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Risks of malignancy Risk factors for malignancy in substernal goiters may include old age, a family history of thyroid pathology, a history of cervical radiation therapy, recurrent goiter, and the presence of cervical adenopathy, thrombotic material within the lumen of a vein in contact with a substernal goiter, and possible preoperative hoarseness. However, the incidence of cancer in substernal goiters is no higher than the incidence of cancer in cervical goiters; 25 series reported malignancy in 0%–22.6% of substernal goiters in literature review. The most common type of carcinoma was papillary, followed by follicular, medullary, mixed or coincident, and anaplastic. Most of the tumors (> 50%–60%) are microcarcinoma (< 1cm). However, the inability to rule out malignancy in substernal goiters provides a further rationale for performing total or subtotal thyroidectomy in these cases.
Diagnosis With addition of pertinent clinical manifestations, substernal goiter is a major diagnostic consideration in evaluating mass lesions in the upper mediastinal region. Neck and chest radiography as well as computed tomography (CT) scan and magnetic resonance imaging (MRI) are essential for diagnosis. Typical radiography discloses a mass with tracheal deviation or myd88 signaling at and below the thoracic inlet, calcification within the tumor, and reflection of the mediastinal pleura below the goiter (Fig. 1A and B). Erbil and colleagues reported that chest radiography might provide the first evidence of a substernal goiter in 77% of patients. CT scanning can further permit detailed evaluation of the intrathoracic extent of the thyroid (for secondary substernal goiter) and displacement of the trachea, esophagus, and regional vessels. MRI may provide a critical tool in the visualization of tissue and local invasion of vascular structures by the mass. Fine-needle aspiration biopsy of substernal goiters for cytologic analysis may be helpful when a large cervical component exists, but this is not usually recommended because it can be dangerous and the material obtained is often inadequate for histologic diagnosis of malignancy. It is accepted that thyroid radionuclide scans are not particularly helpful although more than half of substernal extensions can be detected on scintiscans. Nuclear thyroid imaging may demonstrate thyroid activity in the mediastinum, but the absence of uptake in the mediastinum does not exclude a diagnosis of substernal goiter.
Managements for substernal goiter There is general agreement that medical treatment is ineffective for substernal goiters; thyroxine suppression and iodine-131 ablation are not particularly useful. Moreover, radioiodine therapy may induce acute inflammation and swelling of the gland with the potential for airway obstruction. The treatment of substernal disease is clearly surgical, but there is no consensus on the indications for thyroidectomy, although many authors suggest that thyroidectomy should be performed in all patients with substernal goiter who do not have medical comorbidity excluding them from surgery. This recommendation is based on the risks of airway obstruction and of malignancy, the presence of symptoms in the majority of patients on direct questioning, and the tendency for the goiter to demonstrate time-dependent progressive growth. Besides, surgery is associated with low morbidity when performed by experienced thyroid surgeons. Nevertheless, controversy exists in surgical treatment of asymptomatic substernal goiter. A large observational study that included 32,777 thyroidectomies (of which 1153 were on substernal goiter) from multiple centers within the state of New York in the United States has convincingly revealed that substernal thyroidectomy (in comparison with cervical thyroidectomy) was associated not only with an increased risk of complications, such as recurrent laryngeal nerve damage (2.1% vs. 0.6%, respectively), hypoparathyroidism (5.5%vs. 3.5%, respectively) and postoperative bleeding (2.2% and 0.9%, respectively), but also with increased mortality (1.4% vs. 0.1%, respectively). However, it is generally agreed that radiologic evidence of significant tracheal narrowing and potential airway obstruction may be an indication for surgery in a clinically asymptomatic patient.