8/18/2023 0 Comments External acoustic meatusCurr Probl Diagn Radiol 44:511–516Ĭisneros JC, Lopes PT, Bento RF, Tsuji RK (2017) Sinus pericranii, petrosquamosal sinus and extracranial sigmoid sinus: anatomical variations to consider during a retroauricular approach. These structures may be adjacent, especially on the right side, and presurgical contrast MRI should be included when planning surgeries around the EAM.Ĭhawla A, Ezhil Bosco JI, Lim TC, Shenoy JN, Krishnan V (2015) Computed tomography features of external auditory canal cholesteatoma: a pictorial review. The positional relationship between the EAM and SS is highly variable and inconsistent. In three women, the distance was less than 5 mm on the right side. The shortest distance between the posterior wall of the EAM and the anterior margin of the SS was 12.3 ± 3.9 mm on the right side and 13.0 ± 2.9 mm on the left. The intervening type was the most predominant, accounting for 85%. The positional relationships between the EAM and the anterior edge of the SS were classified into superior, intervening, and inferior types. The relationships and distances between the EAM and SS, in addition to the shape of cross sections of the EAM, were highly variable with left–right asymmetry. In all patients, the EAM and SS were well depicted on both the sagittal and axial images. Imaging data were transferred to a workstation for analysis. In total, 85 patients with an intact EAM, SS, and surrounding structures underwent thin-sliced, contrast MRI. The present study aimed to characterize the relationship using contrast magnetic resonance imaging (MRI). 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.There is no study exploring the positional relationship between the external acoustic meatus (EAM) and the sigmoid sinus (SS) in detail. This is mainly an anteroposterior narrowing and is oval or inverted pear shaped. 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. The cross-section of this area was either an inverted pear or oval shape. 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 isthmus corresponds to the bony and cartilaginous junction, which is traditionally thought to be narrowed by the canal angulation. The mean canal length was 27.7 (range 20–34.8) 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 measurements of the impressions were done by using a micrometer (Vernier caliper), calibrated to 0.1 mm. All abnormal ears were excluded from the study. Materials and Methods: Twelve impressions were taken from 8 adults. 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. A foreign body is more likely to be stuck at the narrowest point of the EAM. Objective: Foreign bodies are commonly impacted in the external auditory meatus (EAM), and removal is sometimes difficult due to the tortuous anatomy.
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