Fine needle aspiration cytology of insular thyroid carcinoma. A report of four cases.

Four cases of poorly differentiated (insular) thyroid carcinoma (ITC) that underwent preoperative fine needle aspiration cytology were studied for the main cytologic features. Although ITC shows heterogeneity of histologic patterns, there are some cytologic characteristics suggesting the correct diagnosis, such as the presence of high cellularity, with large sheets of tumor cells showing a microfollicular pattern or smaller sheets showing a solid or trabecular pattern, intermingled with predominantly single cells on a hematic background with very scanty colloid. Nuclear overlapping is constant. The cytoplasm is poorly outlined, when present. Nuclear hyperchromasia is always present, with coarsely or finely granular chromatin. The variation in nuclear shape and size is moderate, with small nucleoli and occasional mitoses. A papillary arrangement, with the presence of intranuclear cytoplasmic inclusions (vacuoles) and nuclear grooves, is also visible.