Endoscopic third ventriculostomy

Endoscopic third ventriculostomy (ETV) is a surgical procedure for treatment of hydrocephalus in which an opening is created in the floor of the third ventricle using an endoscope placed within the ventricular system through a burr hole. This allows the cerebrospinal fluid to flow directly to the basal cisterns, bypassing the obstruction. Specifically, the opening is created in the translucent tuber cinereum on the third ventricular floor.^[1]

The ETV procedure is used as an alternative to a cerebral shunt^[2] mainly to treat certain forms of noncommunicating obstructive hydrocephalus (such as aqueductal stenosis), but since the ETV was introduced as an accepted treatment modality the range of etiologies for which it is used has grown significantly. Whereas at first it was almost exclusively performed in patients with noncommunicating obstructive hydrocephalus (e.g. aqueductal stenosis or intracerebral tumor), in the present day patients with communicating obstructive hydrocephalus (e.g. post intracranial hemorrhage or post intracranial infection) also may be eligible for treatment by means of ETV.

A major advantage of performing an endoscopic third ventriculostomy over placement of a cerebrospinal fluid shunt is the absence of an implanted foreign body. A shunt has risk of infection and failure for which subsequent surgery is needed. Complications of ETV include hemorrhage (the most severe being due to basilar artery rupture), injury to neural structures (e.g. hypothalamus, pituitary gland or fornix of the brain), and late sudden deterioration.^[3] Infection, hematoma, and cerebrospinal fluid leaks may present in the direct postoperative period.

Failure of the ETV occurs. This can be due to occlusion of the ventriculostomy (e.g. closure of the ventriculostomy, formation of subarachnoid membranes in the pontine cistern or other mechanisms). Although 60 - 90% of failures occur in the first few months after treatment, long-term failure also occurs (failures occurring after 7 years have been reported).^[4] In a very small subgroup of patients a complication of ETV can be rapid late deterioration.^[5] The mechanism is not clear.

さまざまな理由で ETV を実施できない場合、代替治療法として第三脳室前方の終板を開く方法がある。 ^{[ 6 ]}この方法の有効性は確実ではない。^{[ 7 ]}

水頭症の外科的治療の選択肢は、前述のように、脳シャントの埋め込みとETVです。特に最年少グループ（2歳未満）では、どの治療法が優れているかは依然として不明です。現在、この問題に対処するために、大規模な国際多施設共同研究が実施されています。早産歴やその他の関連する脳異常のない、中脳水道狭窄症と診断された2歳未満の患者が対象となっています（国際乳児水頭症研究）。^{[ 8 ] [ 9 ]}

内視鏡的第三脳室開窓術と脈絡叢焼灼術を組み合わせることによる追加的な利点について議論があります。この組み合わせた手術は「ETV/CPC」という略称で呼ばれ、ベンジャミン・ワーフ博士にちなんで「ワーフ手術」とも呼ばれています^{[ 10 ]}。この手術に関する著者らの経験についての研究論文が発表されています。良好な結果を示すデータの大部分はアフリカの患者に関するものです^{[ 11 ]}。欧米諸国の研究グループによる最近の研究でも、ETVと脈絡叢焼灼術の組み合わせは効果的で安全かつ持続性があるように見え^{[ 12 ]}、成功の予測はETV単独の場合と同様であることが示されています^{[ 13 ]} 。乳児における脈絡叢焼灼の程度は、脳神経外科医の経験（学習曲線）に依存する可能性があり、したがって外科医のトレーニングによって結果が改善される可能性があります。^{[ 14 ]} ETV/CPC 手術は現在、ワシントン州シアトル、テキサス州ヒューストン、アルバータ州カルガリー、オンタリオ州トロント、ユタ州ソルトレイクシティ、マサチューセッツ州ボストンなど、米国とカナダの多くの病院で実施されている。^{[ 15 ]}

The chances of success of treatment of a pediatric patient can be calculated using the ETV success score (ETVSS).^[16][17][18] The ETVSS is derived from patient age, etiology of hydrocephalus and history of previous cerebrospinal fluid shunt (e.g. ventriculo-peritoneal shunt). The percentage probability of ETV success = Age score + Etiology score + Previous shunt score. A two years old patient with hydrocephalus due to aqueductal stenosis, without previous shunt would have an 80% chance of success (40 for age + 30 for etiology + 10 for no previous shunt = 80).

ETVSS table^[16]

The ETVSS was derived and validated without the use of adult data and it has inadequate discriminative ability in mixed adult and pediatric populations.^[19]

After a patient gets readmitted with recurrent clinical and radiological symptomatology of hydrocephalus, it is unclear what the next step in treatment should be. Implantation of a cerebrospinal fluid shunt or repeat ETV. Data suggest that a second ETV might be worthwhile if implantation of cerebrospinal fluid shunt can be avoided.^[20][21]

In most countries and neurosurgical centres, the ETV procedure is part of the basic neurosurgery training program. For the sake of teaching and practicing, various simulation models have been developed. Virtual reality simulators,^[22] and synthetic simulators.^[23][24] This allows neurosurgical trainees to practice skills in a low-risk environment. Educators can select either a virtual reality simulator or a physical model for the training of residents, the selection should be based on educational objectives. Where training focused on anatomy and using anatomical landmarks for decision making may better be aided with virtual reality model, the focus on familiarizing the resident with endoscopic equipment and developing manual dexterity may be better learned on a physical model.^[25] The technical skill and competency of a trainee can be evaluated using the Neuro-Endoscopic Ventriculostomy Assessment Tool (NEVAT).^[26]

• Video and more about the ETV procedure from an article on Medscape