Changes of Mastoid Gas Physiology in Virtual Mastoidectomy Model / 대한이비인후과학회지

ABSTRACT

BACKGROUND AND OBJECTIVES: It is essential to understand gas physiology of mastoid cavity to study the pathophysiology of middle ear diseases, and the surface area and volume of mastoid mucosa are important parameters for evaluating gas physiology. However, the surface area and mastoid volume of the mastoid cavity have not been practically measured yet. Therefore, we measured and compared surface area and volume of the mastoid cavity before and after mastoidectomy using a virtual mastoidectomy model. SUBJECTS AND METHOD: We performed a virtual mastoidectomy using 10 cases of temporal bone CT indicating pneumatic mastoid. First, we removed all air cells after outlining with irregular AOI function after loading axial CT images to Image-Pro Plus 4.0. Then we filled the removed area with equal planes using local equalization filter. Finally, we calculated and compared the total surface area, volume and area to volume (A/V) ratio by estimating their circumference and area. RESULTS: The mean surface area of pneumatized mastoid cavity was 127.8 cm2 (range 94.2-165.3 cm2), and the mean volume was 7.1 cm3 (range 5.2-11.0 cm3). The mean surface area and volume were altered to 42.8 cm2 (range 35.9-55.0 cm2) and 12.6 cm3 (range 10.3-18.7 cm3), respectively, after virtual mastoidectomy. As a result, the A/V ratio decreased from 18 to 3.4 after a virtual mastoidectomy in the pneumatic mastoid cavity. CONCLUSION: When a complete mastoidectomy is performed in the pneumatic mastoid, the surface area is decreased by one third compared to a relatively minor increase in volume. Therefore, the surface area per unit volume is expected to greatly decrease after mastoidectomy. Some physiologic problems occurring after mastoidectomy could be more accurately explained using a virtual mastoidectomy model.