In this study we compared surgical parameters, functional outcome and adverse events in a contemporary cohort undergoing surgery for brain metastases in the posterior fossa in either sitting or non-sitting position.
In our cohort, patients undergoing surgery in SP had a significantly better status according to ASA and KPS compared to patients in the NSP group. No relevant differences in age, sex or the number of lateral vs. median craniotomies was found. Functional baseline status is known to affect long term outcome in cancer, which has been shown as well in intraparenchymal lesions of the posterior fossa.
In our study, LOA was significantly shorter in NSP compared to SP. In SP, transesophageal echography is necessary, which might be an explanation for the longer time of anesthesiologic preparation prior to the skin incision. LOS was slightly but not significantly longer in SP, questioning the advantage of possible superior anatomic orientation or atraumatic dissection during surgery. Whether lateral or medial approaches harbor higher complication risks per se is not systematically investigated, but did not show significant correlation to outcome in our population.
Functional status is of utmost importance regarding the outcome in cancer treatment. Therefore, the aim of surgical interventions is to improve the functional status or not deteriorate it towards low KPS, limiting further systemic therapy. In our cohort, postoperative KPS was not significantly different in both groups, but patients undergoing SP deteriorated significantly more often. In the SP group 20% of patients compared to 7% in the NSP group deteriorated to a KPS ≤ 60%, coming from better functional status and therefore possible limiting or delaying adjuvant therapy. Only one patient in each group improved to a KPS > 60% after surgery enabling further therapy. Therefore, SP approach can be regarded as less favorable regarding short term functional outcome. Whether this affects actual overall survival or progression free survival cannot be answered sufficiently from this sample. Nevertheless, overlooking the hospitalization of mean 19 days, reduction in functional status might already delay necessary adjuvant therapy. Postoperative functional outcome also affected LOH, leading to significantly longer hospitalization in the SP group.
Overall adverse event rate was 30% with patients in sitting position experiencing more and more severe adverse events (according to the CDG). Four patients died after surgery in SP during the immediate postoperative course compared to one in the NSP group. In the SP group, two air embolisms occurred compared to zero events in the NSP group. This data points towards a less pronounced risk profile if surgery is performed in NSP. Surgery in SP resulted in a NNH of 2.3. Whether this is due to surgical or perisurgical/anesthesiological factors cannot clearly be distinguished. Nevertheless, direct surgical adverse events were equally distributed among both groups. Whether changing an established workflow further affects complication rates and outcome cannot be ruled out from this data. Nevertheless, if deciding on standards of care and neurosurgical training, possibly worse outcome and adverse event profile have to be taken into account.
This study has several limitations, that have to be clearly addressed. First, the retrospective nature of the study is inherently prone to selection bias. Second, the study was performed in two neurosurgical centers and each center performed only one single type of positioning, according to the local standard protocol, creating an inherent potential selection bias. Nevertheless, this allows us to rule out interindividual patient differences, s.a. location, size or oncological disease to account for the choice of positioning. Furthermore, the LOA can be affected by center specific differences, but we assume an attribution to a more extensive anesthesiological set up in SP. The retrospective design of the study does not allow to adequately control for various confounders and baseline parameters showed significant differences in the KPS and ASA. Counterintuitively the SP group starting from better functional status had more severe deterioration during the postoperative course. The underlying oncologic disease was slightly different in both groups. Whether our findings ultimately affect the oncologic prognosis remains unclear, as no long-term data was collected and the focus of our study was lying on short term outcome, in which underlying oncologic disease is not assumed to play a profound role. This is due to a broad network of specialized outpatient clinics organizing further oncologic treatment with only sporadic follow up visits at the neurosurgical center. Nevertheless, as the prognostic factor of functional outcome is an established parameter, our findings implicate a favorable outcome in the cohort, that underwent surgery in NSP vs. SP.