fluid is then reabsorbed by the body.

    • Shunting

    Another method is to shunt the arachnoid cyst. Shunting involves inserting a tube inserted into the cyst. It will then stay in place to allow the fluid to drain and be reabsorbed in other parts of the body.

    On the other hand, the child or adult patient may become dependent on the shunt to prevent recurrence of symptoms. Living with a shunt can also lead to various consequences, including obstruction or infection.


    If possible, surgical removal (resection) of the arachnoid cyst in the spine can be used to treat the problem. Symptoms usually resolve after pediatric neurosurgery. Complete surgical excision of a spinal cyst may not be possible in some situations. Fenestration or shunting of the cyst to remove fluid is thus necessary.


    Complications of Arachnoid Cyst

    Early diagnosis and treatment of arachnoid cysts is generally important because it helps avoid symptoms from occurring. If the cyst gets a chance to expand, it can put a lot of pressure on the brain or spinal cord, resulting in long-term neurological problems.

    Complications of an arachnoid cyst can be severe, especially if left untreated and in other cases life-threatening. Therefore, following a treatment plan can help reduce the chances of significant problems.

    Some of the complications of an arachnoid cyst include;

    • Brain damage
    • Babies and children who are not developing
    • Hydrocephalus, accumulation of fluid in the skull
    • Permanent nerve injury, including paralysis
    • Seizures and tremors


    Arachnoid cyst prognosis

    Arachnoid Cyst Prognosis

    Many arachnoid cysts are congenital (present at birth). However, they rarely cause symptoms throughout the patient's life. The size and location of the arachnoid cyst in the brain determines whether symptoms will appear or not.

    Small cysts rarely cause any symptoms, and most of them remain the same size. Some, especially if they push against the brain, cranial nerves, or spinal cord, grow in size and eventually produce symptoms.

    Neurological symptoms in children may appear if the cyst puts additional pressure on the brain area. Behavioral problems, developmental delays, inability to control voluntary movements (ataxia), balance and walking problems, and cognitive impairment are possible signs. Hemiparesis (weakness or paralysis of one part of the body) is also possible.

    Treatment usually improves or resolves symptoms. However, arachnoid cysts can cause severe permanent neurological damage if left untreated because the cyst continues to expand or bleeds into the cyst.

    Arachnoid cysts can also cause a subdural hematoma, which most commonly occurs after a head injury. Arachnoid cysts can rupture on their own, but this is a very unusual occurrence.


    Arachnoid Cyst and Anxiety

    Both arachnoid cysts and anxiety are sometimes seen in children and even adults. Arachnoid cysts will not grow larger and put additional pressure on the brain as a result of anxiety. Also, arachnoid cyst patients have increased levels of anxiety and depression, unlike the rest of the general population.

    Patients with right temporal cysts described higher levels of anxiety and depression, unlike patients with left temporal cysts. Anxiety and stress may have no effect on an arachnoid cyst on its own.



    Arachnoid cysts (fluid-filled sacs) usually develop on the arachnoid membrane that covers the spinal cord and brain. Arachnoid cysts are not always associated with symptoms in most cases (asymptomatic).

    Headaches, seizures, and an abnormal buildup of excessive cerebrospinal fluid in the brain (hydrocephalus) are typical symptoms. On the other hand, arachnoid cysts have an unknown etiology. Thus, categorized based on where they are found. When the lesion is at an expected site and has the look of a fluid-filled thin-walled cyst, CT imaging is typically enough to diagnose an arachnoid cyst. The great majority of arachnoid cysts do not require treatment.