MRI of small hepatocellular carcinoma: comparison with US, CT, DSA, and Lipiodol-CT

Thirteen cirrhotic patients with 27 nodules of hepatocellular carcinoma less than 3 cm (small HCC) were examined with ultrasonography (US), MR, pre- and postcontrast CT, digital subtraction angiography (DSA), and CT after injection of Lipiodol (Lipiodol-CT). The accuracy of MR was compared with other diagnostic modalities and MR morphologic and the signal intensity features of HCC were investigated. The detection rate by MR was 63%, by US 67%, by CT 50%, by DSA 74%, and by Lipiodol-CT 93%. The Mc Nemar test showed no difference between the detection rates of MR and CT, MR and DSA, MR and US, and Lipiodol-CT and DSA; however, the differences between the detection rates of MR and Lipiodol-CT and CT and Lipiodol-CT were statistically significant (p less than or equal to 0.05). The difference in sensitivity between the detection rates of Lipiodol-CT and US was just above the level considered significant (P less than or equal to 0.065). On T1- and T2-weighted spin echo images 83% of small HCC were hyperintense relative to the surrounding liver parenchyma. Pseudocapsule was observed in 58% of lesions on T1-weighted images in particular. We believe that US is still the best diagnostic technique for the screening of HCC. We prefer MR to CT as a second level examination to support US in noninvasive diagnosis of small HCC, since MR gives the same or slightly better results than CT without the need of ionizing radiation and large amounts of iodized contrast medium. In our opinion, more invasive examinations, such as DSA and Lipiodol-CT, cannot be avoided in cases where an exact knowledge of the number of lesions is essential for the choice of therapy.