The Operation for Hydrocephalus Due to Posterior Fossa Tumors in Children

Semi-elective tumor surgery – options for managing associated hydrocephalus

ETV prior to tumor surgery

• Is treatment needed? The argument against this option is that it commits the child to a potentially unnecessary ETV. Seventy-five percent of patients with hydrocephalus due to a posterior fossa tumor will not require any permanent treatment for the hydrocephalus.
• Creation of better surgical environment for tumor resection: This option has been put forward by enthusiasts of ventriculostomy on the grounds that it helps the overall condition of the child and provides for smoother operative conditions during tumor resection. These arguments are rarely valid in the authors’ experience. With modern anesthetic management surgical conditions are usually excellent, and ETV is not without possible risks (basilar artery injury, rarely).
• Reduction in need for post-resection shunting: Argument has been made that performing an ETV prior to the tumor resection reduces the incidence of postoperative shunting from 27% to 6% (35).

Shunting or EVD prior to tumor surgery

• Is treatment needed? This choice also commits 75% of the patients to an unnecessary treatment with the possible risks of infection, upward herniation, or hemorrhage within the tumor. Although they rarely happen, these complications are possible.

Shunting or EVD at time of tumor surgery

• Standard management prior to CT and MRI: This option is the classical teaching of Cushing, who in 1914 described the surgical excision of a cerebellar astrocytoma in detail and included in it the routine use of an occipital EVD or at least the placement of an occipital bur hole to allow for emergency drainage of CSF if the patient’s condition deteriorated acutely after surgery. Now, with the availability of CT scans, MRI, and modern anesthesia in most centers, it is rare to see a patient whose condition suddenly deteriorates due to acute hydrocephalus in the postoperative period. Rather, hydrocephalus that requires permanent treatment in the postoperative period typically presents either with a persistent pseudomeningocele and/or CSF leak, or with a failure of the patient to recover rapidly from the tumor resection (assuming that no untoward events have taken place during that surgery).

Occipital bur hole at time of tumor surgery

• Still performed by many: The formation of an occipital bur hole at the beginning or the end of the procedure is still practiced by many neurosurgeons worldwide.

ETV at time of tumor surgery

• Remove the tumor and perform an ETV: The argument against performing an ETV at the time of tumor removal is the same as that for performing an ETV prior to removing the tumor, namely that most patients will not need treatment for post-resection hydrocephalus.

Shunt or ETV for persisting hydrocephalus

• Thoughtful decision to treat hydrocephalus usually possible: Typically, patients are not acutely sick from residual hydrocephalus to a level that threatens their health after they undergo resection of a posterior fossa tumor. Consequently, they can be observed initially in the hope that their hydrocephalus will resolve. Resolution will occur in 75% of cases (5, 7).

Rapid deterioration requiring emergent intervention – options for managing associated hydrocephalus

Emergency EVD, ETV, or shunt insertion

• Typically will not relieve posterior fossa pressure: CSF diversion only (first two options above) is rarely enough, as the pressure within the posterior fossa is elevated. If the tumor is not removed immediately, the patient will have severe brainstem compromise despite CSF drainage.
• ETV – additional danger of rebound pressure: One cannot be sure that any decompression afforded by performing an ETV will be maintained once the CSF that is removed at the time of surgery is replaced by normal CSF production.

Tumor resection

• Emergency tumor resection – reestablish CSF circulation: The authors prefer this choice, as it deals conclusively with the cause of the elevated ICP and the hydrocephalus, namely, the presence of a mass in the posterior fossa. This choice assumes the presence of appropriate facilities and a surgical team attuned to emergency surgery of such magnitude.

Tumor resection and CSF diversion

• Removal of tumor or persisting CSF blockage requires CSF drainage: Occasionally an emergency decompression is required, necessitating removal of CSF. In most cases a simple EVD will suffice. The other options of shunt placement or ETV will add to the operation time, add to the list of possible complications, and probably commit a large majority of children managed in such a way to an unnecessary operation.

Management of postoperative hydrocephalus

Patients with persistent active hydrocephalus after tumor resection often present with persistent pseudomeningocele or CSF leak, or with failure to progress postoperatively. A few drops of CSF or a wet- looking dressing can be managed initially with one or more sutures. Usually this can be seen in the first postoperative days. A more persistent leak or a pseudomeningocele that enlarges and becomes tense is a clinical sign of active hydrocephalus that needs treatment. Imaging options (CT or MRI) may not add more information since the leaking or accumulating subcutaneous CSF at the wound site doesn’t allow for an increase in the size of the ventricular system. Symptoms and signs of acutely raised ICP are uncommon. There are several management options.

Placement of an EVD

• Rarely successful for managing persisting or late hydrocephalus: There is little to be gained in trying to temporize by placing an EVD. This rarely avoids the need for permanent treatment of the hydrocephalus and runs the risk of CSF infection and mechanical problems (accidental removal by children requiring additional anesthesia for replacement).

Perform an ETV

• Preferred by authors: The authors prefer to attempt ETV first, and, if that is inadequate, to resort to a ventriculoperitoneal shunt. The main reason for the initial choice of ETV is to avoid the insertion of shunt hardware with the increased complication rate and the possible shunt dependencies.

Place a ventricular shunt

• Perform with dispatch to lessen risk of infection: In the absence of expertise or equipment to perform ETV, shunting should be performed as quickly as possible to avoid CSF infection if there is CSF leak and speed the patient’s recovery, especially if further treatment is planned (e.g., chemotherapy, radiotherapy).
• Confirm CSF parameters do not predict shunt occlusion: Placement of a permanent shunt requires normal CSF composition, or at least not a high red cell count as this increases the risk for shunt occlusion. There should also be no signs of a CSF infection. A CSF leak should not be left untreated for long, as there is risk of colonization of CSF (before the clinical manifestation of overt meningitis), which will prevent shunt placement.