RESUMO
An ectopic cervical thymoma is an uncommon tumor of the neck displaying the same histologic features as a mediastinal thymoma. Because of its unusual location, this mass is often confused as originating from the thyroid. In this report we describe a case of cervical type AB thymoma. Aspiration cytologic smears were highly cellular and revealed irregular tissue fragments, cohesive sheets, and clusters of crowded epithelial cells intermingled with many small lymphocytes. The epithelial cells had oval and spindle shaped bland-looking nuclei and scant cytoplasm with indistinct cell borders. Mitosis, nuclear atypia, and necrosis were not observed. The cells were focally arranged in a nesting pattern. Many small lymphocytes, a few activated lymphocytes, and lymphoid tangles were seen in the background. A cytologic misdiagnosis of "possible carcinoma" was rendered. Therefore, ectopic thymoma should also be considered in fine needle aspiration cytology of a neck mass when the smear shows epithelial and lymphoid components.