[The tissue characterization of focal liver lesions with magnetic resonance imaging].

This study was aimed at assessing the accuracy of Magnetic Resonance Imaging (MRI) in the characterization of focal liver masses. We prospectively examined 51 patients with focal liver masses: the morphological features were investigated with different pulse sequences and the functional characteristics were studied after the i.v. administration of Gd-DTPA (2 mmol/kg). MR findings were compared with those of gold standard methods, i.e., percutaneous biopsy, surgery or, for hemangiomas, 99mTc-labelled blood cell liver scintigraphy. All hemangiomas presented with typical features: signal intensity was very high on long TE images (> 140 msec) and a globular enhancement pattern, with centripetal progression, was observed after dynamic studies. This signal pattern on T2-weighted images is highly indicative of hemangioma. Five of 7 focal nodular hyperplasias (71%) were isointense with hepatic parenchyma on all pulse sequences; the central scar was observed in 5/7 cases on short TR/TE images and in all cases on long TR/TE images in 16/17 cases (94%). High signal intensity on T1-weighted images was statistically significant for HCC. A pseudocapsule was observed in 12 cases (70%). A mosaic pattern on T2-weighted images was observed in 3 cases. Seventy-four per cent of HCCs exhibited signal enhancement during the arterial phase of the dynamic study. Metastases presented a uniform pattern, i.e., they were hypointense on T1-weighted and hyperintense on T2-weighted images in 12/13 cases (92%). A central hypointense area on T2-weighted images is indicative of coagulative necrosis. A lesion with these morphological features and hypovascular signal is suggestive of metastasis.