74 What Is the Best Treatment for Small- to Medium-Sized Vestibular Schwannoma?
74.1 Introduction
There is probably not a more controversial topic in all of neurosurgery or neurotology than the question of optimal treatment for a small- to medium-sized vestibular schwannoma (VS). Even before there was much of an opportunity to diagnose and treat smaller VSs, controversy surrounded the diagnosis of any VS (typically quite large and life-threatening in the early 1900s). At the beginning of the last century, the surgical mortality from the treatment of a VS was as high as 70 to 80%. It was quite questionable at that time whether surgery of the cerebellopontine angle (CPA) should be undertaken at all. Harvey Cushing, the father of American neurosurgery, advocated a wide bilateral suboccipital craniectomy to decompress the posterior fossa, facilitating safe dural opening, and intracapsular subtotal resection of VS, which reduced operative mortality significantly. This paradigm was relatively quickly challenged by one of Cushing’s most accomplished pupils, Walter Dandy, who alternatively, strongly advocated for a complete resection via a unilateral exposure of the CPA and partial resection of the lateral cerebellar hemisphere to aid safe exposure. A fascinating discussion of this history can be found in Chapter 1, authored by Richard T. Ramsden. Additionally, the article by Akard et al likewise reviews the early evolution of surgical treatment of VS.s. Literatur Once again, one of the main difficulties of that time was that there were no small- or medium-sized VS being diagnosed. They were all large and life-threatening at the time of diagnosis. In fact, in 1921, Cushing opined, “It is possible that someone may someday be able to completely enucleate one of these lesions, but it is not likely until earlier diagnoses are made and tumors of smaller size are exposed.”
Following this contentious debate came the question of which surgical approach should be used; in the 1960s, primarily retrosigmoid versus translabyrinthine. In the 1980s, the role of stereotactic radiosurgery (SRS) versus microsurgery became the primary debate for the next few decades. Most recently, with a better understanding of the benign natural history of many small VSs, the original debate of more than 100 years ago regarding whether treatment is even indicated has emerged again as perhaps the most prominent controversy, especially as it relates to small- and medium-sized VS.
For the past almost two decades, we have had the opportunity to be on various panels, discussion groups, and guideline writing committees and attended national and international meetings during which this important and contentious issue has been debated. Perhaps, most importantly, we have worked together on an essentially daily basis counseling thousands of patients with small- to medium-sized VS. We evaluate approximately 150 brand new VS patients per year. The purpose of this chapter is to relate to the reader our approach in advising patients regarding their options, and try and provide a rationale for how we determine the best treatment for a small- to medium-sized VS in any individual patient.
74.2 Case Example
We recently evaluated a 49-year-old Caucasian woman with no significant past medical history. She reported a several-month history of right-sided tinnitus that sounded “like water running.” It was not particularly intrusive, was not interfering with sleep or concentration, but was present most of the time and in retrospective she noted “fullness” in that ear as well. She also admitted to several episodes of imbalance without true vertigo. She had no history or facial numbness, weakness, or hemifacial spasm. She had no history of prior ear or cranial surgery, radiation exposure to the head or neck, and there was no family history of brain or peripheral nerve tumors. An audiogram confirmed mild high-frequency right-sided sensorineural hearing loss with a pure-tone average of 4 dB on the right and 1 dB on the left. Word recognition scores (WRSs) were 100% bilaterally (Fig. 74‑1 ). An MRI scan of the head with and without gadolinium was performed to investigate her mild asymmetric hearing loss and unilateral tinnitus. The scan revealed an intracanalicular enhancing tumor consistent with a VS (Fig. 74‑2 a–c). It was not readily apparent, even on very thin cut coronal images (Fig. 74‑2 b) whether the tumor was arising from the superior or inferior vestibular nerve. There was a small fundal cap of CSF (Fig. 74‑2 c) indicating the tumor did not extend lateral to the transverse crest. What is the best treatment going forward for this patient?
74.3 What We Think We Know…
74.3.1 Microsurgery
As outlined in Chapter 31, in select patients, microsurgery has an excellent chance of complete tumor removal and preservation of useful hearing and normal facial nerve function. The likelihood of this positive scenario depends on tumor size, extent of tumor involvement of the fundus of the internal auditory canal (IAC), baseline hearing prior to surgery, and experience of the operative team. As has been reviewed elsewhere, smaller tumors centered near the porous (Fig. 74‑3 a), rather than the fundus of the IAC (Fig. 74‑3 b), with 100% WRS are optimal for surgical removal.
For the case example presented, we would offer the patient resection through either a middle fossa or retrosigmoid approach. It is not readily apparent on coronal imaging whether the tumor is more likely from superior or inferior vestibular nerve origin. Typically, tumors that arise from the superior vestibular nerve are better candidates for middle fossa surgery, whereas tumors that extend below the transverse crest are much more challenging (Fig. 74‑3 b). We would estimate a 99% chance that we would remove the tumor in the case example (Fig. 74‑2 a–c) completely and there would be no recurrence in her remaining lifetime. There would be a 95% chance of normal or near-normal facial nerve function (House–Brackmann grades 1–2) 1 year following surgery with an approximately 10 to 15% risk of temporary facial weakness immediately following removal. The chance of maintaining American Academy of Otolaryngology – Head and Neck Surgery (AAO–HNS) class A hearing (>70% WRS and <30 dB pure-tone average) we would estimate to be approximately 50 to 60%. We always include small (1–2%) risks of bleeding, infection, and a 5% risk of cerebrospinal fluid leak. This is based on our experience operating on approximately 650 VSs as the primary surgeons over the past 17 years. We emphasize that most patients are vertiginous or at least have a great deal of disequilibrium for the first 48 hours, postoperatively. The majority of patients spend the first 24 hours at bed rest for this reason and the typical hospital stay is 3 to 4 days. We ask patients to limit exertional activities for 3 months after surgery and feel the same amount of time off work is reasonable, but if the patient has a more or less sedentary occupation, they can return to work 4 to 6 weeks following surgery if they feel ready; however, in our experience, few patients do, usually related to a general feeling of fatigue. We obtain a follow-up MRI and audiogram and see the patient back in 3 months at which time they are released to all activities without restriction. If the 3-month MRI confirms gross total resection, we obtain another MRI at 2 years to look for early recurrence and one 5 years after that (7 years postoperatively) to investigate for later recurrence, which we think is very important in hearing preservation cases. If the 7-year scan is negative for tumor recurrence, we try and get another MRI in 7 to 10 years to look for extremely late recurrence. There remains a gap in the literature, in our opinion, regarding the durability of retained hearing following microsurgery. Most studies addressing this issue have approximately only 5 years of audiometric data and there are a large number of patients in the cohorts that are lost to follow-up.s. Literatur , s. Literatur , s. Literatur , s. Literatur , s. Literatur We have seen rare patients who have late deterioration in their functional hearing with no tumor recurrence. However, we typically counsel patients if they maintain useful hearing following surgery they are likely to keep it long term.
74.3.2 Stereotactic Radiosurgery
The results of SRS to treat VS are well reviewed in Chapters 16 through 19. We have treated more than 800 VSs at the Mayo Clinic over the past 26 years using the Leksell Gamma Unit (Elekta AB, Stockholm, Sweden). For the tumor presented here, we would estimate a 93% chance of long-term tumor control.s. Literatur There is a less than 1% chance of any adverse facial nerve effects (hemifacial spasm or weakness), and an at least 50% chance of retained AAO–HNS class A or B hearing at 5 years which likely drops to only a 25% chance of maintaining useful hearing by 10 years post-SRS.s. Literatur Similar to the expected outcomes from microsurgery, a smaller tumor, not impacted in the fundus of the IAC and occurring in a patient with excellent baseline hearing, is the optimal candidate for SRS. We emphasize to patients, SRS is a 1-day outpatient procedure. Most patients experience mild postprocedure discomfort and swelling at the pin sites for a few days afterward but can resume a completely normal lifestyle with no restrictions usually within 48 hours of treatment, including return to full-time occupation. We obtain follow-up MRI scans and audiograms at 6-month intervals for the first year, then yearly for 2 more years, then every other year for the next 4 years, then every third year for the next 6 years, then every fourth year for the next 8 years and so on. Based on our recent analysis of growing tumors prior to SRS, we strongly prefer to determine if or at what rate the tumor is growing prior to SRS. We found extracanalicular tumors growing more than 2.5 mm/year were less likely to be controlled (69% tumor control rate) with radiation compared to tumors growing less than 2.5 mm/year (97% tumor control rate).s. Literatur We do counsel patients that if the tumor fails SRS, we almost always recommend surgical resection. Surgery after failed SRS is generally more difficult, in particular obtaining gross total resection, but for an intracanalicular tumor, this is much less of a concern compared, for instance, to a tumor 2.5 cm in posterior fossa diameter that fails SRS.s. Literatur , s. Literatur , s. Literatur , s. Literatur , s. Literatur We have recommended repeat SRS four times in almost 20 years in patients who we thought were too ill to safely undergo a general anesthetic for surgery to treat their enlarging VS following prior SRS. Similar to other limited reports in the literature, this has proven safe and, with very limited follow-up, effective to date.s. Literatur , s. Literatur , s. Literatur , s. Literatur , s. Literatur Based on best evidence, the risk of a secondary radiation-associated malignancy or malignant degeneration of a benign VS is extremely low—probably, less than or equal to the risk of dying from an intraoperative or postoperative complication if microsurgery is chosen.s. Literatur The topic of secondary malignancy following radiosurgery for VS is reviewed in Chapter 24.
Related posts:
73 Management of Small Vestibular Schwannoma in Patients with Minimal Symptoms
76 Treatment of Cystic Vestibular Schwannoma
77 Primary Inner Ear (Intralabyrinthine) Schwannomas
75 Management of Sporadic Vestibular Schwannoma in the Only Hearing Ear
16 Gamma Knife Radiosurgery for Treatment of Sporadic Vestibular Schwannoma
45 Avoidance and Management of Vascular Complications During Vestibular Schwannoma Surgery
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