Periportal halo or periportal collar sign refers to a zone of low attenuation seen around the intrahepatic portal veins on contrast-enhanced CT or hypoechogenicity on liver ultrasound. It likely represents periportal edema, which is often used as a synonymous term. Periportal haloes may occur around the central portal veins or their peripheral branches and occur on both sides of the portal triads.
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Pathology
Etiology
This sign is seen when there is fluid accumulation or dilatation of lymphatics in the loose areolar tissue around the portal triads. This sign is non-specific and can be seen in various conditions 1:
secondary cardiac congestion
acute hepatitis, particularly viral hepatitis
lymphadenopathy at the porta hepatis causing lymphatic obstruction
liver transplant and liver transplant rejection
blunt hepatic trauma
blunt abdominal trauma and aggressive fluid resuscitation
Differential diagnosis
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biliary dilatation, in which the low attenuation is seen on only one side of the portal triads
biliary dilatation and periportal halo may, of course, coexist; if so, the stripe of periportal low attenuation on one side may be wider than the other
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