Impact of fat content of oral nutritional intake on visibility and diameter of the thoracic duct: a prospective study

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The aim of this study was to investigate visibility and diameter changes of the thoracic duct (TD) on non-contrast MR-lymphangiography (MRL) after oral nutritional intake with different fat-content. Healthy adults prospectively underwent non-contrast thoracic MRL at 1.5 T on three separate days following an overnight fasting period. After baseline MRL, patients received standardized meals: (1) high-fat, (2) medium-chain-triglyceride (MCT), (3) fat-free. Thereafter hourly MR-scans were obtained for 6 h. TD-visibility was evaluated for the superior and inferior thoracic and abdominal TD-segment on a 6-point-scale (1:best; 6:worst). TD-diameters were measured independently by two readers. Statistical analysis was performed to evaluate systematic differences between the different meals using paired t-tests and a linear mixed-model analysis. 154 MRI-scans were performed in 22 volunteers (16 female, mean age 29.7 ± 14.3 years). Overall TD-visibility improved significantly after the high-fat meal (baseline: 2.9 ± 0.9 vs. 6 h-examination: 2.4 ± 0.8; p < 0.001), while it slightly deteriorated after the MCT-meal (2.7 ± 0.9 vs. 3.2 ± 1.0; p < 0.001) and fat-free meal (2.8 ± 0.9 vs. 3.1 ± 1.0; p = 0.006). TD-diameter increased after the high-fat meal with a maximum at 5 h postprandially in the abdominal (2.4 ± 0.6 mm vs. 2.9 ± 1.0 mm, + 21.5%, p < 0.001) and lower thoracic segment (2.1 ± 0.4 mm vs. 2.5 ± 0.5 mm, + 16.8%, p < 0.001) while the maximum mean increase in the upper thoracic segment was observed at 2 h postprandially (2.0 ± 0.3 mm vs. 2.3 ± 0.5 mm, + 13.8%). In contrast, no significant increase in TD-diameters over time was observed for the fat-free and MCT-meals. The observed improvement in TD visibility and increase in TD diameter after a high-fat meal suggest a relation to lymphatic resorption of long-chain triglycerides. Conversely, this effect was not observed after an MCT- and fat-free meal.

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