The thoracic duct (TD) drains most of the body's lymph back to the venous system via its lymphovenous junction (LVJ), playing a pivotal role in fluid homeostasis, fat absorption and the systemic immune response. The respiratory cycle is thought to assist with lymph flow, but the precise mechanism underpinning terminal TD lymph flow into the central veins is not well understood. The aim of this study was to use ultrasonography (US) to explore the relationship between terminal TD lymph flow, the respiratory cycle, and gravity. The left supraclavicular fossa was scanned in healthy non‐fasted volunteers using high‐resolution (13–5 MHz) US to identify the terminal TD and the presence of a lymphovenous valve (LVV). The TD's internal diameter was measured in relation to respiration (inspiration vs. expiration) and body positioning (supine vs. Trendelenburg). The terminal TD was visualized in 20/33 (61%) healthy volunteers. An LVV was visualized in only 4/20 (20%) cases. The mean terminal TD diameter in the supine position was 1.7 mm (range 0.8–3.1 mm); this increased in full inspiration (mean 1.8 mm, range 0.9–3.2 mm, p < 0.05), and in the Trendelenburg position (mean 1.8 mm, range 1.2–3.1 mm, p < 0.05). The smallest mean terminal TD diameter occurred in full expiration (1.6 mm, range 0.7–3.1 mm, p < 0.05). Respiration and gravity impact the terminal TD diameter. Due to the challenges of visualizing the TD and LVJ, other techniques such as dynamic magnetic resonance imaging will be required to fully understand the factors governing TD lymph flow.

The aortic valve (AV) has been used as a surrogate marker for the superior vena cava‐right atrium (SVC‐RA) junction during the placement of central venous catheters. There is a paucity of evidence to determine whether this is a consistent finding in children. Eighty‐seven computed tomography scans of the thorax acquired at local children's hospitals from April 2010 to September 2011 were retrospectively collected. The distance between the SVC‐RA junction and the AV was measured by dual consensus. The cranio‐caudal level of the junction and the AV were referenced to the costal cartilages (CCs) and anterior intercostal spaces (ICSs). The results confirmed that the SVC‐RA junction has a variable relationship to the AV. The junction was on average 3.1 mm superior to the AV. This distance increased with age. In the <1‐year‐old age group, the junction was on average 1.3 mm superior to the AV (range: −6 to 11 mm). In the 1–2 years old age group: 3.5 mm (range: −8 to 15 mm). In the 3–6 years old: 3.8 mm (range: −9 to 13 mm). In the >7 years old age group: 4 mm (range: −11 to 16 mm). The surface anatomy of the SVC‐RA junction was variable, ranging from the second ICS to sixth CC. The SVC‐RA junction has a predictable relationship to the AV, and this can be used as an adjunct marker for accurate placement of central venous catheters except in the smallest neonates. Clin. Anat. 32:778–782, 2019. © 2019 Wiley Periodicals, Inc.