A sample size analysis showed that a number of visible nodes 150 in total were needed to achieve a sensitivity of 70% (95% CI 56% -80%). Knowing that 5 Iymph nodes are seen in average per patient would necessitate a population of 100 pts. Included. (15% of 100) x5 Iymph nodes= 75 visible benign Iymph nodes + (15% of 100) x5 Iymph nodes = 75 visible malignant lymph nodes.