Pseudolesions of left liver lobe during helical CT examinations: prevalence and comparison between unenhanced and...

Localized low attenuated areas (pseudolesions) in the medial segment of left liver lobe are not rarely seen in the screening of abdomen using helical CT. The purpose of this study was to determine the prevalence of pseudolesions in the routine helical CT of abdomen and to evaluate the morphologic and enhancement features of pseudolesions in the unenhanced and enhanced CT examinations.

We retrospectively evaluated 333 contrast enhanced abdominal CT examination of 328 patients with no known liver disease, to detect the presence of pseudolesion of liver. In the presence of unenhanced and arterial phase examinations, these images were also analyzed. The imaging criteria for pseudolesion of liver was localized low attenuated area with geometric, ovoid or nodular shaped and with no mass effect adjacent to the falciform ligament, gallbladder, or porta hepatis. Previous CT, CTAP and MR examinations were also reviewed to understand the evolution of pseudolesion in patients in whom a pseudolesion was detected in the portal phase of helical CT examination.

We identified a pseudolesion in the 65 (19.8%) of 328 patients in portal phase of helical CT examinations. Pseudolesions were identified in the medial segment of left liver lobe adjacent to falciform ligament in the 92.8% of patients, both sides of falciform ligament in the 1.5% of patients, adjacent to porta hepatis in the 3% of patients and adjacent to gallbladder 3% of patients. These lesions had triangular shape in the 66.1% of patients, ovoid shape in the 18.6% of patients, and nodular shape in the 15.3% of patients. Unenhanced, arterial and portal phase images were exist in the 50.7% of 65 patients. The pseudolesions were not identified on the unenhanced images in the 75.7% of patients and on the arterial phase images in the 55.6% of patients.

Pseudolesions around the falciform ligament are not rarely seen in the routine helical CT examination of liver and abdomen. The pseudolesions are more encountered in the portal phase of helical CT examination. These lesions seem to be likely focal fatty infiltration or perfusion defect due to venous supply variation or both. Nodular shaped pseudolesions may be interpreted as true tumors and further study may require for differential diagnosis.