Study of morphologic variability of incudostapedial angle and its relation with temporal bone pneumatization

Introduction:Optimal sound transmission across the ossicular chain is dependent on the appropriate alignment of the middle ear ossicles.Incudostapedial joint(ISJ)is conventionally considered to be at right angle.Objective:We intended to study the ISJ anatomy and the impact of temporal bone pneumatization on the same.Methods:In a cadaveric study comprising of 47 human temporal bones,canal wall down mastoidectomy was carried out under microscopic guidance keeping the ossicular chain intact.The morphology of ISJ was recorded and analysed with respect to the pneumatization status of the temporal bone.The data analysis was performed using statistical software Stata version 12.0.Results:The mean ISJ angle for the 47 bones was 90.5^0(SD-15^0;range:54^0-122^0).The mean angle in well pneumatized bones was 93.7^0(SD-16.5;Range:54°-122^0)and in sclerotic mastoids was 88.7^0(SD-14;Range:68°-118^0).The difference in the ISJ angle in these two conditions was not statistically significant(p=0.27).The mean angle was found to be significantly more obtuse in the cases with partially eroded ISJ(111.4^0{SD-8.8;range:100.3^0-221.9^0};p=0.0001)and in the cases with an‘adherent/tilted morphology’of the stapes suprastructure with the promontory(mean-95.8^0(SD-13.8;range:70.7^0-120.4^0);p-<0.00001).Conclusion:The ISJ angle shows considerable variations.This variability needs to be taken into account when undertaking middle ear reconstructive procedures,specifically the ones involving the stapes footplate.The mastoid pneumatization does not appear to have an impact on the ISJ angle.

CT virtual endoscopy of the auditory ossicular chain: clinical applications

Objective To evaluate the clinical applications and limitations of CT virtual endoscopy (CTVE) in theauditory ossicular chain.Methods CTVE of the auditory ossicular chain was performed with 1.0 mm collimation at pitch 1.0, bone algorithm, 9.6 cm field of view, and 0.1 - 0.2 mm reconstruction interval in 40 patients with middle ear diseases. 30 cases were confirmed by surgery. Results were compared with the findings of axial high resolution CT (HRCT) and multiplanar reformation (MPR) images and surgery.Results The accuracy of CTVE images in detecting ossicular destruction was 92.6%, significantly higher than that of axial HRCT (83.9%) and multiplanar reformation (76.5%) images. CTVE could also clearty reveal the postoperative condition and congenital dysplasia of the auditory ossicular chain.Conclusions CTVE can clearly demonstrate a three-dimensional image of the auditory ossicular chain and is useful in evaluating diseases of the ear, especially the auditory ossicles. CTVE could not clearly demonstrate abnormal soft tissue within the tympanic cavity, abnormal changes of the tympanic membrane and tympanic walls, and could be easily influenced by artificial factors.