A fine-needle aspiration is a puncture with a very fine needle from a lymph node or a nodule, in order to bring back a few microscopic cells. These cells are spread on a slide which will be sent to the pathology laboratory for study under a microscope. This technique is very useful for studying certain lymph nodes, in particular the axillary hollow, certain mammary nodules or thyroid nodules. This gesture is not painful, the needle used being a very fine needle.