Johannes Sarnthein, Nader Hejrati, Marian C. Neidert, Alexander M. Huber and Niklaus Krayenbühl
During surgeries that put the facial nerve at risk for injury, its function can be continuously monitored by transcranial facial nerve motor evoked potentials (FNMEPs) in facial nerve target muscles. Despite their advantages, FNMEPs are not yet widely used. While most authors use a 50% reduction in FNMEP response amplitudes as a warning criterion, in this paper the authors' approach was to keep the response amplitude constant by increasing the stimulation intensity and to establish a warning criterion based on the “threshold-level” method.
The authors included 34 consecutive procedures involving 33 adult patients (median age 47 years) in whom FNMEPs were monitored. A threshold increase greater than 20 mA for eliciting FNMEPs in the most reliable facial nerve target muscle was considered a prediction of reduced postoperative facial nerve function, and subsequently a warning was issued to the surgeon. Preoperative and early postoperative function was documented using the House-Brackmann grading system.
Monitoring of FNMEPs was feasible in all 34 surgeries in at least one facial nerve target muscle. The mentalis muscle yielded the best results. The House-Brackmann grade deteriorated in 17 (50%) of 34 cases. The warning criterion was reached in 18 (53%) of 34 cases, which predicted an 83% risk of House-Brackmann grade deterioration. Sensitivity amounted to 88% (CI 64%–99%) and specificity to 82% (CI 57%–96%). Deterioration of FNMEPs and a worse House-Brackmann grade showed a high degree of association (p < 0.001). The impact of FNMEP monitoring on surgical strategy is exemplified in an illustrative case.
In surgeries that put the facial nerve at risk, the intraoperative increase in FNMEP stimulation threshold was closely correlated to postoperative facial nerve dysfunction. Monitoring of FNMEPs is a valid indicator of facial nerve function in skull base surgery. It should be used as an adjunct to direct electrical facial nerve stimulation and continuous electromyographic monitoring of facial nerve target muscles.
Bertrand Actor, Johannes Sarnthein, Peter Prömmel, David Holzmann and René L. Bernays
The direct transnasal transsphenoidal approach to the sellar region has become a widely adopted surgical procedure among neurosurgeons and ear, nose, and throat specialists. Nasal complications and their incidence have been investigated, but a systematic testing of olfactory disturbance has not previously been performed. Considering that the sense of smell is deeply anchored and interwoven within the CNS, and that its impairment implies a considerable loss in quality of life, surgical practice should aim at its preservation.
In this retrospective study, pre- and postoperative olfactory performance, nasal airway passage, septal perforation, and epistaxis were assessed in 96 patients who underwent direct transnasal transsphenoidal microsurgery at the authors' department between January 2007 and August 2009. Olfactory performance was assessed using the Sniffin' Sticks test and/or the Zürcher Geruchstest.
After surgery, 47 (49%) of 96 patients improved, 34 (35%) of 96 deteriorated, and 15 (16%) of 96 presented with unchanged olfactory performance. With respect to the underlying pathological entity, the authors noticed a remarkable difference between patients with acromegaly (23 cases) and all other patients (73 cases). Fifteen (65%) of 23 patients with acromegaly improved (others 44%), only 3 (13%) of 23 deteriorated (others 42%), and 5 (22%) of 23 remained unchanged (others 14%) in their ability to distinguish odors. This illustrates a significant shift toward improved postoperative olfactory performance (cross-tabulation, Fisher exact test; p = 0.028) in patients with acromegaly.
In nasal breathing, 77 (80%) of 96 patients noticed no change, 11 (12%) of 96 improved, and 8 (8%) of 96 worsened postoperatively. Of the 11 patients with improved breathing, 6 (55%) had acromegaly. Improved nasal airway patency was more frequent in patients with acromegaly (cross-tabulation, Fisher exact test; p = 0.002).
The data provide the first significant evidence for improvement in olfactory performance in patients with acromegaly after transsphenoidal surgery (TSS) of growth hormone–producing adenomas. Furthermore, postoperative olfactory disturbance in patients treated with transnasal TSS is more frequent than previously reported. Nevertheless, recurrent transnasal TSS can be performed successfully, even multiple times, and does not involve a higher risk of nasal complications.
Victor E. Staartjes, Morgan Broggi, Costanza Maria Zattra, Flavio Vasella, Julia Velz, Silvia Schiavolin, Carlo Serra, Jiri Bartek Jr., Alexander Fletcher-Sandersjöö, Petter Förander, Darius Kalasauskas, Mirjam Renovanz, Florian Ringel, Konstantin R. Brawanski, Johannes Kerschbaumer, Christian F. Freyschlag, Asgeir S. Jakola, Kristin Sjåvik, Ole Solheim, Bawarjan Schatlo, Alexandra Sachkova, Hans Christoph Bock, Abdelhalim Hussein, Veit Rohde, Marike L. D. Broekman, Claudine O. Nogarede, Cynthia M. C. Lemmens, Julius M. Kernbach, Georg Neuloh, Oliver Bozinov, Niklaus Krayenbühl, Johannes Sarnthein, Paolo Ferroli, Luca Regli, Martin N. Stienen and FEBNS
Decision-making for intracranial tumor surgery requires balancing the oncological benefit against the risk for resection-related impairment. Risk estimates are commonly based on subjective experience and generalized numbers from the literature, but even experienced surgeons overestimate functional outcome after surgery. Today, there is no reliable and objective way to preoperatively predict an individual patient’s risk of experiencing any functional impairment.
The authors developed a prediction model for functional impairment at 3 to 6 months after microsurgical resection, defined as a decrease in Karnofsky Performance Status of ≥ 10 points. Two prospective registries in Switzerland and Italy were used for development. External validation was performed in 7 cohorts from Sweden, Norway, Germany, Austria, and the Netherlands. Age, sex, prior surgery, tumor histology and maximum diameter, expected major brain vessel or cranial nerve manipulation, resection in eloquent areas and the posterior fossa, and surgical approach were recorded. Discrimination and calibration metrics were evaluated.
In the development (2437 patients, 48.2% male; mean age ± SD: 55 ± 15 years) and external validation (2427 patients, 42.4% male; mean age ± SD: 58 ± 13 years) cohorts, functional impairment rates were 21.5% and 28.5%, respectively. In the development cohort, area under the curve (AUC) values of 0.72 (95% CI 0.69–0.74) were observed. In the pooled external validation cohort, the AUC was 0.72 (95% CI 0.69–0.74), confirming generalizability. Calibration plots indicated fair calibration in both cohorts. The tool has been incorporated into a web-based application available at https://neurosurgery.shinyapps.io/impairment/.
Functional impairment after intracranial tumor surgery remains extraordinarily difficult to predict, although machine learning can help quantify risk. This externally validated prediction tool can serve as the basis for case-by-case discussions and risk-to-benefit estimation of surgical treatment in the individual patient.