|Year : 2006 | Volume
| Issue : 1 | Page : 31-32
Coiling of ventriculo-peritoneal shunt in the subdural space: A possible etiology
Sil Kaushik, Sandip Chatterjee
Department of Neurosciences, Park Clinic, Kolkata, India
4,Gorky Terrace, Kolkata-700017
Source of Support: None, Conflict of Interest: None
Migration of ventriculo-peritoneal shunt into the subdural space is a reported but rare complication. We report a case of migration and coiling of both ends of the shunt into the subdural space. We also hypothesize that coiling of the shunt tube during packaging predisposes to elastic recoil and tendency of such migration.
|How to cite this article:|
Kaushik S, Chatterjee S. Coiling of ventriculo-peritoneal shunt in the subdural space: A possible etiology. J Pediatr Neurosci 2006;1:31-2
| Introduction|| |
Internal diversion of cerebrospinal fluid by shunt conduits has evolved a long way since the first description by Torkildsen. Although the various described procedures are fraught with problems, yet this remains the most effective form of relieving hydrocephalus till date. Even after almost 85 years of its evolution, shunt surgery still remains an enigma to every neurosurgeon. This technically simple operation can turn to a nightmare if there is a complication. One of the rare but well described complication is both proximal and distal migration of the shunt tube. We describe a case of total migration and coiling of the shunt tube in the subdural space and provide a possible insight into the etiology of the same.
| Case Report|| |
The index case was a male baby born by Caesarean section. He had a low Apgar score, but was adequately resuscitated. He had a large head (head circumference=37.5 cm), with anterior plagiocephaly and an atretic occipital encephalocele. CT head and MRI Brain showed along with hydrocephalus, he had aqueductal stenosis and corpus callosal agenesis [Figure - 1]. The child had increasing head on serial measurements. A ventriculo-peritoneal shunt using Chhabra medium pressure shunt was done at the age of 1 month and 15 days. The CSF was sterile on culture. Two months later, he presented with repeated vomiting, enlarging head circumference and bulging tense anterior fontanelle. Subsequent CT head showed there was no shunt in the ventricles and the tip was coiled in the subdural space [Figure - 2]. A shunt series showed coiling of the whole shunt into the subdural space [Figure - 3]. The shunt was replaced.
| Discussions|| |
To date there has been only 22 case reports of proximal migration of ventriculo-peritoneal shunt. Of these, 11 were found to be intraventricular, and there are only 3 reported cases of shunt migration into the subdural space. Various causes have been postulated in the literature for this cephalic migration. These include technical faults in fixation, "windlass effect", negative intra- ventricular pressure, positive intra-abdominal pressure, vigorous abdominal peristaltic movements, increased neck movements, increased CSF absorption, tortuous subcutaneous tract and use of unishunt catheter. ,,, Our case was unique in that there was both migration of the ventricular and peritoneal ends of the shunt despite seemingly adequate operative fixation and its subsequent coiling. The coiling occurred within the first two months of shunt implantation and cannot be attributed to the growth of the child, or to any vigorous dynamic translocational or expulsion factors. The shunt used in our case was not an unishunt. The Chhabra shunt system used in our case was a spring valve type of differential pressure shunt. There is a cylindrical side-walled slit valve that is housed in a stainless steel spring to protect the slit valve while maintaining the opening pressure.
We decided to analyze the physical properties of the shunt which could predispose to this migration. The shunt comes in a plastic sterile package in a coiled manner. Any tensile material if it is kept coiled behaves as a spring and follows the Hooke's Law of physics (in any elastic material, stress is proportional to the strain - f=k.u, where f=applied force, k= spring constant and u= deformation sustained due to f). As the spring is stretched in the positive x-direction, the potential energy increases , ( U=1/2 kx 2 where u=potential energy, k= spring constant and x=distance stretched). The tendency for the spring is to therefore decrease its potential energy by returning to its equilibrium (unstretched) position, ( f= -k.x where f= restoring force, x= the distance streched and k=spring constant) thus explaining the migration.
The Spring Rate (K) of an extension spring, calculated as the pounds of load per inch of deflection can be calculated to be thus:
K = G d 4 / 8nD 3
where G= modulus of rigidity of the Material, d= diameter of the wire, n= number of active coils, D= mean coil diameter (outer to inner). Hence the tendency to deform is dependent on the number of coils, the coil diameter, the modulus of rigidity of the shunt material being constant. Translated into the case of the used shunt this means that with the number of coils being small as the packaging is in the nature of few coils, the packaging system may be the incriminating factor in determining migration.
In fact, after the new packaging sytem introduced in the same shunt system, where it now comes in straight packaging, we have not encountered a single case of such migration.
| Conclusions|| |
Packaging of the shunt system in a highly coiled manner may be the main factor which predisposes it to recoil. Straight shunts with connectors are probably the best to prevent such complication.
| References|| |
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[Figure - 1], [Figure - 2], [Figure - 3]