In denoting the presence of a prolongation or of the enlargement of the entire thyroid gland behind the sternum or within the thoracic cavity, the terms "substernal" and "intrathoracic" have been used synonymously. In this article, the term intrathoracic goiter will be limited to those growths of the thyroid in which the major portion of the tumor lies within the thorax. This does not necessarily imply that the greater portion of the entire thyroid gland lies concealed, for obviously the greater portion of the goiter may be cervical and confined to one lobe, while there may be a large, but smaller, growth in the other lobe entirely within the cavity of the chest. All other tumors of the thyroid whose inferior projection, varying in depth below the sternal border from 1.25 cm. to 7.5 cm., and equivalent to less than one half of the growth, are classed as substernal goiters.
PEMBERTON JD. SURGERY OF SUBSTERNAL AND INTRATHORACIC GOITERS. Arch Surg. 1921;2(1):1-20. doi:10.1001/archsurg.1921.01110040010001