Olfactory Assessment in Patients Undergoing Endoscopic Skull Base Surgery- Lessons Learnt

Introduction: Olfactory disturbances have been reported following endoscopic approaches to the skull base. These could arise due to the disruption or resection of the arborized olfactory neuroepithelium on the nasal septum during the ablation of a tumor or while creating the sinonasal corridor involving resection of the middle turbinate and parts of the superior turbinate. However, there is lack of consensus on the frequency and severity of dysfunction, which could be largely due to the variations in the surgical technique. This study was undertaken to compare our results with previously published works and to validate our olfactory strip sparing approach.

Study Design: Prospective study to assess olfaction in 50 patients scheduled to undergo endoscopic approach for the resection of skull base tumors.

Methods: After obtaining approval from the institutional review board, 50 patients scheduled to undergo endoscopic endonasal resection for skull base tumors were enrolled in the study. Patients were divided into two groups based on the type of flap. Group I had a posterior pedicle nasoseptal flap and Group II included patients in who rescue flaps were performed. Olfactory outcomes were assessed preoperatively using the University of Pennsylvania Smell Identification test (UPSIT) which is a 40 point reliable and validated test of olfaction, using a scratch and sniff questionnaire. The test was repeated at 6 weeks, 3 months and 6 months following surgery.

Results: 43 patients (8 group I) and (35 group II) were assessed. For group I the score at 6 weeks postoperatively was significantly lower than the baseline (30.25+6.06vs 23.8+5.79; p = 0.03). However by 3 months the scores had improved with no significant difference from the preoperative function(28.75+3.5; p = 0.24). For Group II there was no difference between the baseline and the six week score (31.5+5.3vs29.7+5.9; p = 0.16). At 6 months the score was significantly higher 33.78+3.6(+ 2.21 above baseline; p = 0.04).

Conclusion: Expanded endoscopic approaches to the skull base that involve reconstruction with a nasoseptal flap has a short term (six weeks) negative impact on the olfaction; however, there seems to be no long term effect. Surgical resection of pituitary adenoma with rescue flaps has no negative impact on olfaction. On the contrary when assessed long term we found improvement in olfaction, which can be due to hormonal changes or better conduction of odorants. Acromegalics show a significant improvement in olfaction following surgery associated with a fall in GH levels. Identification of the olfactory epithelium and meticulous harvesting of the flaps seem to be critical to preserve olfaction.