Goiter refers to an enlargement of the thyroid gland. The condition is estimated to affect 5% of the general population. While the definition of substernal goiter varies in the medical literature, goiters usually are considered substernal (also referred to as mediastinal, intrathoracic, or retrosternal) when more than 50% of the thyroid parenchyma is located below the sternal notch. Such tumors have been a focus of interest for surgeons for over 150 years. Klein is credited with being the first to successfully remove a mediastinal goiter in 1820, although the earliest surgical description of mediastinal thyroid extension dates back to Haller in 1749. Today, substernal goiters are treated by a number of different surgical specialists, including thoracic, general, and head and neck surgeons. Goiters account for as many as 10% to 15% of space-occupying mediastinal lesions and are the most common of the superior mediastinal masses.
Mediastinal goiters are classified as primary or secondary. Primary mediastinal goiters, also referred to as ectopic or aberrant goiters, do not possess any direct fibrous or parenchymal connections to the cervical portion of the gland. They are uncommon and represent fewer than 1% of all surgically excised goiters. Ectopic mediastinal thyroid tissue generally lies in proximity to the thymus owing to their shared embryological origins and to an intimate association with the thymothyroid ligament but also has been described in the pericardium and heart. Patients with ectopic thyroid tissue typically are clinically euthyroid, although hyperthyroidism has been described. The blood supply of these goiters originates from a mediastinal source, most commonly a branch from the internal mammary artery, the innominate artery, or the intrathoracic aorta itself. Other criteria used to define a primary mediastinal goiter include a normal or absent cervical thyroid gland, no history of prior thyroid surgery, and a lack of similar pathology in both the cervical and mediastinal portions of the thyroid. Confirmation of an ectopic thyroid gland can occur assuredly only at surgical resection if these criteria are met.1
Secondary mediastinal goiters are a much more common clinical entity. As many as 5% to 15% of all goiters demonstrate some extension into the mediastinum. These goiters derive their blood supply from cervical branches of the superior and inferior thyroid arteries and therefore can be resected almost uniformly via a cervical collar incision. One exception to this rule, to be discussed later, is of special importance to the thoracic surgeon.
Substernal goiters are an important clinical entity for a number of reasons. Patients may eventually develop compressive or obstructive symptoms when the goiter, which is confined within the narrow thoracic inlet, begins to exert extrinsic compression on respiratory, esophageal, vascular, and/or neural structures. There is also a risk of malignant degeneration within the substernal goiter, reported to be as high as 15% to 20% in some published series.2 In most situations, pathologic substernal goiter is an entity that ...