THE VASCULAR PATTERN OF THE MODIOLUS"THE COILED ARTERIOLES"

Abstract

The present study was done in an attempt to clarify the vascular pattern, and the distribution of the coiled arterioles within the modiolus.
Ten healthy guinea pigs were used in this series of experiments.In order to trace the course of the cochlear blood vessels, an India ink solution was perfused systemically through a glass canula inserted into the aorta.After the perfusion, the cochleae were removed and fixed in 10% formalin solution.The specimens were then decalcified, dehydrated with alcohol, and made transparent with xylene and oil of wintergreen.Dissection and observation were performed with the aid of a binocular microscope.
Four cochleae were embedded in celloidin and sectioned for histological study of the blood vessel walls.
In the guinea pig, Arteria cochleae communis divides into two main branches at the base of the modiolus, A.vestibuli posterior and A.cochleae propria.In eight of the ten animals, large coiled arterioles were observed lying between the two arterial subdivisions.
Making an angle of 120 degrees with the internal auditory meatus, A.cochleae propria enters the modiolus where it gives rise to primary and secondary branches as it spirals upward arounds the cochlear nerve trunk.
The secondary branches subdivide into two groups of arterioles:the "upper coiled arterioles", which enter the wedge-shaped bony plates separating the cochlear turns, and the "lower coiled arterioles", entering the osseous spiral lamina. These vessels are surrounded by the loose connective tissues in the perivascular space, and there are no essential differences in the structure of the two sets of arterioles.
The upper coiled arterioles(16 to 19 in number) describe several(never more than six, and usually from two to four) tight coils.These convolutions form ellipsoids or spherics from which four to seven radiating arterioles run out over the scala vestibuli to enter the spiral ligament and the stria vascularis.Careful observations establish the upper coiled arterioles in the basal and second turns;although there are vessels in and above the upper second turn, they lack characteristic coiling.
The lower coiled arterioles, numbering from 8 to 12, are located in the basal turn, and become so increasingly simplified as to lose their identity at the level of the lower second turn.Radiating arterioles to the limbus are given off from the distal members of this group of vessels, in the region where they are no longer tortuous.
Anastomosing vessels are observable between the upper and lower coiled arterioles, and between the upper coiled arterioles themselves.These anastomoses assume a rosary-like appearance when viewed from the apex.No connecting vessels are observed between the individual lower coiled arterioles.
The author, unlike earlier investigators, cannot find any coiled arterioles in the higher levels of the cochlea.In these upper regions, the vessels merely from simple loops, rather than tight coils.
The highly twisted and coiled paths of these arterioles suggest that they may serve as an important mechanism for the regulation of the blood flow through the cochlea.