Computed tomography evaluation of periportal halo in healthy dogs under medetomidine-based sedation and alfaxalone-sevoflurane anesthesia

Periportal halo (PPH) sign on contrast-enhanced computed tomography (CT) is considered a pathological finding; however, recent studies indicate that it may also appear in healthy individuals. We hypothesized that PPH can be observed in healthy dogs and can vary depending on the anesthetic agents. This study assessed the PPH sign in healthy dogs under different anesthetic agents and across different postcontrast phases. In this cross-over study, 10 healthy Beagle dogs underwent non-contrast and postcontrast CT examinations (arterial, venous, delayed, 5-min delayed, and 10-min delayed phases) under two anesthetic agents, medetomidine and alfaxalone, with a 1-week interval. The presence and severity of PPH were assessed on a scale of 0–3 and compared across different postcontrast phases. Significant differences in PPH were noted between the two anesthetic groups. In the medetomidine group, PPH was absent in the arterial phase, peaked at grade 3 in the delayed phase, and gradually decreased thereafter in the 5- and 10-min delayed phases. In contrast, PPH was minimal or absent in the alfaxalone group across all phases. In conclusion, PPH can be detected in healthy dogs depending on the sedative or anesthetic agent. It can particularly be detected with medetomidine in the delayed phase and should not be misinterpreted as a pathological change on postcontrast CT.