29 Neuroendoscopic Considerations in the Pediatric Patient
29.1 Introduction
The origin of neuroendoscopy parallels the history and challenges in battling hydrocephalus in the pediatric population, while its development mirrors our evolving understanding of fundamental tenets underlying microsurgical and skull base neurosurgery. Endoscopy is ideally suited to optimize visualization, minimize injury to the surrounding brain, and navigate around acute angles that may be obstructed by critical neurovascular structures. While neuroendoscopy is considered a form of minimally invasive neurosurgery, it does not necessarily invoke less disruption of normal structures, especially during ventral skull base exposures through an endonasal corridor. However, the ability to leverage and extend the surgeon’s view can expose hidden lesions in challenging anatomical regions. The intrinsic optics of the endoscope may also exceed the range of the microscope in resolution and panorama. Taken together, neuroendoscopy offers an appealing solution to a myriad of challenges posed by the pediatric neurosurgical patient.1
The first neuroendoscopy procedure performed is attributed to Victor L’Espinasse, an urologist most famed for his attempts at testicular transplantation, who used a rigid cystoscope to fulgurate the choroid plexus of two infants with hydrocephalus.2 Walter Dandy followed with attempts at controlling the production of cerebrospinal fluid (CSF) for treatment of hydrocephalus through extirpation of the choroid plexus via an occipital approach (Fig. 29.1). These early efforts invoked egress of the entire ventricular CSF volume, and not surprisingly, resulted in a high morbidity rate.3,4 In 1922, Dandy performed the first third ventriculostomy through a frontal craniotomy with transection of an optic nerve, and later changed to a less morbid subtemporal approach.5
The recognition of the therapeutic potential of bypassing usual CSF conduits in the face of ventricular obstruction prompted W. Jason Mixter to perform the first endoscopic third ventriculostomy (ETV) in 1923, using an urethroscope under visual guidance.6 Although further developments in ventriculoscope optics and the ability to navigate through a fluidfilled medium ensued in the subsequent decades,7,8 the use of endoscopy for treatment of hydrocephalus waned with the introduction of the valved ventricular shunt.9 Endoscopic techniques continued to be used for select indications over the subsequent three decades, but a resurgence of endoscopic techniques to treat hydrocephalus came with concurrent developments in endonasal endoscopic approaches, minimally invasive concepts for skull base lesions, and the development of image guidance systems.
29.2 Indications/Contraindications?
General indications for neuroendoscopy in the pediatric population include treatment of hydrocephalus, biopsy or resection of intraventricular tumors, cyst fenestration, sampling and resection of pineal region and posterior fossa lesions, and endonasal approaches to the sella and parasellar region. Specific conditions and considerations in the pediatric population are discussed below.
29.2.1 Obstructive Hydrocephalus
Obstructive, or noncommunicating, hydrocephalus can result from obstruction in the CSF flow anywhere from the ventricles to the cisterns to its reabsorption into the venous system. One strategy for bypassing such an obstruction is through an ETV (Fig. 29.2).10 ETV candidates have symptomatic obstructive hydrocephalus, patent subarachnoid spaces, and suitable anatomy to permit safe fenestration of the floor of the third ventricle without excessive risk to surrounding neurovascular structures, in particular, the basilar artery complex. Success, as defined by amelioration of the signs and symptoms of elevated intracranial pressure, depends on the etiology, anatomy, age, and management strategy.11,12
Causes of obstructive hydrocephalus can be congenital or acquired (i.e., structural, neoplastic, or infectious). One classic indication for ETV is aqueductal stenosis, with excellent success rates especially in older children and adults as compared with infants under 1 year of age. Aqueductal stenosis in children is most frequently diagnosed based on imaging findings of triventricular hydrocephalus, with a relatively normal size fourth ventricule and occasional appearance of a thin membrane that spans the aqueduct of Sylvius. In some cases, however, aqueductal stenosis may be accompanied by a secondary communicating hydrocephalus due to lack of subarachnoid space development in the neonate. Furthermore, excessive enlargement of the temporal horns may compress midline structures and mimic aqueductal stenosis. Therefore, even a technically successful ventriculostomy may not spare the patient from further procedures or shunt dependency.
Insufficient expansion of the subarachnoid spaces may contribute to a high rate of ETV failure in young infants in general. Indeed, in a series of patients younger than 6 months of age with hydrocephalus due to intraventricular hemorrhage of prematurity, prepontine cistern scarring significantly predicted treatment failure, as defined by the need for another procedure to treat hydrocephalus.13 Intraoperative observation of a patent prepontine cistern and a closed aqueduct independently associates with ETV success.14 Furthermore, a midsagittal magnetic resonance imaging (MRI) fast imaging employing steady-state acquisition (FIESTA) sequence can offer preoperative insight into the status of cisternal constriction, corresponding to intraoperative observations of arachnoidal scarring.13 In addition to open basal cisterns, thinning and inferior bowing of the third ventricular floor may also have positive predictive value for ETV success. If the third ventricular floor anatomy appears less favorable for safe ventriculostomy, fenestration of the lamina terminalis occasionally provides an alternative channel for CSF.
Due to the limited success rate of ETV in young patients for noncommunicating hydrocephalus, there has been a move to combine endoscopic third ventriculostomy with choroid plexus cauterization (CPC), with promising results in some series, with resolution of symptomatic hydrocephalus and reduced shunt dependency.15,16 In particular, Warf and colleagues have reported extensive experience with ETV + CPC in children with hydrocephalus due to aqueductal stenosis, intraventricular hemorrhage of prematurity, Dandy Walker syndrome, myelomeningocele, and infection, and in idiopathic cases.3,17,18,19,20 Variations in success rate across different series of ETV/CPC speak to the critical importance of patient selection and recognition of factors associated with failure.21 On the whole, longer-term follow-up is needed to apply this technique to a wider population.
29.2.2 Cysts
The panoramic view afforded by neuroendoscopy is ideally suited for fenestration of a variety of intracranial cysts, the most common being arachnoid cysts related to the Sylvian fissure, with less than 10% located in the suprasellar space. Arachnoid cysts are postulated to arise from splitting of the arachnoid membrane in early development,22,23,24 and enlargement due to an osmotic pressure gradient, active secretion by the cyst-wall lining, active secretion by ectopic choroidlike structures, or CSF movement through a communication between the subarachnoid space and the cyst related to venous or arterial pulsations.25 A slit valve is often noted between the cyst and basal cisterns, from intraoperative observations as well as cine MRI flow studies.26,27,28 Alternating directions of CSF flow during the cardiac cycle reinforces fluid influx into the cyst and the slit valve promotes cyst enlargement.29 With time, cysts exert mass effect or strategically obstruct CSF outflow to produce symptomatic hydrocephalus.
Traditional management of intracranial cysts includes fenestration or marsupialization via subfrontal, transcallosal, and transcortical transventricular approaches, as well as adjunctive cystoperitoneal or ventriculoperitoneal shunting. Endoscopic ventriculocystostomy offers an effective and less invasiveness approach for treatment of arachnoid cysts at all locations.26,30,31 Especially in the presence of an enlarged ventricle, the endoscope can be introduced through a bur-hole exposure and navigate to deep-seeded lesions to create a wide fenestration of the cyst wall. At times, a small craniotomy might be preferred to allow insertion of dual endoscopic instruments for more facile manipulation of the cyst. Sustainable outcomes with relief of intracranial pressure and low recurrence rates have been reported for endoscopic treatment of arachnoid cysts.
A suprasellar arachnoid cyst, in particular, lends itself to endoscopic surgery given the direct trajectory from a frontal bur hole to the suprasellar region and the basal cisterns once a second fenestration is made at the base of the cyst. When possible, dual fenestration of a suprasellar cyst allows communication between the lateral ventricle and the prepontine cistern, increasing the potential routes for diversion of loculated cerebrospinal fluid.26 A similar strategy is also applicable to choroid plexus cysts, cavum septi pellucidi cysts, collicular plate cysts, and quadrigeminal cistern cysts.
An analogous rationale applies to endoscopic management of symptomatic colloid cysts of the third ventricle (Fig. 29.3 and Fig. 29.4).32 Hydrocephalus from obstruction of one or both foramina of Monro creates a widened corridor for maneuvering of the endoscope; however, the lesion may obstruct physical entry into the third ventricle. Since endoscopy reveals only the tip of the iceberg, alternative routes such as a subfrontal translamina terminalis approach may be necessary for posteriorly located lesions obscured by the roof of the third ventricle. One strategy is to attempt ventriculoscopic resection first, and if unsuccessful for technical reasons, the bur hole is readily converted into a small craniotomy for microsurgical resection of a colloid cyst. Endoscopic resection allows a small cortical incision with low risk of postoperative epilepsy and manipulation of the cyst under direct vision. The relatively avascular nature of the cyst also favors safe endoscopic removal. Care should be taken to avoid excessive traction on a cyst capsule, as bleeding from partially avulsed vessels in the roof of the third ventricle is difficult to control and quickly obscures the operative view. Continuous warm irrigation affords effective hemostasis for mild oozing, while focal hemostasis with bipolar or laser coagulation offers an alternative option for more brisk bleeding. The volume of CSF egress and infused irrigation should be noted to prevent fluid imbalances during the procedure. The septum pellucidum can be fenestrated to ensure free communication between bilateral ventricles. Importantly, patients should be followed for late cyst recurrence,33 especially if following subtotal removal.34
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