Certain intraventricular and paraventricular tumors can be approached endoscopically via dilated ventricles. One of the pioneering applications of the flexible neuroendoscope was in this field, and both pineal region and paraven-tricular tumors were biopsied through custom-made, flexible, fiberoptic neuroendoscopes. Interestingly, the authors of these papers did not consider the possibility of performing a concurrent NTV to relieve hydrocephalus.
The success rate for biopsy was low for those tumors that were not actually in the ventricular system, and this was attributed to the small size of the biopsies. Other problems are that many paraventricular tumors are still separated from the ventricular system by an intact layer of ependyma that must be breached if tumor tissue is to be obtained . The relatively small size of the tissue samples is compounded by crush artifact. This is a particular problem with the flexible neuroendoscope and, wherever possible, a rigid or disposable Channel™ neuroendoscope is preferable because of the larger size of biopsy obtainable. One successful technique is to use a stereotactic biopsy needle passed though the endoscope (J. Firth, personal communication). In view of the age-related predilection for sites on and adjacent to the midline, neuroendoscopy has a considerable role in the management of pediatric brain tumors. The value of neuroendoscopy is not confined to children, and in a Nottingham series of 87 procedures in 77 patients, age ranged from 5 months to 70 years . Relief of hydrocephalus by NTV remains a principal indication with a high level of success: 63 out of 66 cases (95%) in the short term, with durable shunt-free outcome in 55 out of 66 cases (83%). Neuroendoscopic tumor biopsies were successful in providing a tissue diagnosis in 17 out of 29 cases (61%) . A very particular application is in pineal region tumors, in which there is the possibility of delivering "one-stop" neuro-surgery that provides relief of hydrocephalus, tumor biopsy and cerebrospinal fluid sampling for tumor cytology and biochemical evaluation of germ-cell tumor markers.
Very high diagnostic accuracy has been documented ; under these circumstances there can be no justification in performing an open operation for pineal germ-cell tumors unless committed efforts have first been made to make the diagnosis by these alternative means. It has been stated that NTV is contraindicated in those patients who have undergone radiation therapy, both on the grounds of inefficacy and risk of complications ; this has not been the experience of the present author. NTV can be successfully used to relieve hydrocephalus due to posterior fossa tumors . The ideal timing is yet to be defined; in patients with very chronic or massive hydrocephalus, there is a case for leaving an interval of a few days between NTV and definitive posterior fossa exploration. As a relatively small proportion of patients with hydrocephalus in association with a posterior fossa tumor will require a ventricular shunt following tumor resection, it is difficult to justify the routine performance of NTV in such cases, and it might be appropriate to reserve the procedure for those at greatest risk of persistent hydrocephalus, such as children under 5 years of age. The optimum strategy is yet to be established. However, when NTV is performed there is the added value of being able to inspect the ventricular system for possible metastases, to take samples of cerebrospinal fluid for tumor cytology, and, if a flexible neuroendoscope is used, to pass through the cerebral aqueduct and inspect the relationship of the tumor to the floor of the fourth ventricle.
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