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Indications for Surgery
- General indications: The indications for considering treatment of a patient with an ETV begin with the establishment of the need to treat the hydrocephalus. The same considerations are used to determine the need for treatment in a child being considered for a CSF shunt.
- Indications for ETV: There are currently no accepted or proven criteria for identifying a child as a candidate where treatment success is expected. Only relative criteria are established. These include obstructive hydrocephalus due to lesions in or about the midbrain and fourth ventricle, webbing or obstruction of the aqueduct, and obstruction of CSF flow at the level of the fourth ventricle or its outlets (33, 34). Over time the indications have broadened, with some advocating the use of ETVs to manage shunt obstruction, shunt infection, and normal pressure hydrocephalus (31, 59, 60).
- Standard preoperative orders: No special preoperative orders are required for patients undergoing ETV.
- Ventricle dilation: While the ventricle size will not be an issue when performing an ETV on a patient with newly diagnosed hydrocephalus with ventriculomegaly, thought must be given for preparing the ventricular space for navigation by the endoscope in patients who have had shunts and whose ventricles are not enlarged. If a shunt is present, it can be externalized and resistance to outflow increased to enlarge the ventricles; in essence, this represents a controlled shunt failure. The patient should be in a monitored setting when this procedure is performed. It is wise to confirm the adequacy of ventricular enlargement with imaging prior to surgery.
- Imaging: A MRI should be available prior to surgery. It should be analyzed to confirm that the foramen of Monro can be passed safely by the endoscope, that the massa intermedia will not interfere with visualizing the floor of the third ventricle, that the vessels of the circle of Willis are clear of the intended ETV, and that there is an adequate cisternal space below the floor of the third ventricle for performing the ETV.
- Cardiac risks: The anesthesiologist should be aware of the risk for significant autonomic anomalies during the procedure and prepared to intervene (32).
Devices to Be Implanted
- EVD: A temporary EVD may need to be placed, and the necessary equipment should be available.
- Ommaya in selected cases: A permanent access device for removing CSF from the ventricles can be considered, and an Ommaya reservoir can be inserted when this is desired.
Image guidance equipment
- When a patient has relatively small ventricles or abnormal anatomy, image guidance may be needed. Options include ultrasound, intraoperative CT or MRI, or stereotactic image guidance (either frame-based or frameless).
- Endoscope: The endoscope is a delicate piece of equipment ideally sterilized with gas, and thus its availability should be confirmed the day before surgery to avoid having to use alternative means of sterilization. Most neurosurgeons use either a solid lens or flexible scope that has an instrument channel for passing the instruments needed to make the ostomy. Rare descriptions exist of just using the scope to make the ostomy by pushing it through the floor, but the disadvantage of not being able to see the actual creation of the ostomy with the attendant risks is obvious.
- Peel-away sleeve: A correctly sized peel-away catheter with obturator should be available to create a channel through which the endoscope can be introduced into the ventricle.
- Camera, light source, video monitor, video recorder: There are real advantages to being able to visualize the scope’s image on a monitor as opposed to simply looking down the scope through its eye piece. Besides remaining comfortable, the surgeon maintains a sense of orientation of the scope to the patient and to the depth to which it has been advanced. Currently, high-definition cameras (so-called 3 chip) and intense fiber optic illumination provide high clarity of the surgical field without threat of heat injury. Video recording can be of great use in teaching and in analyzing cases after the fact.
- Irrigation pump and tubing: Irrigation should be available, easy to use, and controllable. While a simple setup of an IV extension line and large syringe filled with irrigation fluid can fulfill this need, modern pumps with adjustable rates of infusion add a layer of safety by decreasing the likelihood of acutely over-pressurizing the ventricles.
- Cautery: Although most do not recommend using energy to actually cut through the floor of the third ventricle, it can be useful to have contact cautery available for enlarging the ostomy by cauterizing its edges and to thin a scarred floor of the third ventricle prior to making an opening through it with a blunt probe.
- Instruments: Typically a blunt probe is used to make the initial ostomy, and then an instrument is used to enlarge the ostomy, generally to at least the diameter of the endoscope being used so as to allow its passage into the suprasellar and prepontine cisterns. A Fogarty catheter can also be considered as a tool for the enlargement of the ostomy. When the hydrocephalus is due to an obstructing lesion that one anticipates will be visualized during the procedure, biopsy equipment may be desired and should be available.
- EVD: Materials to set up an EVD should be available in the event that one is needed prior to leaving the operating room.
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