Olfactory function testing
The jet stream olfactometer (JSO; Nagashima Medical Instruments, Tokyo, Japan; Fig. 2) was used for olfactory testing performed according to the guidelines,19-21 using five different olfactory measurement reference odours. The concentration of each odour was set in 8 steps from −2 to 5, with 5 being the strongest, which was sequentially diluted 10 times. However, when the concentration of 5 was not adjustable because of problems with solubility in one type of odour, there were 7 levels up to a concentration value of 4. The test was conducted by pressing the stimulation button twice with a nozzle inserted in the opposite side of the obstructed nasal cavity, and the concentration of each of the five smells was gradually increased from −2; the concentration at which a correct answer was provided was defined as the recognition threshold. Because the olfactory threshold on the good side is defined as the bilateral olfactory threshold,16 for each of the five olfactory reference odours, we selected the lowest recognition threshold between the left and right nostrils as the recognition threshold for the bilateral nasal cavities. This examination was performed twice, once before the surgery and once 3 months after. The change in olfactory function was expressed as the difference between preoperative and postoperative olfactory mean recognition thresholds and defined as ‘improvement’ when the difference was positive and ‘deterioration’ when the value was negative. The degree of improvement was defined as improvement or deterioration when the change in olfactory function had a value of 1 or higher; no change was defined as stable olfactory function.