CD34 and parathyroid gland adenoma: The observation of adventitial fibrosis, with abundant collagen I between TCs/CD34+ SCs, in some arterial vessels of the peripheral parathyroid glands compressed by parathyroid adenomas is an indicator of the role attributed to the adventitia as an important regulator of vascular structure and function, in normal and pathologic conditions [74,75,76,77,78,79].