The periportal region is an anatomic space around the portal vein that comprises of the hepatic artery, bile duct, nerves, lymphatics and a potential space. Pathologies that involve any of these structures focally, diffusely or secondarily may demonstate a "periportal hypodensity" around the portal veins. Synonyms of periportal hypodensity include periportal halo, periportal tracking, periportal collar, hypodense periportal zones and periportal ring or tramline. This hypodensity may represent fluid (including lymph and blood), dilated lymphatics or tumor infiltration in the loose interstitial tissue around the portal triad structures. While this CT finding is nonspecific, it is often abnormal and should prompt a thorough evaluation of the liver for an underlying etiology [1].
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