Sonographic analysis of the intercostal spaces for the application of high-intensity focused ultrasound therapy to the liver

OBJECTIVE. The purposes of this study were to assess the widths of the intercostal spaces of the right inferior human rib cage through which high-intensity focused ultrasound therapy would be applied for treating liver cancer and to elucidate the demographic factors associated with intercostal space width. SUBJECTS AND METHODS. From March 2013 to June 2013, the widths of the intercostal spaces and the ribs at six areas of the right inferior rib cage (area 1, lowest intercostal space on anterior axillary line and the adjacent upper rib; area 2, second-lowest intercostal space on anterior axillary line and the adjacent upper rib; areas 3 and 4, lowest and second-lowest spaces on midaxillary line; areas 5 and 6, lowest and second-lowest spaces on posterior axillary line) were sonographically measured in 466 patients (214 men, 252 women; mean age, 53.0 years) after an abdominal sonographic examination. Demographic factors and the presence or absence of chronic liver disease were evaluated by multivariate analysis to investigate which factors influence intercostal width. RESULTS. The width of the intercostal space was 19.7 ± 3.7 mm (range, 9-33 mm) at area 1, 18.3 ± 3.4 mm (range, 9-33 mm) at area 2, 17.4 ± 4.0 mm (range, 7-33 mm) at area 3, 15.4 ± 3.5 mm (range, 5-26 mm) at area 4, 17.2 ± 3.7 mm (range, 7-28 mm) at area 5, and 14.5 ± 3.6 mm (range, 4-26 mm) at area 6. The corresponding widths of the ribs were 15.2 ± 2.3 mm (range, 8-22 mm), 14.5 ± 2.3 mm (range, 9-22 mm), 13.2 ± 2.0 mm (range, 9-20), 14.3 ± 2.2 mm (range, 9-20 mm), 15.0 ± 2.2 mm (range, 10-22 mm), and 15.1 ± 2.3 mm (range, 8-21 mm). Only female sex was significantly associated with the narrower intercostal width at areas 1, 2, 3, and 5 (regression coefficient, 1.124-1.885; p = 0.01-0.04). CONCLUSION. There was substantial variation in the widths of the intercostal spaces of the right inferior rib cage such that the anterior and inferior aspects of the intercostal space were relatively wider. Women had significantly narrower intercostal spaces than men.