Endoscopic placement of a triventricular stent for complex hydrocephalus and isolated fourth ventricle: illustrative case

Abstract

BACKGROUND

Hydrocephalus is commonly encountered in pediatric neurosurgery. The etiology is diverse, and complexity in management increases in patients with loculated or trapped ventricles. The authors sought to examine a treatment option of endoscopic placement of a triventricular stent in a pediatric patient with complex hydrocephalus and a trapped fourth ventricle.

OBSERVATIONS

In this case, the authors present the treatment of complex hydrocephalus with a trapped fourth ventricle in a pediatric patient using endoscopic placement of a triventricular aqueductal stent. The patient had a complex neurosurgical history, which included over 15 surgeries for shunted hydrocephalus. This case highlights the unique approach used, and the authors discuss surgical nuances of the technique, as well as learning points.

LESSONS

Complex hydrocephalus can be difficult to manage because patients often have multiple catheters, loculated or trapped ventricles, and extensive surgical histories. Endoscopic placement of a triventricular stent can decrease shunt system complexity, restore normal cerebrospinal fluid pathway circulation across the cerebral aqueduct, and promote communication between the ventricles. The authors’ treatment modality resulted in the successful resolution of the trapped fourth ventricle and symptomatic improvement in hydrocephalus.

Hydrocephalus is generally defined as an imbalance between cerebrospinal fluid (CSF) production and reabsorption rates.^1–6 Physiologically, CSF absorption must correlate with venous outflow to ensure constant intracranial volume per the Monro-Kellie doctrine.^2,7 Because of a variety of etiologies, hydrocephalus causes disturbances of CSF production and flow, leading to pathophysiological changes in the brain.^1,2,6 Complex hydrocephalus can have several clinical features, including extensive surgical revision histories, loculated or trapped ventricles, and/or multiple catheter systems. This pathological entity represents one of the great challenges in pediatric neurosurgery.^1,2,5,6

In 2.5%–3% of hydrocephalus cases, an isolated fourth ventricle occurs after obstruction of CSF inflow/outflow pathways (cerebral aqueduct and foramina of Magendie and Luschka).^8–13As CSF production into this closed space continues, intraventricular pressure builds, leading to bulbar dysfunction or even brain herniation.^10,11 Although the exact pathophysiological mechanism of fourth ventricular isolation or “trapping” is unclear, it is more common in pediatric patients. It usually occurs secondary to hemorrhagic, infective, or postsurgical conditions that induce intracranial inflammatory processes and scar tissue formation.^8–11,14 Treatment for these patients often involves complex, multiple catheter or multiple shunt systems.

Herein, we present the treatment paradigm for complex hydrocephalus with a trapped fourth ventricle via endoscopic placement of a triventricular stent (in conjunction with a single-catheter Ommaya reservoir) that spans the lateral, third, and fourth ventricles to enhance communication across the foramen of Monro and cerebral aqueduct. This case demonstrates a simplified technique for treating a trapped fourth ventricle and complex hydrocephalus while maintaining a single ventriculoperitoneal (VP) shunt system. We report this case to highlight additional surgical considerations and salient learning points to aid in complex hydrocephalus management in children.

Illustrative Case

Presentation

A 16-year-old patient with a complex history of cerebellar pilocytic astrocytoma had undergone extensive neurosurgical interventions at an outside institution. They had undergone over 15 surgeries, including tumor resection, multiple supratentorial shunt surgeries, as well as placement and removal of a fourth-ventricle VP shunt system. The patient had also undergone endoscopic aqueductoplasty and septostomy with some success. The patient represented to the emergency room with 2 weeks of headaches and nausea, and a physical examination revealed a chronic fourth and sixth cranial nerve palsy of the right eye. Magnetic resonance imaging (MRI) revealed worsening of the upper cervical spinal cord syringomyelia and marked enlargement of the fourth ventricle compared with prior imaging (Fig. 1A–D).

FIG. 1.

Sagittal (A) and axial (B) T2-weighted MRI scans 3 months prior to surgery. Preoperative sagittal (C) and axial (D) T2-weighted MRI sections showing dilatation of the fourth ventricle and development of syringomyelia. Postoperative sagittal (E) and axial (F) computed tomography immediately after surgery, showing the stent spanning the lateral, third, and fourth ventricles. Two-week postoperative sagittal (G) and axial (H) T2-weighted MRI sequences show reduced dilatation of the fourth ventricle and syringomyelia in the upper cervical spinal cord as compared with the preoperative image (C).

Imaging and clinical presentation were concerning for an ongoing trapped fourth ventricle despite previous aqueductoplasty. Because the patient had previously undergone multiple ventricular shunt placements, an endoscopic aqueductoplasty procedure, and a fourth ventricular shunt placement without success, the placement of a triventricular stent was offered to the patient and family. The triventricular aqueductal stent was chosen as the management strategy to relieve the reobstruction of the cerebral aqueduct, which was thought to be caused by persistent inflammation and rescarring, leading to the trapped fourth ventricle. In an effort to preserve and maintain a single shunt system to reduce complexity, we planned to anchor the triventricular stent with an Ommaya reservoir to avoid catheter migration.

Intraoperative Course

After being anesthetized, the patient was positioned supine on a horseshoe headrest. Brainlab neuronavigation with electromagnetic detection was used to register the patient to preoperative MRI and plan a low left frontal approach trajectory beginning from just below the hairline to the left lateral ventricle, through the foramen of Monro and cerebral aqueduct, and into the fourth ventricle (Fig. 2). The left side was selected because the patient had a functional right-sided VP shunt, with the proximal catheter in the right frontal horn, which we aimed to preserve. The area was sterilely prepped and draped. A curvilinear incision was made at the hairline in the midpupillary line, a burr hole was created, and the dura was opened. The Brainlab electromagnetic stylet was used to navigate a 9-French peel-away sheath into the left frontal horn of the ventricular system.

FIG. 2.

Neuronavigation images from the preoperative surgical approach planning. Three-dimensional skull reconstruction demonstrates the entry point (A), and axial (B), sagittal (C), and coronal (D) MRI sections show the planned trajectory through the foramen of Monro.

The ventricular stent was then prepared. For this, an antibiotic-impregnated shunt catheter was selected and measured to the length of the trajectory, 13 cm. In addition to the fenestrations on the distal 2 cm of the catheter, multiple fenestrations were placed at both 4–6 cm and 6–9 cm using the small Leksell rongeur, which corresponded to the area within the third and lateral ventricles, respectively (Fig. 3). A ShuntScope (16 cm in length, Karl Storz) was then inserted into the stent and passed down the peel-away sheath into the lateral ventricle. Ventricular anatomy was used to visually navigate through the foramen of Monro and into the third ventricle.

FIG. 3.

The Storz ShuntScope and stent. The stent was cut according to the preoperative measurement and fenestrated as described in the text.

From the third ventricle, the obstruction of the cerebral aqueduct by scar tissue was visualized and fenestrated. Via the cerebral aqueduct, the endoscope was advanced into the fourth ventricle. The catheter was navigated to the target and deployed via the Seldinger technique as the endoscope was withdrawn. CSF egressed spontaneously from the end of the catheter after placement. The catheter was affixed to an Ommaya reservoir and secured to the periosteum, providing access via the reservoir if needed. The wound was closed in a multilayered fashion.

Postoperative Course

Postoperative computed tomography assured appropriate placement of the stent (Fig. 1E and F). The patient symptomatically improved, with the resolution of nausea and improvement in headaches. The patient was discharged home, in stable condition, on postoperative day 2. At the 2-week follow-up, the patient was doing well with the resolution of nausea and headaches and no neurological changes from their baseline. MRI at 2 weeks reshowed appropriate placement of the ventricular stent (Fig. 1G and H). The lateral and third ventricles remained stable in size, the upper cervical T2 signal changes improved, and the fourth ventricle decreased in size, with a maximal transverse diameter of 23 mm compared with 29 mm. At 6 months postoperatively, the patient was tolerating a regular diet and had returned to school full-time. The chronic headaches were greatly improved and managed with anti-inflammatory medications.

Patient Informed Consent

The necessary patient informed consent was obtained in this study.

Discussion

Observations

Herein, we present a minimally invasive treatment option for a child with complex hydrocephalus and a trapped fourth ventricle by using the endoscopic placement of a triventricular stent that spanned the lateral, third, and fourth ventricles to enhance communication across the foramen of Monro and cerebral aqueduct. This treatment plan avoids a complex VP shunt system of catheter connectors and/or additional valves and distal catheters, which often add complexity in subsequent encounters for shunt interrogations. This treatment paradigm provides additional options for dealing with complex hydrocephalus and new insights into the management of an isolated fourth ventricle.

Trapped Fourth Ventricles

In the 20th century, Dandy and Hawkins identified isolated or trapped fourth ventricles as a rare complication of lateral ventricular shunt insertion to treat hydrocephalus.^12,15,16 Entrapment of a ventricle occurs with occlusion of its outlet due to an ependymal reaction after intraventricular infection or hemorrhage.^8,10,16,17 Experimental studies have suggested intracerebral inflammatory contributors that lead to increased parenchymal and perivascular deposition of extracellular matrix proteins and the probable upregulation of transforming growth factor-β.³ This inflammation occurs in arachnoiditis, meningeal fibrosis, and subependymal gliosis, impairing flow and resorption of CSF.^14,18–20

As in our case, fourth ventricular trapping can also occur as a result of scarring following posterior fossa tumor surgery.^{1,4,10,18–23} The rate of postresection hydrocephalus for tumors in the posterior fossa ranges from 10% to 40% in children.^4,23–25 It is likely that tumor location and subtype have some degree of influence on the development of hydrocephalus.^{1,4,9,23–29} Patients can present with global signs of elevated intracranial pressure (headache and vomiting) or subtle progressive cerebellar or brainstem dysfunction (truncal instability, poor feeding, disconjugate eye movements, or somnolence) at any point postoperatively.^1,9,27–31 They can also present after a period of improvement after shunting for communicating hydrocephalus.^27,32

Surgical Management of a Trapped Fourth Ventricle

Surgical treatment is typically indicated if patients present with brainstem compression symptoms or if significant progression of a trapped fourth ventricle is shown on imaging.^12,27,30 Treatment strategies are variable, including microsurgical fenestration for drainage, CSF diversion, endoscopic procedures, or some combination of these approaches.^10,24,26,31 Regardless of the treatment modality used, complications and failures are a constant problem.^{12,20,21,24,26,31,32} Microsurgical fenestration aims to directly reopen the fourth ventricle.^11,13,30,33 In conjunction, an additional catheter is commonly connected to a preexisting shunt system or a separate drainage device.^13,33,34 However, this approach increases the shunt system’s complexity and may further alter the patient’s CSF dynamics, which can have long-term implications.^23,30

Endoscopic access to the ventricular system typically occurs through a precoronal burr hole to the foramen of Monro or through a suboccipital approach to the fourth ventricle.^8,10,34,35 Endoscopic aqueductoplasty can be performed with dilatation or opening of the cerebral aqueduct with or without stent placement.^{9,10,23,36,37} This carries the advantages of both being minimally invasive and avoiding the introduction of a second shunt system or catheter.^9,35,36,38 However, it should be noted that endoscopic aqueductoplasty without stenting carries a 66% rate of restenosis, as demonstrated in this case.^4,8,9,30 Although stenting has been cited to reduce the incidence of restenosis, catheter migration can cause cranial nerve palsies (diplopia and facial weakness) or long tract signs (paresis and sensory deficits) as well as stent malfunction.^{17,20,32,34,39} The current literature debates the advantage of using an Ommaya or shunt system with an aqueductal stent to decrease the risk of migration.^{7,29,35,40–43}

Surgical Nuances and Considerations for Triventricular Stenting

A single triventricular stent catheter allows direct CSF communication between supra- and infratentorial brain regions. This option can avoid multiple catheters or shunt systems in the same patient, thus reducing the likelihood of restenosis and additional surgical interventions.^{7,13,32,35,44} However, such endoscopic techniques require advanced skill and experience. Understanding ventricular anatomy is also imperative because cases can have distorted anatomy.

The anatomy of the cerebral aqueduct is highly variable in pediatric patients with hydrocephalus, necessitating a careful study of patient imaging preoperatively.^29,35 The cerebral aqueduct is generally ventrally concave; extra care must be taken when using catheters and endoscopes to avoid damaging the surrounding periaqueductal gray matter, tegmentum, and tectum.^{20,24,29,31,35} Given the proximity of structures important for eye movement control, transient ophthalmoparesis is the most commonly reported complication of stent placement.^9,36,38,43 This can occur in the oculomotor nuclei ventral to the periaqueductal gray (midbrain Edinger-Westphal nuclei), trochlear nuclei, medial longitudinal fasciculus, tectum, and dorsal longitudinal fasciculus.^{9,13,17,36,37} Other complications include infection, brainstem irritation or trauma, stent malfunction, cranial nerve palsies, and overdrainage.^13,17,32 When endoscopically placing an aqueductal stent catheter, surgical adjuncts, including navigation and appropriate endoscope selection, are paramount, along with a good knowledge of anatomy. Defining the trajectory with neuronavigation is crucial to selecting a safe and appropriate approach. In addition, using navigation with the selected endoscope can assure an appropriate trajectory and placement. Herein, we employed the Storz ShuntScope for several reasons. It is semirigid, thin enough to fit within the stent/shunt tubing, able to traverse the planned trajectory, and long enough to reach the target distance. Recent publications have described incorporation of the ShuntScope as a surgical adjunct to CSF diversion procedures.^40–42 This endoscope allows the placement of shunt catheters or stents with good visualization, thereby increasing accessibility for a wide range of cases.

Lessons

We believe this case highlights an important treatment option for a difficult pathology that is not entirely uncommon in pediatric neurosurgery. Patients with complex hydrocephalus and isolated ventricles can be treated by a variety of methods. We believe that simplified CSF diversion systems allow the greatest longevity and ease of interrogation. Triventricular or aqueductal stents can be safely used by experienced surgeons to simplify VP shunt systems or even preclude their need entirely in select patients.

Author Contributions

Conception and design: DeCuypere, Horak, Gulsuna. Acquisition of data: DeCuypere, Horak, Gulsuna. Analysis and interpretation of data: DeCuypere, Gulsuna. Drafting the article: Horak, Gulsuna, LoPresti. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: DeCuypere. Administrative/technical/material support: Horak. Study supervision: DeCuypere.