A brain cyst is a non-cancerous sac that forms within the skull, containing fluid or semi-solid material. While the presence of any growth in the brain may sound alarming, the majority of these lesions are benign and do not spread. These sacs are typically slow-growing and often congenital, meaning they have been present since birth. For many individuals, these cysts never cause problems and remain asymptomatic throughout their lives.
Common Types of Brain Cysts
Arachnoid cysts are the most frequently encountered type, forming in the meninges, the layers of tissue that surround the brain and spinal cord. They are situated between the brain and the arachnoid membrane. These sacs are filled with cerebrospinal fluid (CSF), the clear liquid that bathes and cushions the central nervous system. They are often found near the lateral sulcus, a deep groove on the side of the brain, or in the posterior fossa, the lower back part of the brain.
Colloid cysts are characterized by their gel-like or semi-solid contents rather than thin fluid. These cysts are almost exclusively located in the third ventricle. Their placement is significant because the third ventricle is a narrow space, making even small cysts a potential source of problems.
Epidermoid cysts are slow-growing lesions that contain skin-like material. They form when tiny fragments of surface tissue become trapped during fetal development. The contents slowly accumulate cholesterol and keratin, common products of skin cells. They are often found near the junction where the brainstem meets the upper part of the brain.
Pineal cysts occur near the pineal gland, a small endocrine gland located near the center of the brain. These cysts are frequently discovered incidentally during imaging scans performed for other reasons. They account for about one percent of all intracranial masses.
How Brain Cysts Cause Symptoms
A brain cyst causes clinical signs primarily through two mechanical processes: mass effect and obstruction. Mass effect refers to the physical pressure exerted by the cyst’s volume on the surrounding brain tissue. Symptoms are directly related to the cyst’s size and, more importantly, its precise location within the skull. A small cyst in a critical area, such as one controlling balance, can cause more noticeable issues than a large cyst in a less critical space.
The second major mechanism is the blockage of cerebrospinal fluid (CSF) circulation. Cysts near the brain’s ventricular system, such as colloid cysts, can impede the normal flow and reabsorption of CSF. This obstruction leads to a buildup of fluid, known as hydrocephalus, which increases pressure inside the skull. This increased intracranial pressure is the underlying cause for many generalized symptoms.
Common symptoms resulting from this pressure include persistent headaches, often accompanied by nausea and vomiting. Pressure on brain regions controlling movement can lead to balance or gait difficulties. Irritation of the brain’s surface tissue can also trigger seizures.
Detection and Treatment Options
The initial step in managing a brain cyst is accomplished primarily through medical imaging. Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) scans are the standard tools used to determine the cyst’s size and location in relation to nearby structures. It is common for cysts to be found incidentally when a patient undergoes a scan for unrelated reasons.
Once a cyst is detected, management involves two primary approaches: observation versus intervention. For cysts that are small, stable, and not causing symptoms, the recommendation is watchful waiting. This involves monitoring the cyst with periodic follow-up scans to ensure it does not grow or begin to cause problems.
Intervention is reserved for cysts that are actively causing symptoms or those showing signs of growth or imminent obstruction. Surgical procedures aim to relieve the pressure exerted on the brain. Fenestration involves creating small openings in the cyst wall, allowing the internal fluid to drain and be reabsorbed by the body. Shunting may also be performed, particularly if the cyst has caused hydrocephalus, to divert excess CSF away from the brain. In rare cases, complete surgical excision of the cyst may be considered.