Excessive Endothelial Cell Proliferation Occurring in an Organizing Thyroid Hematoma: Report of a Case and Review of the Literature.

The authors report a case of a thyroid hematoma containing an exuberant endothelial cell proliferation. No underlying vascular neoplasm was apparent and the hematoma occurred in a substernal goiter from a 90-yr-old male. Review of the literature revealed four similar previously reported cases of endothelial cell proliferation found in thyroid hematomas for a total of five cases. A fine needle aspiration or biopsy procedure antedated the definitive surgery in four patients and may be responsible for the formation of the hematoma in these cases. Areas of the endothelial proliferation resembled papillary endothelial hyperplasia (Masson's hemangioma) in four cases and cavernous hemangioma in three. However, these lesions occurred outside of vascular lumina and instead were intimately associated with fibrinous material of the hematoma. In addition, two cases contained foci of endothelial cells with nuclear atypia or intracytoplasmic lumens requiring distinction from angiosarcoma. These vigorous endothelial proliferations most likely represent alterations in the organization of a thyroid hematoma, a process similar to papillary endothelial hyperplasia, which is usually intravascular. Primary vascular neoplasms of the thyroid are exceedingly rare. Nevertheless, awareness of exuberant endothelial cell proliferation as a potential, albeit rare, manifestation of a thyroid hematoma should prompt careful attention to distinguish this reactive process from vascular neoplasms such as hemangioma or angiosarcoma.