The pseudocapsule in hepatocellular carcinoma: correlation between dynamicMR imaging and pathology

Nodular hepatocellular carcinoma (HCC) is characterized by the presence of a pseudocapsule (constructed usually from connective fibrous tissue) that a ppears hypointense on T1- and T2-weighted spin-echo (SE) and gradient-echo (GE) MR imagine sequences without a contrast medium. The presence of vascul ar structures inside the tumor, which are verified by histological exam, af fects enhancement of the PC after administrating the contrast medium. The i mpregnation is more evident in the dynamic study but also persists on the d elayed T1-weighted SE images. The accuracy of MR in detecting the pseudocap sule of HCC and contrast enhancement of the pseudocapsule during dynamic st udies were evaluated and related to pathological findings. Thirty-seven HCC were examined in 33 patients and afterwards resected. In capsulated nodule s, besides usual hematoxylin, eosin. and trichrome stainings, histochemical and immunohistochemical methods were performed. On a 1.5-T MR unit, T1- an d T2-weighted SE and GE FLASH 2D sequences after intravenous injection of G d-DTPA (dynamic study) were used. In a later phase, T1-weighted SE sequence s were repeated. Histologically, the pseudocapsule (thickness 0.2-6 mm) nas present in 26 of 37 nodules (70%). The dynamic study was the most suitable technique to show the: pseudocapsule, which was recognized in 80.7% (21 :o f 26 nodules). In 5 of 26 cases, the pseudocapsule, not demonstrated by MR, was thinner than 0.4 mm. In 16 of 21 cases, in the early portal phase (30- 60 s), the pseudocapsule had an early enhancement, which was more evident l ater; in 5 of 21 cases the enhancement was observed only in the late portal phase (1-2 min). At histological examination, 14 of 16 pseudocapsules with early enhancement showed a more prominent vasculature than those with enha ncement in the equilibrium phase. Magnetic resonance wets a reliable tool i n demonstrating the pseudocapsule of HCC. The histological examination demo nstrated a good correlation between the enhancement behavior and the vessel number of the pseudocapsule.