Endoscopic Approach to Intraventricular Brain Tumors

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Chapter 29 Endoscopic Approach to Intraventricular Brain Tumors

Jeffrey P. Greenfield, Mark M. Souweidane, Theodore H. Schwartz

Endoscopic surgery for intraventricular brain tumors is a logical application of endoscopic technology. Because of the central and deep location of intraventricular brain tumors, conventional neurosurgical approaches have a relative increase in potential morbidity. Auspiciously, the location of intraventricular tumors being within a cerebrospinal fluid (CSF) compartment affords excellent light and image transmission. The fact that most intraventricular tumors cause hydrocephalus makes endoscopic surgery particularly attractive since simultaneous procedures can be employed both for CSF diversion and tumor management. In addition, the inherent benefits of minimally invasive techniques including reduced surgical time, improved cosmetic results, shortened hospital stay, and reduced cost also factor into the appeal of neurosurgical endoscopy for managing intraventricular tumors.¹ Five commonly employed endoscopic procedures are highlighted including endoscopic fenestration, endoscopic tumor biopsy, simultaneous tumor biopsy with endoscopic third ventriculostomy (ETV), endoscopic removal of solid tumors and endoscopic removal of colloid cysts.

Patient Selection

Patient selection is critical in optimizing the desired surgical goal, avoiding unnecessary procedures, and minimizing surgical morbidity. The intended surgical goal must be carefully established prior to surgery. Many patients that can undergo endoscopic surgery may not be logical candidates since they will ultimately require conventional surgical tumor removal or no surgery. Examples that serve to highlight this point are the patient with a large intraventricular tumor of the ventricular atrium or the patient with a biochemically proven malignant germ cell tumor. In selecting patients, the less experienced surgeon should begin with less demanding cases (septal fenestration and endoscopic third ventriculostomy) and eventually incorporate more complex cases (colloid cyst and solid tumor resection). Although endoscopic surgery can be accomplished in patients with normal sized ventricles, concomitant hydrocephalus affords easier ventricular cannulation and intraventricular navigation.²

Equipment

Endoscopes vary in the type of optics (fiberoptic or solid lens), diameter of the scope, and the dimension and number of working portals. While the fiberoptic systems are appealing for their light weight and reduced cost, the greater image resolution with a sold lens system is preferred by the author for most endoscopic tumor surgery. For all procedures featured in this article, scopes should have at the very least one working channel, one irrigation port, and a dedicated egress channel. Navigational guidance is strongly encouraged not so much for ventricular cannulation, but for selecting an optimal trajectory (Figs. 29-1 and 29-2). This simple integration greatly reduces the tendency to torque once in the ventricular compartment thus reducing potential hemorrhage and neurological injury. Endoscopic courses are a useful means for becoming familiar with the requisite instrumentation and surgical techniques.

FIGURE 29-1 A solid lens endoscopic sheath integrated with an infrared navigational tracking device is being registered at the time of surgery.

FIGURE 29-2 The endoscopic path is superimposed upon the preoperative MRI in selecting the ideal trajectory in a patient with a third ventricular tumor. The dimension of the endoscope is depicted so as to simulate the true size of the scope.

Endoscopic Tumor Procedures

Endoscopic Fenestration

Septal fenestration and tumor cyst fenestration are two of the simplest endoscopic procedures owing the relative avascular nature of these membranes. Fenestration of the septum pellucidum should be considered in any patient in which a tumor mass is situated in the anterior third ventricle or within the lateral ventricle at the foramen of Monro resulting in compartmentalized hydrocephalus (Fig. 29-3). Shunt burden can thus be reduced in the former situation or eliminated in the latter by simple endoscopic septal fenestration. Endoscopic fenestration of the septum pellucidum generally is performed via an entry site that lies more lateral than the conventional coronal burr hole. The entry site is thus positioned at least 4 cm from the midsagittal plane. It is recommended that the site of septal fenestration be positioned between the larger tributaries of the septal veins and as superior as possible from the fornix. Generous fenestrations are made with cautery and confirmation of effective communication is established with identification of contralateral ventricular landmarks including the choroid plexus and ependymal veins.

FIGURE 29-3 A coronal T1-weighted MRI obtained after gadolinium contrast administration shows a third ventricular tumor—pure geminoma—in a 12-year-old girl who presented with headache and polydipsia. A unilateral ventriculoperitoneal shunt was placed after endoscopic tumor biopsy and septal fenestration.

Tumor cyst fenestration is an appealing therapeutic option when a patient’s symptoms can be relieved by cyst decompression and when aggressive tumor resection may be avoided (Fig. 29-4). Craniopharyngiomas, hypothalamic/chiasmatic astrocytomas, and suprasellar germ cell tumors are examples of such tumors.³ Transventricular endoscopic cyst decompression is a minimally invasive method for temporarily or permanently alleviating obstructive hydrocephalus or visual loss. For most cystic tumors causing obstructive hydrocephalus at the level of the third ventricle, a standard coronal approach is an ideal trajectory. The transcavum interforniceal endoscopic approach⁴ to the third ventricle is a further refinement of the technique for biopsy or fenestration of lesions within the third ventricle in those patients a large cavum vergae.

FIGURE 29-4 A sagittal T1-weighted MRI obtained after gadolinium contrast administration shows a presumed craniopharyngioma in a patient presenting with a bitemporal hemianopia. Visual fields normalized after a transventricular endoscopic cyst decompression. The residual mass was treated with fractionated stereotactic radiotherapy.

Tumor Biopsy

Endoscopic biopsy is a well-established method for sampling intraventricular brain tumors.⁵^–⁷ The procedure should always be considered in situations in which surgical tumor removal may not be necessary or when the diagnosis would significantly alter the therapeutic approach. Primary examples of these situations include marker-negative germ cell tumors, Langerhans cell histiocytosis, and infiltrative hypothalamic gliomas. Candidates should have overt intraventricular extension of their tumor mass rather than a lesion that is entirely subependymal in location. The diagnostic yield is high and the risk is low.⁸ In the authors’ current series of 65 patients who have undergone endoscopic tumor biopsy the diagnostic yield was 98%. To maintain diagnostic accuracy it is imperative to avoid cauterizing the tumor prior to sampling. The samples are small and histologic interpretation can be challenging without superimposed artifact from cautery. If bleeding is encountered, continuous irrigation through the endoscope or an external catheter is recommended until the efflux clears.