Bone scanning in patients with pleural effusion--experience in 76 cases.

Seventy-six patients with malignant or benign pleural effusion were studied to determine the incidence of accumulation of 99mTc-MDP in relation to effusion, and reveal the mechanism. Of 76 patients, 46 (61%) were found to have diffuse uptake of 99mTc-MDP in the hemithorax, with almost the same positive rate in malignant and benign effusions, i.e. 62% and 57%, respectively. Of 46 patients, 32 (70%) showed diffuse, slight accumulation in the hemithorax, and the positive rate had a tendency to be higher with the increase in the effusion volume. We are convinced that the major mechanism of unilateral intrathoracic accumulation of 99mTc-MDP in pleural effusion is a passive transudation.