Imaging appearances of programmable ventricular shunt systems : What the radiologist needs to know

Transcription

1 Imaging appearances of programmable ventricular shunt systems : What the radiologist needs to know Poster No.: C-2030 Congress: ECR 2012 Type: Educational Exhibit Authors: A. Gontsarova, S. C. Thust, J. Shand Smith, H. S. CHANDRASHEKAR; London/UK Keywords: Cerebrospinal fluid, Technical aspects, Surgery, Shunts, MR, CT, Conventional radiography, Neuroradiology brain DOI: /ecr2012/C-2030 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 25

2 Learning objectives To illustrate radiographic appearances of the ventricular shunt system with programmable valves which are currently used in Europe and to assist radiologists in the identification of programmable shunt valves to complete the assessment of skull radiographs in patients with shunts. Background Hydrocephalus affects 1-2% of the population. The prevalence of congenital and infantile hydrocephalus lies between 0.48 and 0.81 per 1000 births (including live and still births). In the United Kingdom and Ireland, the number of shunt operations is estimated to range between 3500 and 4000 per year according to the Cambridge based UK Shunt Registry. In the United States, about shunt procedures are carried out annually. Although to this date fixed-pressure shunt valves remain the most frequently inserted valve type in the UK, the adjustable (often-called programmable) valve has become an important tool in hydrocephalus treatment, particularly in the normal pressure hydrocephalus population and in pediatric patients with complex hydrocephalus. Programmable valves are more expensive, but offer an advantage in that the operating pressure of the valve can be altered by the use of an external magnet as a simple noninvasive procedure. The proportion of programmable valves used in the UK and Ireland has increased from 4.9% in 2000 to 22.4% in Page 2 of 25

3 Fig. 1: Graphic representation of the Miethke progav valve setting change. References: Reproduced with permission from Aesculap, Inc. One-third of all shunts fail within 1 year of placement, and in children 4.5% per year thereafter. Manifestations of shunt failure are variable so patients with shunts frequently undergo radiographic evaluation. The important part of the evaluations include plain radiographs of the shunt system. Most CSF shunts consist of 3 components: a ventricular catheter, a valve, and a distal catheter. A shunt is a completely internalized system, as opposed to an external ventricular drain in which a ventricular catheter drains to a collection system at the bedside. Page 3 of 25

4 Fig. 2: Typical ventricularperitonel shunt system with a programmable valve. References: Department of Radiology, National Hospital Neurology and Neurosurgery, UCLH, London/UK 2012 The catheter components of a shunt are made from Silastic (Dow Corning, Midland, Michigan), a form of rubber tubing resistant to breakdown in the body. They are frequently impregnated with radiopaque material to aid in their radiographic visualization. The ventricular catheter sits within 1 of the ventricular spaces in the brain, most commonly the right lateral ventricle. The ventricular catheter is connected to a valve that regulates flow. To counter a siphoning effect associated with upright posture, many shunt systems also include an antisiphon device or gravitational unit; this reduces overdrainage when the patient is standing. Page 4 of 25

5 The gravitational unit is a cylindrical structure and it function of the gravitational unit is to prevent postural overdrainage. Its opening pressure gradually increases as the patient moves from a supine to an upright position. Multiple models of the gravitational unit are available, each with a different maximal opening pressure. Images for this section: Fig. 1: Graphic representation of the Miethke progav valve setting change. Page 5 of 25

6 Fig. 2: Typical ventricularperitonel shunt system with a programmable valve. Page 6 of 25

7 Imaging findings OR Procedure details The Codman Hakim Programmable Valve (Codman/Johnson & Johnson, Raynham, Massachusetts) permits regulation of the opening pressure between 30 and 200 mm H2O. The valve component consists of a hyperdense disk with a notched edge and hyperdense valve. Fig. 3: Radiographic appearance of the Codman Hakim Programmable Valve. Note that a proper radiograph will be taken when the film is shot perpendicular to the plane of the valve with the non-implanted side of the patient's head resting on the plate. The film must be taken in relation to the valve and not the patient's anatomy. References: Reproduced with permission from Codman/Johnson & Johnson. The valve setting is interpreted on the basis of the position of the notch and orientation marker. Current product literature states that patients with an implanted Codman Hakim Programmable Valve can safely undergo MR imaging under the following conditions: 1) static magnetic field of #3T 2) spatial gradient of #720 G/cm and 3) limited radio-frequency energy to a whole-body-averaged specific absorption rate of 3 watts per kilogram for 15 minutes. The manufacturer advises that the setting should checked on a plain radiograph after MR imaging to ensure that no change in opening pressure has occurred. Page 7 of 25

8 Fig. 4: Plain film appearance of the Codman Hakim Programmable Valve References: Department of Radiology, National Hospital Neurology and Neurosurgery, UCLH, London/UK 2012 The PS Medical Strata valve (Medtronic, Minneapolis, Minnesota) is an adjustable flowcontrol valve. The Strata valve has 5 settings or performance level (P/L), ranging from 0.5 to 2.5. Each level corresponds to a range of opening pressures and flow rates. Page 8 of 25

9 Fig. 5: Radiographic appearance of the Cranial Strata valve. References: Department of Radiology, National Hospital Neurology and Neurosurgery, UCLH, London/UK 2012 Generally, a lower performance level corresponds to a lower pressure. The range of opening pressures is between 15 and 170 mm H2O. For example, level 1.5 corresponds to the opening pressure 35 to 95 mm H20 at 0 hyrostatic pressure (patient in the supine position). Multiple models of the Strata valve have been introduced, including the Strata II valve and the Strata small valve. All make use of the same radiographic scheme for setting assessment; the position of a notched disk relative to 2 small dots defines the P/ L setting. Current product literature states that patients with Strata valves may undergo MR imaging by using a static field of #3T but that inadvertent changes of the setting are possible. It advises that the setting be checked after MR imaging to ensure that this has not occurred. Page 9 of 25

10 Fig. 6: Plain Film appearance of the Strata Valve used in lumbar peritoneal shunt. References: Department of Radiology, National Hospital Neurology and Neurosurgery, UCLH, London/UK 2012 Sophysa (Orsay,France) has developed 2 programmable valves, the Sophy and the Polaris. The Polaris valve is a newer valve and it setting is determined by the position of the rotating central rectangular structure relative to a fixed peripheral dot. Page 10 of 25

11 Fig. 7: Polaris valve (Low, Standart, and 2 High Pressure valves) as seen on the plain radiograph. References: Reproduced with permission from Sophysa. Fig. 8: Plain film appearance of the Polaris valve. Note the gravitation unit connected in line with a shunt. Page 11 of 25

12 References: Department of Radiology, National Hospital Neurology and Neurosurgery, UCLH, London/UK 2012 The Polaris valve permits a total of 5 positions; in the most common SPV model (opening pressures between 30 and 200 mm H2O). Product literature states that the Polaris has been tested in MR imaging fields #3T and that no inadvertent setting changes have been seen. The Polaris is also less susceptible to inadvertent setting changes by household magnets. Nevertheless, product literature advises that patients with either a Sophy or Polaris valve have their setting checked immediately after MR imaging. The Miethke progav Programmable Shunt System (Aesculap, Tuttlingen, Germany) is a posture-dependent valve. This means that the opening pressure varies depending on the body position of the patient and consists of 2 components in series, the adjustable unit and the gravitational unit. In order to configure the progav according to the patient s individual needs, the surgeon determines the opening pressure required for both the horizontal and vertical positions. The adjustable unit is a circular structure with a rotating central pointer. Page 12 of 25

13 Fig. 9: Scheme to demonstrate appearance of the progav valve on the plain film. References: Reproduced with permission from Aesculap, Inc. The adjustable unit can be changed to a pressure setting between 0 and 20 cm H2O. The gravitational unit is a cylindrical structure and it function of the gravitational unit is to prevent postural overdrainage. Its opening pressure gradually increases as the patient moves from a supine to an upright position. Multiple models of the gravitational unit are available, each with a different maximal opening pressure. This opening pressure of the gravitational component is determined by the number of rings at the end of the cylinder (0-4 rings) and the size of the component itself (small versus large) In its current product literature, Aesculap recommends checking the setting of the valve after each MR imaging. Page 13 of 25

14 Fig. 10: Plain film appearance of the Sprung reservoir, progav valve and Gradient unit shunt system. References: Department of Radiology, National Hospital Neurology and Neurosurgery, UCLH, London/UK 2012 Some times an additional componet called Sprung Reservoir is connected in line with a valve. The Sprung Reservoir is flushing reservoir for control of the ventricular catheter's patency and the distal share of drainage. Page 14 of 25

15 The Miethke Programmable Shunt Assistant (ProSA) (Aesculap (Tuttlingen,Germany), shunt system has recently been introduced into clinical use. The valve appears simmilar to the progav valve on the plain film. Fig. 11: Scheme to demonstrate appearance of the prosa valve on the plain film. References: Department of Radiology, National Hospital Neurology and Neurosurgery, UCLH, London/UK 2012 Its adjustability is supposed to affect CSF drainage only in the vertical body position. The prosa is an adjustable gravitational valve whose opening pressure automatically adapts to the patient's body position. In the supine position, the opening pressure of the prosa is 0 cmh In this mode, the shunt opening pressure is completely defined by the differential pressure unit. When the patient is in an upright body position, the gravitational unit and Page 15 of 25

16 the differential pressure unit work together, i.e. the opening pressure of the shunt system as a whole is the sum of the differential pressure level and the pressure level set at the gravitational unit. Fig. 12: ProSa valve appearance on the skull radiograph. References: Department of Radiology, National Hospital Neurology and Neurosurgery, UCLH, London/UK 2012 Images for this section: Page 16 of 25

17 Fig. 2: Typical ventricularperitonel shunt system with a programmable valve. Page 17 of 25

18 Fig. 4: Plain film appearance of the Codman Hakim Programmable Valve Page 18 of 25

19 Fig. 5: Radiographic appearance of the Cranial Strata valve. Page 19 of 25

20 Fig. 8: Plain film appearance of the Polaris valve. Note the gravitation unit connected in line with a shunt. Page 20 of 25

21 Fig. 9: Scheme to demonstrate appearance of the progav valve on the plain film. Page 21 of 25

22 Fig. 10: Plain film appearance of the Sprung reservoir, progav valve and Gradient unit shunt system. Page 22 of 25

23 Fig. 12: ProSa valve appearance on the skull radiograph. Page 23 of 25

24 Conclusion Patients who undergo an insertion of the programmable valve often undergo repeated adjustment of the shunt valve to optimize shunt function. Changes in ventricular caliber can be the result of shunt dysfunction, shunt exchange or simply a change in the valve setting. For example, enlargement of the ventricles on serial cross-sectional imaging may be the result of obstruction in the shunt or an intentional increase in the setting of the shunt. Distinguishing between these requires a working knowledge of adjustable valves in current use and an ability to interpret the valve setting on a plain radiograph. The setting codes can be found in the each manufacturer manual which are readily available on-line. This poster provides radiologists and radiographers with a guide to programmable valves so that they may better assist clinicians in evaluating shunt function. It also provides brief MR imaging safety information. All adjustable valves described in this poster are MR imaging#compatible up to 3T. They require prompt setting assessment/readjustment after each MR imaging to correct potential changes in opening pressure induced by magnetic fields to avoid an undetected dengerous change in opening pressure. Personal Information References Greenberg MS. Handbook of Neurosurgery. 6th ed.new York: Thieme Medical Publishers; 2006 Richards H et al. Are adjustable valves effective? Data from the UK Shunt Registry. Cerebrospinal Fluid Research 2007, 4(Suppl 1):S30 doi: / s1-s30 Stein SC, Guo W. Have we made progress in preventing shunt failure? A critical analysis. J Neurosurg Pediatr 2008;1:40-47 GalliaGL, Rigamonti D, Williams MA. The diagnosis and treatment of idiopathic normal pressure hydrocephalus. Nat Clin Pract Neurol 2006;2: Lollis SS, Mamourian AC, Vaccaro TJ et al Programmable CSF Shunt Valves: Radiographic. Identificationand Interpretation. AJNR : Codman. Procedure Guide. Codman Hakim Programmable Valve system for hydrocephalus. VAL _CHPV%20Procedure%20Guide.pdf Accessed January 30,2012 Page 24 of 25

25 7. Sophysa. Polaris adjustable valve: The MRI compatible valve. Accessed January 30, Shellock FG, Habibi R, Knebel J. Programmable CSF shunt valve: in vitro assessment of MR imaging safety at 3T. AJNR Am J Neuroradiol 2006;27: prosa instructions for use. Tuttlingen, Germany: Aesculap english/3_produkte/3_3_prosa/3_3_1_beschreibung/3_3_1_prosa.html Accessed January 30, progav- product description english/3_produkte/3_2_progav/3_2_1_beschreibung/3_2_1_progav.html Accessed January 30, 2012 Page 25 of 25