How may abdominal meteorism or distension influence ultrasonographic assessment of adiposity?.

Purpose Ultrasonography (US) is one of the most suitable tools for the differential assessment of subcutaneous and visceral adiposity in clinical practice. In recent years several studies have reported a good accuracy and reliability of such method in the assessment of abdominal adiposity measurements, compared with gold standard (CT-MRI) and with anthropometric and clinical indexes. Although some limitations of US in this field are intuitable, studies evaluating the influence of technical issues on affecting US measurements and methods are missing in literature. The aim of our study was to investigate the impact of abdominal distension on US abdominal fat measurements and the difference of reliability between two US equipments of different generations. Methods and Materials We prospectively enrolled 18 subjects (10 males, 8 females; 28.5±2.6 year-old; body mass index 22.8±4.2 Kg/m2) with no history of abdominal pathology or surgery. Subjects were submitted to US examination before and 45 minutes after a standardized meal. Seven main parameters representative of subcutaneous and visceral abdominal fat depots were independently measured by two expert radiologists, both using two US equipments of different generations: Equipment 1 - Hitachi EUB 525 eidos-1998 (Hitachi Denshi, Tokyo, Japan). Equipment 2 - Esaote Technos MPX-2003 (Esaote, Genoa, Italy). All measurements were collected by a third radiologist, to blind the study, and these were analyzed by Lin's concordance correlation, linear regression analysis and Student's t-test. Results Abdominal distension: subcutaneous measures were not affected by abdominal distension, as expected. Among visceral fat parameters, intra-abdominal fat showed important variations before and after the meal: mean (± standard deviation) measures 48.2±16.7 mm and 57.7±14.6 mm, respectively (#%=24.3±22.9, p<0.0001). Aorto-mesenteric distance also showed significant variations, even if less pronounced: measures 2.6± 0.7 and 3.2 ± 0.9 mm, before and after the meal, respectively (#%= 28.5±49.8, p< 0.005). US equipments: notwithstanding the important technological gap between the two US equipments, no significant differences resulted in the measurements performed by the two machines. Intra- and inter-observer agreements: were good to excellent for all parameters and for both machines, independently from gastrointestinal distension (# values ranging 0.74-0.98 for reproducibility, 0.81-0.99 for repeatability), with the exception of mesenteric fat and aorto-mesenteric distance, that showed poor reliability (# between 0.68-0.36 and between 0.57-0.28, respectively). Conclusion Although some limits of US in the assessment of abdominal adiposity may be intuitable, very few studies are focused on this kind of analysis. Our results, even if collected in a limited number of subjects, underline that abdominal distension should be taken into consideration in the evaluation of intra-abdominal fat, a crucial index of abdominal adiposity. On the other hand, our study did not show significant differences between reliabilities of the two different US equipments; if these results will be confirmed in larger cohorts and in populations with different features, many old US equipments could be still useful for this purpose.