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Imaging appearances of programmable ventricular shuntsystems : 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: 10.1594/ecr2012/C-2030

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Learning objectives

To illustrate radiographic appearances of the ventricular shunt system withprogrammable valves which are currently used in Europe and to assist radiologists inthe identification of programmable shunt valves to complete the assessment of skullradiographs in patients with shunts.

Background

Hydrocephalus affects 1-2% of the population. The prevalence of congenital and infantilehydrocephalus 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 rangebetween 3500 and 4000 per year according to the Cambridge based UK Shunt Registry.In the United States, about 125000 shunt procedures are carried out annually.

Although to this date fixed-pressure shunt valves remain the most frequently insertedvalve type in the UK, the adjustable (often-called programmable) valve has becomean important tool in hydrocephalus treatment, particularly in the normal pressurehydrocephalus population and in pediatric patients with complex hydrocephalus.Programmable valves are more expensive, but offer an advantage in that the operatingpressure of the valve can be altered by the use of an external magnet as a simple non-invasive procedure. The proportion of programmable valves used in the UK and Irelandhas increased from 4.9% in 2000 to 22.4% in 2006.

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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 yearthereafter. Manifestations of shunt failure are variable so patients with shunts frequentlyundergo radiographic evaluation. The important part of the evaluations include plainradiographs of the shunt system.

Most CSF shunts consist of 3 components: a ventricular catheter, a valve, and adistal catheter. A shunt is a completely internalized system, as opposed to an externalventricular drain in which a ventricular catheter drains to a collection system at thebedside.

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Fig. 2: Typical ventricularperitonel shunt system with a programmable valve.References: Department of Radiology, National Hospital Neurology and Neurosurgery,UCLH, London/UK 2012The 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 frequentlyimpregnated with radiopaque material to aid in their radiographic visualization. Theventricular catheter sits within 1 of the ventricular spaces in the brain, most commonlythe right lateral ventricle. The ventricular catheter is connected to a valve that regulatesflow. To counter a siphoning effect associated with upright posture, many shunt systemsalso include an antisiphon device or gravitational unit; this reduces overdrainage whenthe patient is standing.

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The gravitational unit is a cylindrical structure and it function of the gravitational unit is toprevent postural overdrainage. Its opening pressure gradually increases as the patientmoves from a supine to an upright position. Multiple models of the gravitational unit areavailable, each with a different maximal opening pressure.

Images for this section:

Fig. 1: Graphic representation of the Miethke proGav valve setting change.

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Fig. 2: Typical ventricularperitonel shunt system with a programmable valve.

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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 mmH2O. The valve component consists of a hyperdense disk with a notched edge andhyperdense valve.

Fig. 3: Radiographic appearance of the Codman Hakim Programmable Valve. Notethat a proper radiograph will be taken when the film is shot perpendicular to the planeof the valve with the non-implanted side of the patient's head resting on the plate. Thefilm 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 orientationmarker. Current product literature states that patients with an implanted Codman HakimProgrammable 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-frequencyenergy to a whole-body-averaged specific absorption rate of 3 watts per kilogram for 15minutes. The manufacturer advises that the setting should checked on a plain radiographafter MR imaging to ensure that no change in opening pressure has occurred.

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Fig. 4: Plain film appearance of the Codman Hakim Programmable ValveReferences: Department of Radiology, National Hospital Neurology and Neurosurgery,UCLH, London/UK 2012

The PS Medical Strata valve (Medtronic, Minneapolis, Minnesota) is an adjustable flow-control valve. The Strata valve has 5 settings or performance level (P/L), ranging from0.5 to 2.5. Each level corresponds to a range of opening pressures and flow rates.

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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 ofopening pressures is between 15 and 170 mm H2O. For example, level 1.5 correspondsto the opening pressure 35 to 95 mm H20 at 0 hyrostatic pressure (patient in the supineposition). Multiple models of the Strata valve have been introduced, including the StrataII valve and the Strata small valve. All make use of the same radiographic scheme forsetting 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 undergoMR imaging by using a static field of #3T but that inadvertent changes of the setting arepossible. It advises that the setting be checked after MR imaging to ensure that this hasnot occurred.

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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 thePolaris. The Polaris valve is a newer valve and it setting is determined by the position ofthe rotating central rectangular structure relative to a fixed peripheral dot.

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Fig. 7: Polaris valve (Low, Standart, and 2 High Pressure valves) as seen on the plainradiograph.References: Reproduced with permission from Sophysa.

Fig. 8: Plain film appearance of the Polaris valve. Note the gravitation unit connectedin line with a shunt.

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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 (openingpressures between 30 and 200 mm H2O). Product literature states that the Polaris hasbeen tested in MR imaging fields #3T and that no inadvertent setting changes have beenseen. The Polaris is also less susceptible to inadvertent setting changes by householdmagnets. Nevertheless, product literature advises that patients with either a Sophy orPolaris 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 dependingon the body position of the patient and consists of 2 components in series, the adjustableunit 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 thehorizontal and vertical positions. The adjustable unit is a circular structure with a rotatingcentral pointer.

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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 toprevent postural overdrainage. Its opening pressure gradually increases as the patientmoves from a supine to an upright position. Multiple models of the gravitational unit areavailable, each with a different maximal opening pressure. This opening pressure of thegravitational 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 productliterature, Aesculap recommends checking the setting of the valve after each MR imaging.

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Fig. 10: Plain film appearance of the Sprung reservoir, proGav valve and Gradient unitshunt 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 avalve. The Sprung Reservoir is flushing reservoir for control of the ventricular catheter'spatency and the distal share of drainage.

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The Miethke Programmable Shunt Assistant (ProSA) (Aesculap(Tuttlingen,Germany) , shunt system has recently been introduced into clinical use. Thevalve 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 2012Its adjustability is supposed to affect CSF drainage only in the vertical body position. TheproSA is an adjustable gravitational valve whose opening pressure automatically adaptsto the patient's body position. In the supine position, the opening pressure of the proSA is0 cmH In this mode, the shunt opening pressure is completely defined by the differentialpressure unit. When the patient is in an upright body position, the gravitational unit and

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the differential pressure unit work together, i.e. the opening pressure of the shunt systemas a whole is the sum of the differential pressure level and the pressure level set at thegravitational 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:

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Fig. 2: Typical ventricularperitonel shunt system with a programmable valve.

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

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Fig. 5: Radiographic appearance of the Cranial Strata valve.

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Fig. 8: Plain film appearance of the Polaris valve. Note the gravitation unit connectedin line with a shunt.

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Fig. 9: Scheme to demonstrate appearance of the proGav valve on the plain film.

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Fig. 10: Plain film appearance of the Sprung reservoir, proGav valve and Gradient unitshunt system.

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Fig. 12: ProSa valve appearance on the skull radiograph.

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Conclusion

Patients who undergo an insertion of the programmable valve often undergo repeatedadjustment of the shunt valve to optimize shunt function. Changes in ventricular calibercan be the result of shunt dysfunction, shunt exchange or simply a change in the valvesetting. For example, enlargement of the ventricles on serial cross-sectional imaging maybe the result of obstruction in the shunt or an intentional increase in the setting of theshunt. Distinguishing between these requires a working knowledge of adjustable valvesin current use and an ability to interpret the valve setting on a plain radiograph. The settingcodes 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 valvesso that they may better assist clinicians in evaluating shunt function. It also providesbrief MR imaging safety information. All adjustable valves described in this poster areMR imaging#compatible up to 3T. They require prompt setting assessment/readjustmentafter each MR imaging to correct potential changes in opening pressure induced bymagnetic fields to avoid an undetected dengerous change in opening pressure.

Personal Information

References

1. Greenberg MS. Handbook of Neurosurgery. 6th ed.New York: ThiemeMedical Publishers; 2006

2. Richards H et al. Are adjustable valves effective? Data from the UKShunt Registry. Cerebrospinal Fluid Research 2007, 4(Suppl 1):S30doi:10.1186/1743-8454-4-S1-S30

3. Stein SC, Guo W. Have we made progress in preventing shunt failure? Acritical analysis. J Neurosurg Pediatr 2008;1:40-47

4. GalliaGL, Rigamonti D, Williams MA. The diagnosis and treatmentof idiopathic normal pressure hydrocephalus. Nat Clin Pract Neurol2006;2:375-81

5. Lollis SS, Mamourian AC, Vaccaro TJ et al Programmable CSF ShuntValves: Radiographic. Identificationand Interpretation. AJNR 2010 31:1343-1346

6. Codman. Procedure Guide. Codman Hakim Programmable Valve systemfor hydrocephalus. http://www.depuy.com/sites/default/files/onlinelib/VAL-10-002_CHPV%20Procedure%20Guide.pdf Accessed January30,2012

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7. Sophysa. Polaris adjustable valve: The MRI compatible valve. http://www.sophysa.com/sophysa-neurosurgical-valve-polaris_142_1.htmlAccessed January 30, 2012

8. Shellock FG, Habibi R, Knebel J. Programmable CSF shunt valve: invitro assessment of MR imaging safety at 3T. AJNR Am J Neuroradiol2006;27:661-65

9. proSA instructions for use. Tuttlingen, Germany: Aesculap http://www.miethke.com/english/3_produkte/3_3_proSA/3_3_1_beschreibung/3_3_1_proSA.htmlAccessed January 30, 2012

10. proGAV- product description http://www.miethke.com/english/3_produkte/3_2_proGAV/3_2_1_beschreibung/3_2_1_proGAV.htmlAccessed January 30, 2012