Empty sella syndrome

Definition

Empty sella syndrome is the appearance, by radiograph (x ray) of the skull, that the sella turcica, which normally contains the pituitary gland, is empty.

Description

Sella turcica is Latin for "Turkish saddle," which roughly describes the U–shaped appearance of this bony pocket when seen by x ray. It is a concavity in the middle of the sphenoid bone measuring about 1.5 × 1.0 × 0.5 cm. The sphenoid bone forms a portion of the base of the skull just behind the eyes, at about the midpoint and just below the cerebral hemispheres.

The pituitary gland has a bulbous shape, extending on a stalk below the hypothalamus. The pituitary normally completely fills the sella turcica. The subarachnoid space, filled with cerebrospinal fluid (CSF), surrounds the pituitary stalk. The dura mater (see Meninges ) normally extends away from the bony upper portion of the sella turcica forming a barrier between the subarachnoid space and the pituitary gland below. This barrier formed by the dura mater surrounding the top of the pituitary gland is known as the diaphragma sella.

In most cases when an empty sella is seen by x ray, the sella turcica is not truly empty. In fact, CSF has entered the space normally occupied by the pituitary and has compressed the gland against the wall of the sella. A truly empty sella, i.e., missing pituitary gland, is rare.

Demographics

The true incidence of empty sella syndrome in the population is not known. However, statistics collected from autopsies have shown that an empty sella is found as an incidental finding in anywhere from 5% to 25% of cases. These do not include cases in which the pituitary gland was surgically removed or irradiated.

Most cases of empty sella syndrome are seen in middle–aged, obese women, who often have hypertension. Children with empty sella syndrome are more often symptomatic, which most often manifests as growth hormone deficiency. About half of children with growth hormone deficiency are found to have an empty sella, but only 2% of children with normal pituitary function have the finding.

Causes and symptoms

Primary empty sella syndrome is thought to be congenital (present at birth) in most cases, and is caused by a failure or opening of the diaphragma sella. This may be an accidental occurrence, with no known triggering or causative factors. In some cases the sella turcica may grow larger than normal.

Secondary empty sella (acquired) may be caused by a medical procedure, such as surgery or radiation for a pituitary tumor. Disease or trauma may also reduce the size of the pituitary, or eliminate it completely. Abnormally low production of one or more pituitary hormones is known as hypopituitarism. A specific type of acquired empty sella syndrome associated with hypopituitarism, known as Sheehan's syndrome, is caused by infarction (loss of blood supply) of the pituitary brought on by shock or hemorrhage after labor and delivery. In cases of acquired empty sella, the condition is a byproduct of some other process.

Probably less than 10% of individuals with primary empty sella syndrome have some symptoms of hypopituitarism. Symptoms related to secondary empty sella syndrome would be those of the underlying cause, except in the case of empty sella syndrome due to trauma.

Hypopituitarism can result in one or more of the following:

• Hypothyroidism. Decreased production of the thyroid gland, which can result in diminished metabolism, intolerance of cold temperatures, fatigue , mental and physical sluggishness, constipation, muscle aches, dry skin, and dry hair.
• Hypogonadism. Decreased production of sex hormones, which can result in loss of pubic hair, decreased sex drive, impotence in men, and amenorrhea (absence of menstrual cycle) in women.
• Hypoadrenalism. Decreased production of the adrenal gland, which can result in low blood pressure and hypoglycemia (low blood sugar).

Diagnosis

Other than those cases detected directly at autopsy (usually incidentally), empty sella syndrome is always diagnosed by some type of imaging study of the brain (x ray, CT scan , or MRI ). Again, in many of these cases the empty sella is detected as a coincidental finding on an imaging study ordered for some other reason. Only occasionally is the diagnosis made because empty sella syndrome was suspected from some type of endocrinological abnormality suggesting hypopituitarism.

Treatment

Treatment of symptomatic empty sella syndrome would typically involve replacement therapy for any deficient hormones. For instance, hypothyroidism would require treatment with synthetic thyroid hormone, hypoadrenalism could be treated with steroids (cortisol), and hypogonadism might require sex hormone replacement therapy. Treatment of endocrinological dysfunction can be especially difficult because of the complicated way in which the many hormones of the body interact with and affect each other. In addition, all treatments for empty sella syndrome would be symptomatic treatments; there is no method to restore the pituitary gland to its normal size.

Prognosis

In most cases in which hypopituitarism accompanies empty sella syndrome, treatment for the symptoms would be lifelong. In all cases in which disease or medical intervention has reduced or eliminated the pituitary gland, there is no method of completely restoring normal pituitary function. Replacement therapies are effective when well-managed. However, even someone with optimum therapy is unlikely to feel completely "well," in relation to normal pituitary function, all of the time.

Special concerns

Symptoms of empty sella syndrome may be subtle, and may mimic other conditions. Since an accurate diagnosis of empty sella syndrome requires imaging studies of the brain, there is a risk that the condition could be misdiagnosed, or go undiagnosed.

Resources

BOOKS

DeMyer, William. Neuroanatomy, 2nd ed. Baltimore: Williams & Wilkins, 1998. pp. 312-316.

Gilroy, John. Basic Neurology, 3rd ed. New York: McGraw-Hill, 2000. pp. 521-523.

Reinhardt, Shelley, et al, eds. Basic & Clinical Endocrinology, 6th ed. Philadelphia: McGraw Hill, 2001. pp. 128-129.

Wilson, Jean D., et al, eds. Williams Textbook of Endocrinology, 9th ed. Philadelphia: W.B. Saunders Company, 1998..

OTHER

Empty Sella Syndrome Information Page. The National Institute of Neurological Disorders and Stroke. (September 10, 2003). http://www.ninds.nih.gov/health_and_medical/disorders/emptysella.htm.

Scott J. Polzin, MS, CGC