Purpose: The mosaic pattern is a characteristic CT appearance for hepatocellular carcinoma (HCC). This study was designed to assess the tissue composition responsible for the CT mosaic pattern.
Method: Gross and whole-mount histologic sections of 10 HCC tumors from eight patients were prepared at identical levels as preoperative CT sections. CT features of the mosaic tumor pattern were spatially registered with the corresponding pathologic sections.
Results: CT of mosaic HCC demonstrated enhancing nodules (9/10), low attenuation areas (9/10), and internal septa (3/10). Spatial registration of CT and microscopic sections showed that enhancing tissue was viable tumor in nine of nine. Low attenuation areas were either necrotic (4/9) or of mixed tissue (5/9), including areas of necrosis, fibrosis, and hemorrhage.
Conclusion: The variable tissue composition of HCC accounts for the mosaic CT pattern. In most patients, enhancing nodules indicate viable tumor cells, and low attenuation areas represent necrosis, fibrosis, or hemorrhage.