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| Year : 2000 | Volume
: 48
| Issue : 4 | Page : 347-50 |
Preoperative shunts in thalamic tumours.
Goel A
Department of Neurosurgery, King Edward Memorial Hospital and Seth G. S. Medical College, Parel, Mumbai, 400012, India.
Correspondence Address:
Department of Neurosurgery, King Edward Memorial Hospital and Seth G. S. Medical College, Parel, Mumbai, 400012, India.
Thirty one patients with thalamic glioma underwent a pre-tumour resection shunt surgery. The procedure was uneventful in 23 patients with relief from symptoms of increased intracranial pressure. Eight patients worsened after the procedure. The level of sensorium worsened from excessively drowsy state to unconsciousness in seven patients. Three patients developed hemiparesis, 4 developed paresis of extra-ocular muscles and altered pupillary reflexes, and 1 developed incontinence of urine and persistent vomiting. Alteration in the delicately balanced intracranial pressure and movements in the tumour and vital adjacent brain areas could be the probable cause of the worsening in the neurological state in these 8 patients. On the basis of these observations and on review of literature, it is postulated that the ventricular dilatation following an obstruction in the path of the cerebrospinal fluid flow by a tumour could be a natural defense phenomenon of the brain.
How to cite this article:
Goel A. Preoperative shunts in thalamic tumours. Neurol India 2000;48:347 |
[TAG:2]Intorduction [/TAG:2]
Hydrocephalus and resultant raised intracranial pressure, secondary to obstruction at the level of third ventricle, is a common presentation of a moderate to large sized thalamic glioma. A preoperative shunt or some form of ventricular drainage has been advocated to temporarily ameliorate the symptoms, facilitate safe retraction and handling of the brain during the surgery and to prevent future acute rise in intraventricular pressure in case of recurrent tumour growth.[1] Some surgeons advocate the use of bi-ventriculo-peritoneal shunts.[2],[3],[4],[5] There are not many instances of neurological complications, unrelated to the technical problems and the shunt device itself, being reported following shunting procedure in cases of supratentorial intra-axial brain tumours.[6],[7],[8],[9],[10],[11]We report our experience with preoperative shunts in cases with thalamic gliomas. The need for a preoperative shunt operation or any other ventricular cerebrospinal fluid (CSF) drainage procedure is critically analysed.
A total of sixty patients with thalamic gliomas were treated between the years 1986 to 1993 at our Institute. 31 cases underwent a preoperative shunt operation. There were 15 male and 16 female patients in this series and their ages ranged from 7 to 60 years (average 28 years). There was clinical evidence of increased intracranial pressure in all the cases. The clinical features at the time of presentation and their duration are shown in [Table I]. The insertion of a preoperative shunt was usually guided by the severity of the hydrocephalus, size and nature of the tumour, clinical status of the patient and the extent of presumed surgical resectability. The shunt was performed on the side contralateral to the tumour, to avoid interference by the tube during the surgery on the tumour. All cases were investigated with computerised tomography (CT) scanning. Moderate to severe hydrocephalus was present in all the cases. In 2 cases biventriculo-peritoneal shunt was performed, while in the rest, one sided ventriculoatrial (26 cases) or ventriculo-peritoneal (3 cases) shunt was performed. For various reasons, ventriculoperitoneal shunts have been preferred over ventriculoatrial shunts in our department after 1991, the latter being abandoned after 1992.
Preoperative shunt was performed in 31 cases. Manometric intraventricular pressure recordings were not done. In 22 cases 'very high' ventricular CSF pressure was recorded. In other cases this information was not available from the hospital records. In one patient, the shunt had to be revised due to the pericatheter CSF leak. One patient developed shunt infection and the shunt assembly was removed. No patient developed immediate or delayed blockage. Twenty three patients underwent the procedure uneventfully and were relieved of the raised intracranial pressure symptoms to varying degrees.
The neurological condition worsened in [eight] patients after the shunt. These cases have been summarised in [Table II].
Sensorium worsened in seven patients. Of these, 4 became abnormally drowsy (obeyed only simple commands on coaxing) and 3 became unconscious after the insertion of the shunt. In all cases the altered state of sensorium was noticed within 8-10 hours after the insertion of the shunt. The sensorium recovered in about 36 hours in four cases. Rest of the patients were operated upon for the tumour removal in the altered state of consciousness. One patient developed persistent vomiting and incontinence of urine, which lasted for 2 days. Three patients developed hemiparesis on the side contralateral to the tumour. Two patients recovered from hemiparesis within 36 hours. In the third patient hemiparesis progressed to hemiplegia in 24 hours. Three patients developed abnormality of extra-ocular movements and gaze.
The abnormalities included right sixth nerve weakness, restriction of upward gaze and nonparalytic squint with restriction of vertical movements in one patient each. In 2 patients the pupils were noted to be sluggish in reaction and in one there was pupillary inequality. In 2 of these patients a blocked shunt was considered to be the cause of the worsening in sensorium. In one case ventricular tapping was done through an additional burr hole, and in the other case the shunt was revised. The CSF pressure was seen to be low in both of these cases suggesting an adequate functioning of the shunt. In four patients a CT scan was done to assess the intracranial state and to rule out a clot. In all the three patients the ventricles had collapsed in size and there was no evidence of any intracranial haemorrhage. No movement of tumour could be demonstrated on CT.
In our earlier reports on the effect of pre-operative shunt surgery in patients with posterior fossa tumours[12] and extra-axial suprasellar tumours,[13] movements of the tumour towards the brain stem and hypothalamus respectively were observed on the basis of clinical and operative findings. Such a movement was considered to be the cause of neurological worsening and operative difficulties. In the absence of radiological evidence of actual shifts, it was postulated in these reports that the ventricular dilatation in cases of tumour obstructed hydrocephalus could be a natural protective mechanism of the brain. In this retrospective study the effects of a preoperative shunt surgery on intra-axial thalamic tumours have been evaluated.
The ventricular and subarachnoid CSF is the principal buffer system of the brain assisting in accommodating the mass lesion. An intra-axial tumour along with brain reaction in the form of cerebral oedema, results in flattening of the gyri, obliteration of the subarachnoid cisterns and narrowing and displacement of ventricles. Obstructive hydrocephalus results in situations where the tumour obstructs the pathway of cerebrospinal fluid flow. The dilatation of the ventricles is frequently considered to be a part of the pathology and responsible for the prominent presenting symptoms. Preoperative shunt surgery or temporary drainage of CSF or diverting its flow have been advised in various situations. This procedure is done in an attempt to reduce the raised intracranial pressure and relieve the patient's symptoms, to normalise the altered cerebral blood flow and to 'relax' the brain, which would assist the surgeon in the definitive surgical procedure on the tumour.
Ventricular enlargement of moderate to severe degree is present in most cases of large thalamic gliomas. The symptoms of increased intracranial pressure are usually of long duration while the symptoms primarily due to tumour invasion and compression are less frequent and late. The hydrocephalus itself is rarely an emergency. Even though the tumour is responsible for blockage of the CSF pathway, it is only rare that the pathways are totally blocked or that there are no alternative pathway available for the CSF outflow. Such a life threatening raised pressure situation was not encountered in this series, despite the relatively large size of the tumours.
In the present series, neurological status of 8 patients worsened. In the absence of any other explanation for the development of these major neurological complications, it is apparent that an abnormal stretch or pressure on the hypothalamus, internal capsule and midbrain developed after the drainage of the ventricular CSF. Considering the proximity and relationship of thalamic tumours to these structures, it appears that the raised pressure as a result of the obstruction in the CSF pathway was in some way protecting these vital organs.
Haemorrhages in cranial tumours, impaction of the spinal tumours and resultant neurological deficits, and other such events which result following drainage of either ventricular or lumbar cerebrospinal fluid have been frequently reported.[11],[14],[15],[16],[17],[18] Such effects could be due to movements in the lesions secondary to alteration of the critically balanced intracranial pressure mechanism. In cases of thalamic tumour, the dilatation of the lateral ventricles could assist in limiting the tumour pressure over the surrounding vital structures. Sudden drainage of the cerebrospinal fluid from the lateral ventricles could result in superior migration of the tumour and secondary stretch over the internal capsule. hypothalamus, and brain stem. As in the series with suprasellar tumours,[13] it was observed that the tumours were of comparatively large size in those worsened after shunt. Patients with relatively smaller tumours fared well after the shunt surgery. This suggests that the natural protective mechanism of the brain are stretched to their limit in large lesions and any alteration in CSF pressure levels could critically upset the balance.
Our present experience, and that reported earlier,[19] leads to an important clinical observation that the ventricular dilatation following obstruction in the pathways of CSF flow by a tumour could be a natural protective mechanism of the brain. The ventricular dilatation and consequent rise in the supratumoural pressure could be a phenomenon whereby the brain presses over the dome of the tumour to minimise its pressure effects on surrounding vital neural centres so as to preserve functions important for the survival of human being. In the absence of radiological evidence of shifts following a shunting procedure and actual laboratory experimentation, it is hypothesized that preoperative shunt or any form of ventricular drainage could artificially alter the intracranial pressure and can affect the dynamics that is adjusted to an optimum level, by nature, as a part of protection of the body against the growing tumour. This is of course a highly delicate and controversial issue and further studies are warranted before any conclusion can be drawn.
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