Measurement of internal auditory canal on normal Korean adult
To diagnose the acoustic neuromas early and treat with minimal morbidity, there have been various studies. Among them the internal auditory cisternography is one of the most reliable device to confirm early erosion, widening and change of the internal auditory meatal shapes.
To know the abnormality of the internal auditory meatal contour, it essentially required to have the reference normal one. Even though there have been several scattered reports on the dimension of the internal auditory meatus, there is no one for Korean.
Author has studied the measurements of the internal auditory meatus with 41 skulls(82 ears) of normal Korean adults directly with a impression cast and indirectly with a conventional X-ray and then compared them with each other.
The followings are the results;
1. The mean lengths of anterior, posterior, superior01(from the upper margin of the porus to the Bill's bar), superior-2(from the upper margin of the porus to the crista falciformis), inferior-1(from the lower margin of the porus to the lamina cribrosa), and inferior-2(from the lower margin of the porus to the crista falciformis) are 13.65mm, 7.85mm, 9.95mm, 8.45mm, 11.5mm and 9.9mm on casts. But length on X-ray which is considered to be correspond with the anterior wall on cast is 14.85mm.
2. The mean diameters of casts are different according to that of measuring planes. On horizontal planes; porus-10.75mm, medial-4/9mm, middle-4.4mm and lateral-3.9mm and on vertical planes which are more important because it is more closure to the projection plane of X-ray; porus-6.25mm, medial-4.2mm, middle-4.95mm and lateral-4.9mm. On the other hand, the medial portion which is more easier and distincts to measure on X-ray is 5.35mm on Caldwell's projection. The side differences on cast and X-ray are less than 1.0mm in 90% and there is no one case which shows more than 2.0mm side difference on cast and X-ray.
3. For shape on cast, the orders of frequency are narrow medially-54.9%, oval-28%, straight-11.0%, dumb-bell-3.7% and narrow laterally-2.4% on the vertical plane, and to the contrast on the horizontal plane narrow laterally is most common with the incidence of 63.4% and oval-15.8%, straight-11.0%, dumb-bell-6.1% and then narrow medially-3.7%.
On X-ray, straight is most common with the incidence of 76%, narrow medially-19% and then oval-5%.
4. The mean value of the angle between the porus plane and long axis of meatus is 125.5 degree and the mean volume of the empty internal auditory meatal canal is 0.225ml on cast. But it is impossible to check on X-ray.
5. The mean distances from the porus to the lateral sinus and the foramen spinosum are 21.8mm and 191.mm on dry skull but it is impossible to check on X-ray.