Psammoma body is considered to be the most characteristic and specific cytological feature of a papillary cancer. It corresponds to a calcified papillary structure and has a concentric appearance. It is best to observe by finely varying the focus during microscopic analysis: we can see several concentric figures in different depth.
The occurrence of psammoma body is related to the size of the needle used during aspiration, because psammoma body is a relatively large structure. We prefer to use thin needles (23 G and 25 G) in order to avoid bloody material, therefore we have found psammoma bodies in less than 2% of papillary cancers.