Indications

The most common indication for mediastinal exposure is the presence of a substernal goiter or true posterior descending goiter (see Chapter 7, Surgery of Cervical and Substernal Goiter). Although substernal goiter is a relatively common finding, the need for mediastinal exposure is infrequent but often cannot be determined until the time of surgery. Thyroid cancer that involves mediastinal structures or is associated with enlarged mediastinal nodes is another indication. Certain thyroid malignancies may involve the trachea, larynx, and esophagus, necessitating a cervical exenteration with mediastinal tracheostomy requiring extensive mediastinal exposure. Tumors may involve vascular structures requiring proximal and distal control only achieved by mediastinal exposure. Occasionally, parathyroid adenomas descend into the mediastinum and require access to the mediastinum.

Substernal goiter is the most common clinical problem requiring mediastinal exposure. The typical patient with a substernal goiter is shown in Figure 8-1. This type of patient can almost always have the goiter removed through a low collar incision. Substernal goiters represent between 3% and 47%^1–6 of all goiters removed, depending on the definition of what constitutes a substernal goiter (see Chapter 7, Surgery of Cervical and Substernal Goiter). The indications for removal of substernal goiter include actual or impending airway obstruction or threat of malignancy (about 2% to 3%). The majority of substernal goiters can be removed through a cervical incision. In our experience about 3% have required an upper or full sternotomy.^2,3 The only case requiring a full sternotomy in our series was a patient who had previous goiter surgery through a posterior thoracotomy (Figure 8-2). A full sternotomy was required to safely remove a recurrent goiter because of massive size, location, and prior thoracotomy (see Figure 8-2).

Figure 8-1 Chest radiograph showing a typical substernal goiter. This type of sternal goiter can almost always be removed through a low cervical collar incision.

Figure 8-2 This chest radiograph (A) and computed tomographic scan (B) are of a patient requiring full median sternotomy for removal. The patient had previously undergone goiter surgery through a right thoracotomy many years ago.

Mediastinal exposure for substernal goiter is required infrequently in part because extension of the neck acts to migrate the gland into the neck. Conventional techniques of capsular dissection allow gradual delivery into the neck. Thyroid surgeons should be aware of additional techniques described by others for delivery of difficult substernal goiters. These techniques include the use of a spoon,⁶ a Foley balloon catheter,⁷ and, rarely, morcellation.⁸

The true posterior descending goiter is an uncommon entity. The largest experience was reported by DeAndrade.⁸ DeAndrade reported a total of 9100 patients with goiters, 1300 (14.2%) of whom were intrathoracic (substernal); only 128 were posterior mediastinal in location. Interestingly, all of these were removed through a cervical exposure. The ability to remove posterior goiters through a cervical approach is undoubtedly related to the preservation of some connection to the cervical gland and cervical blood supply, making delivery possible. The use of sternotomy, thoracotomy, or trapdoor incision advocated by some^9,10 is rarely indicated currently.

True ectopic thyroid masses (i.e., thyroid tissue separate from the thyroid gland) are extremely uncommon.¹¹ Such lesions may derive their blood supply from the mediastinum. Sternotomy or thoracotomy may be used in these cases because the preoperative diagnosis may be in doubt or concern exists about control of mediastinal vessels (see Chapter 7, Surgery of Cervical and Substernal Goiter).

Surgical Options for Exposure

Partial Sternotomy

Positioning patients with an inflated thyroid bag under the shoulders to extend the neck brings the carina to the level of the angle of Louis. Division of the manubrium to just beyond the angle of Louis exposes the upper mediastinum and is all that is required for most circumstances. This is accomplished by making a longitudinal skin incision from the midpoint of the collar incision, carrying it down just below the angle of Louis (Figure 8-3). It is important to dissect the suprasternal notch free of surrounding attachments. This allows the surgeon to insert a finger behind the manubrium and clear the areolar attachments. This maneuver is important to sweep the innominate vein and the pleura free from the back of the manubrium. Division of the innominate vein is the greatest risk to division of the upper sternum. Once the back of the manubrium has been cleared, the midline should be identified and scored with the cautery. The manubrium can be divided in a variety of ways. Some prefer the sternal saw. We rely on the Lebsche knife (Figure 8-4). The Lebsche knife has a sharp edge to divide the bone, a broad surface to allow striking with a mallet, and a footplate to allow some control over the depth of division of the sternum. To use the Lebsche knife, the footplate is inserted under the sternal notch and the tip angled upward toward the back of the sternum. The Lebsche knife is vigorously pulled up, lifting the sternum as the mallet strikes it. It is important to divide the manubrium in the midline to allow for reapproximation when the operation is completed. When the manubrium is divided, it is gently spread with a right-angled retractor to allow placement of a small pediatric sternal spreader (Figure 8-5). The spreader is gradually opened to prevent fracture; however, if fracture does occur, it can be reapproximated with expected good results if it is fractured on one side only. This exposure is sufficient for most problems confronting the thyroid surgeon. With the sternal spreader in place, the exposure to the mediastinum is greatly improved. This gives access to the trachea, esophagus, innominate vein, and artery. Dissection can be achieved in the tracheoesophageal groove and into the angle formed by the arch of the aorta and the innominate artery. Mediastinal exposure can be further enhanced with the addition of partial sternotomy (Figure 8-6).

Figure 8-3 The low collar incision is utilized to explore patients to determine whether further exposure is needed. If additional exposure is needed, an incision is carried inferiorly from the midpoint of the collar incision to just below the angle of Louis.

Figure 8-4 The Lebsche knife is seen on the left and the mallet on the right. The handle at the top holds the knife, and the sternum is elevated in this fashion. The footplate seen at the bottom is inserted under the sternal notch. The mallet strikes the knife on the flat surface just above and posterior to the footplate.

Figure 8-5 A small pediatric sternal spreader is inserted in the divided manubrium to give additional exposure to the mediastinum.

Figure 8-6 A sternal spreader is inserted following manubrial and partial sternal division to give wide exposure to the mediastinum.

At the conclusion of the surgical procedure, we prefer sternal wires to reapproximate the sternum, and we usually use two sutures. The sutures are placed through the bone rather than around it at this level. This avoids injury to the internal mammary vessels or violation of the pleura.

The most significant complication of sternotomy is the division of the innominate vein. This almost always necessitates completing the full sternotomy to gain control of the vessel. Direct finger pressure on the divided vein to compress it against the back of the sternum is the first maneuver. Once the vein is controlled in this fashion, the two ends are identified and clamped. The vein can usually be reapproximated with no tension. A running 5-0 Prolene is used. It is important to avoid purse stringing and narrowing the vein. Intravenous infusion into the left arm should be stopped until continuity is restored. If for some reason the vein cannot be reconstructed, division is well tolerated with the only complication being left arm swelling. The arm should be elevated following surgery, and no intravenous fluids should be infused into this arm.

If the pleura are violated and a pneumothorax develops, a chest tube should be inserted anteriorly in the midclavicular line between the second and third rib. If it can be determined that the lung is not injured, a catheter attached to suction can be inserted into the pleural space. A pursestring suture is placed in the pleura around the catheter. The anesthesiologist inflates and holds the lung as suction is applied to the catheter. The catheter is quickly removed as an assistant ties the pursestring suture. A chest radiograph must be obtained to determine whether there is a pneumothorax. A small pneumothorax can be followed. The presence of a significant pneumothorax requires placement of a chest tube.

Sternal infection usually manifests itself in a delayed fashion. Symptoms can be subtle. The classic findings are fever, leukocytosis, sternal clicking, erythema, and purulent drainage. Computed tomography (CT) of the chest should be obtained if doubt exists. Telltale findings include separation of the sternum, the presence of retrosternal air, and fluid collections. If it is determined that infection exists, the wound should be opened, the sternum debrided, and the wound packed. Frequent dressing changes and debridement allow the wound to granulate and ultimately close. If a full sternotomy has been utilized, the problem is more significant. Reopening the sternum for debridement and irrigation is required. An attempt at closure with povidone-iodine (Betadine) irrigation is favored by some. If this fails, debridement and rotation of muscle flaps may be required.