Muscular cushions of the vessel wall at the periphery of thyroid nodules.

Insufficient vascular compliance might be the cause of regressive changes commonly observed within long-standing thyroid nodules. This hypothesis induced us to study the morphology of vessels at the periphery of nodular thyroid lesions. A series of 104 consecutive nodular goiters and 10 follicular adenomas were collected and stained for elastic fibers and alpha smooth muscle actin to study the morphology of vessel walls. Ninety carcinomas of different histologic type were reviewed as well. Cases of diffuse thyroid enlargement, such as Grave's disease and Hashimoto's thyroiditis, served as controls. In the peripheral zone of eight follicular adenomas and of about 50% of nodular goiters, muscular cushions, connected with the vessel walls, were merged within the fibrous tissue. Such structures were found only in five out of 90 cases (6%) of carcinomas and only when the tumors developed in a gland affected by long-standing nodular goiter. Muscular cushions were never observed in cases of diffuse thyroid enlargement. Such cushions were stained with anti-smooth muscle actin antibody and showed variable amount of elastic fibers, suggesting an origin either from arterial or vein walls. We suggest that the muscular cushions of the vessel walls are the result of nodular thyroid disease and that they should be considered real anatomical entities with a specific function as sphincteric structures.