Preparation for Surgery for Hydrocephalus due to Posterior Fossa Tumors in Children

Indications for Surgery

Hydrocephalus treatment only

• EVD: EVD is the emergency treatment of hydrocephalus due to increased ICP signs if for any reason the team is not ready to proceed to tumor resection (night time, poor clinical condition, no proper scans available). Attention must be paid to CSF loss due to upward herniation risk. A right frontal bur hole (Kocher’s point) is used, and samples are sent for microbiology and cytology. Initially, the drainage is set at 15–20 cm H2O. Risk for CSF infection increases after prolonged use (> 7 days). If the planed tumor resection to follow is to take place in the sitting position, the presence of the EVD will increase the risk for extradural hematomas (35).
• Ventriculoperitoneal shunt: The indications for use are the same as those for EVD. There is a much lower infection risk. The ventricular catheter is connected to a separate reservoir so that it can be used later for CSF cytology studies or intraventricular chemotherapy administration. A high-pressure valve setting is used initially (if adjustable valve used). There is a theoretical risk for peritoneal seeding with tumor cells as well as a risk for future shunt dependency and shunt complications (obstruction, malfunction). One side of the neck is left for future long-line insertion, and the abdominal incision is done away from midline for future gastrostomies.

Tumor resection

• Gross tumor resection favored: Total or gross total tumor resection without any new neurological deficit is the optimum target for cerebellar and fourth ventricular tumors. Resection will provide tissue diagnosis, prevent further neural tissue compression and damage, and restore CSF pathways. For the majority of posterior fossa tumors in children, the extent of the first resection is an independent and important factor for favorable outcome.

Preoperative Orders

• IVF rate: NaCl 0.9% + 20 mEq/l KCl or NaCl 0.45% at 4 ml/kg for first 10 kg, 2 ml/kg for second 10 kg, and 1 ml /kg for each subsequent Kg (15).
• Antibiotic: One dose of second generation cephalosporin IV, 30 min prior to incision. Repeat dose after 3 hours if the operation is still continuing.
• Clamp time for CSF drain: Clamp time is usually 2 hours before the operation. Close neurological observation is required after that.
• Surgical site scrub: For elective procedures, a whole body wash with octenidine lotion is performed the night before and 2 hours before the operation. The surgical site is scrubbed with povidone iodine or chlorexidine in many centers.

Anesthetic Considerations

• Positioning: The patient is positioned (prone, concorde, park bench, sitting) according to the surgeon’s preference and planning. Most surgeons prefer a prone position for posterior fossa tumors. When the patient is in the sitting position the potential for air embolism needs to be accounted for.
• Protection for “tight brain”: Management of brain edema, venous drainage and ICP before dura opening (position, medications, hyperventilation, CSF drain) is basic to successfully treating hydrocephalus in these patients.
• Intraoperative monitoring: If neuromonitoring (SSEPs, BSAER) is being considered, such considerations should be communicated to the anesthesiologist so conflicts between agents they might use and the intended monitoring do not occur.

Devices to Be Implanted

• Ventriculoperitoneal shunt: Tubing is selected according to the surgeon’s preference (plain silicone, antibiotic- impregnated, silver-processed). Different types of valves are available (fixed – differential pressure, adjustable, etc). A small profile is needed for pediatric patients and high pressure settings due to upward herniation risk. A separate subcutaneous reservoir (Rickham, Ommaya) is connected to the ventricular catheter for future CSF sampling and possible intraventricular chemotherapy administration. Antisiphon devices are used. Tumor filters have no proven efficacy and high obstruction rates.
• EVD: Antibiotic-impregnated or silver-processed catheters are used. Long tubing is used for infection resistance. Draining systems are used for bedside application with centimeter scale for pressure measurement and a collection chamber for estimation of 24-hour losses.

Ancillary/Specialized Equipment

A fully equipped operating room is needed for tumor resection:

• Microscope: A microscope is mandatory. It can be preset to the surgeon’s preferences and incorporated into the operating room’s navigation system, wherever available.
• Endoscope: The endoscope can be used for ETV before tumor resection or during resection to reach difficult angles (e.g., foramina of Luschka in ependymoma surgery) and trajectories.
• Neuronavigation: Now widely available, neuronavigation can help with surgical planning and orientation. The surgeon must be familiar with the limitations of its use in the posterior fossa and the drawbacks (brain shift due to CSF loss). Operating rooms with intraoperative MRI facilities provide additional assistance and may enable more aggressive tumor resection with a second or even third look whenever appropriate.
• Ultrasound: Ultrasonography is valuable in experienced hands. It can be used before corticotomy for a better approach and during tumor removal for imaging of the tumor cavity and possible residual.
• Ultrasonic tumor aspirator: This tool can be useful for most tumors except for those that are highly calcified (which are not commonly seen in the posterior fossa). Great attention is needed when it is used in proximity to delicate structures (floor of fourth ventricle, cranial nerves).