If the thyroid gland is enlarged bilaterally, which of the following maneuvers is appropriate?

19 What is the appropriate therapy for an intrathoracic goiter?

Intrathoracic goiters are typically cervical goiters with mediastinal extension, although primary intrathoracic goiters do occur secondary to abnormal descent of the thyroid during development. The incidence of carcinoma residing in intrathoracic goiters is reported as high as 17%; moreover, approximately 40% of patients present with compressive symptoms resulting from impingement on the airway, esophagus, vascular structures, or nerves. Radioiodine ablation is not typically recommended because of the risk of transient enlargement of the goiter during initiation of therapy, potentially resulting in life-threatening airway compromise. Thus the presence of an intrathoracic goiter is generally accepted as an indication for thyroidectomy. Because the arterial supply of intrathoracic goiters originates in the neck, the vast majority of these tumors can be resected through a cervical approach. Extension into the posterior mediastinum, malignancy, or compression of the vena cava may necessitate a combined cervical and sternotomy approach, although this is required in less than 5% of cases.

Surgery for Substernal Goiter

SSG was first described by Haller in 1749.27 Crile described SSG as a situation in which the goiter went down to the aortic arch.28 Although the term remains somewhat ill defined, Katlic and coworkers29 characterized SSG as having greater than 50% of its mass inferior to the thoracic inlet. Indications for surgery include compression of adjacent structures, prevention of the same, and diagnosis.30

The majority of SSGs originate from downward extension of a cervical goiter along the fascial planes of the neck, through the thoracic inlet, and into the mediastinum. The blood supply of an SSG arises primarily from the interior thyroid artery. Absence of a palpable mass in the neck does not exclude SSG. Sometimes a cervical component is not enlarged because the bulk of the gland is in the mediastinum.

Unlike a goiter in the neck, which can grow to enormous proportions and remain asymptomatic, SSG is symptomatic early in its course. The clinical symptoms are attributed to compression of the adjacent aerodigestive tract and the mediastinal great vessels at the thoracic inlet. Shortness of breath while lying in bed and difficulty swallowing, even pills, are the most common symptoms. Patients with SSG are vulnerable to acute airway obstruction, which generally arises from hemorrhage in the gland.

CT scanning is a valuable source of information about SSG because it will demonstrate the relationship of the goiter to the trachea, the esophagus, and the great vessels and heart. We have had many cases in which SSG extended to the aorta, which we removed through a cervical approach, and one that went posterior to the heart and required a combined transcervi-cal and partial medial sternotomy approach. Patients should be seen in consultation by a thoracic surgeon for examination and review of the CT scan. The patient's best interest is served by having thoracic surgical colleagues standing by in the possible, but unlikely event that a medial sternotomy is necessary.

An SSG can virtually always be removed through a cervical incision. The important consideration is that the neck must be placed in extreme extension to mobilize the gland out of the mediastinum. Both recurrent laryngeal nerves must be identified. The inferior and superior thyroid arteries are ligated. Before any attempt at mobilization of the thyroid gland from the mediastinum, Berry's ligament is transected bilaterally. Transection may be facilitated by dividing the isthmus in the midline to separate the thyroid gland from the larynx and trachea and permit upward traction on the substernal component of the thyroid gland. There are instances in which an SSG is actually linked to the thyroid lobe by a very small isthmus of thyroid tissue, or it may in fact not be attached to the thyroid lobe at all. At this point the surgeon's finger can be introduced into the superior mediastinum and a cleavage plane developed around the capsule of the gland to separate the gland from the soft tissues. At the same time that the gland is being mobilized from below, gentle but firm traction should be exerted in the superior direction to deliver the thyroid gland from the mediastinum. The exception to this technique may be cancers with extracapsular extension and adherence to vital structures. This condition can be anticipated by imaging and preoperative diagnosis of cancer by FNAB. In these circumstances, medial sternotomy may be required for identification and control of vascular structures.

Substernal Goiter

Substernal goiters are usually extensions of the thyroid into the mediastinum. Most show continuity with the cervical portion of the gland, although some have only a fibrous band connecting the substernal and cervical thyroid tissues. Many are asymptomatic and incidentally detected on CT as an anterior upper mediastinal mass. As they enlarge, they may cause symptoms of dyspnea, stridor, or dysphagia. Scintigraphy can confirm the thyroid origin of the mass.

Uptake in substernal goiters is often lower than thyroid bed activity. Tc-99m pertechnetate is not ideally suited for this purpose because of its high mediastinal blood pool activity, although the study can sometimes be diagnostic (Fig. 6-20). I-131 has been used because it can be imaged at 24 to 48 hours and thus will have high target-to-background ratio (Fig. 6-21). Currently, I-123 is usually the first radiopharmaceutical of choice with images obtained at 4 hours. Single-photon emission computed tomography (SPECT), but particularly SPECT with CT (SPECT/CT) can be confirmatory (Fig. 6-22).

Sternotomy for Substernal Goiter

Multiple substernal goiter series show sternotomy rates of between 1% and 8% (see Chapter 7, Approach to the Mediastinum: Transcervical, Transsternal, and Video-Assisted).11,20,56,58,86,90,91,101,203,204 Resection of the medial one-third of the clavicle can also be used to increase the bony confines of the thoracic inlet (see Figure 6.10).205 Sternotomy must, in all cases, be discussed preoperatively with the patient and thoracic surgical colleagues. Clearly, there is increased morbidity associated with the addition of a transthoracic approach. In a National Surgical Quality Improvement Program (NSQIP) database review of 2716 patients with substernal goiter, Khan et al. showed increased rates of unplanned intubation, need for transfusion, and length of hospital stay.206 The decision to perform sternotomy should be considered carefully and may be needed in the following circumstances:

Known or suspected malignancy extending into the mediastinum

Posterior mediastinal goiter if associated with contralateral extension (substernal goiter type IIB)

Cases in which goiter blood supply is mediastinal. This information may not always be available preoperatively. Patients with isolated mediastinal goiter (substernal goiter type III) are at higher risk for having noncervical blood supply.

Cases associated with true SVC syndrome identified preoperatively, which suggests substantial neck base/mediastinal venous obstruction. True SVC syndrome should raise the specter of mediastinal malignancy rather than benign substernal goiter.

Recurrent large substernal goiters

Any case in which delivery maneuvers reveal an immobile substernal component or where goitrous adhesions to surrounding mediastinal vessels and pleura are identified. Increased fibrosis or scarring may be seen with prior radiation or surgery of the neck or chest.

Cases in which substernal goiter delivery is associated with substantial mediastinal hemorrhage

Cases in which the diameter of the intrathoracic component of the goiter is substantially greater than the diameter of the thoracic inlet

Cases where there is a long thin stalk from the cervical to the substernal component. Such stalks may fragment with significant retraction, especially if the mediastinal component is wide and bulbous.

Sternotomy or thoracotomy, as an isolated approach to substernal goiter, is not appropriate because of the greater risk to the RLN during such a procedure and the inability to effectively control the inferior thyroid artery.91,96

Intrathoracic Goiter

Most intrathoracic goiters result from extension of cervical thyroid goiters into the mediastinum and typically affect women. Although patients are usually asymptomatic, compression of the trachea or esophagus rarely causes symptoms such as dyspnea or dysphagia. The risk of malignant degeneration is small. Most intrathoracic goiters are located in the anterosuperior mediastinum, usually on the right side, but other compartments may be affected. Ectopic intrathoracic goiter without a cervical component rarely occurs. Chest radiography often reveals a cervicothoracic mass that produces mass effect on the trachea. CT demonstrates a lobular, well-defined mass with heterogeneous attenuation resulting from hemorrhage, cystic change, and calcification (Figure 71-17). Intense and sustained contrast enhancement is common. In functioning goiters, uptake of radioactive iodine (iodine 123 [123I] or iodine 131 [131I]) and technetium 99 m (99mTc) pertechnetate is diagnostic. Symptomatic or large goiters may be surgically excised.

ANATOMIC CONSIDERATIONS

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The location for intrathoracic goiter includes anterior mediastinum, posterior mediastinum, and ectopic, and intrathoracic thyroid tissue (primary intrathoracic goiter).

Anterior goiters: 80% to 90% of intrathoracic goiters196,201 and usually leftward as it descends through the thoracic inlet.183,203

Posterior goiters: 10% to 20% of intrathoracic goiters198,202 and usually rightward as it descends through the thoracic inlet.203,204

Usually retrotracheal space

Occasionally retroesophageal

Primary intrathoracic goiters: 2% of intrathoracic goiters.180,193 The tissue originates from the embryonic foregut endoderm separate from the cervical thyroid and draws its blood supply locally.180,205

Posterior Mediastinal Thyroid

Posterior mediastinal goiters represent roughly 10% of all substernal goiters and are more common in women and in patients over 50 years of age. Posterior mediastinal goiters result in complex vascular and especially neural relationships that must be clearly understood regardless of the surgical approach; these will be reviewed in detail elsewhere in this text (see Chapter 6, Surgery of Cervical and Substernal Goiter). Although benign goiters in the posterior mediastinum are less likely, they are more likely to be symptomatic than anterior intrathoracic goiters. Patients may present with a palpable or visible cervical mass on physical examination and report symptoms resulting from compression of adjacent structures, including the trachea and esophagus. These symptoms include dyspnea on exertion or when supine, stridor, hoarseness, and dysphagia. Migration of the mass into the thoracic inlet can cause Pemberton’s sign, with facial flushing or a choking sensation with arms raised and may occur also when the patient is supine. Patients may develop Horner’s syndrome due to compression of the sympathetic chain, or jugular venous distention, thrombosis, cerebrovascular steal syndrome, or superior vena cava syndrome if the mass compresses mediastinal venous structures. When identified, these masses should routinely be resected, even in the absence of symptoms, given the risk for development of compressive symptoms with continued growth. They are often continuous with the cervical thyroid gland and can usually be excised through a cervical incision. In the largest published series to date, DeAndrade et al. reported that out of a total of 9100 patients with goiters, 1300 (14.2%) had intrathoracic lesions, with only 128 located within the posterior mediastinum.10 In this series, all of these goiters were removed through a transcervical approach and did not require thoracic exposure. Nevertheless, familiarity with thoracic approaches is beneficial should the need arise for enhanced exposure intraoperatively, either for complete dissection, or in the case of inadvertent injury to adjacent vessels, nerves, or to the aerodigestive structures.

Standard Open Thyroidectomy

Open or conventional thyroidectomy remains a necessary approach in many patients, especially those with thick necks or large, substernal goiters (see Chapter 6, Surgery of Cervical and Substernal Goiter and Chapter 31, Principles in Thyroid Surgery). A 6- to 12-cm incision is placed in a natural skin crease with the specific length determined according to the patient and the disease characteristics. Subplatysmal flap elevation is not necessary; avoiding this step minimizes tissue trauma, the likelihood of both seroma formation, supraincisional flap edema, and the potential for skin to strap muscle tethering (with untoward skin movement with swallowing postoperatively).

SUPERIOR VENA CAVA OBSTRUCTIONS

Various conditions can obstruct the superior vena cava, including tumors, aortic aneurysms, mediastinal masses, hilar adenopathy, and intrathoracic goiter.481–483 This obstruction produces edema and cyanosis of the face and neck (pumpkinhead appearance) as well as dilated vessels in the head, neck, chest, and upper extremities.484 Obstruction of the superior vena cava increases intracranial pressure, which leads to headache, stupor, vertigo, seizures, and mental changes. The associated ocular findings include exophthalmos, papilledema, and prominent blood vessels in the conjunctiva, episclera, and retina. Intraocular pressure is elevated, and the IOP increase is greater when the patient is in the supine position.485 There is a clinical impression that glaucomatous cupping occurs infrequently with superior vena cava obstruction despite the elevated IOP. Some researchers propose that cupping does not occur because the IOP is counterbalanced by elevated intracranial pressure.486 Therapy in this situation is directed toward relieving the obstruction.487 During this period, the IOP elevation is treated primarily with medications that decrease aqueous production, such as β-blockers and topical or systemic CAIs; α agonists may also be helpful.

Considerations on the Thyroid Growth

Thyroid is covered anteriorly by thin structures (strap muscles, subcutaneous tissue, and skin); enlarging thyroid usually grow outward

Substernal goiter is the elongation of the thyroid below the sternal notch; almost always by inferior thyroid growth

The incidence is 1 in 2000–5000 people; increases in the elderly and with the longer goiter duration

Substernal (retrosternal) goiter if the greatest diameter of the thyroid is above the sternal handlebars and intrathoracic if it is below

Most intrathoracic goiters are in the anterior mediastinum, but up to 10% may be primarily located in the posterior mediastinum

Bilobular and/or posterior enlargement may compress and narrow the tracheal luminal diameter

Tracheomalacia is uncommon

Most are benign goiters: 50% multinodular, large follicular adenomas 44%, chronic autoimmune thyroiditis 5%

Reported thyroid cancer incidence is 4%–17%; mostly with little clinical significance especially in the elderly