Can one predict when ultrasound will be useful with percutaneous liver biopsy?

OBJECTIVE: We previously showed that ultrasound altered position of biopsy in 15% of cases by demonstrating intervening structures. This study was designed to test whether one could predict in which cases ultrasound would be useful.
METHODS: A standard percussion technique was used. The site chosen was marked. Criteria were established to indicate whether a move might be predicted to be likely. If 10 or more points were assigned, then it was predicted that ultrasound would change position. A difficult percussion was assigned 10 points; obesity, 5 points; and chest deformity, 5 points. The ultrasound was then applied to the marked spot in every case. If an intervening structure was present within 6 cm, the biopsy site was moved. Otherwise, the biopsy was taken from the marked site.
RESULTS: One hundred seventeen consecutive liver biopsies were included between January 1999 and January 2000. The criteria predicted the desirability of nine moves. No moves were made, however, in these cases. In 17 cases (14.5%), moves were made because of intervening structures. None of the cases were predicted. A move was made in 1 of 23 obese patients. There was no statistical difference in moves made between obese and nonobese patients.
CONCLUSIONS: Using criteria of difficult percussion, obesity, and unusual chest shape, we could not predict when ultrasound would be useful. This is in contrast to the belief that ultrasound can be applied to selected liver biopsies considered in advance to be more difficult, as in the obese patients, and instead suggests that to avoid intervening structures, one should apply ultrasound to all cases.