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.