The patient had thyroidectomy for cancer and radioiodine therapy. On chest X-ray suspected small fluidothorax on the left. To exclude malignancy sent for pleural puncture.

The ultrasound examination found the presence of small fluidothorax, maximum size up to 1 cm. Pleural biopsy performed under ultrasonographic guidance. 15 ml of straw yellow effusion collected. Cytology serous reactive pleurisy, with no malignant cells.