22.2.1 Radiomorphological Classification Of Aqueductal Stenoses

We divide aqueductal stenoses (AS) into three subtypes:

Type 1 AS is characterized by a small transverse membrane in the aqueduct, leading to a prestenotic proximal ampullar dilation of the aqueduct. This is the case where it is appealing to just open the transverse membrane to re-establish cerebrospinal fluid (CSF) flow. However, in our experience, patients have significant reclosure rates.3,4,5,6,7,8,9 Therefore, endoscopic third ventriculostomy (ETV) with a higher longterm success rate and less risk for the patient would be the better alternative (Fig. 22.1).

Type 2 AS is caused by a tumor or a cyst closing the aqueduct either by direct obstruction (e.g., tectal glioma) or secondary compression (e.g., tumor from the pineal region). There is a high likelihood that the aqueductoplasty will reclose within a short time postoperatively. Placement of a stent in circumstances of distorted anatomy and vulnerable surrounding tissue carries significant risk. We consider tumor biopsy (if indicated and possible) and ETV as the surgical treatment of choice (Fig. 22.2).

Type 3 AS is related to an isolated fourth ventricle. Here we find the radiomorphology of an AS combined with the cystic dilation of an isolated fourth ventricle, compressing the brainstem against the clivus and the cerebellum against the tentorium. Communication via the foramina of Luschka and foramen of Magendie with the subarachnoid space seems not to be sufficient. Patients all share the same past medical history: posthemorrhagic or postmeningitic hydrocephalus within the first year of life, early placement of a ventriculoperitoneal (VP) shunt, and clinical and radiographic signs of overdrainage (Fig. 22.3a–c).

22.2.2 Clinical Decision-Making

Type 1 (membranous) and type 2 (tumor and/or cyst associated) AS should be treated by ETV.

In our experience, patients with symptomatic isolated fourth ventricle (type 3 AS) are the best and only candidates for EAPS. It is important to point out that only short distance or membranous aqueductal stenoses should be treated. Aqueductoplasty (with stenting) is not a surgical technique to treat hydrocephalus but to allow communication between isolated ventricular compartments. Patients will require placement of a VP shunt to treat the hydrocephalus. Aqueductoplasty only establishes communication between the formerly isolated compartments: the stent is mandatory to avoid reclosure. The other surgical option in the management of trapped fourth ventricle is VP shunt placement into the fourth ventricle under direct endoscopic visualization.10

22.3.1 Endoscopic Anatomy

The typical anatomical landmarks within the posterior third ventricle are the entry into the aqueduct, the posterior commissure, the pineal recess, the habenular commissure, the suprapineal recess, and the posterior roof of the third ventricle (the latter usually seen only with a 30º or 45º scope).

The anatomical landmarks within the fourth ventricle are anteriorly the floor of the ventricle (the rhomboid fossa), inferiorly and medially the foramen of Magendie, and laterally on both sides the foramina of Luschka. The cerebellum, the cerebellar hemispheres, and the vermis can be seen posteriorly.

22.3.2 Endoscopic Equipment

For the endoscopic procedures, we use the Lotta ventriculoscope11 manufactured by Karl Storz GmbH & Co. KG, Tuttlingen, Germany. For orientation in the ventricles and for positioning of the trocar, the 6º working optic is used. Additionally, 30º or 45º optics can be utilized to visualize surrounding structures or the entry of the aqueduct. Additionally, the flexible scope following the “two in one concept” can be used to go through the aqueduct and explore the fourth ventricle. For all surgeries, we use a pneumatic selfretaining holding device (Pointsetter from Mitaka Corp., Tokyo, Japan), high-definition (HD) camera and monitor (Karl Storz GmbH & Co. KG, Tuttlingen, Germany), and, in selected cases, neuronavigation (BrainLAB, Heimstetten, Germany) (Fig. 22.4).