Intraparenchymal pericatheter cyst as an indicator of ventriculoperitoneal shunt malfunction: A case-based update

INTRODUCTION

Ventriculoperitoneal shunt (VPS) is the main surgical intervention for communicating or obstructive hydrocephalus and idiopathic normal-pressure hydrocephalus. It can also be performed in idiopathic intracranial hypertension (IIH) when there is no response to medical therapy or there is visual dysfunction worsening. Although standard in several conditions, the procedure shows a considerable rate of complications (~23.8% in adults).[7]

Intraparenchymal pericatheter cyst (IPC) is a rare complication of VPS, occurring mainly in children. To date, only 35 cases have been reported in the literature, of which, 14 were in adults, and four were in IIH patients. The aim of this article is to present a case of IPC formation in an adult, as well as to review the literature on the subject.

CASE PRESENTATION

A 22-year-old woman with a history of leukemia presented with progressive headache, papilledema, and visual loss at admission. Magnetic resonance imaging (MRI) was normal [Figure 1]; however, lumbar puncture with cerebrospinal fluid (CSF) pressure measurement confirmed the diagnosis of IIH (pseudotumor cerebri), requiring treatment with VPS [Figures 1 and 2].

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Figure 1:: Imaging comparison. MRI at admission (before VPS surgery): (a) axial T2 view demonstrating no hydrocephalus. The lumbar puncture confirmed the diagnosis of idiopathic intracranial hypertension. MRI at revaluation (3 months later): (b) lower axial T2, (c) upper axial T2, and (d) parasagittal T2W1 views demonstrating the catheter pathway with an intraparenchymal pericatheter cyst and perilesional edema.

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Figure 2:: Imaging comparison. CT after VPS surgery: (a) coronal view demonstrating the catheter pathway without any parenchymal lesion. CT at revaluation (3 months later): (b) coronal view demonstrating the catheter pathway with an intraparenchymal pericatheter cyst and perilesional edema, without hydrocephalus. CT after shunt revision (postoperative): (c) coronal view demonstrating the new catheter pathway with cyst regression and mild intracystic hemorrhage.

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The patient was readmitted 3 months later due to the recurrence of headache symptoms and visual impairment. Computed tomography (CT) [Figure 2] showed a parenchymal lesion around the ventricular bypass catheter with surrounding edema, but without hydrocephalus (never present in this case). MRI [Figure 1] revealed a round-shaped lesion, with content isointense to CSF, and a thin nonenhancing wall. These findings were compatible with the diagnosis of IPC. Abdominal CT was benign, without evidence of distal causes of obstruction.

VPS revision was performed, and a proximal obstruction identified [Figure 3], then managed by catheter replacement and subsequent cyst drainage. Postoperative CT [Figure 2] revealed cyst regression and an intracystic hemorrhage. At 3-month follow-up, significant improvement in headache and visual impairment was observed, with a normal neurological examination and no surgical complications.

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Figure 3:: Intraoperative image: view of the obstruction of the proximal catheter tip during shunt revision.

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DISCUSSION AND LITERATURE REVIEW

VPS is a very common procedure, used mainly for treating hydrocephalus or idiopathic normal-pressure hydrocephalus. However, it is also an alternative for IIH, particularly in refractory cases or those involving visual deterioration.[3] In the literature, hydrocephalus was the main cause for VPS surgery (31 of 35 published cases, ~91%). Despite being frequent, VPS has a significant rate of complications, commonly divided into foreign body related (e.g., migration, infection, fibrosis, and allergic reaction), abdominal (e.g., pseudocyst) and surgical complications (e.g., overdrainage), and those resulting in hydrocephalus (e.g., obstruction and disconnection).[21]

IPCs, however, are very rare complications of VPS. Although they can also appear in Ommaya reservoirs, only VPS cases were considered in this review. Furthermore, only reports with adequate clinical and imaging descriptions were included in the study [Table 1].[9,11-13,15,17-20,22,23,25,26] IPC formation probably results from a weakening of ependymal cells, which, associated with VPS malfunction, cause increased CSF pressure and subsequent parenchymal collection.[21] Then, depending on the degree of the pericatheter gliosis, a cyst can be formed, sometimes associated with vasogenic edema.[8,14] Possibly, another factor is the more compliance of the white matter surrounding the catheter compared to the ependyma. The CSF diffuses through the catheter orifice created in the ependyma and accumulates in the white matter during the course of the occluded catheter. Moreover, those who have IIH without ventricular dilation may present less compliant ventricles. The intracranial pressure increases, but as there is a low resistance outlet (catheter orifice), the liquid exits there, without ventricular dilation. Therefore, the presence of ventricular dilatation may not be a precise or the sole factor to estimate the correct functioning of the shunt system. These mechanisms may explain why such cysts are more common in children, since their cerebral parenchyma and ventricles are softer and more elastic, respectively.[4,14] Children account for 60% of the 35 reported cases.

Table 1:: Analysis of “IPC in VPS for hydrocephalus or IIH” bibliography.

Patients with this complication present with varied symptoms, the most frequent being headache (~40%), vomiting (~27%), and visual changes (~10%). There have also been reports of decreased levels of consciousness, hemiparesis, speech and gait disorders, tinnitus, and epileptic seizures. One patient was asymptomatic at re-evaluation, and the IPC was found by routine imaging tests.[24] Interestingly, the diagnosis of this complication can occur in a variable time from shunt implant, with cyst onset being reported years, months, and even days after surgery.

Imaging tests are of utmost importance to make a differential diagnosis of parenchymal lesions in VPS patients as well as to identify concomitant conditions significant to the therapeutic approach. The CT examination can assist in the diagnosis of IPCs, and it is very often the initial imaging test. However, MRI is the most helpful examination as it allows the correct distinction between cysts and their differential diagnoses due to its better resolution.[6] Alternative imaging techniques, such as CT cisternography and nuclear medicine scans, can be useful to recognize a cyst-ventricle communication or catheter obstruction, respectively.[4,8]

CSF edema, tumors, abscesses, and dysembryogenetic lesions are all considered cyst-like lesions.[6,14] Porencephalic cysts (or porencephaly) share the same clinicoradiological features as IPCs, although they can be considered a differential diagnosis[6] and are divided into communicating or noncommunicating, depending on whether they are contiguous with the intraventricular and/or subarachnoid spaces. A cyst-ventricle communication was well described in two cases.[8,10] Certain imaging conditions can present concomitantly to the pericatheter cyst, such as CSF edema and hydrocephalus. Dual cyst presentation is also possible.[5] Perilesional CSF edema was the only known accompanying condition in the presented case [Figures 1 and 2].

Early recognition and treatment of an IPC can provide complete clinical improvement and cyst regression.[5,8] A shunt revision is the most common approach for IPCs (29 of 33, ~88%), typically in symptomatic cases with catheter obstruction. There were no instances of cyst recurrence. However, a new cyst was formed after a contralateral shunt placement[1] and a pseudocyst identification after an apparent cyst regrowth.[2] Both cases were managed with shunt revision (followed by a cystoperitoneal shunt placement in the first). There have only been four reported cases of IPCs after VPS surgery for IIH, all of them in adults, and a shunt revision was performed in three of them, resulting in near-complete cyst resolution.[4] The age and management features were also similar to the presented case.

Some authors have questioned the necessity of shunt revision, especially in asymptomatic patients. Revision was not performed in four cases, three of them being managed conservatively with clinical and imaging surveillance,[5,24] and one being lost to follow-up.[4] No patient who underwent conservative treatment showed symptoms of shunt malfunction. All remained asymptomatic and two evolved with cyst regression.[16] Sinha et al.[16] supported conservative treatment, especially in asymptomatic patients. This type of approach has the advantage of avoiding surgery, though an obstruction, even if partial, may lead to the necessity of shunt revision.[14]

CONCLUSION

Although rare entities, it is important to understand and consider IPCs as complications of VPS surgery, including in adult patients and IIH cases. Shunt revision is the standard approach, though conservative treatment has been performed in specific conditions.