Neurosurgery Department, Cork University Hospital, Cork, Republic of Ireland

Transcription

1 J Neurosurg 103: , 2005 Use of a simple intraoperative hydrostatic pressure test to assess the relationship between mobility of the ventricular stoma and success of third ventriculostomy MAHMOUD HAMDY KAMEL, M.S., F.R.C.S., PH.D., MICHAEL KELLEHER, M.D., F.R.C.S., KRISTIAN AQUILINA, F.R.C.S., CHRIS LIM, M.D., A.F.R.C.S.(I), JOHN CAIRD, M.D., F.R.C.S., AND GEORGE KAAR, F.R.C.S.(S/N), PH.D. Neurosurgery Department, Cork University Hospital, Cork, Republic of Ireland T Object. Neuroendoscopists often note pulsatility or flabbiness of the floor of the third ventricle during endoscopic third ventriculostomy (ETV) and believe that either is a good indication of the procedure s success. Note, however, that this belief has never been objectively measured or proven in a prospective study. The authors report on a simple test the hydrostatic test to assess the mobility of the floor of the third ventricle and confirm adequate ventricular flow. They also analyzed the relationship between a mobile floor (a positive hydrostatic test) and prospective success of ETV. Methods. During a period of 3 years between July 2001 and July 2004, 30 ETVs for obstructive hydrocephalus were performed in 22 male and eight female patients. Once the stoma had been created, the irrigating Ringer lactate solution was set at a 30-cm height from the external auditory meatus, and the irrigation valve was opened while the other ports on the endoscope were closed. The ventricular floor ballooned downward and stabilized. The irrigation valve was then closed and ports of the endoscope were opened. The magnitude of the upward displacement of the floor was then assessed. Funneling of the stoma was deemed to be a good indicator of floor mobility, adequate flow, and a positive hydrostatic test. All endoscopic procedures were recorded using digital video and recordings were subsequently assessed separately by two blinded experienced neuroendoscopists. Patients underwent prospective clinical follow up during a mean period of 11.2 months (range 1 month 3 years), computerized tomography and/or magnetic resonance imaging studies of the brain, and measurements of cerebrospinal fluid pressure through a ventricular reservoir when present. Failure of ETV was defined as the subsequent need for shunt implantation. The overall success rate of the ETV was 70% and varied from 86.9% in patients with a mobile stoma and a positive hydrostatic test to only 14.2% in patients with a poorly mobile floor and a negative test (p 0.05). The positive predictive value of the hydrostatic test was 86.9%, negative predictive value 85.7%, sensitivity 95.2%, and specificity 66.6%. Conclusions. The authors concluded that the hydrostatic test is an easy, brief test. A positive test result confirms a mobile ventricular floor and adequate flow through the created ventriculostomy. Mobility of the stoma is an important predictor of ETV success provided that there is no obstruction at the level of the arachnoid granulations or venous outflow. A thin, redundant, mobile third ventricle floor indicates a longstanding pressure differential between the third ventricle and the basal cisterns, which is a crucial factor for ETV success. A positive hydrostatic test may avert the need to insert a ventricular reservoir, thus avoiding associated risks of infection. KEY WORDS cerebrospinal fluid flow obstructive hydrocephalus hydrostatic test endoscopic third ventriculostomy Abbreviations used in this paper: CSF = cerebrospinal fluid; ETV = endoscopic third ventriculostomy. HE recent resurgence of interest in ETV has arisen out of a dissatisfaction with the complications and longterm outcomes of conventional CSF shunt systems. Third ventriculostomy is designed to treat noncommunicating hydrocephalus with patent subarachnoid spaces and adequate CSF absorption. Results of ETV are most closely associated with the origin of hydrocephalus encountered as well as with the clinical and neuroimaging features in an individual. 11 Patients with acquired aqueductal stenosis or tumors obstructing third ventricular outflow have demonstrated the highest success rates following ETV, exceeding 75% in carefully selected series of patients. 5,9,10,13,16,17,21 Among those who have undergone shunt placement, patients with or without myelomeningocele, tumors, or cystic abnormalities leading to fourth ventricular outflow obstruction (for example, arachnoid cysts or Dandy Walker malformations) and patients with congenital aqueductal stenosis have shown an intermediate response. 2,10,13,15,16,22 Infants suffering from hydrocephalus after hemorrhage or infection or with associated myelomeningocele (without a previously inserted shunt) have demonstrated a poor response to ETV. 2 4,6,7,12,17 20 Clinical presentations indicative of elevated intracranial pressure have been associated with the highest rate of ETV success (83%). Patients with other presentations (memory disturbances, incontinence, and focal deficits with associated tumors) have exhibited success rates of approximately 50% or less. Neuroimaging criteria include clear evidence of ventricular noncommunication, favorable third ventricle anatomy with a wide foramen of Monro sufficient to accommodate the endoscope, and a wide, thin, downward bulging floor draped over the clivus. 11 According to data from multiple pediatric studies, there seems to be a significant association between increasing patient age and a more favorable ETV outcome. 3,4,10,13 16,21,22 Results of several stud- 848

2 Hydrostatic test showing endoscopic third ventriculostomy success TABLE 1 Demographic characteristics and disease origin in 30 patients with obstructive hydrocephalus Case Age, No. Sex* Origin 1 34, M aqueductal stenosis 2 16, F aqueductal stenosis 3 15, M aqueductal stenosis 4 9, M aqueductal stenosis 5 14, M aqueductal stenosis 6 23, F midbrain astrocytoma 7 54, M pineal metastases from renal cell carcinoma 8 65, F aqueductal stenosis 9 11, F arachnoid cyst of third ventricle 10 19, M aqueductal stenosis 11 11, F cerebellar astrocytoma 12 24, M midbrain astrocytoma 13 33, M aqueductal stenosis 14 30, M posterior fossa arachnoid cyst 15 31, M previous myelomeningocele, Chiari malformation Type II 16 37, M midbrain astrocytoma 17 9 days, M aqueductal stenosis 18 9, M aqueductal stenosis 19 13, M aqueductal stenosis 20 8 mos, M aqueductal stenosis 21 7 mos, M aqueductal stenosis 22 35, F aqueductal stenosis 23 21, F posterior fossa arachnoid cyst 24 52, M aqueductal stenosis 25 73, M normal-pressure hydrocephalus 26 54, M aqueductal stenosis 27 19, M cerebellar astrocytoma 28 54, M normal-pressure hydrocephalus 29 35, M aqueductal stenosis 30 60, F cerebellar hemorrhagic infarct * Unless otherwise indicated, the listed age represents years. ies show success rates at or below 50% in patients younger than 2 years 10,13,16 or 1 year 3,4,21 of age, regardless of disease origin. Traditional neuroimaging techniques have several limitations in assessing the success of the procedure, mostly in the early postoperative period. Indeed, a decrease in ventricle size is often minimal and not visible before 3 to 4 weeks post-etv. Magnetic resonance imaging studies obtained to detect the presence of a flow void signal through the third ventricle floor reportedly have a significantly high incidence of false positives. 1 All previous studies have been focused on the preoperative prognostic factors or on postoperative neuroimaging data, but how can a surgeon know if the ETV will work intraoperatively? In this report we assessed the intraoperative predictors of ETV success including mobility of the stoma and flow through it by using a simple, objective intraoperative test. Clinical Material and Methods Twenty-two male and eight female patients, ranging in age from 9 days to 73 years, were included in this study. Each patient suffered from obstructive hydrocephalus, whose origins are listed in Table 1. All patients presented with symptoms and signs of increased intracranial pressure, FIG. 1. Illustrations of sagittal section of brain with arrows indicating the direction of CSF flow. Upper: During the first stage of the hydrostatic test, the floor of the third ventricle ballooned downward. Lower: During the second stage of the test, the floor funneled up. The free flow of CSF downward and then upward during the two stages of the funnel test indicates a positive test result. and some presented with manifestations of an underlying tumor. The origin of obstructive hydrocephalus was congenital aqueductal stenosis in 17 patients, tumor of the third ventricle in four (three midbrain tumors and one pineal tumor), tumor of the posterior fossa (cerebellar astrocytoma) in two, posterior fossa cyst in two, normal-pressure hydrocephalus in two, and arachnoid cyst of the third ventricle, myelomeningocele, and cerebellar hemorrhagic infarction in one patient each. During a period of 3 years between July 2001 and July 2004, 30 ETVs for obstructive hydrocephalus were performed using a rigid Gaab 0 neuroendoscope. Once the stoma had been created, the irrigating Ringer lactate solution was set at a 30-cm height from the external auditory meatus, and the irrigation valve was opened for 10 seconds while the other ports on the endoscope were closed. If there is good flow through the stoma, fluid travels into the basal cisterns, accumulating volume there at increased pressure. The floor of the third ventricle ballooned downward and stabilized (Figs. 1 upper and 2 upper left and right). The irrigation valve was then closed and ports of the endoscope were opened. This action caused the accumulated fluid in the basal cisterns to flow back through the opening into the third ventricle, elevating the edges of the stoma. The magnitude of the upward displacement of the floor was 849

3 M. Hamdy Kamel, et al. FIG. 2. Two endoscopic views of a positive hydrostatic test. The floor of the third ventricle ballooned down by irrigation (upper left and right) and funneled up once irrigation was stopped (lower left and right). assessed. Funneling of the stoma was deemed to be a good indicator of floor mobility, adequate flow, and a positive hydrostatic test (Figs. 1 lower and 2 lower left and right). We made a small opening in the dura mater and arachnoid so that the endoscope fit snugly in the cortical tract, with minimal CSF leakage around the endoscope, because this leakage could interfere with the accuracy of the test. All endoscopic procedures were recorded using digital video and recordings were subsequently assessed separately by two blinded experienced neuroendoscopists. Patients underwent prospective clinical follow up for a mean period of 11.2 months (range 1 month 3 years), computerized tomography and/or magnetic resonance imaging studies of the brain, and measurements of CSF pressure through the ventricular reservoir when present. Failure of ETV was defined as a subsequent need for shunt implantation. Results The hydrostatic test was performed in all cases, and we considered the movement of debris or blood through the stoma to be an indication of adequate flow (Table 2). The ETV success rate was 70% overall and varied from 86.9% in patients in whom the hydrostatic test was positive to only 14.2% in patients with a negative test. Test sensitivity was 95.24%, specificity 66.67%, positive predictive value 86.96%, and negative predictive value 85.7% (odds ratio 40, z = 2.96, p = 0.003, 95% confidence interval ; Table 3). In the patient in Case 13 the test was initially negative. On enlarging the stoma and fenestrating a secondary membrane, however, there were dynamic pulsations in the floor of the third ventricle and the test became positive (Fig. 3). Discussion Endoscopic third ventriculostomy is an internal bypass between the third ventricle and the interpeduncular cistern. Thus, all patients with obstructions between the third ventricle and the subarachnoid space are potential candidates for ETV. The more definitive the site of obstruction, the better is the physician s ability to predict the outcome of ETV. 20 Clear neuroimaging evidence of ventricular noncommunication and a wide, thin, downward bulging floor of the third 850

4 Hydrostatic test showing endoscopic third ventriculostomy success TABLE 2 Summary of results of hydrostatic test, success rate, and follow up Case Funnel Successful or Duration of No. Test Failed ETV Follow Up (mos) 1 positive successful 8 2 positive successful 10 3 positive successful 13 4 positive successful 11 5 positive successful 9 6 negative failed (worked 3* for 3 wks) 7 negative successful 9 8 negative failed 0 9 positive successful positive failed 0 11 positive successful positive successful 6 13 positive successful 2 14 positive successful 5 15 negative failed immediately 0 16 positive successful positive failed (worked 2* for 2 wks) 18 positive successful positive successful positive successful positive failed (worked 1* for 1 wk) 22 positive successful positive successful negative failed 0 25 negative failed 0 26 positive successful 1 27 positive successful 1 28 positive successful 1 29 positive successful 1 30 negative failed 0 ventricle draped over the clivus have been associated with a high success rate for ETV. 11 The latter indicates a longstanding pressure differential between the third ventricle and the basal cisterns, which is a crucial factor for ETV success. In this study we assessed the mobility of the third ventricle s floor as a predictor of ETV success by using the hydrostatic pressure test. In cases of obstructive hydrocephalus (usually due to a blocked aqueduct) on irrigating the third ventricle, fluid passes through the stoma into the subarachnoid space thus accumulating fluid under pressure. Once irrigation is stopped and fluid pressure is released, fluid flows backward into the third ventricle, elevating the edges of the newly created stoma and indicating free flow downward and upward through the opening. If the aqueduct is not blocked and there is an element of communicating hydrocephalus, however, fluid will partially escape from the third ventricle into the aqueduct and fluid pressure below the stoma will be low, resulting in a negative hydrostatic test. Moreover, if there is obstruction in the subarachnoid space or a small stoma, insufficient fluid pressure will build up and the test will again register negative results. The importance of this test is twofold: it can be used to assess objectively the mobility of the third ventricle floor and to confirm good flow through the stoma. The ETV success rate was significantly higher in patients with a positive hydrostatic test, that is, in those in whom the TABLE 3 Logistic model for success of hydrostatic test in patients with obstructive hydrocephalus Factor Value no. of positive funnel tests successful ETV 20 unsuccessful ETV 3 no. of negative funnel tests successful ETV 1 unsuccessful ETV 6 false-positive rate for true failure (%) false-negative rate for true success (%) 4.76 false-positive rate for positive funnel test (%) false-negative rate for negative funnel test (%) correctly classified cases (%) floor was mobile with adequate flow through the ventricle (p 0.05). We think that a mobile floor correlates directly with the success of ETV for two reasons. First, a mobile floor is a sign of a dilated third ventricle indicating a pressure differential between the third ventricle and subarachnoid space, confirming the obstructive nature of the hydrocephalus. Second, it indicates good flow through the created stoma. The latter can also help to confirm adequate size of the stoma and rule out the presence of a secondary arachnoid membrane below the stoma, as occurred in the patient in Case 13. Zohdi and Ibrahim 23 reported that the success of ETV could be predicted from the profuse downward flow of CSF through the perforation, the whirl sign. Note, however, that this fluid movement could have been due to irrigation fluid filling a deflated system rather than flow through the stoma. Upward funneling on release of ventricular fluid pressure after stabilization may be a more definite indicator of adequate flow. It is important to note that a positive hydrostatic test indicates a pressure differential and good flow, but ETV success also depends on the absorptive capacity of the subarachnoid FIG. 3. Case 13. Endoscopic view demonstrating a secondary membrane (arrow) underneath the newly created stoma. 851

5 M. Hamdy Kamel, et al. space. Some patients in the present study (Cases 17 and 21) had a positive hydrostatic test with good flow through the stoma and a good initial result for 1 to 3 weeks; thereafter treatment failed despite proof of a working stoma on cine phase-contrast magnetic resonance imaging. The two patients were infants younger than 9 months and had open fontanels. We think that the initial success of the procedure was caused by the presence of a pressure differential between the ventricles and the basal cisterns at an early state. Subsequently, when the subarachnoid space has filled with CSF and its absorption is insufficient, the pressure rises secondarily. Lumbar puncture and withdrawal of CSF following the reemergence of hydrocephalus in the patient in Case 17 led to immediate softening of the fontanels, indicating good flow through the created stoma and conversion from obstructive to communicating hydrocephalus. Funneling may not occur if the third ventricle floor is thick and noncompliant, as in cases of acute hydrocephalus, or if the stoma is very large. Nevertheless, it was easy to interpret test positivity by the free downward and then upward movements of the edge of the stoma in the two stages of the test. The objectivity of the test and its easy interpretation were reinforced by the accurate agreement between the two referees. We also noted the flow of brain particles or even blood through the stoma when fluid pressure was varied another indication of good flow through the stoma. The positive and negative predictive values were high (86.96 and 85.71%, respectively), indicating the test s accuracy and reliability. At our center we do not implant a ventricular access device (half a shunt, or a shunt without a peritoneal catheter) if the test is positive, thus reducing cost and risk of infection. Feng, et al., 8 assessed preoperative prognostic factors in a multiple logistic regression model. They concluded that ETV is most effective in cases of obstructive hydrocephalus caused by aqueductal stenosis and space-occupying lesions. In patients with infections or intraventricular bleeding, ETV has considerable effects in selected cases with confirmed CSF dynamic studies. It would be interesting to know how much information the funnel test adds to these preoperative prognostic factors. We could not address this question on the basis of our data but we will assess it in future studies. The number of cases in this study is small and additional series with a greater number of cases are needed to draw more solid conclusions. Conclusions The results of this case series indicate that there is a correlation between the mobility of the third ventricle floor and the prospective function of ETV. This may be because mobility is a sign of good flow and a dilated third ventricle. 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