The anatomy of the human promontory for laser Doppler flowmetry.

Studies of the dynamic characteristics of cochlear blood flow (CBF) utilizing laser Doppler flowmetry (LDF) in laboratory animals have provided a new approach to the understanding of control mechanisms of CBF and the role of the CBF in cochlear disorders. However, few studies exist indicating that LDF of human CBF may be possible. Since bone thickness, density, structure characteristics, and blood flow all greatly affect LDF recording, we examined the anatomy of the human promontory for inter-individual variations in thickness, quality and vascularity of the bone and mucosa and recorded middle ear topographic relationships to the underlying cochlear lateral wall vasculature. Temporal bones from 21 cadavers without known premortem histories of ear disease were obtained. India ink was infused selectively via the vertebral or carotid system to study the origin of bone/ mucosa circulation to the otic capsule. Light microscopy revealed that the human promontory was characterized as cortical bone having few blood vessels. The thickness of the bone measured at four horizontal levels and mucosa at the top of promontory and anteriorly around the tympanic plexus varied from 1.67 +/- 0.64 to 1.13 +/- 0.26 mm for bone and 0.06-0.13 mm for mucosa. The thinnest bone was found around the tympanic plexus, where the bone thickness varied from 0.6 to 1.2 mm. Previous data indicate that current LDF instruments can provide a linear measure of blood flow through bone thicknesses of 1-3 mm or more (depending on the type of bone). Data from the current study indicate that direct valid dynamic measures of CBF are possible in humans. Since the optimal area available is small, the topography of the middle ear should be well known and the recording site well defined to obtain valid results.