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.

Simultaneous Tumor Biopsy and Endoscopic Third Ventriculostomy

The prominence of pineal region tumors in children coupled with the high frequency of tumors that may not necessitate aggressive surgical resection converges nicely with endoscopic applications. Notably, primary central nervous system germ cell tumors (CNS GCT), both pure germinomas and nongerminomatous germ cell tumors, can be effectively treated without radical resection. Thus, children who present with noncommunicating hydrocephalus with a pineal region tumor should always be considered for primary endoscopic management by way of ETV and tumor biopsy. Serum biochemical analysis for alfafetoprotein (AFP) and human chorionic gonadotropin (HCG) should always precede endoscopic biopsy since marker-positive GCTs should be initially managed with neoadjuvant chemotherapy.^9–12 When performing simultaneous ETV and tumor biopsy, the CSF diversion should always be performed first. This recommendation is based on the fact that the patient’s hydrocephalus is the more emergent clinical condition requiring treatment. Further, when tumor biopsy is performed some intraventricular hemorrhage is expected that may obscure vision. Given that the trajectory for ETV and pineal region tumor biopsy are different one must select between using one or two entry sites for performing these simultaneous procedures. The typical entry site for performing ETV is at the coronal suture 2 cm from midline while that for accomplishing a pineal region tumor biopsy is 4 to 6 cm precoronal. While two separate entry sites can be used one single entry site that is midway between these has been shown to be successful. It is the authors’ preference to use a single precoronal approach that lies between the ideal entry sites for either separate procedure. This site is routinely dictated based upon stereotactic guidance. With the use of a 30-degree angled endoscope, it is rare that both procedures will not be possible simultaneously.