A brain cyst is a fluid-filled sac that can develop within the brain or in the surrounding tissues. These formations are typically enclosed pouches containing fluid, often cerebrospinal fluid (CSF). Brain cysts are relatively common findings in both children and adults. The vast majority are non-cancerous (benign) and frequently do not cause health problems. Many individuals are unaware they have one, as they are often discovered incidentally during imaging tests performed for unrelated reasons.
Defining Brain Cysts and How They Form
The cyst consists of a membranous wall that encloses a collection of liquid or semi-solid material. The fluid inside can vary, including CSF, blood, pus, or a more gelatinous substance, depending on the cyst’s type and origin. These sacs typically form from the membranes or structures adjacent to the brain, not the brain tissue itself.
The mechanisms by which brain cysts form are divided into two main categories: congenital and acquired. Congenital cysts are present from birth, resulting from developmental anomalies during fetal development. These malformations can involve the splitting or duplication of the arachnoid membrane, one of the brain’s protective coverings, leading to a fluid-filled pouch.
Acquired cysts develop later in life, often as a result of an external factor or condition. Potential causes include head trauma, infections such as meningitis, or association with certain types of tumors. In both cases, the cyst forms due to a localized buildup of fluid that becomes encapsulated within a defined space.
Common Types of Intracranial Cysts
Intracranial cysts are classified based on their location, composition, and the cells that form their lining. Arachnoid cysts are the most frequently encountered type, accounting for approximately one percent of all intracranial masses. They are found between the brain and the arachnoid membrane, a delicate layer covering the central nervous system, and contain cerebrospinal fluid.
Colloid cysts are typically located within the third ventricle, a central reservoir for CSF deep within the brain. These cysts are filled with a thick, gelatinous material and are usually diagnosed in adulthood. Due to their location, colloid cysts risk intermittently blocking the normal flow of CSF, which can lead to a sudden buildup of pressure.
Pineal cysts are common incidental findings located on or near the pineal gland, a small endocrine gland in the center of the brain. They are frequently discovered during imaging for other conditions and often do not cause symptoms. Other less common types include epidermoid and dermoid cysts, which are congenital lesions formed when skin cells or other tissues become trapped during embryonic development.
Recognizing Potential Signs and Symptoms
While many brain cysts are asymptomatic, symptoms may arise when a cyst grows large enough to interfere with normal brain function. A growing cyst can exert pressure on surrounding brain tissue (mass effect) or obstruct the pathways that circulate cerebrospinal fluid. This obstruction can lead to hydrocephalus, a buildup of fluid that increases pressure inside the skull.
The specific symptoms experienced are related to the cyst’s size and its precise location within the brain. Common complaints include new or persistent headaches, particularly those that are severe, and episodes of nausea and vomiting. Pressure on certain brain regions can also cause vision changes, issues with balance and walking, dizziness, or seizures.
Clinical Diagnosis and Approaches to Management
The diagnostic process begins with a thorough neurological examination and is confirmed through medical imaging. Magnetic Resonance Imaging (MRI) is the preferred diagnostic tool because it provides detailed images of soft tissues, allowing clinicians to determine the cyst’s size, location, and fluid characteristics. Computed Tomography (CT) scans may also be used, but MRI offers better contrast for differentiating the cyst from surrounding structures.
Management strategies are individualized and depend on the cyst’s type, size, and whether it is causing symptoms. For small, stable, asymptomatic cysts, the standard approach is observation, also called “watchful waiting.” This involves periodic follow-up scans, typically with MRI, to monitor for any changes in the cyst’s size or characteristics.
If a cyst is symptomatic, rapidly growing, or causing complications like hydrocephalus, intervention is necessary. Surgical options aim to relieve pressure by draining the fluid or removing the cyst wall. A common procedure is fenestration, which involves creating a small opening in the cyst wall to allow the trapped fluid to drain into the normal CSF circulation pathways, often using minimally invasive endoscopic techniques. In some instances, a shunt may be placed to permanently divert excess fluid away from the brain.