37.1 Introduction

Discussing the middle cranial fossa (MCF) approach for vestibular schwannoma (VS) resection would be incomplete without acknowledging Dr. William F. House, who first introduced this technique in 1959.s. Literatur In his initial 1961 publication with the neurosurgeon Theodore Kurze, House described the MCF approach for four patients; initial pathologies that were treated included cochlear otosclerosis through decompression of the cochlear nerve, a facial nerve tumor, tinnitus, and Ménière’s disease for vestibular nerve section. The authors reported no resulting facial paralysis or major intracranial complications. House intuitively realized the utility of the MCF approach for VS resection after incidentally discovering a small VS during a vestibular nerve section. Believing the patient’s symptoms were related to Ménière’s disease, he discovered the small tumor and removed it, resulting in an improvement in the patient’s hearing.

Based on countless hours of cadaveric dissection, House further refined his ideas about the MCF dissection. For example, he identified the internal auditory canal (IAC) by exposing the geniculate ganglion and then tracing the labyrinthine segment of the facial nerve to the canal. Other advancements still used today were the use of diamond burrs and continuous irrigation to reduce risk of injury to neurovascular structures in the IAC.

House’s initial experience developed without modern skull base techniques, such as intraoperative monitoring of facial or cochlear function or preoperative magnetic resonance imaging (MRI) scans. He favored early treatment of smaller intracanalicular VS to reduce risk of neurologic injury and increase rates of hearing and facial nerve preservation. He correctly realized that bleeding, damage, or thrombosis of the labyrinthine artery could cause profound hearing loss, and he also noted that the vascularity of the facial nerve was more resilient than that of the cochlear nerve. By 1968, the time of his second MCF publication, House had resected nearly 200 VS by a variety of approaches.s. Literatur Hearing was preserved in 4 of 5 (80%) patients with tumors limited to the IAC, and 3 of 14 (21%) patients with larger tumors extending up to 1 cm into the cerebellopontine angle (CPA).s. Literatur

37.2 Advantages and Limitations of the MCF Approach

Since House’s initial studies on the MCF approach, the treatment for VS has evolved to include observation, stereotactic radiation, and surgery. If surgery is selected, three main approaches can be used—translabyrinthine (TL), retrosigmoid (RS), and, the focus of this chapter, the MCF approach.s. Literatur

The main advantage of the MCF approach is direct access to the contents of the IAC, allowing for preservation of both hearing and facial nerve function with excellent exposure of small, primarily intracanalicular, tumors. For this subset of VS, rates of hearing preservation tend to be higher in the MCF approach compared to the RS approach, although the rate of transient facial nerve paresis may conversely favor the RS approach.s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur The advantage for hearing preservation using the MCF may be size dependent. In a systematic review of 35 studies with more than 5,000 patients who underwent VS surgery, Ansari et al concluded that the MCF approach was significantly less likely than the RS approach to cause loss of serviceable hearing for tumors ≤ 15 mm (44 vs. 64%, respectively, p < 0.001).s. Literatur However, for tumors larger than 15 mm, the MCF approach tended to result in worse hearing outcomes, with 82% of cases losing serviceable hearing versus 71% for the RS approach, though this difference was not statistically significant.s. Literatur There are likely several reasons for improved hearing results with the MCF approach for small VS confined to the IAC. First, many intracanalicular tumors extend to the fundus, which is more directly visualized with the MCF approach. With the RS approach, the posterior semicircular canal and vestibule obscure visualization of the lateral third of the IAC. Conversely, more fundus can be directly accessed with the middle fossa, although the extreme inferior compartment of the fundus may still be blocked by the transverse crest.s. Literatur Additionally, it has been theorized that the vessels of the IAC are more easily seen and protected via the MCF approach as opposed to the RS approach. Finally, the cochlear nerve is located deep in dissection with the MCF, compared to the RS approach.

Compared to stereotactic radiosurgery, which is often offered as an alternative to surgery for comparably sized tumors, long-term hearing preservation rates may be better with the MCF approach. Several authors have reported 5-year hearing preservation rates of 65 to 89%.s. Literatur ^,​ s. Literatur ^,​ s. Literatur By comparison, hearing degrades over time following radiosurgery. In a recent study of this modality with long-term follow-up, Carlson et al reported a 5-year hearing preservation rate of 48% and a 10-year preservation rate of 23%.s. Literatur Further discussion regarding hearing preservation following radiosurgery is presented in Chapter 52.

Some authors have found early postoperative facial paresis to be more common after the MCF compared to the RS approach; however, no difference is usually seen at 1 year after surgery.s. Literatur ^,​ s. Literatur Others have found no difference in facial nerve preservation with these two approaches.s. Literatur The facial nerve is often located over the superior pole of the tumor within the lateral IAC, between the surgeon and the tumor with the MCF, explaining this finding.

The MCF approach offers limited exposure to the CPA; therefore, significant extension (i.e., greater than 0.5–1 cm) of the tumor into this compartment is a relative contraindication to this procedure and is associated with lower rates of hearing preservation and a potentially higher risk of intracranial complications.s. Literatur ^,​ s. Literatur

37.3 Patient Selection

With the increased utilization of contrast-enhanced MRI, increasingly smaller VS are being diagnosed every year. Given the fact that the smaller tumors may have a period of quiescence, an initial period of observation is generally warranted for the asymptomatic tumor.s. Literatur If growth is observed or the tumor becomes symptomatic, surgical resection or stereotactic radiosurgery are offered to the patient. Older patients, or those not amenable to surgery, can anticipate excellent tumor control rates and modest long-term hearing preservation with stereotactic radiosurgery.s. Literatur For young, healthy patients with serviceable hearing, surgical resection via the MCF approach may provide the best opportunity for long-term hearing preservation and facial nerve function (Table 37‑1 ).s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur In those patients classified as having nonserviceable hearing (i.e., American Academy of Otolaryngology–Head and Neck Surgery class C or D), the MCF approach may still be offered in an attempt to preserve some hearing, which can later be augmented with a cochlear implant or even traditional or nontraditional hearing aids. Even marginal hearing may be valuable to the patient with contralateral hearing loss and, for others, may still be useful to facilitate sound localization. Although somewhat controversial, the MCF approach may also be used for IAC decompression in order to maximize the duration of hearing preservation in patients at risk for bilateral, profound hearing loss such as those with neurofibromatosis type 2 or VS in an only hearing ear.s. Literatur