41.1 Background

The controversy over partial resection of large vestibular schwannomas (VSs) is in no way a new topic. The question dates back to two of the earlier protagonists of VS surgery, namely, Harvey Cushing and Walter Dandy. Possibly fueled by aversion to one another’s growing prominence, this issue became one of the central points of their feud.s. Literatur Dandy, advocated a total resection of these tumors,s. Literatur whereas Cushing was the main proponent of partial resection.s. Literatur While every one of Dandy’s patients suffered complete facial paralysis, many of Cushing’s patients demised from recurrence of large remnants a few years after surgery.s. Literatur With the advances in microsurgery over the next century, most surgeons came to endorse total resection in all but select elderly and fragile patients.s. Literatur ^,​ s. Literatur However, as the focus of surgery has now shifted from preservation of life to preservation of function, many surgeons are more willing to entertain less-than-total resection of larger tumors in favor of preservation of facial function.

41.2 Definition of Subtotal and Near-Total Resection

Currently, there is no widely acceptable definition of degree of resection when the entire tumor has not been extirpated. One encounters terms such as “partial,” “subtotal,” “near-total,” “intracapsular,” and “radical subtotal” for various degrees of less-than-total resection. The most widely accepted terms are “near-total” and “subtotal” resection (Fig. 41‑1 ). Many surgeons resort to descriptive terms and do not provide exact dimensions or percentage of the tumor resected when using subtotal (STR) or near-total (NTR) designation.s. Literatur ^,​ s. Literatur ^,​ s. Literatur Few have adopted criteria established by the consensus meeting in 2003.s. Literatur In this consensus statement, NTR was defined as tumor residual measuring less than 2% of the original tumor by volume, and partial resection deemed as up to 5% of the tumor and any larger tumor remnant was designated as STR. As the authors attested, this classification is very subjectives. Literatur and there are major issues with its adoption. First, it is very difficult for most surgeons to make a precise measurement of the tumor remnant during surgery. Several studies have confirmed the poor relation between postoperative MRI findings and surgeon’s estimation of tumor remnant volume.s. Literatur ^,​ s. Literatur Second, using percentage as a defining criterion is faulty as 5% of a tumor measuring 2 cm in diameter (volume of approximately 4.19 cm³) is 0.21 cm³ but 5% of a 4-cm tumor (volume of approximately 33.51 cm³) measures 1.67 cm³. The latter tumor remnant is eight times larger than the former. Others have proposed a definition based on actual size of the remnant. For example, Bloch et al recommended a remnant of 5 × 5 × 2 mm or smaller to be considered a NTR and anything larger to be categorized as STR (Fig. 41‑2 ). What this definition does not account for is the potential clinical outcome difference between remnants measuring 0.5 and 5 cm³ both of which are considered STRs.

41.3 Facial Nerve Outcomes as Related to Degree of Resection

The impetus behind a less-than-total resection is mostly preservation of facial nerve function. The majority of the literature demonstrates that excellent short-term and long-term facial nerve preservation rates are not optimal for larger tumors after gross-total resection (GTR). Surgeons with large series have reported rates between 33 and 73% of good facial nerve outcomes (i.e., House–Brackmann [HB] grades I–II) following more definitive surgery.s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur Conversely, when surgeons have performed planned STR as first stage of treatment to be followed by radiation or a second-stage operation, they have achieved much better results. It is not surprising that rates of 85 to 100% good facial nerve function are achieved when the plane between the tumor and thinned-out frail facial nerve or the brainstem is not engaged.s. Literatur ^,​ s. Literatur In a systematic review of studies on resection of large VSs, the extent of tumor resection was reported on 471 of the 1,688 patients eligible for the analysis. The review demonstrated a strong and significant association between degree of resection and good/excellent facial nerve outcome (HB grades I–II). The rate of good facial nerve function was 92.5% for the 80 patients receiving STR, compared to 74.6% (n = 55) for NTR and 47.3% (n = 336) for GTR.s. Literatur

The intraoperative decision as to when any further dissection would result in deterioration of the facial nerve has been largely left to the surgeon discretion. As one can imagine, this point is highly dependent on surgeon’s comfort and experience as well as what they envision appropriate based on patient’s demographics and wishes. More recently, some surgeons have advocated use of electrophysiologic properties of the nerve to help guide the extent of resection. In the study of Haque et al, the authors advocated for STR if a minimum of 0.3 mA was needed to stimulate the nerve at the brainstem or an increase of 0.1 mA from baseline was observed.s. Literatur In a similar study, continuous intraoperative evoked facial nerve electromyography (EMG) demonstrated worse outcome when the amplitude fell 50% below the initial value.s. Literatur Schmitt et al reported reliable prognostic value using pulsed constant-current stimulation at supramaximal levels at the root exit zone compared to the peripheral segment exiting the stylomastoid foramen. They reported that for patients who had proximal-to-distal drop off of over 69%, the rate of long-term poor facial function was 44% compared to 6% for patient with values less than 69%. This method was suggested by the authors as a potential viable method to guide degree of less-than-total resection.s. Literatur Further discussion regarding facial nerve function prognostication using intraoperative stimulation testing is reviewed in greater detail in Chapter 27.

41.4 Tumor Control Rate as a Function of Degree of Resection

The main concern with performing less-than-total resection is that the remnant tumor would require treatment within a few years. As is the case with defining the degree of resection, currently no universal definition exists for “growth of remnant” or “failure of treatment” in our literature. Studies have used radiologic definitions anywhere between 1 and 5 mm of growth in the diameter of the tumor as clinical definition of failure.s. Literatur ^,​ s. Literatur ^,​ s. Literatur This is one reason why the rates of recurrence after less-than-total resection vary so widely in the literature.s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur A second source of variance in reporting is the duration of follow-up. It is clear in the literature that the reported rate of recurrence increases as the duration of follow-up is extended. Thus, the risk of recurrence is best summarized using time to event analysis, such as the Kaplan–Meier method. On average, approximately one-third of patients who have undergone STR would develop tumor regrowth, whereas the regrowth rate among GTR and NTR patients is usually in single digits. For example, Bloch et al found that the rate of regrowth for their NTR population was 3% compared to 32% for STR.s. Literatur Similarly Seol et al reported statistically significant regrowth rates of 3.8, 9.4, and 27.6% in their GTR, NTR, and STR population, respectively.s. Literatur Table 41‑1 summarizes select large publications reporting rates of regrowth following less-than-complete VS resection.