Objective: Foreign bodies are commonly impacted in the external auditory meatus (EAM), and removal is sometimes difficult due to the tortuous anatomy. A foreign body is more likely to be stuck at the narrowest point of the EAM. This study was designed to determine the location and cross-sectional shape of the narrowest point of the EAM, i.e., the isthmus, by using silicone casting material in human cadaver ears. Materials and Methods: Twelve impressions were taken from 8 adults. All abnormal ears were excluded from the study. The measurements of the impressions were done by using a micrometer (Vernier caliper), calibrated to 0.1 mm. Results: The narrowest point of the EAM, i.e., the isthmus, was located at the junction of the medial two thirds (mean 17.9 mm) to the lateral one third (mean 9.8 mm) of the canal. The mean canal length was 27.7 (range 20–34.8) mm. The isthmus corresponds to the bony and cartilaginous junction, which is traditionally thought to be narrowed by the canal angulation. This narrowing was 5.7 (range 3–7) mm wide in the anteroposterior plane, but 8.2 mm (range 6.5–10) mm wide in the vertical plane. The cross-section of this area was either an inverted pear or oval shape. Conclusions: The isthmus is a bony-cartilaginous junction, and the narrowest point of the EAM is situated at the junction of the outer one third of the inner two thirds of the canal length. This is mainly an anteroposterior narrowing and is oval or inverted pear shaped. Foreign bodies impacted at this point could be removed by use of aural hook, using the potential space at the superior portion of the isthmus.

Keywords:
External auditory meatus, Isthmus
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© 2001 S. Karger AG, Basel
2001
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