DEFINITION AND CLASSIFICATION
The term "primary empty sella "P.E.S" or "intrasellar arachnoidocele" defines an anatomical condition in which the sella turcica is mainly occupied by an arachnoid diverticulum, containiiig cerebro-spinal fluid whilst the abnormally small pituitary gland appears flattened against the infero-posteriorwall of the sella. An inherent feature is the absenxe or extreme incompetence of the diapliragma sellae.
First described by BUSCH in 1951, it was a chance autopsy finding. A later study of 788 autopsies demonstrated this finding in 5.5 percent of cases. Careful study showed altered volume relationship between pituitary and sella turcica in another 19 per cent of cases. The relationship was normal in only 75 percent of cases.
At the same time other Authors reported similar anatomical conditions in patients operated for pituitary tumours or treated with radiotherapy for pituitary tumours. This condition caused a delayed visual deterioration without recurrence of tumour and has been called "empty sella syndrome".Other Authors described true cystic formation into the sella, simulating the "empty sella". Complete different anatomical and pathological conditions were thus grouped under the finition of "empty sella" and therefore, later on, a classification of the various conditions creating an "empty sella" has been suggested. The various types of empty sella can be classified as follows:
A) Primary empty sellar or intrasellar arachnoidocele, partly on a congenital basis.
B) Secondary types of empty sella, due to pituitary infarction, atrophy or spontaneous necrosis of pituitary tumours. Pituitary surgery or radiotherapy.
C) Benign intrasellar cyst, which presents typical anatomo-clinical, radiological and surgical features. Our report is on four cases of "primary empty sella" or "sellar arachnoidocele" corresponding to the first description of BUSCH, and observed in black Eastern African patient.
PYSIOPATHOLOGY OF THE PRIMARY EMPTY SELLA
The "primary empty sella" or "intrasellar arachnoidocele" represents an abnormal dilatation of the mfradiaphragmatic cistern, detrimental to the pituitary gland. A necessary anatomical prerequisite for its formation is an "incompetent" diaphragma sellae, of BUSCH’S third type which is found in normal subjects with a frequency varying between 5.5 and 10 per cent. To explain the pathogenetic mechanism causing the formation of the primary empty sella there are various hypothesis. A first hypothesis, BUSCH 1951, is that a congenitally incompetent diaphragm allows the arachnoid to descend below the diaphragm, alongside the pituitary stalk. Communicating freely with the suprasellar cystems it is intensely pulsatile and this pulsations causes a progressive enlargement of the arachnoid diverticulum and consequent damage to the pituitary gland. Two factors argue against this hypothesis: Firstly the frequency of the empty sella in only the half of cases with incompetent diaphragm; secondly the primary empty sella is much more frequent in the females whereas variations in the diameter of the diaphragm are unrelated to sex.
In the second hypothesis, formulated by KAUFMAN in 1968, increased intracranial pressure ( as in the pseudo tumour cerebri or benign intracranial hypertension) causes hemiation of the arachnoid via the congenitally incompetent diaphragm into the sella turcica. Whilst it is more likely that an empty sella may be formed when there are associated incompetent diaphragm and increased intracranial pressure, it is unlikely and statistically improbable that this mechanism explains the majority of the cases of primary empty sella. A third hypothesis, which nowadays seems the more tenable, is related to the developmental alterations of the pituitary and of the sella. After the first structural changes that occur between birth and about four years of age, the sella remains unchanged until puberty, when progressive enlargement take place until the adult shape is reached. Knowing that the primary empty sella is far more frequent in females and that the pituitary in females is larger than in males, and that the pituitary increases distinctly during pregnancies, it is likely that increased pressure within the pituitary fossa, more than pressure above it, can cause the diaphragm to atrophy. With the volume of the pituitary increasing and decreasing in the females, it is understandable that if there is a congenital wide opening of the diaphragma sellae, there will be a larger space into the infradiaphragmatic cystern such to lead, with the successive pregnancies and subsequent athropy of the diaphragmatic orifice, to the primary empty sella formation. Primary empty sella would be therefore not so much an antomica! variant but the outcome of complex, progressive, paraphyssological phenomena involving mainly the pituitary gland and secondarily the structures surrounding ihe pituitary gland and secondarily the structures surronding the pituitary (sella, diaphragma sellae, arachnoid, cerebro - .spinal fluid)
Typicaiiy the clinical syndrome includes headaches, visual disturbances, obesity with or without disfunction signs in young to middle aged women, more frequently women with several pregnancies.
Neurological signs Headache is the most frequent symptom and is found in about 50 per cent of cases. The hedaches is usually fontal or retrobulbar, severe, continuous. deep. often intractable. Seizures has been reported together with other neurlogical signs from time to time. but too infrequent to be characteristic of the primary empty sella. Visual disturbances are quite frequent and the decrease in visual acuity are often symmetrical and can occur acutely with sudden blindness. Primary optic atrophy is often present. Visual field defects are more irregular, asymmetric, sometime with concentric peripheral constriction.
Diencephalic signs Obesity is quite common, whilst narcolepsy, PICKWICK syndrome, poliuria and polydipsia are rare.
Pituitary endocrine disfunction . Endocrine manifestation vary from case to case, with variable fequencies of presentation. Panhypopituitarism, thyroid insufficiency, adrenal cortex insufficiency, amenorrhoea and various other hypo or hyper pituitary functions has been described. It has become evident that the fault lies with the hypothalamic-pituitary regulation. This is the only constant finding and there is no other endocrine symptomatology characteristic of the primary empty sella.
CSF rhinorrhoea Rarely some cases present with the serious symptoms of cerebro - spinal rhinorrhoea which may be accompaned by recurrent episodes of meningitis. The CSF fistula is usually located in the antero-inferior wall of the sella, which is both a zone of less resistance and also the area most affected by the pulsatile action of the arachnoid diverticulum.
It is apparent that the diagnosis of primary empty sella on clinical data alone is rather problematic. The symptoms are too variable to provide a diagnosis and therefore neuroradiological investigations are essential. Plains films of the skull and tomography of the sella may provide useful informations. Many types of alteration of the sella have been described, the most usual changing being its enlargemet. This is generally mild or moderate and take place in all directions, causing ballooning. It is difficult that bony changes alone are enough to differentiate between an empty sella and a pituitary adenoma. An empty sella of normal size is fairly common (BERNASCONI et al 1972).
The computerized tomography of the head should be helpful in the differentia] diagnosis between empty sella and pituitary tumour: for reliable results a study must include magnified axial and coronal planes, with densilometry of inlrasellar structures. Sometimes the herniation of brain tissue into the sella makes the diagnosis of empty sella difficult also with the CT Scan. The positive contrast eysternography combined with computerized tomography may be the investigation of choice in this cases (HOFMAN et al. 1980).
Although much progress has been made in understanding (lie various problems associated with the primary empty stella. it is still under discussion which method of treatment produces the best results.
In asymptomatic cases, where the intrasellar arachnoidocele is a chance finding, and in cases with minor clinical signs such as headache and obesity, surgery is contraindicated. At the same time, however, surgery will almost always relieve headaches, by decrasing the intrasellar pulsatile pressure. It may therefore be convenient to operate in cases where the headache becomes unbearable and cannot be relieved by medical treatment. Surgery is indicated when there is either a CSF rhinorrhoea or impaired vision, is debatabel in cases of hypotituitarism. Cerebro spinal fluid rhinorrhoea is an indication for urgent surgery, especially when there have been episodes of recurrent meningitis. The repair of the CSF fistula, usually located in the antero - inferior wall of the sella, is very successful and the operation can be carried out through a frontal approach or through a transphenoidal route.
Visual disturbances are not always reversible, despite effective treatment. Established visual field defects and acuity less rarely improve following surgery, but their progress is usually halted and this of itself is a sufficiently good result to he an indication for surgery. A similar argument can be made for an empty sella associated with partial or complete hypopituilarism. Surgical removal of the arachnoidoccle not only relieves pituitary compression and stretching of the infundibulum and the hypothalamus. but at the same time, it ends the effects of the pulsatile pressure of CSF on the pituitary. In this case indications lor surgery are not clear cut, because the hormonal disorder may be not progressive and the post operative recovery of pituitary function is not necessarily assured.
Surgery via upper route allows chiasmapexy by filling the sella with muscle or with gelfoam or with silicone. The upper route also allows the optic structures ot be freed from arachnoidal adhesions if present, hi cases with rhinorrhoea. the upper route can be useful for identifying cxtrusellar fistulas. Surgery through the transplienoid.il or lower route aims at chiasmapexy and removal ol the arachnoid divcrliculum by filling in the residual sellu cavity, by cither an intradural or extradural approach. In agreement with many oilier Authors, it is believed that the traJisphenoulal route is preferable if the primary empty sella can be diagnosed preppcratively, maily because of same results causing less trauma.
Z.A. 45 years old female. Had her first period at the age ol’twelve lor only 6 months. No dcvelopmctn of secondary sexual characters. In 1976, 10 years before admission suirtcd compalining of headaches, loss of vision in the left eye. Two yc-.’rs before admission started left sided rhinorrhea with several episodes of meningitis. The neurological examination showed that she was blind in the left eye. Hail a temporal hemianopia in the right eye. Bilateral primary optic atrophy. She was obese, had an infantile breast, infantile genitalia, lack of pubic and axillary hairs. The plain x-rays of the skull showed a very enlarged primary sella. Tlie left carotid angiography was of no diagnostic help. Endocrine evaluation disclosed hypopiluitarism and hypothyroidism. At operation (transfrontal approach) the sella was found filled up with CSF with a dural defect in the anterior - inferior aspect of the size of 1 mm., the site of the CSF leak. With the aid of the microscope the dural defect wa repaired and the sella filled up with muscle.She was dicharged on endocrine replacemnt therapy. She had an improvement of the visual acuity in the right eye persisting one year after surgery when she was last seen.
B.M. 16 years old female. At the age of 12 years the normal growth arrested. No development of secondary sexual characteristic. Amenorrhea. Two years before ad- mission she started complaining or retrorbital headache and loss of vision in the left eye. On examination she had an infantile aspect. Infantile breast, infantile genitalia, lack of pubic and axillary hair. Bilateral primary optic atrophy. Can see the movements of the hand with the left eye nasally. Can count the fingers with the right eye, better nasally. Endocrine evaluation disclosed hypopituitrism. The skull x-rays showed mild ballooned sella. The C.T. Scan was positive for pituitary tumour. At operation (transfrontal approach) the sella appeared filled up with CSF, the pituitary flattened postero - inferiorly, brain hemiation into the sella. The sella is filled up with muscle. No post - operative treatment was given. She had no visual improvement and at the check up nineteen months later the visual situation was unchanged.
W.N. 31 years old female. Periods at the age of 12. Married with 5 children. Started complaining of headaches and irregularity of her periods followed by loss of vision in the left eye, 2 years before admission. On examination she had primary optic atrophy in the left eye with loss of vision but no visual field defect. Slight obesity. Endocrine evaluatin showed a enlarged primary sella. The CT Scan was not informaive of the diagnosis. At operation (transfrontal approach) the sella appeared filled up with CSF. The sella was filled up with muscle. No post - operative treatment was given. The visual acuity was not changed six years alter surgery.
M.M. 36 years old female. Since three years severe progressive headaches followed by loss of vision and amenorrhea. Has had four children. On examination, obese, is blind in the right eye. can see hand movements in the left eye. Primary optic atrophy more in the right eye. Endocrine evaluatin showed hypotituitarism and hypothyroidism. The plains skull xrays showed only slight ballooning of the sella. The C.T. scan was normal. At operation the sella was filled up with CSF with typical findings of primary empty sella. The sella was filled up with muscle. She was discharged on the endocrine replacement therapy.
She had an improvement in the visual acuity immediately after surgery in the left eye that persisted up to one year after surgery when slie was last seen.
In all our cases the main symptoms were headache, severe visual disturbances and hypothalamic - pituitary disfunction with obesity and hypotituitarism. CSF rhinorrhoea with recurrent mengingitic episodes was present in one case. No epilepsy has been recorded. Contrary to many other reports of primary empty sella with no visual involvement and often no hypopitutarism or other neurological signs and symptoms, our patient had all the full picture of the sellar lesion .with severe visual and pituitary disfunction. This most probably has been the cause for the referral of this patients with a diagnosis of pituitary tunour. In fact the preoperative diagnosis has been of pituitary tumour. In two cases (case one and case two) and optochiasmatic arachnoiditis in the other two cases (case three and case four).
The plain x-rays showed a primary sella in two cases, and ballooning of the sella in other two cases. The C.T. Scan was normal in two cases and showed a possible pituitary tumour in one case. In the first case, only angiography was performed and was reported normal. Certainly the positive contrast cysternography combined with C.T. Scanning may offer better informations in the P.E.S. cases. The operative findings were in all cases typical for P.E.S. with almost absent diaphragma sellae with brain hcmiation into the seila in two cases. In one case the CSF fistula was located antero-inferiorly. All cases were explored through a transfrontal approach: the transphenoidal approach may be better in case of correct , preoperative diagnosis.
The post operative course was uneventful in all cases. Two cases had an improvement, but no deterioration following surgery at the follow up one and six years later. The P.E.S has been found to have an incidence of 3.4 per cent of all cases of sellar and parasellar tumours operated by one of the Authors.