Anatomical variations and relations in the medial wall of the bony portion of the eustachian tube.

The medial wall of the bony portion of the Eustachian tube was examined, by anatomical and histological methods, in 150 temporal bones of adults. This wall consists of two parts: posterolateral (labyrinthine) and anteromedial (carotid), whose shapes, sizes and relations depend upon the position of the a. carotis interna. If it is located nearer the tympanic opening of the tube, the labyrinthine part of the wall is smaller and has a triangular shape. The further the artery is removed from the tympanic opening of the tube, the greater and more rectangular the shape of this part of the wall. The part of the medial wall which corresponds to the a. carotis interna can differ in each case and in 69% of the cases this part extended more or less into the lumen of the tube. The average thickness of this part of the wall is 1.5 mm (minimum is wafer-thin and maximum is 3 mm). In 2% of the cases the bony wall above the a. carotis interna was missing, so that the artery projected into the protympanum. Through a bone defect, aneurysm of the artery can develop. In one case, during an operation, it was established that the protrusion of the a. carotis interna into the tympanic cavity was due to a defect in the medial wall of the Eustachian tube.