Intranuclear inclusions are the most important cytological signs in the diagnosis of a papillary carcinoma. These are invaginations of nuclear membrane and are in fact pseudoinclusions. These are characteristically sharp. Such inclusions occur only rarely in benign thyroid lesions except for oxyphilic cells. Drying artifacts present a similar appearance, but in this case the borders of the holes are irregular (see left picture in the 5th row). Projections of vacuoles may cause more serious differential diagnostic problem. Compare images in the 4th and 6th rows. In the case of papillary cancer a dark rim surrounds the light hole which is absent in vacuoles projected to the nucleus.