Identification of Ryu's segmentation of the liver using MDCT analysis

Couinaud's segmentation is widely used for clinical segmentation of the liver. Recently, a new method of liver segmentation was described by Ryu. In this method, the right posterior sector in Couinaud's segmentation is regarded as 1 segment, and the right anterior sector is subdivided into the antero-ventral segment (AVS) and the antero-dorsal segment (ADS), which are demarcated by the anterior fissure vein (AFV). We used data from multi-detector row computed tomography (MDCT) to identify the portal and hepatic veins that are used as anatomical landmarks in both Couinaud's segmentation and Ryu's segmentation.

We analyzed data from 100 patients who had no space occupying lesions of the liver and had undergone abdominal CT examination from June through September 2008. MDCT was used to obtain contrast-enhanced helical scans of the whole liver during the portal venous phase. Using thin-slice data, we attempted to identify the portal and hepatic veins, in particular the anterior fissure vein (AFV), the antero-ventral portal vein (AVPV), and the antero-dorsal portal vein (ADPV), all of which are used in Ryu's segmentation.

In all cases, we were able to identify the hepatic segments of Couinaud's segmentation. However, in several cases, we were unable to identify the segments used in Ryu's segmentation. The AFV flowed into the intermediate hepatic vein (IHV) in 88% of cases and into the right hepatic vein (RHV) in 12%. Among the former, the AFV flowed into the proximal IHV in 53% of cases. Although the AFV could be identified in these cases, it was difficult to determine the border between the AVS and the ADS.

Our findings indicate that the use of MDCT data to identify hepatic anatomy was more difficult in Ryu's segmentation than in Couinaud's segmentation, because the AFV could not be easily identified in the former. Indeed, even when the AFV could be identified, its use as a landmark was often questionable.