Mechanical shunt failure in hydrocephalus: a common but remediable complication with technical nuances

Background A ventriculoperitoneal (VP) shunt is a cerebral shunt that diverts excess cerebrospinal fluid (CSF). Obstruction in the normal outflow or decreased absorption of the fluid is the usual cause. Hydrocephalus is treated by cerebral shunts.In paediatric patients, untreated hydrocephalus can be lethal and leads to many adverse effects including increase irritabilities, chronic headaches, learning difficulties, visual disturbances, and, in more advanced cases, severe mental retardation. Malfunction of the shunt with excess CSF accumulated can increase the intracranial pressure resulting in cerebral oedema and ultimately herniation. Objective To study and evaluate the mechanical causes of shunt failure and their surgical remedies and reduce the preventable morbidity, cost and mortality associated with shunt failure. Methods We conducted a prospective observational study including 70 patients who developed pure mechanical shunt failure for the first time from 2017 to 2020 in the Department of Neurosurgery Sher-i-kashmir Institute of Medical Sciences. Patients with previous shunt surgeries which include VP shunting and shunt revision or failure and shunt infections were excluded. Identity of all the patients has been kept anonymus. Written informed consent was obtained from all patients or their guardians in case of minors. Shunt malfunction was in the form of catheter misplacement, kinking, displacement from the ventricle or peritoneal cavity, disconnection, migration,inadvertent suturing of the catheter, air in shunt bulb. Results We found kinking at the proximal end in 25 (35%) patients as the most common cause of shunt failure. It was mostly as a result of inadequate and less spacious tunnelling made for the reservoir. Inadvertant suturing of shunt while closing abdomen in 7 (10%), shunt disconnection in 6 (8.5%), air in shunt bulb in 2 (2.8%), wrong placement at ventricular end in 10 (14.2%), shunt migration into the brain parenchyma in 5 (7.1%), shunt migration through the anal canal in 1(1.4%), pseudomeningocele around catheter valve in 3 (4.2%), placement of lower end into the preperitoneal space in 4 (5.7%) patients. Conclusions Shunt surgery is seemingly a straightforward operation for neurosurgeons. But considering the incidence of shunt failure and its associated morbidity and mortality, it should always be done with trepidation and extreme caution. Exclusive mechanical shunt malfunction is a major concern and leads to great deal of morbidity in the shunt operations. However, there are trivial remedies and technical nuances which needs to be followed during surgery to avoid these complications.


Introduction
A ventriculoperitoneal (VP) shunt is a cerebral shunt that diverts excess cerebrospinal fluid (CSF).Obstruction in the normal outflow or decreased absorption of the fluid is the usual cause.Hydrocephalus is treated by cerebral shunts.In paediatric patients, untreated hydrocephalus can be lethal and leads to many adverse effects including increase irritabilities, chronic headaches, learning difficulties, visual disturbances, and, in more advanced cases, severe mental retardation [1,2].Malfunction of the shunt with excess CSF accumulated can increase the intracranial pressure resulting in cerebral oedema and ultimately herniation.These shunts drain the CSF into the peritoneal cavity, the atrium, or the pleura, thus appropriately called ventriculoperitoneal, ventriculoatrial, and ventriculopleural shunts.CSF shunt systems fail up to 85% within 10 years from initial insertion [3,4].Hospitalisations for hydrocephalus have reached alarming 70,000 per year in the USA.Almost every patient with hydrocephalus (98%) will experience shunt failure in their lifetime [5].50% of failures occur due to tissue obstruction of the proximal (i.e.ventricular) catheter within the paediatric population [6] .The aetiology underlying this failure are still poorly understood.It was Sekhar et al. [7] who provided the description of the cell types involved in shunt catheter occlusion, and more studies have showed that astrocytes and microglia play a key role in this tissue obstruction [8].
Objective We studied and evaluated the seemingly trivial but important pure mechanical causes of shunt failure and their remedies to reduce the preventable morbidity, cost and mortality associated with shunt failure.

Methods
Our prospective observational study included 70 patients who developed pure mechanical shunt failure for the first time from 2017 to 2020 in the Department of Neurosurgery Sher-i-kashmir Institute of Medical Sciences.Patients with previous shunt surgeries which include VP shunting and shunt revision or failure and shunt infections were excluded.We have de-identified all the patients in the study.Written informed consent was obtained from all patients or their guardians in case of minors.Shunt malfunction was in the form of catheter misplacement, kinking, displacement from the ventricle or peritoneal cavity, disconnection, migration, inadvertent suturing of the catheter, air in shunt bulb.We have de-identified all patients defined shunt failure as the requirement for additional shunt surgery for any part of the shunt system because of mechanical shunt fault.Clinical criteria for shunt impairment required a history compatible with neurological decline confirmed by CT or MRI changes.The patient characteristics were studied according to age, sex, mechanism of hydrocephalus,prognosis, and clinical features.We used frontal approach in 22 patients where Kocher's point is used which is an entry point that is 11 cm superior and posterior from the nasion, 3 cm off the midline along the mid-pupillary line, and 1 to 2 cm anterior to the coronal suture; catheter was passed to a depth of 5-6 cm.We performed parieto-occipital approach in 48 patients where Keen's point is used which is approximately 2.5 to 3 cm superior and posterior to the pinna and the catheter was advanced to a depth of 4 to 5 cm.

Results
Thee age range of the study patients was between 1 week and 65 years admitted to SKIMS tertiary care hospital and included purely mechanical shunt failure during 2017 to 2020 for first time.Forty-five (64.2%) patients were male and 25 (35.7%) were female.Forty-five (64.2%) patients were infants, 7 (10%) were in toddler age group and 18 (25.7%)were adults.The most common cause was congenital abnormalities (68.5%) followed by tumour (14.2%), post-traumatic (8.5%) and post-hemmorhagic(8.5%)as shown in Table 1.
Infants mostly presented with abnormal increase in head circumference (71.1%) followed by bulging fontanelle (42.2).Delayed development, sunset sign,vomiting in gushes, irritability and reduced consciousness were the other clinical features.Toddlers and adults presented with a different set of clinical features, most common being headache(88%) followed by nausea and vomiting(40%).Diplopia, irritability and seizures were the other features as shown in Table 2.
Frontal approach was used in 22 patients where Kocher's point was used.We used Keen's point in 48 patients.Kinking at the cranial end (35%) was the most common culprit for mechanical shunt failure.Inadvertent suturing of the shunt while closing abdominal wound was responsible in (10%) of cases.Shunt disconnection at the Shunt migration of the proximal end of catheter into the brain parenchyma as shown in Fig. 1 and shunt migration of the distal end of catheter through the anal canal were responsible for shunt malfunction in 5 and 1 patients, respectively.
Wrong placement of catheter at ventricular end with tip of catheter crossing septum pellucidum as shown in Fig. 2,(4), catheter just touching the frontal horn (4), catheter tip in supra-sellar cistern (2) was found in 10 (14.2%) patients.
We found lower end of shunt into the preperitoneal space with collection at the abdominal end in 4( 5.7%) cases and pseudomeningocoele at the valve site in 3(4.2%) cases which was responsible for shunt failure as shown in Table 3.

Discussion
This prospective observational study evaluating 70 patients established the trivial yet indispensable and correctable causes of pure mechanical shunt failure.Most shunt malfunctions were because of kinking of the catheter at the proximal end.

Interpretation of findings
In our study,VP shunt failure occurred at the site of the proximal catheter, the valve, or the distal catheter.Our first finding was that shunt failure was predominant in male group than in female group.Most of the studies reported that VP shunt complications occurred more common in males than females [9], which was compatible with the current study as males represent 64.2% of the cases.Although the incidence of hydrocephalus is almost equal in both genders,still the shunt related problems occurring more in males needs to be elucidated further.
Our second finding was the higher risk of shunt failure in patients of younger age which was consistent with various reports that mostly depicted that the younger age group had higher shunt.malfunction rates [10,11] [12][13][14].However, multiple studies did not find age as a risk factor for shunt malfunction [15,16] As the patients with congenital hydrocephalus undergo shunt placement earlier when we compare to patients with other aetiologies, which may reinforce the belief that younger patients have a higher failure rate.We find few mechanical causes of failure restricted to congenital hydrocephalus like migration of distal end through anal canal and migration of proximal end predominantly in infant age group.
We found an association between shunt failure and aetiology more of congenital causes developed malfunction in our study.This may be attributed to gross hydrocephalus and displacement of the of the proximal end from an overtly CSF filled ventricle into the cortical mantle, complete displacement of whole catheter into the ventricle as shown in Fig. 3 migration through the anal canal due to size of catheter in relation to the body of the infant, more chances of kinking again due to the comparative size of the catheter.Studied on particular aetiology associated with shunt malfunction was mixed [17][18][19].Congenital hydrocephalus was identified as a predominant risk factor for initial shunt failure in multiple studies [20,21].
W e found kinking at the proximal end as the most common cause of shunt failure.It was mostly as a result of inadequate and less spacious tunnelling made for the reservoir.So we advocate giving ample time in making spacious tunnel for reservoir by releasing all adhesions and tissues.Albert M Issacs et al. showed that there were 4 (2%) patients with proximal failures, mostly within the first 100 days of surgery.Neuronavigation  aided the revision of these failed shunts with complete success [22].However, proximal end shunt failure was the predominant cause in our study.
The shunt was wrongly placed and misdirected into the ventricle in 10 cases.This may be due to lack of familiarity with the ventricular anatomy and freehand technique.It becomes extremely important to know the Fig. 2 Malposition of the proximal catheter crossing septum pellucidum landmarks precisely and gauge the ventricular depth on imaging prior to the procedure especially in freehand technique.Hamada and Abou Zeid depicted that misplacement of proximal catheter was founded in two (7.1%) patients of their shunt failure series [23].
Shunt disconnection was found at the junction of proximal and distal end.It was mainly due to lack of a proper knotting while fixing the ventricular end to peritoneal end.Proper surgical knotting should be done and knot should be placed on the exact junction to prevent obliteration of the catheter by the knot.Shunt disconnection also leads to the formation of psudomeningocoele around the valve area as shown in Fig. 4 further contributes to the failure of the shunt.Air in the shunt bulb leads to blockage and subsequent shunt failure.The remedy to prevent this was to make the reservoir air free by dipping the distal end in the kidney tray full of normal saline and pressing the bulb constantly till air bubbles disappear.15% of their shunt malfunctions were due to shuntfracture and that occipitally placed shunts had a higher migration rate than frontally placed shunts as per Aldrich and Harmann [24] Migration of the distal end through the anal canal was the cause of failure in infants.Persistence of unobliterated Fig. 3 Complete migration of catheter into the ventricle processus vaginalis in paediatric patients was responsible for higher likelihood of VP shunt distal catheter drifting into the scrotum [25].Previous studies reported that age and aetiology are predominant risk factors of initial shunt failure [12,26].In consensus with these studies, our study showed that age and aetiology were notably associated with shunt failure where 48 (68.5%) patients with VP shunt failure were congenital in nature.Migration at the proximal end was due to lack of proper three point fixation especially in congenital gross hydrocephalus.Inadvertent suturing of the shunt while closing abdominal layers and inadvertent placing of the shunt in the preperitoneal place leads to collection and pseudocyst formation resulting in shunt failure in cases.This misadventure can be prevented by visualising the gut loops by holding it into Babcock forceps and confirming the distal end is in the peritoneal cavity.Inadvertent suturing can be prevented by maximising the use of retractors and closing the abdomen in layered fashion with constant vigil about the position of the catheter.Abdominal complications of VP shunt are not uncommon with extra peritoneal misplacement of the catheter and sub-cutaneous or intra-abdominal cerebrospinal fluid (CSF) collections being the predominant causes [27].

Conclusions
Shunt surgery is seemingly a straightforward operation for neurosurgeons.But considering the incidence of shunt failure and its associated morbidity and mortality, it should always be done with trepidation and extreme caution.Exclusive mechanical shunt malfunction is a major concern and leads to great deal of morbidity in the shunt operations.However there are trivial remedies and technical nuances which needs to be followed during surgery to avoid these complications.Congenital hydrocephalus and younger age are the predominant risk factors for mechanical shunt malfunction.

Fig. 1
Fig. 1 Displacement of the proximal catheter tip into the brain parenchyma

Table 1
Demographic profile and aetiology of our study patients . Studies by Tuli et al., Liptak and McDon-ald, and Liptak et al. depicted that shunts introduced in patients younger than 1 year had a greater failure rate

Table 2
Clinical features of shunt malfunction in infants and adults

Table 3
Entry point and types of mechanical failure in our study patients