Ectopic thymoma can mimic benign and malignant thyroid lesions on fine needle aspiration cytology: a case report and literature review.

Background: Ectopic cervical thymomas are rare and there are few descriptions of the cytologic findings based on fine needle aspiration. Their appearances can be misinterpreted as either benign or malignant lesions of the thyroid. The authors report such a case occurring in a patient with Sotos syndrome, a genetic disorder characterized by somatic overgrowth and cognitive impairment.

Case Report: The patient developed a neck mass that was examined first by fine needle aspiration and then by pathologic examination of the resected specimen. On fine needle aspiration, a diagnosis of papillary carcinoma of the thyroid was favoured, based on the presence of large cohesive sheets of anastomosing papillary tissue fragments with fibrovascular cores. Pathologic examination of the resection specimen showed a thymoma, subtype B3. The cytologic findings correlated with the presence of nuclear palisading of tumour cells around perivascular spaces.

Conclusion: To the best of our knowledge, this histologic subtype of thymoma has never been reported in ectopic cervical thymic tissue, nor these particular cytologic findings that can lead to an erroneous diagnosis of thyroid carcinoma. Moreover, this is the first description of thymoma in association with Sotos syndrome.