The pituitary gland is a small, pea-sized structure located at the base of the brain, nestled in a protective bony pocket called the sella turcica. It is often described as the master gland because it produces and releases hormones that regulate many essential functions, including growth, metabolism, and reproduction. A cyst in this area is simply a fluid-filled sac, distinct from a solid tumor. Pituitary cysts are common, often discovered incidentally during a magnetic resonance imaging (MRI) scan for an unrelated reason, such as headaches or a head injury.
Classification of Pituitary Cysts
The vast majority of pituitary cysts fall into a category known as Rathke’s Cleft Cysts (RCCs), which are benign lesions. These cysts originate from the remnants of Rathke’s pouch, a structure that forms the anterior part of the pituitary gland during fetal development. If this pouch does not fully close, it can leave a space that fills with a mucus-like fluid over time.
RCCs are frequently present in the general population; autopsy studies show them in 12% to 33% of normal pituitary glands. The content of the cyst can vary in consistency, sometimes being watery or thick and proteinaceous. Although often found in adults between 30 and 50, most small RCCs remain clinically silent throughout life.
These simple cysts must be distinguished from other lesions, such as a pituitary adenoma. While both are located near the pituitary gland, an adenoma is a typically benign overgrowth of hormone-producing cells, making it a solid mass rather than a fluid-filled sac. Other less common types include arachnoid cysts, which arise from the meningeal layer surrounding the brain, and epidermoid cysts, formed from misplaced skin-like tissue.
When Cysts Cause Problems
The seriousness of a pituitary cyst is determined by whether it grows large enough to interfere with pituitary function or compress nearby brain structures. When a cyst enlarges, the restricted space leads to mass effect, which accounts for the most common symptoms. The optic chiasm, where the optic nerves cross, sits directly above the pituitary gland.
Compression of this visual pathway leads to changes in vision, most characteristically a loss of peripheral vision in both eyes. Since these changes occur gradually, visual loss may not be noticed until it is advanced. The pressure can also cause frequent, sometimes severe, headaches.
Beyond compression, a cyst can disrupt the normal production of pituitary hormones, a condition known as hypopituitarism. This occurs when the cyst pushes against or infiltrates the hormone-producing cells, causing an underproduction of one or more hormones. The resulting hormone deficiencies manifest as a variety of nonspecific symptoms, making diagnosis challenging.
For example, a lack of thyroid-stimulating hormone (TSH) can lead to fatigue, weight gain, and sensitivity to cold. A deficiency in gonadotropins (FSH and LH) can cause irregular menstrual cycles and low libido. In rare instances, the cyst can cause increased prolactin secretion, leading to breast discharge or loss of periods.
Determining the Severity
A cyst’s severity is determined by objective testing that assesses both its physical impact and functional consequences. High-resolution magnetic resonance imaging (MRI) is the primary tool used to visualize the cyst within the sellar region and is essential for diagnosis. The MRI provides specific details about the cyst’s size, location relative to the optic chiasm, and internal characteristics like fluid consistency and cyst wall thickness.
Imaging helps distinguish a simple fluid-filled cyst from other complex lesions that may have a cystic component, such as certain tumors. The imaging sequence can show if the cyst is actively pressing on the optic chiasm, which is a major factor in determining the urgency of intervention. Regular follow-up MRIs monitor the cyst’s growth rate over time, indicating its potential severity.
An endocrinological evaluation uses blood tests to check the function of the pituitary gland. A full hormonal panel measures the levels of various pituitary hormones (TSH, cortisol, prolactin, and growth hormone) to identify any deficiencies or excesses caused by the cyst’s pressure. The severity of hypopituitarism is proportional to the functional impact of the cyst, and test results guide replacement therapy if needed.
An ophthalmologic assessment is the third necessary component, specifically focusing on visual field testing. This test maps a person’s complete field of vision and can detect subtle losses of peripheral vision that may not be consciously noticed. The presence of characteristic visual field deficits, particularly those that respect the vertical midline, strongly indicates compression of the optic chiasm and determines the need for intervention.
Treatment Approaches
For the majority of pituitary cysts that are small, asymptomatic, and not causing hormonal deficiencies, the recommended approach is conservative management, or watchful waiting. This strategy involves regular monitoring, typically with yearly MRI scans and blood tests to check hormone levels. Observation is appropriate because many cysts remain stable in size or grow very slowly, potentially never requiring active intervention.
If the cyst grows and begins to cause progressive vision loss, severe headaches, or significant hormonal dysfunction, surgical intervention is generally indicated. The primary goal of surgery is to decompress surrounding structures by draining the fluid and removing a portion of the cyst wall. The most common method is transsphenoidal surgery, a minimally invasive technique where the surgeon accesses the pituitary area through the nasal passages and the sphenoid sinus.
This approach avoids touching the brain itself, which minimizes the risk of damage to surrounding neural tissue. Following surgery, vision and headaches often improve or resolve completely, though recurrence is reported to be up to 33%. Post-operative care includes close monitoring for potential complications, such as new hormone deficiencies that might necessitate lifelong hormone replacement therapy.