The importance of microstructure of the middle ear in otosurgery

The purpose of this paper is to review important anatomical variations and relations in the middle ear that may occur on the human temporal bones. We presented findings of specimens that demonstrated morphological variations involved: the facial nerve canal, an internal carotid artery and upper jugular bulb and pointed out their clinical and surgical importance. The studies were performed on the large collection of the temporal bones (2000 temporal bone specimens) in our laboratory for anatomical and surgical examinations, over the period of many years. In our study the facial nerve dehiscence was commonly present just above the oval window, in about 65% of the specimens. The middle ear cavity is closely related to the internal carotid artery, which extends medially from the promontory. This part of the wall could be noticed since the carotid channel is always more or less protruded into the lumen of the tube. In some cases (2/150) we noticed a bone defect above the internal carotid artery up to the level of tympanic orifices. In 38 (25.3%) of the cases, we found that jugular bulb protruded into the cavum tympani, elevating its bottom. The absence of bone wall above the bulb, as well as its dehiscence, could make infection spread from the middle ear spaces more easily, thus possibly causing thrombophlebitis. A highly positioned jugular bulb in the cavum tympani could lead to difficulties in differential diagnosing. In cases with clinical symptoms of jugular foramen mass, it is important to make identification of an expanding process (cholesteatoma, paraganglioma, meningeoma), but also the presence of vascular anomalies. CT scan of the temporal bone, performed before any ear surgery, is the main modality for identification of such anomalies and preventing possible insults.