Intrathyroidal hematopoiesis: a rare histological finding in an otherwise healthy patient and review of the literature.

Background And Aims: Multinodular goiter represents the most common thyroid disease in Europe and the United States. Regressive changes like hemorrhage, infarction or fibrosis are frequently observed. Calcifications have also been detected by microscopic investigation of thyroid tissue. Extramedullary hematopoiesis has been described in almost every organ, especially in patients with hematologic diseases. However, true bone formation is uncommon and to date only two cases of metaplastic bone formation with extramedullary hematopoiesis in the thyroid have been reported in the literature.

Materials And Methods: We present a case of total thyroidectomy due to multinodular goiter harboring an area of mature bone and hematopoiesis in an otherwise healthy female patient. Furthermore, we reviewed and summarized for the first time all available cases from the literature.

Results: We report the third case of metaplastic bone formation with foci of hematopoietic tissue in the thyroid gland. All three patients were young females without any obvious stimulus for extramedullary hematopoiesis.

Conclusion: Isolated extramedullary hematopoiesis seems to be more frequent in the thyroid gland than metaplastic bone formation with hematopoiesis, particularly in older people with underlying hematologic disorders. It also represents an important differential diagnosis of anaplastic carcinoma of the thyroid, particularly in intra-operative frozen sections and fine-needle aspiration biopsy.