The role of surgery in relieving calcified shunt site-related pain in patients with functioning VP shunt

Shunt calcification is a known late sequela of ventriculoperitoneal (VP) shunt insertion and is associated with shunt malfunction. However, in some patients, while shunt functionality is preserved despite calcification of the catheters, they experience nociceptive symptoms. In this paper, the authors present their surgical experience in managing patients with a functional VP shunt and experiencing pain secondary to shunt calcification. We analysed outcomes of patients presenting with pain at the level of a calcified shunt who underwent surgical untethering of the calcified catheter from the soft tissues. This procedure was commenced by the senior author in 2015. Patients were collected prospectively from the databases of two institutions. Evidence of shunt calcification was confirmed on neuroimaging. Seven patients, two male and five female, were included. The mean age at untethering was 13.5 years. The mean time interval between primary shunt surgery and symptom onset was 12 years (range 6–16 years). The commonest site of tethering was the neck (50%) followed by abdomen and chest (both 25%). Six patients underwent untethering of the catheter from soft tissues. One patient had removal of a redundant segment of calcified shunt left in situ during a previous revision. All patients experienced pain relief following shunt untethering. Untethering of calcified VP shunt catheters from soft tissue can be considered an effective treatment of shunt site pain and offered to patients presenting with a functional VP shunt.


Introduction
Ventriculoperitoneal (VP) shunt insertion is one of the commonest procedures performed in paediatric neurosurgery. Complications following shunt insertion are common [1] and often require multiple revisions of the system with a negative impact on patients' quality of life [2].
The calcification of a ventriculoperitoneal shunt is part of the long-term natural history of the catheter and affects 12 per 100 shunt insertions, often developing between 2 and 9 years post-insertion [3,4]. Several studies have described VP shunt dysfunction, pain, and skin irritation secondary to shunt calcification [5][6][7]. In these cases, management entails complete shunt removal.
However, there is a paucity of evidence regarding appropriate management of patients presenting with a functional shunt and severe pain or unpleasant discomfort secondary to calcification of the shunt. To the best of our knowledge, no study focused on the role of the untethering of the calcified shunt catheter from soft tissues, i.e. muscles and subcutaneous tissue, and the impact on patient symptom relief and quality of life.
We therefore aimed to assess whether surgical untethering of the calcified catheter from the soft tissues, without changing the VP shunt, is an effective procedure in treating the shunt pain site in these patients.

Methods
All patients who underwent shunt untethering or removal of redundant calcified shunt catheter for pain relief purposes from January 2015 to January 2022 were retrospectively reviewed from a prospectively kept database (Table 1) by the senior author of this paper.
Data collection was performed across two paediatric neurosurgical institutions where the senior author operated. All patients included in the database had no clinical or radiological signs of shunt malfunction. Demographic data, aetiology of hydrocephalus, age at initial shunt insertion, onset of pain symptoms, and surgical management details were retrieved from in-hospital patient records and operation notes. Presence and location of the shunt calcification were confirmed on radiographic study (Figs. 1 and 2). "Although in the authors' experience calcified shunts can be associated to fracture, there was no evidence of fractured shunt elements in our small patient cohort". All patients were operated on by the same paediatric neurosurgeon across both neurosurgical centres.
Ethics approval of our study was deemed not required and not appropriate by our hospital trust Research and Development Department since our study is a retrospective observational cohort study.

Surgical technique
Below is a case from our cohort to illustrate the key steps of removal of a redundant calcified shunt catheter (left from previous shunt revision) from the soft tissues. Although in this example the redundant catheter can be also removed, the technique can be generalised with appropriate adjustments made for patients on a case-by-case basis.

Patient is placed in the supine position with head turned
to the contralateral side of the calcified shunt tubing. 2. A 2.5-cm skin incision was made parallel to the length of the calcification (Fig. 3). 3. Monopolar diathermy is used to completely untether the calcified catheter from the surrounding soft tissue (Fig. 4). 4. The calcified shunt catheter is removed completely (Fig. 5). 5. The wound is closed in the subcuticular layers with 3/0 Vicryl and skin with 3/0 Monocryl.
In all cases the shunt was left in situ, we completely removed the calcified wrap around the catheter during the untethering procedure in order to prevent future retethering and symptoms' relapse.

Results
A total of seven patients underwent untethering of a calcified but functional VP shunt for pain relief. There was a total of two males and seven females. The mean age at the time of untethering following onset of symptoms was 13.5 years. All children were less than 2 years old when they had the primary shunt insertion. Indications for primary shunt insertion included post-haemorrhagic hydrocephalus, myelomeningocele-associated hydrocephalus, post-infectious hydrocephalus, and obstructive hydrocephalus ( Table 1). The shortest interval between primary shunt insertion and

Discussion
Ventriculoperitoneal (VP) shunts are used commonly for management of hydrocephalus. The catheters are essentially made up of silicone-coated silastic rubber with variations in the form of catheters impregnated with antimicrobial substance including antibiotics (Bactiseal©) and silver (Sil-verline©) or any other impregnated catheters available in the market. Iatrogenic dystrophic calcification is well known to occur in VP shunts [8,9]. The most common cause of shunt malfunction is blockage and fracture, which itself is precipitated by calcification of the shunt tubing. This report focuses on the symptoms and management of those calcified silicon catheters becoming tethered to the soft tissues in its proximity. This can elicit pain that can be evident on clinical examination confirmed subsequently by radiological investigation.
All children had normal serum calcium and phosphate levels to rule out any medical reasons contributing to the calcification.
Three case reports [4][5][6] and one small series [3] have described catheter calcification as a late-onset complication following VP shunt insertion [3][4][5][6]. The management typically consisted of complete shunt removal, new shunt insertion, or endoscopic third ventriculostomy [3]. To the best of our knowledge, there is no previous report of untethering an existing functional shunt without removing it for pain relief.
It seems possible, considering the paucity of the report, that most neurosurgical centres manage localised pain related to functional shunts in a conservative way. We do feel long-term analgesia is justified in these patients despite the risk of adverse effects such as constipation, dizziness, and fatigue [10].
In our series, the catheters that were noted to calcify were predominantly impregnated catheters (Silverline© and Bactiseal©). In 1998 Boch et al. described that bariumimpregnated catheters showed profound signs of distal tubing calcification [11]. It is not possible to conclude if these newer silicon catheters are more prone for calcification, and we could not find any study on a similar topic on the catheters used in this series. However, we can clearly infer that these catheters have remained functional over a period Our experience has shown that VP shunt untethering is a reasonable safe treatment option for pain relief in patients with functional calcified shunts. In our series, all patients remained pain-free post untethering at last follow-up. None of the patient in our series developed post-surgical infection or other complications adding validity to this approach.
Prior the untethering, it is essential to establish catheter patency and shunt functionality. Although serial radiographs successfully visualise calcifications in the majority of the patients, the length of the calcified catheters and its twodimensional lumen patency is essential. Aralar et al. have proposed a more specific imaging modality utilising sonographic assessment of CSF flow within the VP shunt [12]. Regardless of the modality employed, it remains crucial to diagnose a dysfunctional shunt which may contribute to the recurrence of hydrocephalus independent of any attempts for pain relief. The primary goal in such circumstance is to install a new working VP shunt.

Conclusion
Calcification of shunt catheter is a recognised event in the natural history of a ventriculoperitoneal shunt. Our series shows that in patients presenting with a functioning shunt (or a redundant calcified shunt tube) and pain unresponsive to the medical treatment along the shunt tract calcification, untethering of the calcified catheter from the soft tissues (or its removal if a redundant piece of catheter) is a safe and effective treatment option. Funding There are no financial or other disclosures to make. We can confirm that we have read the Journal's position on issues involved in ethical publication and confirm that this report is consistent with the guidelines.
Availability of data and material Can be obtained upon request.

Declarations
Ethics approval and consent to participate Our study is a retrospective observational cohort study. Such study is deemed not requiring and not appropriate for our hospital trust Research and Development Department.

Consent for publication Not applicable.
Conflict of interest Not applicable.