42.2.1 Indications and Preoperative Considerations

Staged resection is generally reserved for large vestibular schwannomas; however, if intraoperative factors dictate, it may be considered for medium-sized tumors as well. Patients and families should be educated preoperatively on the possibility of staged surgery with the goal of improved long-term facial nerve function. Although the decision for staged surgery is usually made intraoperatively, it is our opinion that it is acceptable to preoperatively plan a staged resection based on tumor size alone. Our experience has been that patients and families are accepting of more than one surgery if it offers improved long-term quality of life and facial nerve outcomes. Often, the patient’s recovery after subsequent surgeries is shorter and easier due to prior vestibular function loss and compensation.

42.2.2 First-Stage Surgery

Traditionally, first-stage surgery has consisted of a retrosigmoid approach. The medial tumor is debulked and removed from the cerebellopontine angle (CPA) with preservation of neurovascular structures. Advantages of the first-stage retrosigmoid approach include keeping an undissected plane around the facial nerve in the internal auditory canal (IAC). If the tumor has favorable intraoperative factors for tumor removal and neural preservation, bone can then be removed over the IAC and dissection continued. If intraoperative factors dictate a staged resection, the bony IAC is not drilled and Silastic sheeting (0.004″) is placed within the CPA to reduce adhesions between the cranial nerves, brainstem, cerebellum, and the residual tumor.

More recently, a first-stage translabyrinthine approach instead of a retrosigmoid approach has been advocated.s. Literatur Even if the preoperative plan was to stage the tumor because of very large size, we generally still pursue near-total or gross-total resection if intraoperative factors permit. If the resection does not favor a single-stage surgery, eggshell thin bone overlying the IAC is left intact, and the tumor is removed from the CPA and Silastic sheeting placed. Preserving the bony IAC allows virgin dissection planes during the subsequent surgery.

42.2.3 Intraoperative Factors

Since the first series published by Sheptak and Jannetta, intraoperative factors have served as driving forces for staged microsurgery. As mentioned earlier, some surgeons may decide preoperatively to perform a staged resection, based on patient’s health, tumor size, and degree of brainstem compression. Most often, however, intraoperative factors are used as an “ending point” for the first surgery. Early reports cited tumor adherence to the brainstem as the primary indication for staged resection; however, with technological advancements, further criteria have been found beneficial as outlined later.

The advent of facial nerve monitoring has dramatically improved facial nerve outcomes in large tumors. At the author’s institution, we routinely employ the use of stimulating dissectors to maximize the benefit of facial nerve monitoring. These instruments include stimulating needles, round knifes, and other instruments which are insulated to the tips (Fig. 42‑1 ). These instruments allow for “active” monitoring in which the surgeon is alerted to the proximity of the nerve by continuous electrical stimulation. This is in contrast to intermittent stimulation with a neurostimulator probe, or “passive” monitoring that only provides feedback to the surgeon when there is stretching or mechanical injury. Higher levels of current (e.g., 1 mA) are used to map the general location of the facial nerve, whereas low levels (e.g., 0.1 mA) are used to differentiate tumor from the adjacent neurovascular structures. The use of stimulating dissectors allows for more confident dissection of the tumor and more precise localization of the facial nerve, both of which reduce intraoperative injury to the nerve and facilitate efficient dissection.

Changes in facial nerve excitability will often lead surgeons to temporarily or definitively stop resection. Prolonged or train EMG potentials indicate nerve irritation and potential damage, and should prompt the surgeon to modify dissection. An increase in the threshold of stimulation signifies facial nerve injury and serves as an indicator to stop tumor resection and consider staged surgery. The tumor and facial nerve relationship is also important in determining whether large tumors need to be staged. A thinned or splayed facial nerve and a densely adherent facial nerve are commonly cited indications for staged resection. Additionally, a meandering course of the facial nerve over the superior pole of the tumor, or much less commonly over the dorsal tumor capsule, portends a poorer facial nerve outcome and may benefit from staged surgery. Other less common indications to stage tumor resection include vital sign changes (abrupt bradycardia), prohibitive cerebellum or brainstem edema, or peritumoral bleeding.

Considering the aforementioned criteria, the guiding principle for staged surgery is the concept of “taking only what the tumor gives.” A single-stage, “conventional surgery” is ideal when facial nerve function can reasonably be preserved; however, a staged surgery or multimodality treatment (e.g., adjuvant stereotactic radiosurgery) should be considered if facial nerve preservation or patient health is potentially compromised. The use of intraoperative monitoring with stimulating instruments and surgeon experience allows the surgeon to know when facial nerve injury is imminent and modify or terminate the surgery. Understanding the above factors including the principle of “taking only what the tumor gives” should guide surgeons in making the appropriate intraoperative decision to stage tumor resection or continue with a single-stage surgery. The interested reader may also review Chapter 27 on intraoperative facial nerve monitoring, Chapter 32 on intraoperative management of the facial nerve, and Chapter 41 on subtotal resection.