The term "empty sella" refers to the anatomic state occurring as the result of intrasellar herniation of the subarachnoid space through an incompetent and enlarged diaphragma sellae. The result is a compressed and posteriorly displaced pituitary gland housed within an enlarged and demineralized sella. These features lend a seemingly "empty" appearance to the sella, both grossly and radio-graphically. It is of clinical, pathophysiologic, and occasionally therapeutic importance to distinguish those cases occurring without an identifiable cause ("primary" empty sella) from those arising as the result of loss of intrasellar volume, which may accompany infarction, surgical resection, or radionecrosis of an intrasellar tumor ("secondary" empty sella).
Though frequently considered the simple consequence of a developmentally enlarged diaphragmatic aperture, the primary empty sella syndrome is a far more complex condition, in which diaphragmatic defects represent only one of several incompletely understood pathophysiologic components. Autopsy studies have repeatedly shown that anatomic defects of the diaphragma sellae of 5 mm or more are present in almost 40% of consecutive autopsies, with more than 20% exhibiting intrasellar extension of the subarachnoid space and 5% showing a fully developed empty sella (142). Insofar as the majority of these findings are incidental autopsy findings in persons without neurological or endocrine symptoms, it is likely that additional factors contribute to the development of the clinical syndrome. One potentially important contributing factor is elevated intracranial pressure. ICP elevations have been documented in patients with the empty sella syndrome, and at least 10% of patients with benign intracranial hypertension also have a coexisting empty sella (143). The latter relationship is especially intriguing in that both syndromes share overlapping clinical profiles.
The overwhelming majority of patients with primary empty sella syndrome are asymptomatic, with their empty sellae being an incidental radiographic finding typically discovered during the investigation of an unrelated complaint. Of the minority of patients who are symptomatic, their clinical profile is often characteristic. More than 80% of symptomatic patients are middle-aged women, many of whom are obese, multiparous, and hypertensive (144). Long-standing headache is the most common and frequently the only presenting complaint. Only rarely are visual field deficits attributable to this syndrome, because symptomatic compression or intrasellar prolapse of the optic chiasm rarely occurs. Complaints of blurred vision or ophthalmologic findings such as papilledema, decreased acuity, enlarged blind spot, and optic atrophy are likely to be the result of coexisting intracranial hypertension. Isolated accounts of atypical facial pain and sensory loss in the distribution of the trigeminal nerve have been noted. Clinically apparent pituitary dysfunction is unusual, although instances of pituitary deficiency, ranging from subtle abnormalities on dynamic endocrine testing (blunted GH response to insulin-induced hypoglycemia) to rare cases of panhypopituitarism, have periodically been reported (144,145). Moderate hyperprolactinemia, as the result of stalk compression, has been variably reported in approx 5% of patients (146). Hypersecretion of other anterior pituitary hormones suggests a coexisting pituitary adenoma. Finally, CSF rhinorrhea is a complication of empty sella syndrome in approx 10% of patients (147,148). As the result of CSF pulsations, the sella floor becomes progressively thinned, eventually providing communication between the intrasellar subarachnoid space and the sphenoid sinus.
The radiologic diagnosis of this entity is usually straightforward. Lateral skull X-rays reveal a symmetrically enlarged and thin-walled sella, one that retains its normal configuration. Both CT and MRI scanning show clearly the CSF space extending from the hypothalamus down to a flattened pituitary gland, a finding that virtually excludes the possibility of other cystic lesions. If the diagnosis is still in doubt, CT cisternography demonstrates filling of the sella and conclusively secures a diagnosis of empty sella syndrome.
This entity is the occasional consequence of prior surgical therapy or radio-necrosis of an intrasellar tumor. Occasionally, the condition may occur long after auto-infarction of a pituitary adenoma or a nontumorous pituitary gland, as may occur with apoplexy and Sheehan's syndrome, respectively. The diaphragma may be either developmentally deficient, eroded by the tumor, or disrupted by therapeutic intervention, thus permitting the descent of the chiasmatic cistern into the sella. Intrasellar prolapse of the optic chiasm is a frequent accompaniment, wherein it becomes entrapped and kinked by adhesions and scar tissue.
Clinically, the secondary empty sella syndrome is distinct from the primary form. Both sexes are equally affected, and there is no predilection for any particular body habitus. Visual dysfunction is the most common presenting symptom and may occur weeks or even years after surgery or radiotherapy. Bitemporal and binasal hemianopic defects, as well as asymmetrical deficits in the form of constrictions, segmental defects, or scotomas, may occur. The visual loss is often progressive; however, abrupt deterioration has also been known to occur. Endocrine dysfunction is not unusual and is likely to be the residual effect of prior surgery and/or radiation for an intrasellar tumor and not the result of secondary empty sella. Elevated ICP, headache, and CSF rhinorrhea are occasional features of this condition.
Relatively few patients with primary or secondary empty sella syndrome require surgical intervention. After establishing the diagnosis and excluding other intrasellar cystic pathologies, the management of these conditions rests primarily on the recognition and treatment of potential complications (endocrine, ophthalmologic, and CSF rhinorrhea). The endocrine status of the patient requires careful laboratory evaluation, both at the time of diagnosis and periodically thereafter. Hypopituitarism, if present, requires appropriate hormone replacement therapy. Except for the case of low-grade hyperprolactinemia, hormonal hypersecretion warrants the exclusion of a coexisting hypersecreting microadenoma with MRI. When radiologically occult GH, adrenocorticotrophic hormone (ACTH), or prolactin-secreting microadenomas are suspected, transsphenoidal exploration may be necessary. Low-grade hyperprolactinemia (of stalk compression origin), because of its long-term adverse effects, should be treated if associated with symptoms of hypogonadism, such as amenorrhea, and is often exquisitely responsive to low-dose dopamine agonist therapy.
Deteriorating visual function necessitates careful evaluation. In primary empty sella syndrome, this is usually the result of benign intracranial hypertension. Accordingly, appropriate therapy for the latter should be initiated. Documented progressive visual loss in the case of the secondary empty sella syndrome is usually the result of chiasmal prolapse, the extent of which can be assessed with MRI. In such cases, transsphenoidal exploration and elevation of the chiasm with fat or muscle ("chiasmopexy") may halt progression of visual loss, and in some instances may actually improve vision (149), although this is controversial.
CSF rhinorrhea, because it seldom stops spontaneously, virtually always requires definitive operative repair. The usual cause is a transsellar fistula into the sphenoid sinus; however, occasionally the site of leak may be along the anterior fossa floor. Accordingly, preoperative radiologic visualization of the precise site of leak is always desirable. This is best achieved by high-resolution coronal CT cisternography. For transsellar leaks, transsphenoidal exploration, sealing the leak with fibrin glue, and packing the sella and sphenoid sinus with fat or fascia constitute the treatment of choice. Leaks from the anterior fossa floor require repair by frontal craniotomy. Transnasal endoscopic methods are sometimes useful for the repair of such leaks.
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