Empty Sella Syndrome (ESS) is a condition where the bony structure that cradles the pituitary gland appears partially or completely filled with cerebrospinal fluid (CSF) on imaging scans. This saddle-shaped bony compartment is known as the sella turcica. When CSF enters this space, it exerts pressure on the gland, causing it to flatten or shrink against the walls of the sella. The appearance of an “empty” space gives the syndrome its name, though the space is actually occupied by fluid. Understanding the causes of ESS requires a look at the anatomy and the mechanisms that allow CSF to displace the gland.
The Anatomy of the Sella and the Role of Cerebrospinal Fluid
The sella turcica is a depression in the sphenoid bone at the base of the skull that offers physical protection to the pituitary gland. A membrane called the diaphragma sellae usually covers the opening of this bony compartment, acting as a partial barrier. This membrane is part of the dura mater, protecting the brain, and it has a small hole to allow the pituitary stalk to connect the gland to the brain.
Cerebrospinal fluid is the clear liquid that surrounds and cushions the brain and spinal cord. The space containing this fluid is under pressure, known as intracranial pressure. When the diaphragma sellae has a defect or weakness, the pulsating pressure from the CSF can push a pouch of the arachnoid membrane into the sella turcica. This intrusion of the fluid-filled membrane compresses the pituitary gland, leading to its characteristic flattened appearance on scans.
Causes of Primary Empty Sella Syndrome
Primary Empty Sella Syndrome (PES) is the most common form and is caused by an intrinsic anatomical or structural weakness. This means there is no known prior trauma or disease affecting the pituitary gland itself. The underlying cause is often a congenital deficiency or weakness in the diaphragma sellae, the protective membrane covering the sella turcica. This defect allows the normal pressure of the cerebrospinal fluid to slowly push the arachnoid lining into the sella over time.
This structural vulnerability is often compounded by factors that increase CSF pressure inside the skull. Obesity is a frequently associated factor, particularly in women, and contributes to idiopathic intracranial hypertension (IIH), where CSF pressure is abnormally high. Arterial hypertension, or high blood pressure, is another condition that can increase pressure within the cranial cavity. The combination of a structurally weak barrier and chronic, slightly increased intracranial pressure gradually compresses the pituitary gland.
Causes of Secondary Empty Sella Syndrome
Secondary Empty Sella Syndrome (SES) results from an identifiable, acquired event that causes the pituitary gland to shrink or be removed. The sella turcica becomes “empty” after the gland tissue has been damaged or destroyed by a specific disease or medical intervention. This acquired damage creates a void that is subsequently filled by cerebrospinal fluid, leading to the same radiographic appearance as PES.
Medical procedures targeting the pituitary are a common cause of SES. These include the surgical removal of a pituitary tumor, known as hypophysectomy, or radiation therapy aimed at the gland. Radiation can cause the pituitary tissue to shrink and atrophy over time. Both surgery and radiation reduce the physical volume of the gland, leaving a larger space for the CSF to occupy.
Specific pathological events can also lead to the destruction and shrinkage of the pituitary gland. Pituitary apoplexy, a sudden hemorrhage or lack of blood flow (infarction) within the gland, causes acute tissue necrosis that dramatically reduces the gland’s volume. Sheehan syndrome is a related event that occurs after severe blood loss and shock during childbirth, resulting in the death of pituitary cells. In all secondary causes, the loss of pituitary tissue volume precedes the influx of cerebrospinal fluid.