Department of Neurosurgery, Tuen Mun Hospital, Tuen Mun, Hong Kong

Transcription

1 J Neurosurg Pediatrics 12: , 2013 AANS, 2013 Programming jammed Codman Hakim programmable valves: study of an explanted valve and successful programming in a patient Report of 2 cases Sui-To Wong, M.B.B.S., Eleanor Wen, M.B.Ch.B., and Dawson Fong, M.B.B.S. Department of Neurosurgery, Tuen Mun Hospital, Tuen Mun, Hong Kong Malfunction of a Codman Hakim programmable valve due to jamming of its programmable component may necessitate shunt revision. The authors report a method for programming jammed Codman Hakim programmable valves by using a Strata II magnet and additional neodymium magnets. The programming method was derived after studying a jammed valve in the laboratory that was explanted from an 10-year-old boy with a history of fourth ventricle ependymoma. Programming the explanted valve with a Codman programmer failed, but rotating a Strata II magnet above the valve resulted in rotation of the spiral cam in the valve. It was found that the Strata II magnet could be used to program the jammed valve by rotating the magnet 90 or multiples of 90 above the valve. The strength of the magnetic field of the Strata II magnet was able to be increased by putting neodymium magnets on it. The programming method was then successfully used in a patient with a jammed Codman Hakim programmable valve. After successful programming using this method, clinical and radiological follow-up of the patient was advised. ( Key Words Codman Hakim programmable valve malfunction programming failure salvage method hydrocephalus Malfunction of a Codman Hakim programmable valve due to failure of its programmable component usually requires shunt revision; the reported rate of valve explantation for this reason is as high as 9%. 1,3 8,10,11,14 16 The causes of failure of the programmable component include loosening or even dislodgement of the spiral cam (ratchet wheel, stator) and the radiopaque marker, valve damage by direct impact, and extensive deposits within the valve. 7,8,12,13 The dislodgement of the spiral cam has been addressed with design changes in the valve implemented in However, the programmable mechanism of a Codman Hakim programmable valve always involves rotation of the spiral cam by externally applied magnetic force; 2 deposits within a valve always pose the risk of hindering the rotation of the spiral cam, which may cause programming failure, or specifically, a jammed valve. Trou bleshooting methods for a jammed Codman Hakim programmable valve include reverse programming (placing the transmitter upside down against the flow direction) and exposure to the magnetic field of an MRI magnet. 8 In this article, we first report the study of a Codman Hakim programmable valve that was explanted from a patient because of programming failure; we then describe the application of the information obtained in this study to a patient with a jammed Codman Hakim programmable valve. Case 1: Study of a Jammed Codman Hakim Programmable Valve History and Examination. A 10-year-old boy experienced a jammed Codman Hakim programmable valve 2 years after its insertion. This patient had had a WHO Grade II fourth-ventricle ependymoma that was gross-totally excised in June 2010; he also underwent insertion of a ventriculoperitoneal shunt with a Codman Hakim programmable valve because of hydrocephalus. Three months after the shunt insertion, adjuvant radiation therapy was delivered to the tumor bed with a 1-cm margin and a total dose of 46.7 Gy. The boy recovered well and had a Karnofsky Performance Scale score of 80. In the 2 years after the operations, the boy had 6 sets of MR images of the brain and spine obtained using either 1.5-T or 3-T MRI machines; the shunt was reprogrammed and its pressure setting was confirmed with fluoroscopy following each MRI examination. 160 J Neurosurg: Pediatrics / Volume 12 / August 2013

2 Programming jammed Codman Hakim programmable valves The shunt pressure setting was increased stepwise from 60 mm H 2 O to 140 mm H 2 O. In May 2012, after an MRI examination, the pressure setting of the valve decreased to 30 mm H 2 O, and could not be programmed back to the setting before the MRI examination (140 mm H 2 O). Reverse programming with the Codman programmer and exposing the patient to a T2- weighted MRI examination did not change the pressure setting of the valve, 8 and the valve was explanted. Parameters of the CSF samples obtained at the initial shunt insertion and at explantation were both unremarkable (Table 1); swabs of the valve and CSF within the valve at explantation yielded no microbial growth. Investigation of the Explanted Jammed Valve. The following assessment methods were used in the study: 1) visual inspection with an operative microscope was performed to detect structural changes in the valve; 2) fluoroscopy was used to read the pressure setting of the valve, 2 and the angles of a particular pressure setting were measured on the fluoroscopic images with reference to a predefined axis (Fig. 1A); and 3) the lactated Ringer solution infusion technique was used to determine the working pressure of the explanted valve, which was defined as the infusion pressure resulting in a fluid flow compatible with the definition of working pressure. 2 The effects of the following methods on the pressure setting of the explanted valve were assessed: 1) programming with a Codman programmer; 2) rotating a Strata II magnet (Medtronic) above the valve; and 3) exposing the valve to a 3-T MRI magnet. For a Strata II magnet, there are both a magnetic north pole and south pole on its undersurface, and the strength of its magnetic field can be increased by adding magnets (N48 neodymium magnets of inches; Apex Magnet) to its upper surface (Fig. 2). The setup of the Strata II magnet for programming the explanted valve is illustrated in Fig. 1. The explanted valve was placed below the Strata locator tool with the cam of the valve at the center; the Strata II magnet was then placed in the locator tool and turned either clockwise or counterclockwise. Programming with the Codman programmer was conducted by both the usual method and the reverse method. 8 The pressure settings of the explanted valve after each manipulation were recorded using fluoroscopy, and the reference angle measured. When programming using the Strata II magnet, a coupling index was calculated, which was defined as follows: Coupling Index = Change in the cam s angle after rotating the Strata II magnet by X / X A coupling index of 1.0 indicates that the spiral cam rotates together with the Strata magnet completely. A coupling index of 0.0 indicates that the spiral cam does not rotate at all despite rotating the Strata magnet. A smaller coupling index indicates a greater rotational force is required or a greater adhesive force must be overcome when other parameters remain constant. Investigation of a Normal Codman Hakim Programmable Valve. To characterize the effect of a Strata II magnet on a normal Codman Hakim programmable valve, a sample valve was studied using the setup of the experiment as in J Neurosurg: Pediatrics / Volume 12 / August 2013 TABLE 1: Cerebrospinal fluid parameters in Case 1* CSF Parameters Shunt Insertion Shunt Removal protein (g/l) glucose (mmol/l) WBCs (cells/mm 3 ) 4 1 RBCs (cells/mm 3 ) 12 2 smear, culture negative negative * RBCs = red blood cells; WBCs = white blood cells. the study of the explanted valve (Fig. 1). The sample valve was set at several specified pressure levels (30, 60, 90, 120, 150, 180, and 200 mm H 2 O) with a Codman programmer. A Strata II magnet was then rotated above it 90, 180, 270, or 360 in either a clockwise or counterclockwise direction. The coupling index was then calculated. Findings in the Explanted Jammed Valve. Examination under a microscope revealed that the explanted valve was intact, but there were whitish deposits coating the spiral cam, spring, and chassis. The valve pressure setting at explantation was confirmed to be 30 mm H 2 O using fluoroscopy; the corresponding working pressure of the measured valve was 35 mm H 2 O. The pressure settings of the explanted valve after 25 consecutive steps of programming with a Codman programmer or Strata II magnet, or exposure to a 3-T MRI magnet, were recorded. In a Codman Hakim programmable valve, the difference in angle between 2 adjacent pressure settings (a difference of 10 mm H 2 O) was 18 for pressure settings between 30 mm H 2 O and 200 mm H 2 O. When programming with the Codman programmer using the usual method or the reverse method, the pressure setting of the explanted valve did not change to any significant degree; the change in the angle of the spiral cam was at most 16. With the Strata II magnet rotating clockwise, the explanted valve s pressure setting could be increased from 30 mm H 2 O to 180 mm H 2 O; the coupling index was when the valve pressure setting was between 30 mm H 2 O and 110 mm H 2 O, but much smaller ( 0.08) when the pressure setting was greater than 110 mm H 2 O. When the Strata II magnet was rotated counterclockwise, the pressure setting could be decreased from 180 mm H 2 O to 30 mm H 2 O, but the spiral cam could not be rotated further counterclockwise due to the spiral feature of the cam 2 (the coupling index was between 0.10 and 0.21). The explanted valve was brought inside a 3-T MRI suite, placed on the MRI table, and then brought out of the suite; these maneuvers caused only a small change in the pressure setting, from 140 mm H 2 O to 130 mm H 2 O. The working pressure of the explanted valve was measured at 2 additional pressure levels. With pressure settings at 130 mm H 2 O and 180 mm H 2 O, the measured working pressures were 120 mm H 2 O and 165 mm H 2 O, respectively. Findings in the Normal Valve. In the normal valve, when the Strata II magnet was rotated clockwise, the coupling index ranged between 0.17 and 0.71 (mean 0.29), 161

3 S. T. Wong, E. Wen, and D. Fong Fig. 1. Diagrams and photographs showing the setup for programming a Codman Hakim programmable valve with a Strata II magnet. A: Illustration of the cam s angle in relation to the chassis. B and E: Positioning a Strata locator over a Codman Hakim programmable valve. C and F: After putting a Strata II magnet in the locator (B), the starting position of the Strata II magnet is shown. The arrowhead is its magnetic north pole; the Strata II magnet is turned either clockwise or counterclockwise (curved arrows) when programming the valve. D F: Sketch diagrams showing the use of a Strata II magnet on a patient. except for 5 readings when the starting positions of the cam were 60 mm H 2 O or 90 mm H 2 O. When the Strata II magnet was rotated counterclockwise, the coupling index ranged between 0.12 and 0.54 (mean 0.24), except when the starting position of the cam was 30 mm H 2 O, which was expected because of the shape of the spiral cam. 2 After programming the sample valve with the Strata II magnet with and without additional magnets on its upper surface (Fig. 2), the valve could still be successfully programmed with the Codman programmer to all pressure settings between 30 mm H 2 O and 200 mm H 2 O. with rotation of 90, 180, and 360 did not change the valve s pressure setting. With additional neodymium magnets (Fig. 2), rotating 360 clockwise led to an increase of 10 mm H 2 O in the valve s pressure setting. To reach the targeted pressure setting of 180 mm H 2 O, a second 360 rotation was performed and the target pressure setting was reached (Fig. 3); the coupling index was At the time of the 4-month follow-up, the patient was doing well clinically, and serial imaging studies showed increased size of the lateral ventricles compared with the slitlike baseline. Case 2: Programming a Jammed Codman Hakim Programmable Valve History and Examination. This 18-month-old boy with a jammed Codman Hakim programmable valve had undergone shunt insertion for hydrocephalus due to poststreptococcal meningitis at 3 months of age. Initially the shunt pressure was set at 100 mm H 2 O. His head circumference percentile progressively decreased and serial MRI showed small ventricle size; therefore the valve pressure setting was increased stepwise from 100 mm H 2 O to 160 mm H 2 O in an 8-month period. He had 4 sets of MR images obtained during that period, using either 1.5-T or 3-T MRI machines. At 9 months after shunting, after an MRI examination, the pressure setting was jammed at 160 mm H 2 O, despite attempts at increasing it to 180 mm H 2 O. The pressure setting stayed at 160 mm H 2 O despite the reverse programming method and 2 more sets of follow-up MRI examinations. Programming the Jammed Valve. The shunt was not revised because it was structurally intact on radiography, and was functioning clinically. The method we used for Case 2 was based on the study of Case 1 s explanted valve. However, using the Strata II magnet alone, programming Fig. 2. Photographs of the undersurface (A and C) and upper surface (B and D) of a Strata II magnet. The magnetic poles on the undersurface of the Strata II magnet (A) were demonstrated using iron fillings. The Strata II magnet is also pictured with additional magnets to increase the strength of its magnetic field (C and D). The additional magnets used in this study were N48 neodymium magnets inches in size. 162 J Neurosurg: Pediatrics / Volume 12 / August 2013

4 Programming jammed Codman Hakim programmable valves Fig. 3. Fluoroscopic pictures of the valve used in Case 2 before programming with the Strata II magnet (left), and after programming with the Strata II magnet (right) with additional neodymium magnets (Fig. 2). Discussion Jammed Codman Hakim programmable valves may necessitate shunt revision, which can potentially be avoided in some cases if a method for programming jammed valves is available. In the explanted valve we found whitish deposits, as has been reported in the literature. 6,8 However, we could not identify what had caused their formation; the CSF parameters at the time of shunt insertion were normal and there was no shunt infection. In patients with jammed valves, it is likely that deposits inside the valve chamber lead to increased adhesive force between the movable components of the valve, which results in an increase in the force required to rotate the cam. The small coupling index in the explanted valve and in Case 2 s valve supports this hypothesis. Apart from the strength of rotational force required, the coupling index is also affected by other factors, such as the strength of the magnetic fields of the spiral cam and of the Strata magnet, the distance between the valve and the Strata magnet, the thickness of the scalp, and the alignment of the center of the spiral cam with the center of the Strata magnet. Another factor for consideration when managing a jammed Codman Hakim programmable valve is the function of the valve. There is usually a concern that a jammed valve s pressure setting might not reflect its true working pressure. In our explanted valve, we found that there was still satisfactory correlation between the pressure setting and the measured working pressure of the jammed valve, but that was only a single example. Therefore, when a jammed valve is not revised with or without programming using the method illustrated in this report, the patient needs more vigilant clinical and radiological follow-up. Concerning the programming method described here, the Strata II magnet was chosen because it is widely available and the strength of its magnetic field is standardized. We aligned the magnetic north-pole-to-south-pole direction of the Strata magnet with the CSF flow direction of the valve as the starting position of the rotation of the Strata magnet for ease of demonstrating the method (Fig. 1). Actually, the starting position of the magnetic poles of the Strata II magnet is not important, because the cam consists of a circle of micromagnets with their south poles on the upper surface of the cam (Fig. 4). However, the direction of rotation of the Strata magnet (clockwise or counterclockwise) is more important; clockwise is the direction for increasing the pressure setting from 30 mm H 2 O to 200 mm H 2 O, and counterclockwise is the direction for decreasing the pressure setting. And due to specific features of the spiral cam, rotating clockwise beyond 200 mm H 2 O, the pressure falls to 30 mm H 2 O, but when rotating counterclockwise beyond 30 mm H 2 O, movement will be blocked and will not increase to 200 mm H 2 O. 2 Despite the potential use of this programming method, we believe the manufacturer should investigate the use of a standardized but higher power magnet for salvage of jammed Codman Hakim programmable valves. Presently, we use a protocol (Fig. 5) for management of jammed Codman Hakim programmable valves. In successful programming attempts, the patient is monitored clinically and with imaging studies for features of overdrainage and underdrainage; if the shunt system is suitable, measuring the intracranial pressure should be considered. 9 Whether failed Fig. 4. Lateral view of the cam on a suture needle showing the north pole of the cam (A), undersurface of the cam showing the small magnets (the north poles; B), and the upper surface of the cam (the south poles; C). J Neurosurg: Pediatrics / Volume 12 / August

5 S. T. Wong, E. Wen, and D. Fong Fig. 5. Flow chart showing the protocol for management of jammed Codman Hakim programmable shunt (CHPS) valves at our hospital. Asterisk indicates certain patients might be observed without immediate shunt revision. attempts should be followed immediately by shunt revision or a period of observation will depend on the individual clinical situation. In summary, we report a method for programming jammed Codman Hakim programmable valves by using a Strata II magnet and, when necessary, additional neodymium magnets. Disclosure The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper. Author contributions to the study and manuscript preparation include the following. Conception and design: Wong. Acquisition of data: Wong, Wen. Analysis and interpretation of data: Wong. Drafting the article: Wong. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Wong. Study supervision: Fong. Acknowledgment The authors would like to thank Professor Dachling Pang (Oakland, CA) for performing the tumor excision surgery in the patient in Case 1. References 1. Black PM, Hakim R, Bailey NO: The use of the Codman-Medos Programmable Hakim valve in the management of patients with hydrocephalus: illustrative cases. Neurosurgery 34: , Codman: Procedure Guide. Codman Hakim Programmable Valve System for Hydrocephalus. Raynham, MA: Cod man & Shurtleff Inc., 2006 ( com/binary/org/codman/pdf/val chpv-procguide.pdf) [Accessed April 24, 2013] 3. Katano H, Karasawa K, Sugiyama N, Yamashita N, Ohkura A, Kamiya K: Clinical evaluation of shunt implantations using Sophy programmable pressure valves: comparison with Codman- Hakim programmable valves. J Clin Neurosci 10: , Kay AD, Fisher AJ, O Kane C, Richards HK, Pickard JD: A clinical audit of the Hakim programmable valve in patients with complex hydrocephalus. Br J Neurosurg 14: , J Neurosurg: Pediatrics / Volume 12 / August 2013

6 Programming jammed Codman Hakim programmable valves 5. Kestle JRW, Walker ML: A multicenter prospective cohort study of the Strata valve for the management of hydrocephalus in pediatric patients. J Neurosurg 102 (2 Suppl): , Mangano FT, Menendez JA, Habrock T, Narayan P, Leonard JR, Park TS, et al: Early programmable valve malfunctions in pediatric hydrocephalus. J Neurosurg (6 Suppl) 103: , Mauer UM, Kunz U: More malfunctioning Medos Hakim programmable valves: cause for concern? Clinical article. J Neurosurg 115: , Mauer UM, Schuler J, Kunz U: The Hakim programmable valve: reasons for reprogramming failures. J Neurosurg 107: , Pang D, Grabb PA: Accurate placement of coronal ventricular catheter using stereotactic coordinate-guided free-hand passage. Technical note. J Neurosurg 80: , Pollack IF, Albright AL, Adelson PD: A randomized, controlled study of a programmable shunt valve versus a conventional valve for patients with hydrocephalus. Neurosurgery 45: , Rohde V, Mayfrank L, Ramakers VT, Gilsbach JM: Four-year experience with the routine use of the programmable Hakim valve in the management of children with hydrocephalus. Acta Neurochir (Wien) 140: , Sato K, Shimizu S, Utsuki S, Suzuki S, Oka H, Fujii K: Disparity between adjusted and actual opening cerebrospinal fluid pressure in a patient with the Codman Hakim programmable valve: occult form of shunt failure due to head banging. Case report. J Neurosurg (5 Suppl) 105: , Sgouros S, Dipple SJ: An investigation of structural degradation of cerebrospinal fluid shunt valves performed using scanning electron microscopy and energy-dispersive x-ray microanalysis. J Neurosurg 100: , Takahashi Y: Withdrawal of shunt systems clinical use of the programmable shunt system and its effect on hydrocephalus in children. Childs Nerv Syst 17: , Zemack G, Bellner J, Siesjö P, Strömblad LG, Romner B: Clinical experience with the use of a shunt with an adjustable valve in children with hydrocephalus. J Neurosurg 98: , Zemack G, Romner B: Seven years of clinical experience with the programmable Codman Hakim valve: a retrospective study of 583 patients. J Neurosurg 92: , 2000 Manuscript submitted September 10, Accepted April 22, Please include this information when citing this paper: published online May 24, 2013; DOI: / PEDS Address correspondence to: Sui-To Wong, M.B.B.S., Department of Neurosurgery, Tuen Mun Hospital, Tuen Mun, Hong Kong. wongsuito@hotmail.com. J Neurosurg: Pediatrics / Volume 12 / August