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PART 5 — ABDOMINAL
Figure 22-2 Portal vein diameter measured near where portal vein (PV) crosses the inferior vena cava (IVC).
include clear views of the adjacent liver paren- chyma. The main portal vein diameter is measured during quiet respiration where this vessel crosses the IVC (Fig. 22-2).
Spectral Doppler waveforms and velocity measure- ments should be documented from the following:
• Main, right, and left portal vein
• Right, middle, and left hepatic veins
• Splenic vein
• Superior mesenteric vein
• IVC
• Hepatic artery proper (angle-corrected velocity)
TECHNICAL CONSIDERATIONS
When scanning the abdominal vasculature, imaging parameters such as depth, field of view, frame rate, and flow sensitivity are very important. Although imaging depths vary based on patient body habi- tus, transducer frequencies between 2 and 4 MHz may be required to penetrate depths of up to 20 cm. Higher transducer frequencies between 4 and 5 MHz are used in thin adults and children. Selection of the transducer should be made such that adequate depth penetration is achieved while selecting the highest transducer frequency because the higher frequencies provide better resolution. Most often, a 3-6 MHz pulsed Doppler is required for spectral analysis of abdominal vessels. Elec- tronic phased sector transducers with 13- to 20-mm scan heads are more effective in obtaining acous- tic windows using the intercostal approach. High- resolution convex (4-8 MHz) and linear (5-15 MHz) transducers are useful when imaging anterior ab- dominal wall varices and assessing the liver surface for nodularity.
PITFALLS
The ability to complete a hepatoportal examination depends, in part, on the experience of the technol- ogist or sonographer as well as the patient. Major limitations affecting the success of the examination include patient obesity, diffuse liver disease, asci- tes, and bowel gas. Patients with severe abdominal pain, those unable to remain still, those unable to breathe quietly or vary their depth of respiration, and combative patients also present limitations to the examination.
DIAGNOSIS
There are multiple criteria to assess when evaluating the hepatoportal system. Major diagnostic character- istics are summarized as follows.
PORTAL VEIN
Portal veins have bright, echogenic borders due to collagenous tissue within the walls. Respiration and ingestion of food affect portal vein diameter and velocity flow. In normal patients, the portal vein diameter is 􏰀13 mm in quiet respiration and may increase to 16 mm with deep inspiration.5 Portal vein diameter is increased in patients with portal hyper- tension, congestive heart failure, constrictive peri- carditis, and portal vein thrombosis.
Portal venous flow is normally directed toward the liver with constant antegrade flow throughout the cardiac cycle. This is referred to as “hepatopetal” flow. Portal vein velocity does vary with cardiac ac- tivity and respiration. During inspiration, it decreases and increases during expiration. This is due to the di- aphragm descending during inspiration, resulting in an increase in intra-abdominal pressure. This also im- pedes venous return to the right atrium, thus decreas- ing flow in the IVC and its tributaries, including the hepatic veins. Portal venous flow and velocity also decrease during exercise (related to the significant re- duction in mesenteric arterial blood flow that occurs with exercise) and changes in posture (from supine to sitting or standing) attributed to venous pooling in the legs. It increases with expiration and ingestion of food, as a result of splanchnic vasodilatation and hy- peremia. Postprandially, flow velocity increases 50% to 100%. Resting peak systolic velocities range from 10 to 30 cm/s. Mean flow velocity is approximately 15 to 18 cm/s. The Doppler spectral waveforms are monophasic and are slightly pulsatile or undulating (Fig. 22-3). Increased pulsatility has been described, particularly in thin patients. Principle determinants attributing to portal vein pulsatility may include