A partially empty sella is an anatomical finding where the brain’s protective fluid partially fills the space normally occupied by the pituitary gland. This condition is often discovered incidentally during magnetic resonance imaging (MRI) or computed tomography (CT) scans performed for unrelated reasons. A partially empty sella frequently represents a benign anatomical variation rather than a disease state. The finding is defined by the pituitary gland being compressed or flattened against the walls of its bony enclosure.
Understanding the Sella Turcica and the Pituitary Gland
The sella turcica is a saddle-shaped depression located in the sphenoid bone at the base of the skull. This bony compartment cradles the pituitary gland, which produces and regulates several hormones that govern growth, metabolism, and reproduction.
In this condition, the subarachnoid space, which contains cerebrospinal fluid (CSF), extends into the sella turcica. This fluid presses down on the pituitary gland, causing it to flatten against the inner walls of the sella. The condition is labeled “partial” when less than 50% of the sella is filled with CSF, and the pituitary gland remains visible, typically with a thickness greater than three millimeters.
Primary and Secondary Factors Leading to the Condition
The causes of a partially empty sella are categorized into two types: primary, where the cause is unknown, and secondary, where a specific event or condition is identifiable. Primary empty sella is the more common subtype. It is hypothesized to result from a defect in the diaphragm sellae, the membrane that covers the top of the sella turcica. A congenital or acquired weakness in this barrier allows the arachnoid membrane and CSF to herniate into the sella compartment.
This herniation is often combined with normal or slightly increased intracranial pressure, which provides the force necessary to push the CSF sac into the sella. Primary empty sella is frequently observed in middle-aged women, particularly those who are obese or have high blood pressure. It is sometimes linked to conditions like idiopathic intracranial hypertension (pseudotumor cerebri).
Secondary causes of this condition are those directly traceable to damage or regression of the pituitary gland itself. This acquired type can follow brain surgery in the pituitary region, especially procedures for tumor removal. Significant trauma to the head or radiation therapy directed at the brain can also cause tissue damage that leads to the sella filling with CSF.
Other specific medical events, such as pituitary apoplexy (the sudden infarction or hemorrhage of the pituitary gland), can cause the gland to shrink, leaving a residual empty space. Spontaneous regression of a pituitary tumor, where the mass shrinks or disappears on its own, is another mechanism that results in a secondary empty sella.
Clinical Presentation and Associated Hormonal Issues
In the majority of people, a partially empty sella is asymptomatic and does not impair the function of the pituitary gland. For these individuals, the finding is purely anatomical, and no clinical intervention is required. When symptoms do arise, they generally fall into two categories: neurological manifestations and endocrine dysfunction.
The most frequent neurological symptom reported in symptomatic cases is chronic headache, which may be related to the increased pressure from the cerebrospinal fluid within the skull. Though less common, the continuous pressure from the CSF can rarely cause visual field defects. This occurs if the optic chiasm, the structure where the optic nerves cross, prolapses downward into the enlarged sella, causing compression.
Endocrine dysfunction, known as hypopituitarism, is a deficiency in one or more of the hormones produced by the compressed pituitary gland. While severe hormone deficiency is less common in a partial empty sella compared to a complete one, a minority of patients may exhibit low levels of specific hormones. These can include growth hormone, thyroid-stimulating hormone (TSH), or adrenocorticotropic hormone (ACTH), which regulates cortisol production.
Deficiencies in sex hormones, such as luteinizing hormone and follicle-stimulating hormone, may also occur, leading to symptoms like irregular menstruation or reduced libido. Elevated levels of prolactin, a hormone that stimulates milk production, have also been observed in a smaller subset of patients.
Diagnosis and Treatment Approaches
The definitive diagnosis of a partially empty sella is primarily achieved through medical imaging, with Magnetic Resonance Imaging (MRI) being the preferred method. MRI provides detailed images that clearly show the cerebrospinal fluid filling a portion of the sella turcica and the resulting compression or flattening of the pituitary gland against the sellar wall. A CT scan may also be used if MRI is contraindicated, but it offers less detailed visualization of the soft tissues.
Following the imaging diagnosis, a complete endocrine evaluation is necessary to determine if the anatomical finding has translated into functional hormonal deficits. This involves blood tests to measure the levels of various pituitary hormones, such as TSH, cortisol, and sex hormones, to check for signs of hypopituitarism. Regular follow-up with an endocrinologist is often recommended, even for asymptomatic individuals, to periodically monitor hormone levels.
For patients who are asymptomatic and whose hormonal function is normal, no specific treatment is necessary, and the standard approach is observational, often termed “watchful waiting”. Treatment is only initiated when symptoms or hormonal deficiencies are present. If a hormonal deficiency is detected, the primary treatment involves hormone replacement therapy to restore the missing hormones to normal physiological levels. Very rarely, if severe visual impairment or significant leakage of CSF from the nose occurs, surgical intervention may be considered to repair the defect or reduce pressure.