In communicating hydrocephalus, ventriculoperitoneal shunt (VPS) is the treatment of choice. Unfortunately, shunt malfunction within 2 years following surgery is reported up to 31%5,8). The diagnosis of shunt malfunction can be challenging since neuroimaging evaluation is not always correlated with clinical outcomes. Cranial computed tomography (CT) often reveals the persistent distension of the cerebral ventricles in clinically improved patients9,10). Invasive cerebrospinal fluid (CSF) dynamic tests have been recommended by neurosurgeons16) to evaluate shunt malfunction.

The CSF shunt tap is another shunt malfunction diagnosis method but it still remains controversial among neurosur-geons13). Therefore, the diagnosis of shunt malfunction remains difficult.

The purpose of this study was to evaluate a simple, minimally invasive CSF lumbar tapping test that predicts under-drainage in hydrocephalus patients with programmable valve shunting devices.

From July 2000 to October 2007, a total of 155 patients had shunt operations using a programmable shunting device (Micro Valve with RICKHAM^® Reservoir, Codman & Shurtleff, Inc., Raynham, MA, USA). Of them, 48 patients underwent CSF lumbar tapping. Twenty patients were males and 28 patients were females. The patients’s ages at implantation ranged from 21 to 78 years (mean, 58.54±14.0 years). The etiologies of hydrocephalus included 16 cases of subarachnoid hemorrhage (SAH) after aneurysmal rupture, 21 cases of traumatic brain in jury (subdural hematoma, SAH, and contusion), 8 cases of in tracerebral hemorrhage and intraventricular hemorrhage (IVH), a case of tumor, a case of arteriovenous malformation and a case of moyamoya disease (Table 1). All patients had communicating type hydrocephalus. Forty-four patients had normal pressure type hydrocephalus (classified as such when lumbar or ventricular tapping pressure is ≤180 mmH₂O, be cause the normal CSF pressure’s upper limit is 180 mmH₂O), and four patients had high pressure type hydrocephalus (classified as such when lumbar or ventricular tapping pressure is >180 mmH₂O). Dilated ventricles, presence of periventricular lucency, effaced cortical sulci, and presence of hydrocephalus symptoms were our indications for shunt operations. In questionable patients, we first performed a lumbar tapping test or drainage test. If there was some improvement of symptoms after daily drainage of 20 mL CSF for 1–3 days or daily lumbar drainage of 100–200 mL CSF for 5–7 days, VPS operation was performed.

Two to 3 weeks after the shunt operation, we evaluated the symptoms of the patients, performed CT, and used a skull X-ray to rule out spontaneous resetting of the valve and routinely per formed CSF lumbar tapping. We compared shunt vale opening pressure and CSF lumbar tapping pressure. Shunt malfunction was suspected by no clinical improvement or enlarged ventricle size on CT scan.

A comparative analysis of 99 cases from 48 patients who had lumbar tapping after VPS operation was performed by comparing shunt valve opening pressure and lumbar tapping pressure. The mean pressure difference of all patients was 2.21±24.57 mmH₂O. The frequency of CSF lumbar tapping was 2.06±1.26 times.

Eighty five cases of 41 patients showed that their VPS function was normal which was consistent with clinical improvement and decreased ventricle size on CT scan. The mean pressure difference in these patients was −3.69±19.20 mmH₂O. The mean frequency of CSF lumbar tapping was 2.07±1.25 times. Fourteen cases of 10 patients revealed suspected VPS malfunction which were consistent with radiological results and clinical symptoms, defined as changes in ventricle size and no clinical improvement. The mean pressure difference was 38.07±23.58 mmH₂O. The mean frequency of CSF lumbar tapping was 1.44±1.01 times. Of them, the VPS of 3 patients initially functioned normally but malfunction was suspected during the follow-up period. The other 7 patients showed the evidence of suspected VPS malfunction and required neurosurgical intervention. The causes of VPS malfunction included 5 cases of tube and VPS valve malfunction, 3 cases of proximal tip obstruction and 2 valve partial obstruction and distal tube obstruction. These patients underwent shunt replacement operations. Two patients who had shunt infection were treated with antibiotics and their shunts were removed. One patient had an IVH after VPS operation. Two patients who had suspected shunt malfunction by enlarged ventricle size on CT scan and no clinical improvement but refused further evaluation such as shuntography or surgical exploration. The mean pressure difference of these two groups (normal function vs. suspected malfunction) was statistically significant. In term of age, sex, mean lumbar tapping time, there were no statistically significant differences. Pressure difference greater than 35 mmH₂O was shown in 2.35% of the normal VPS function group (2 of 85) whereas it was shown in 64.29% of the suspected VPS malfunction group (9 of 14). The difference was statistically significant (p=0.000001) (Table 2). Receiver operating characteristic analysis (ROC) was performed to get the best cut-off value of pressure difference. ROC analysis of pressure difference showed that the area under the curve was 0.91 and the cut-off value was 37.50 with sensitivity of 64.3% and specificity of 98.8% (Fig. 1).

Shunt malfunction after VPS operation is a common problem that leads to severe problems. If undiagnosed and left untreated, permanent neurological injury or death may occur. However, the diagnosis of shunt malfunction can be challenging as neuroimaging results are not always correlated with clinical outcomes.

VPS malfunction is usually suspected if there is no clinical improvement or sustained ventriculomegaly despite of shunt valve opening pressure adjustment. CT often reveals the persistent distension of the cerebral ventricles in clinically improved pa tients9,10). Alternatively normal ventricular size is not enough to rule out shunt malfunction when there is no clinical improve ment17). CSF dynamic tests are made possible through previously inserted subcutaneous reservoir prechamber type shunt valve. The results of the tests in patients underwent VPS have been proved to be effective to rule out shunt malfunction and recommended by some neurosurgeons9,12,16). But the test remains invasive and requires special equipment as well as demands highly skilled technique16).

Sakka et al.15) suggested otoacoustic emission test which is a noninvasive test for VPS functionality but this test is not familiar to neurosurgeons and its efficacy is questionable. Pennell et al.11) suggested noninvasive measurement of VPS malfunction using an ultrasonic transit time flow sensor but this procedure has not yet commercialized and requires insertion of a sensor device during VPS operation. Lumbar tapping CSF pressure measurement is an easy and less invasive test that can be used for hydrocephalus patients with programmable shunt devices.

To the authors’ knowledge, this is the first study of lumbar CSF tapping pressure usage for suspected VPS under- drainage in programmable valve devices.

In our cohort, the normal VPS function group tended to show a lower CSF tapping pressure value compared to programmed shunt valve opening pressure. The pressure differences was −3.69±19.20 mmH₂O. Lower CSF tapping pressure value com pared to the valve opening pressure is predicted over-drainage because the VPS valves we used did not have anti-siphon devices. Programmable shunting device (Micro Valve with RICK HAM^® Reservoir, Codman & Shurtleff, Inc.) was used for all patients in our study. This valve is a differential pressure valve without an anti-siphon device and drains unphysiologically high quantity of CSF (436 mL/h) in the up right position even if the opening pressure is set at 200 mm H₂O14). Therefore, there is a risk or possibility of over-drainage2,7). In some patients, CSF lumbar tapping pressure was higher than the set valve opening pressure which suggested that either they were on bed rest or the VPS was partially functioning. Patients showing irritability or increased blood pressure due to the pain at CSF lumbar tapping procedure may be a contributing factor of a high lumbar tapping CSF pressure. Even in these cases, the pressure difference is usually same and less than 35 mmH₂O. The two standard deviation of the pressure difference of the nor mal VPS function group was 34.71 (−3.69±19.20) mmH₂O. A meaningful value was shown when the pressure difference >40 mmH₂O. Although a pressure difference value of more than 20 mmH₂O was meaningful, 35 mmH₂O was determined as a cut-off value because pressure differences 20–30 mmH₂O were the most frequently shown in the normal VPS function group.

ROC analysis of pressure difference showed that the area under the curve was 0.91 and the cut-off value was 37.50 with specificity of 98.8%. Approximate 35 mmH₂O was determined as a cut-off value because of lowering false positive rate at cut-off value was 37.50 mmH₂O.

The suspected VPS malfunction group tended to show higher CSF tapping pressure values compared to their VPS valve opening pressures. The mean pressure difference was 38.07±23.58 mmH₂O. When measured CSF lumbar tapping pressure was higher than the VPS valve opening pressure, this result may be inferred VPS under-drainage due to VPS malfunction, patients’ positional effects or discordance between the valve opening pressure and the CSF hydrodynamics. So we lowered the valve opening pressure by 30 mmH₂O if patients were tolerable and showed no over-drainage symptoms. Two to 3 weeks after the adjustment of valve opening pressure, we evaluated the symptoms of the patients, performed CT, and used a skull X-ray to rule out spontaneous resetting of the valve. If the patients CT findings sustained enlarged ventricle size or there was no clinical improvement, a shuntography was performed. VPS mal function was determined by shuntography, and the patients underwent VPS revision. Some patients showed rapid deterioration because of complete obstruction by IVH or proximal or distal obstruction or infection. Emergency VPS revision was performed for these patients.

Since Nulsen and Spitz first inserted a modern valve system in a hydrocephalus patient in 1949, fixed pressure valves have been used6). If the valve opening pressure does not match the CSF hydrodynamics of a patient, CSF over-drainage or CSF under-drainage symptoms can develop. When using a fixed pres sure valve, postoperative changes in the valve opening pressure can be accomplished only by performing another operation to insert another pressure-setting valve4). The use of programmable shunt devices offers many advantages in the management of patients with hydrocephalus because they are noninvasive adjust able-pressure valve systems3). So, in the case of over-drainage or under-drainage of CSF, surgeons can adjust the valve opening pressure by making only transcutaneous changes. In this study, a programmable shunting device without an anti-siphon device was used for all patients. Thus, the valve opening pressure could be easily adjusted according to patient symptoms; if over-drain age was suspected the valve opening pressure was elevated and under-drainage was suspected the valve opening pressure was lowered. Nevertheless, it is difficult to differentiate VPS malfunction and under-drainage because their symptoms are similar. Therefore, lumbar tapping pressure can help to diagnose shunt under-drainage. Indeed, in our case, some patients showed no clinical improvement and radiologic changes after the VPS operation, and we repeatedly lowered the valve opening pressure and misdiagnosed as shunt malfunction. Depending on adjust able valve opening pressure, it is possible to misdiagnose the VPS malfunctions. Therefore, it is suggested that under-drain age of CSF should be suspected when the pressure difference between the valve opening pressure and lumbar tapping pres sure is greater than 35 mmH₂O.

Lumbar tapping pressure measurement is an easy and less invasive method to diagnose VPS malfunction. In conclusion, under-drainage of CSF should be suspected if CSF lumbar tapping pressure is 35 mmH₂O higher than the valve opening pressure and shunt malfunction evaluation or adjustment of the valve opening pressure should be made.