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Q1: What is the abnormality seen on magnetic resonance imaging (see p 430)?
Coronal contrast enhanced T1 weighted MRI scan through pituitary region demonstrates an enlarged sella turcica (C) with normally enhancing pituitary tissue (I) displaced inferiorly, an abnormality suggestive of empty sella. Optic chiasm (E), intracavernous carotid arteries (A: right and B: left side and sphenoid sinus (D, F) are clearly visible. This is often an incidental radiological finding and in most cases there is no associated abnormality of pituitary function. Pituitary fossa enlargement is a result of communicating extension of subarachnoid space (chiasmatic cistern) into the pituitary fossa. This promotes remodelling and enlargement of the bony sella. The pituitary gland is usually flattened against the floor of the sella, and the pituitary stalk may be deviated laterally.1
Q2: What are the two main types of this abnormality?
An empty sella can occur as a result of congenital diaphragmatic defect (primary empty sella) or damage to the diaphragm by surgery, radiation therapy, or pituitary tumour infarction (secondary empty sella).
A primary empty sella is a fairly common incidental radiological finding and is usually associated with only minor disturbances of pituitary function. In this condition the sella tends to be symmetrically ballooned without bony erosion. Suprasellar subarachnoid space (chiasmatic cistern) herniates through an incomplete diaphragma sella, so that the sella is filled with cerebrospinal fluid (CSF) within an arachnoid lined sac. An incomplete diaphragma sella appears to be a prerequisite. Whether persistently or transiently increased CSF pressure is required to produce sella enlargement in these patients is not clear. CSF pressure is generally normal, when measured, in these patients. Pituitary volume is usually normal; this is in contrast with partially empty sella caused by a degenerated pituitary adenoma, where the pituitary volume is usually increased.
Most patients with primary empty sella are obese, multiparous women with headaches; about 30% have hypertension.2 Selection bias cannot be excluded in case reports, since skull radiographs may be obtained in patients with headache, which in turn, uncovers the empty sella. Most patients with a primary empty sella have normal pituitary function, and approximately 15% have mild hyperprolactinaemia (usually <100 μg/l, with or without galactorrhoea and amenorrhoea). Hyperprolactinaemia may be due to stalk stretching or coincidental microprolactinomas. Since even a mild prolactin increase may result in gonadal dysfunction, this may merit treatment, but patients should be reassured that this problem is usually unlikely to result in additional pituitary dysfunction. The development of pituitary dysfunction appears to be related to the degree of sellar enlargement as demonstrated by computed tomography in 56 adults with normal pituitary function and 11 patients with hypopituitarism.3 Development of growth hormone secretory reserve is often abnormal in these patients, probably as a result of obesity. Spontaneous CSF rhinorrhoea and pseudotumour cerebri have each been reported in 10% of these patients, but this association may represent an ascertainment bias.2 CSF rhinorrhoea may need surgical correction. Visual field defects have been reported and are thought to be due to herniation of the optic chiasm into the sella turcica. Once diagnosis of primary empty sella syndrome is established on MRI or computed tomography, further diagnostic studies should be performed to exclude hormone excess or deficiency: when hormone concentrations are normal, therapy is reassurance.
Primary empty sella syndrome can also occur in children, with an incidence of 48% in children with either an isolated growth hormone deficiency or a combination of pituitary hormone deficiencies; only 2% of children with normal pituitary function have empty sella.3 Primary empty sella syndrome may be associated with central precocious puberty.4 Association with midline defects and cleft palate has been documented.5
Primary empty sella
Common incidental radiological finding.
Pituitary functions usually normal.
Mild hyperprolactinaemia occurs in 15% of patients.
Secondary empty sella
Result of damage to diaphragma sella by surgery or radiotherapy.
Result of pituitary tumour infarction.
Partial or complete hypopituitarism: common.
In secondary empty sella associated with destruction of pituitary gland, hypopituitarism is the outcome. Pituitary destruction occurs when a large pituitary adenoma undergoes infarction (usually a haemorrhage) or as a consequence of surgical resection. Hypopituitarism may be partial or complete, and measurement of serum pituitary and target organ hormones is necessary to establish the diagnosis of hormone deficiency and to determine the central (hypothalamic or pituitary) cause of the dysfunction.6
This patient's serum corticotrophin and cortisol; thyrotrophin and thyroxine, luteinising hormone and testosterone, and prolactin concentrations were normal. The patient refused to undergo stimulation tests for growth hormone deficiency. He was reassured and treated symptomatically for his headache with good results. Cause of the headache is most likely tension, and is unrelated to primary empty sella syndrome. He is on regular follow up in the endocrinology clinic.
Primary empty sella syndrome and tension headache.