Vol. 93 No.2 February　2000

Focal Microcirculation Disorder and Idiopathic Sudden Hearing Loss

 Tomoyuki Hoshino (Hamamatsu University School of Medicine )

           Focal microcirculation lesion in the latetal wall of the cochlea was made by photochemical reaction in guinea pigs. The damage was made by systemic injection of rose bengal and green light illumination to the bony cochlear wall. The diameter of the lesion was 0.9-1mm. The effects of the lesion were evaluated using a non-contact laser blood flowmeter, the endocohlear potential (EP) and the compound action potential (CAP). The cochlear blood flow gradually decreased during the 30 min observation period parallel to the gradual decline of the EP. The average CAP threshold was significantly increased 15 min and thereafter. Mid-lesion EP measurements were obtained at various intervals up to 3 weeks. EP reached the minimal value after 3 days and recovered to almost normal after 2 weeks. Off-lesion EP values 3 days after illumination were depressed at all measured sites apical to the lesion but remained unchanged at sites basal to the lesion. Two weeks after illumination, decreased apical EP was found to have returned to normal. Focal damage in the lower cochlear turn may have a depressant effect on EP measured apical to the lesion. This reversible depressant effect of a focal lesion on apical EP could account for the clinical course in certain cases of idiopathic sudden hearing loss.

Key words: focal strial lesion, idiopathic sudden hearing loss, photochemical reaction, endocochlear potential