Empty sella is a radiological diagnosis based on CT or MR investigation.  Either a normal sized (empty sella) or enlarge sella (empty enlarged sella) presents partly or totally filled with cerebrospinal fluid.  The radiological diagnosis does not mean a pathological situation in every instance.  Many patients present without specific symptoms and the diagnosis is made by chance.  Empty sella syndrome is the pathological variant of a radio logically verified empty sella.

Primary empty sella is an idiopathic form of an empty sella which occurs in the absence of prior pituitary surgery or radiation therapy or medication with DOPA agonists. 

Secondary empty sella occurs as a result of surgical resection or irradiation of a sellar expansion. 

Anatomy:

The disphragma sellae normally forms a circular fold that constitutes a roof for the sella turcica with only a small central opening for the passage of the pituitary stalk.  Busch in 1951 performed an autopsy study of 788 subjects without known pituitary disease.  In 38.4% he found a complete covering of pituitary gland by the diaphragm.  He observed an empty sella in 5.5%.  Other studies described significant defects in the sellar diaphragm in 22% to 72% of cases.  These defects were frequently accompanied by intrasellar extension of subarachnoid space and downward displacement of the optic chiasm.

Busch and others have measured the volume of the sella and of the sellar contents.  These measurements are widely variable because the definition of the lateral and superior boundaries of the sella is arbitrary.  However, Bjerre(1990) concludes that a sella with a volume exceeding 1.1-1.2cm³ calculated from X-ray is an enlarged sella. 

Incidence:

A 5:1 female male predominance exists in the incidence of diaphragmatic defects.

Over 80% of the cases occur in women, the majority between the ages of 40 and 49.  78% to 90% of these patients were described as obese, multiparous and 31% were hypertensive (Neelon, 1973).

An empty sella of normal size without clinical significance was found in some 10% (Brisman, 1978). In children radiological incidence of primary empty sella was reported as 1-48% with a male-female ratio of 1.4:1.0 (Rappaport, 1991). 

Etiology:

Primary empty sella

An empty sella (either normal sized or enlarged) may simply be a normal anatomical variation so that concurrent symptoms are unrelated to the radiological appearance.

If a deficient diaphragma sellae is present, increased intracranial pressure, as in pseudotumor cerebri, displaces the suprasellar arachnoidal and cerebral structures into the sellar cavity.  This may cause sellar enlargement and partial emptiness, as well as posteroinferior displacement and compression of the pituitary gland, and  displacement of the optic chiasm and erosion of the sellar floor and dura. The theory is supported by the following observations.

1. An empty sella syndrome is observed frequently in patients with benign intracranial hypertension.  Weisberg (1975) reported an incidence of 10% in 50 cases with benign intracranial hypertension.
2. Continuous intracranial pressure monitoring in patients with empty sella syndrome revealed intermittent asymptomatic increases in pressure in some patients (Kaye, 1982).
3. Intracranial tumors of slow growth have been associated with a deficient sellar diaphragma.  The incidence of an abnormal sellar configuration in patients with intracranial tumors and empty sella syndrome is about 24%.
4. Patients with known empty sella followed for some years exhibit progressive changes of their radiological sellar appearance.

Another theory relates the empty enlarged sella to a previous pituitary hyperplasia or hypertrophy (e.g. during pregnancy or because of primary peripheral endocrine gland insufficiency).  This theory explains the fact that empty enlarged sella is often combined with primary thyroid dysfunction, obesity and the female preponderance in most series. 

Based on observations in patients with acromegaly and hyperprolactinaemia associated with an empty sella syndrome, sequellae of pituitary apoplexy (extensive hemorrhage or necrosis within a pituitary adenoma) is blamed.  

Another theory proposes an autoimmune hypophysitis with resulting secondary protrusion of the arachnoid membrane through an incompetent diaphragma sellae.  Antipituitary antibodies were diagnosed in 47% to 75% of adult patients with primary empty sella syndrome. 

Sheehan’s syndrome postpartum necrosis of the pituitary gland may be the cause in some. 

Secondary empty sella has been noted to follow:

1. Sellar or parasellar surgery
2. Radiation therapy for an intrasellar expansion
3. Bromocriptine therapy for a pituitary adenoma

Clinical features:

Empty sella has been associated with pseudotumor cerebri, hypopituitarism, visual field defects, and headache.

1) Headache is the most common symptom.  Some 70% of patients complain about pain. Pulsations of CSF against the dura of the sella could be responsible.

2) Visual alterations may be due to traction on the chiasm or involvement of chiasmal blood vessels.  Incidence is about 20% in primary empty sella syndrome.  In secondary empty sella syndrome the incidence is much higher because of the underlying sellar pathology.  Clinically the patients complain about clouding of vision, color vision defects, photophobia, and various visual field defects (bitemporal hemi-, or quadrantanopia, generalized filed constriction, quadrine constriction, central scotoma, homonymous hemiachromatopsia mimicking the lesion in patients with a suprasellar pituitary tumour.  On fundoscopy changes to the retina and papilledema can be observed.  The symptoms sometimes resemble a low pressure glaucoma thus necessitating detailed ophthalmologic examination with particular attention being paid to intraocular pressure and optic disc appearance. 

3) Endocrinological disturbances: There is general agreement in the literature that anterior pituitary dysfunction necessitating hormonal replacement therapy is rare in primary empty sella syndrome.  However, subtle dynamic endocrine testing is able to reveal some degree of hypothalamic-pituitary dysfunction in up to 80% of the patients assessed.  Gallardo in their series of 76 patients with empty sella syndrome (1992) found endocrine disturbances in 55.3% (hyperprolactinaemia 31.6%, acropmegaly 4%, Cushing’s syndrome 2.6% hypopituitarism 15.8%, diabetes insipidus 2.6%.

Buchfelder (1989) in a series of 52 patients found hyperprolactinaemia in 32.7%, secondary hypogonadism in 7.7%, secondary hypothyrodism in 9.6%, secondary adrenocorticcal failure in 5.8%, growth hormone deficiency in 25.5%, panhypopituitarism in 5.6%.  Only 31% of the patients were referred for endocrinological problems.

Pituitary hypertsecretioon strongly points to the presence of a pituitary adenoma that is partly necrosed.  In cases of mild hyperprolactinaemia delivery of prolactin inhibiting factor may be inhibited by compression, angulation or elongation of the pituitary stallk (similar to a pituitary stalk compression syndrome) was reported in 70% to 76%.  In children evaluated for growth hormone deficiency, primary empty sella varies from 10% to 58%.

Involvement of the posterior pituitary gland occurs very rarely.

In patients with evidence of previous hemorrhage the incidence of pituitary insufficiency is much higher than in those without pituitary apoplexy. 

4) Spontaneous cerebrospinal fluid rhinorrhoea:  The etiology is poorly understood.  Considerable proportions of patients with cerebrospinal fluid rhinorrhoea harbour a pituitary tumour or present radiologically with an empty sella of normal size or an empty sella syndrome.  Incidence of cerebrospinalfluid rhinorrhoes associated with an empty sella is reported up to 15%. 

Investigations: 

Plain skull radiographs:

Empty enlarged sella: radiographs typically show symmetrical enlargement but maintenance of the normal configuration of the sella.  Sometimes demineralization of the dorsum sellae, double contour of the sellar floor and signs of erosion can be observed.  All these findings can occur with pituitary tumors. 

Computer tomography:

An area of hypodensity or decreased attenuation is seen confined to abnormal sized or enlarged sella turcica on a coronal or horizontal plane. In some cases the most specific and sensitive modality for diagnosis is CT scanning employing metrizamide or air contrast.  Magnetic resonance: This is the investigation of choice, which shows cerebrospinal fluid within the sella turcica, discrimination of the pituitary stalk, pituitary gland and optic chiasm, and allows estimation of the degrees of compression, atrophy, and displacement of the structures.  Angiography:

empty sella-MRI.sag

Sometimes bilateral and symmetrical lateral shift of the carotid artery can be seen, or descent of the initial portion of the anterior cerebral artery into the empty sella turcica occurs occasionally. 

Treatment:

Primary as well as secondary empty sella syndrome is usually benign conditions not requiring any treatment. 

However, in some cases the clinical and endocrine status necessitates hormonal replacement therapy.  Evidence of pituitary hypersecretion indicates the presence of a hypersecreting adenoma or remnant or recurrent tumor after surgical resection or radiotherapy that should be treated accordingly. 

Visual field disturbances usually are mild and should therefore only be followed carefully.  Surgery should be reserved for cases with progressive deterioration and radiological evidence of traction or angulation of the optic nerves and chiasm. 

The surgical process of propping up the optic chiasm was called chiasmopexy. Several methods are described with good results:

a) Inserting muscle, carilage, or silicone sponge under the optic chiasm,

b) Packing the sella with fat, muscle, or cartilage to elevate the pituitary gland, pituitary stalk and chiasm via the transsphenoidal route,

c) Packing the sella by transsphenoidal placement of a detachable balloon (Cybulsky 1989),  

d) Mortata (1970) demonstrated improvement of visual field defects in a patient with empty enlarged sella and descent of

CSF rhinorrhoea may require prompt surgical intervention since spontaneous obliteration is unlikely.  After appropriate preoperative localization of the fistulous tract (fluorescein) endoscopic or transsphenoidal closure is the treatment of choice.