Clinical data: a 77-year-old woman presented with an increasing mass in the left thyroid lobe. Laryngology revealed palsy of the right recurrent nerve. She had dyspnea and difficulties in swallowing. The tumor evolved over 2 to 3 months.

Palpation: a very hard nodule was palpable in the right lobe.

Functional state: euthyroidism.

Ultrasonography: there is a hypoechogenic nodule occupying the right lobe and the isthmus. The nodule contained amorphous hyperechogenic foci and cystic degeneration which corresponded to necrosis. The dimensions of the nodule were 49x25x51 mm.

Cytological picture: there is no colloid in the background. There are naked, atypical, pleomorphic cells resembling lymphoblast on the smear. They are dissociated, no specific cell groups can be identified. Most of the cells present severe degenerative changes. Note loss of structure. The cytological pattern highly resembles that of anaplastic cancer or a high grade malignant lymphoma.

Cytological diagnosis: malignant tumor. Suspicion of anaplastic cancer.

Histopathology: medullary cancer.

Comment: the tumor did not presented typical cytological signs of a medullary cancer. The cellular details are difficult to judge because of degenerative changes. The possibility of a high grade malignant lymphoma could be excluded because there were no enlarged lymph nodes.