Substernal Goiter (Retrosternal Goiter) Treatment & Management

Suppressive therapy generally is ineffective in the management of substernal goiters, but consider this therapy when a contraindication for surgical intervention exists. Radioactive iodine therapy may be useful in the treatment of hyperthyroidism associated with goiters but usually is unhelpful in the management of obstructive symptoms.

Surgical intervention is the treatment of choice for substernal goiter. ^{[5, 7]} In the case of benign disease, the extent of surgery is determined by the removal of the entire substernal component of a goiter as well as any other thyroid tissue responsible for obstructive symptomatology. If this goal of surgery can be met, while limiting surgery to removal of a single lobe and the isthmus, the risk of complication is reduced because injury of the contralateral recurrent laryngeal nerves and parathyroid glands is avoided. ^[8] In the case of malignant disease, total thyroidectomy is generally recommended, particularly in tumors larger than 2 cm in which postoperative radioactive iodine treatment may be used.

Indications

Most authors consider the mere presence of a substernal goiter an indication for surgical removal. The rationale for this recommendation is primarily related to the risk of serious complications that can occur because of compression of visceral or vascular structures within the bony thoracic cavity, the most significant of which is airway compromise. Recognize that airway compromise, while generally occurring slowly and progressively, can occur precipitously, thus resulting in the need for emergent airway management.

Additional arguments in favor of thyroidectomy for even small substernal goiters include the relative ineffectiveness of suppressive therapies and concerns that delaying surgery until symptoms develop may render the operation more technically difficult.

Finally, malignancy has been reported in 5-15% of substernal goiters, and fine-needle aspiration for cytology may be dangerous or impossible. However, reasonable arguments could be made that close observation may be appropriate for a small substernal goiter observed in an asymptomatic patient of very advanced age without radiographic evidence of visceral or vascular compromise.

Contraindications

Thyroidectomy for substernal goiter is contraindicated in patients who are inappropriate candidates for surgery in general (eg, patients who have conditions that carry significant or more serious comorbidity). Many practitioners consider the known presence of anaplastic carcinoma of the thyroid a relative contraindication to surgery for substernal goiters because treatment of this condition often is futile, and the likelihood of malignant invasion of critical structures (including the great vessels) may be high. Finally, while toxic substernal goiters may ultimately require surgery for cure, hyperthyroidism requires preoperative medical management to avoid thyroid storm intraoperatively.

Preoperative management for substernal thyroidectomy focuses on (1) avoidance of thyroid storm, (2) detailed comprehension of the patient's anatomic considerations, and (3) preparation for airway difficulties during anesthesia. Accordingly, all patients undergoing thyroid surgery should have preoperative thyroid function studies as well as appropriate medical management of any thyrotoxicity. Although passing an endotracheal tube through and past an area of extrinsic tracheal compression caused by benign substernal goiters rarely is problematic, distortion of the normal position of the larynx may make peroral intubation more difficult.

In addition, patients who have difficult upper airway anatomy and tracheal compression from substernal goiter or those who become symptomatic with neck extension may pose significant hazards during induction of anesthesia. Therefore, an appropriate preoperative discussion with the anesthesiologist regarding airway management issues is recommended. Additionally, the anesthesiologist should have access to and expertise in fiberoptic intubation. The use of an appropriate endotracheal tube for intraoperative recurrent laryngeal nerve monitoring is also an appropriate consideration.

Computed tomography scanning is currently the most useful tool in preoperative assessment of patient anatomy. In most cases, substernal goiters can be removed successfully through a transcervical approach, although transthoracic approaches are occasionally required. Certain radiographic findings may alert the surgeon to the possible need for such an approach. For example, posterior mediastinal and posterior intrathoracic goiters may be difficult or impossible to remove through a cervical incision. Occasionally, removal of massive centrally located goiters that are wedged between the sternum and spine presents difficulties. These anatomic characteristics or substernal goiters occurring in patients who have had prior thyroid surgery (in which fibrosis can make dissection more difficult) may necessitate the assistance of a surgeon experienced in sternotomy or thoracotomy. ^{[9, 10]}

Many substernal goiters that are not easily detected by palpation of a patient in a sitting patient can become detectable in a supine patient whose neck is properly extended.

After standard preparation and draping (taking into consideration the possible need for sternotomy or thoracotomy), commence the procedure using a low collar incision followed by elevation of subplatysmal flaps superiorly above the thyroid notch and inferiorly to the clavicle. Generally, transection of the strap muscles is unnecessary. Therefore, initially divide the strap muscles in the midline and retract them laterally to expose the cervical portion of the thyroid gland.

Carefully examine the gland by palpation, using cautious blunt finger dissection around the lobe extending into the mediastinum. Some authors advise ligation of the middle thyroid vein and inferior thyroid artery in the neck before attempting to deliver the goiter from the mediastinum. This author prefers to work first in the mediastinum, using gentle finger dissection and working circumferentially around the substernal extent, carefully separating fibrous attachments. At this point, using both hands sometimes helps to dissect and carefully lift the goiter from the mediastinum into the neck.

Whether the substernal goiter can be delivered into the neck through the collar incision can usually be determined at this early juncture in the procedure. If such determination cannot be made, consider alternative exposures. In most cases in which the goiter cannot be removed through a neck incision, a ministernotomy or partial upper sternotomy provides excellent exposure with little or no additional morbidity. Alternative approaches include partial resection of the clavicular head or thoracotomy. While many authors have correctly pointed out that the vast majority of substernal goiters can be successfully removed through a neck incision, ^[11] the ability to pursue transthoracic approaches when circumstances warrant nevertheless is important.

Generally, identification of the parathyroid glands or the recurrent laryngeal nerve before delivering the goiter from the mediastinum is not possible. Once the goiter is elevated from the mediastinum, complete the balance of the operative procedure as with any standard thyroidectomy. Identify and ligate the middle thyroid vein, followed by identification and preservation of the recurrent laryngeal nerve and parathyroid glands. Next, ligate the superior pole vessels and trace the recurrent laryngeal nerve to its entry into the larynx below the cricothyroideus muscle. Then, identify and ligate terminal branches of the inferior thyroid artery, after which the Berry ligament can be sharply divided with the isthmus elevated off the underlying trachea.

In most cases, lobectomy and isthmusectomy are the appropriate extent of surgery. At this point, assess the trachea for any residual displacement or distortion. If significant tracheomalacia with residual narrowing or kinking of the lumen exists following goiter removal, the tracheal airway may be improved by using traction sutures placed around cartilaginous rings. The sutures then are secured to strap muscles or are brought out through the skin tied over a button. Suction drains are commonly employed because of the significant dead space often created by removal of large goiters.

Monitor the serum calcium level. In certain cases of massive multinodular goiter, particularly with significant cervical and substernal involvement, identification of the parathyroid glands may be difficult. Even when dissection is limited to a single tracheoesophageal groove, typically transient hypocalcemia may ensue.

Removal of substernal goiters carries a very low risk of operative morbidity or mortality. In the hands of experienced surgeons, such removal can be considered safe. Potential complications include vocal cord paralysis, hypoparathyroidism, bleeding, mediastinal infection, tracheal or esophageal perforation, or pneumothorax. Removal of substernal goiters that require extensive dissection or total thyroidectomy may be associated with a somewhat greater risk of morbidity when compared with thyroidectomy in general. However, many authors have reported overall incidence of complication in removal of substernal goiters as similar to that for standard thyroidectomy.