A study on the transient hepatic abnormal enhancement in the hepatic arterial phase during dynamic contrast-enhanced spiral CT

Objective: To define the features of transient hepatic abnormal enhancement (THAE) in the hepatic arterial phase (HAP) during dynamic contrast-enhanced spiral CT, and to investigate the causes of THAE and emphasize its importance in CT scanning of the liver. Methods: In 32 months, spiral CT studies of the liver or upper abdomen in 926 patients with various causes were performed. Unenhanced spiral CT images were routinely obtained before injection of contrast material, then spiral CT scans were performed during the HAP(25-30 seconds) and the portal venous phase (PVP) (65-70 seconds), respectively, and delayed phase scans of the local lesion in some patients were also acquired 3, 5 and 10-15 minutes after the initiation of injection. Eighty-two patients (72 men, 10 women; age range, 26-78 years) were identified to have THAE. The appearances of THAEs and the lesions in unenhanced and all of enhanced imaging (HAP, PVP and delayed phase imaging for the local lesion) were carefully analyzed. Results: There were 122 THAEs in the 82 (8.9%) patients. In unenhanced imaging, most (n=110, 90.2%) of THAEs showed no attenuating abnormality, while some of them (n=12, 9.8%) were faintly hypoattenuating. All of 122 THAEs in HAP imaging showed homogeneous hyperattenuating, and they changed to isoattenuating (n=109, 89.3%) or slightly hyperattenuating (n=13, 10.7%, among them, 10 THAEs with delayed phase imaging changed to isoattenuating) in PVP imaging. The morphology of THAE in HAP imaging was wedge-shaped or fan-shaped in 83(68.0%), irregular shape in 29(23.8%), and others in 10 (8.2%) THAEs. There were 46(37.7%) THAEs to be located right next to hepatic tumors or other lesions, 20 (16.4%) THAEs close to tumors or other lesions bordering on the livers, and 56 (45.9%) THAEs far from tumors or other lesions both inside and outside the livers. In PVP imaging, the portal vein (or its left branch) or splenic vein displayed marked stenosis or obstruction (i.e, not enhanced by contrast media) in 29 patients, in whom there were 50 THAEs which were mostly located in the left lobes (P<0.01) and they could be demonstrated as segmental or lobar hyperattenuating in HAP imaging. Conclusion: In HAP of dynamic contrast-enhanced spiral CT, THAE may not be unusual. The features of THAE could distinguish it from liver parenchymal lesions. The cause of THAE is varied. It is highly important to recognize and to distinguish THAE, which could increase the level of diagnosing diseases both inside and outside liver and avoid unsuitable biopsy or treatment