Although many large goiters dip beneath the clavicles for a short distance, true intrathoracic goiters with extension downward as far as the arch of the aorta are relatively rare. In a series of thyroidectomies performed on 11,800 patients at the Cleveland Clinic Hospital there were only 97 cases in which the goiter descended to the arch of the aorta or below it, an incidence of less than 1 per cent.
It is a safe rule to consider all intrathoracic goiters to be adenomas originating in normally situated thyroid glands. All large intrathoracic goiters are adenomatous; in no instance in this series did a diffuse goiter descend to the arch of the aorta, and in all cases the adenomas had their origin in normally situated thyroid glands. We have seen several cases in which papillary adenomas arising in aberrant thyroid tissue and not connected with the thyroid itself were present in the superior mediastinum. However, these tumors are extremely rare and must be considered as a separate entity from the ordinary endemic goiter.
Intrathoracic goiter is a disease of the mid and latter span of life, the average age of the patients in this series being 53 years. The youngest patient was 32 years of age and in only 7 per cent of the cases were the patients under 40 years of age.
Since only adenomatous goiters become intrathoracic, it is not surprising to find the incidence of intrathoracic goiter highest in the older age groups in which adenomas. . .