Substernal Thyroidectomy

Anatomy and Physiology

Intrathoracic goiters are subdivided into acquired and truly intrathoracic or aberrant ones. The acquired goiters originate from thyroid glands, which expand rapidly or over the years from the cervix to the retrosternal space and are the most common category. The truly intrathoracic goiters arise from ectopic thyroid tissue congenitally located in the mediastinum and account for less than 1% of surgically removed goiters. The great majority of substernal goiters occupy the anterior mediastinum in front of the brachiocephalic and subclavian vessels. Only 10% to 15% of these extend posteriorly to the trachea, while a very small subgroup expands in a retro esophageal position.[5] Because several different definitions of intrathoracic goiters have been proposed, Huins and colleagues suggested a classification in 2008 that relies on the anatomical expansion of the goiter and which can be useful in determining appropriate individualized pre-operative planning for different patients. This defines three grades of substernal goiters. Grade 1 defines thyroid tissue located above the aortic arch, grade 2 tissue between the aortic arch and the pericardium, and grade 3 tissue extending to the right cardiac atrium.[6]

Indications

Overall, there are 3 major indications of surgical management of multinodular goiters, and these are:

• Suspicious or confirmed thyroid cancer
• Compression of the adjacent organs
• Cosmetic reasons [7]

Most surgeons would argue for excision of the mass even if asymptomatic as most substernal goiters continue to grow and become more complex to resect when larger in size. The most urgent and common indication for substernal thyroidectomy is compression of the cervical and mediastinal noble structures, such as the trachea, the esophagus, and the superior vena cava. The trachea is compressed in most symptomatic cases, while superior vena cava syndrome is a rare complication and is most often linked to thyroid malignancy.[5]

Surgical excision of symptomatic mediastinal goiters is based on the following facts:

• Goiters tend to grow over the years.
• The use of radioiodine, which is an alternative to surgery, can potentially lead to acute goiter enlargement and further compression symptoms.
• Thyroid cancer can exist in up to 25% of these goiters.
• Transcervical goiter excision is possible in up to 90% of cases.[4]

Patients with asymptomatic intrathoracic goiters and normal spirometry tests are not an absolute indication for surgery, and conservative management is usually recommended. Nevertheless, suspicion or proof of malignancy constitutes an indication of thyroid excision. Additionally, young, healthy patients are usually operated on because asymptomatic substernal goiters tend to grow, and they have a high risk for malignancy.[3] Older patients and patients of poor health constitute cases for observation or radioactive iodine treatment.[8] The Pemberton sign is a test used to have the patient raise their hands above their head. This causes facial flushing and dilation of the neck veins and can even produce stridor from compression of the trachea. This test is an indication of surgery. 

Indications for Selection Between Transcervical and Extracervical Approaches

Indications for an extracervical approach vary among different studies. First, it should be performed in primary retrosternal goiters or goiters with diameters exceeding that of the thoracic inlet.[9] Additionally, conditions such as recurrent goiters, intrathoracic thyroid cancer, and thyroid tissue invading the retrotracheal or retroesophageal space usually require a sternotomy.[7] As described by Vaiman and Bekerman, the exact anatomy of the thyroid gland and the chest should be considered before operating. More specifically, the tracheal-diameter-to-thoracic-inlet ratio is of great importance, and thus, the diameters and areas of the trachea and the superior thoracic aperture should be calculated. A wide trachea with a narrow inlet usually requires an extracervical approach, while a narrow trachea with a wide inlet is a transcervical one.[10]

According to Simo et al, surgeons can rely on the multiplanar computed tomography (CT) findings, such as indicative signs of malignancy and calcification of the thyroid capsule, leading to difficult excision, to decide the ideal surgical approach.[4] Moreover, surgeons can use the Huins et al. criteria. Based on these criteria, grade 1 substernal goiters require a transcervical approach. Grade 2 and 3 goiters usually require extracervical approaches. Grade 2 requires a manubriotomy, and grade 3 a full sternotomy.[6]

Contraindications

Medical management of intrathoracic goiters should be individualized. Several factors should be considered, such as the clinical presentation, the goiter size and growth rate, and finally coexistence of cardiovascular and pulmonary diseases. Thus, the inability to tolerate full anesthesia in high-risk patients is the main absolute contraindication to substernal thyroidectomy. In that case, conservative management or radioiodine treatment is usually preferred.[4]

Equipment

The following equipment is necessary for performing a substernal thyroidectomy:

• Surgical operating room
• Sterile drapes, gowns, gloves
• Operative instruments (sutures, vessel loops, bone wax)
• Sternotomy saw
• Code cart
• Anesthesia
• Shoulder roll
• Laryngeal nerve monitoring system (monitor the superior and recurrent laryngeal nerve)
• NG tube

Personnel

The following personnel are necessary for performing a substernal thyroidectomy:

• Ear nose throat/thoracic/endocrine surgeon
• Anesthesia team
• Surgical first assistant
• Operating nursing staff and scrub techs
• Oncology
• Internal medicine
• Endocrinology 

Preparation

Full history taking and clinical examination should be conducted in patients with suspicion of intrathoracic goiter, followed by thyroid function and antibody tests. Surgical planning before substernal thyroidectomy should include fiberoptic nasendoscopy to assess the airway and vocal cord status.[7] Although ultrasound-guided fine-needle aspiration cytology is the most useful clinical tool to evaluate thyroid nodules in cervical goiters, this does not apply to extracervical goiters because of its difficulty in conductance and low risk of occult thyroid cancer.[4] Proper surgical management requires a multiplanar CT to plan the most suitable surgical technique. CT scanning, or MRI scanning rarely, helps determine the goiter anatomy and relationship to the adjacent structures, which are the trachea, esophagus, aortic arch, and great vessels. It also helps recognize possible tracheal obstruction and pathological lymph nodes. Finally, it is the work of a multidisciplinary team, including an endocrinologist, anesthetist, oncologist, head and neck, and thoracic surgeons, to take part in a discussion of possible oncological cases.[4]

Technique or Treatment

According to several studies, the main surgical approach to substernal thyroidectomy is the transcervical approach, while in about 2% of cases, an extracervical one is preferred.[7] However, total thyroidectomy must be performed in patients with bilateral goiter since the risk of recurrence is high (>10%) in less-than-total thyroidectomy. Different studies have shown that total thyroidectomy for benign thyroid disease results in lower recurrence (0% to 0.5%) and similar complication rates compared to a subtotal procedure.[7]

In patients with unilateral goiter and with no suspicion of malignancy, thyroid lobectomy can be performed with low recurrence rates.[7] On the other hand, hyperthyroid patients and patients with thyroid cancer should be treated with total thyroidectomy.[4] To achieve a substernal goiter excision, an extended Kocher incision is usually performed in the lower cervical region, providing sufficient exposure to the goiter. The excision can be extended through a midline sternotomy. Should a lateral neck dissection be performed, a modified, extended Kocher incision is executed.[7]

During a total thyroidectomy, it is often useful to commence with mobilization of the smaller lobe to facilitate the excision of the whole gland and the identification of the recurrent laryngeal nerve and the parathyroid glands. Preservation of the parathyroid glands, especially the superior ones, is of great importance. In cases of very large goiters, the sternothyroid muscles can be divided unilaterally or bilaterally to help identify and ligate the middle thyroid veins, preserve the anatomical structures, and mobilize the goiter. Additionally, the isthmus can be divided and the two lobes removed separately. Mobilization of the upper thyroid lobes facilitates traction of the gland towards the head and excision of the retrosternal goiter.

Localization and preservation of the recurrent laryngeal nerve is the milestone of total thyroidectomy. In cases of goiters, the position of the nerves is usually distorted and should be carefully identified at the cricothyroid junction or near the inferior thyroid artery. Nowadays, neuromonitoring of the nerves bilaterally is an invaluable tool. Attention is needed while managing Berry ligament because of its proximity to the recurrent laryngeal nerve. Light traction should be exerted on the thyroid gland during this procedure to avoid nerve damage.[7]

When an extracervical approach is required, several different techniques can be performed. Traditionally, full sternotomy, manubriotomy, and different types of thoracotomies have been described. Nevertheless, newer techniques have arisen during the last few years. Partial median sternotomy is most commonly performed in heart surgery, but good outcomes have also been reported in substernal thyroidectomies. The use of a microde-brider for volume reduction of large retrosternal goiters, followed by a transcervical excision has also been described.[4]

Mediastinoscopy and video-assisted mediastinoscopy (VAM) can be used to excise benign goiters invading the mediastinum up to the aortic arch. The mediastinoscope enters through a cervical incision. Major bleeding in 0,4% of VAM operations is an important complication, which may require a thoracotomy.[4] Minimally invasive video-assisted thyroidectomy (MIVAT) is performed partially through endoscopy and partially under transcervical vision and concerns about 20% of these patients. Criteria for this procedure include thyroid volume of less than 25 cm³, dominant nodule diameter of less than 35 mm, presence of posterior nodules suspicious of malignancy, and the presence of infiltrated lymph nodes. MIVAT has similar complication rates to classic operations.[8] Robot-assisted trans-axillary thyroidectomy is a minimally invasive technique commonly used in Asia but is less popular in the US. RATT is reported to have lower complication rates in comparison to sternotomy and is considered oncologically safe. However, it is much more expensive.[8]

Complications

Nowadays, total thyroidectomy is preferable to subtotal thyroidectomy, not only because of its lower recurrence rates but also because of its similar complication rates.[7] On the other hand, a substernal thyroidectomy is considered to result in higher complication rates related to the excision of a cervical goiter. More specifically, patients undergoing surgery for retrosternal goiters are more likely to present with transient and permanent unilateral recurrent laryngeal nerve injury, transient and permanent bilateral recurrent laryngeal nerve injury, and permanent hypoparathyroidism, in comparison to surgery for cervical goiters.[9][11]

In a review by Knobel, following a transcervical excision of a retrosternal goiter, the chance for transient unilateral recurrent laryngeal nerve damage is 2% to 5.4%, for permanent unilateral nerve damage 1% to 2%, for transient hypocalcemia 33.9%, for permanent hypocalcemia 2.1% and tracheomalacia 3%.[8] Injury of the recurrent laryngeal nerve is considered a severe complication of thyroidectomy. Unilateral damage can result in unilateral vocal fold fixation and voice alterations, dysphagia, and aspiration pneumonia. Bilateral injury, however, leads to acute airway obstruction that requires tracheostomy.[4]

Hypocalcemia constitutes another complication of thyroidectomy. Substernal thyroidectomy usually poses difficulties to localization of the parathyroid glands, the excision of which leads to hypoparathyroidism and, thus, low blood calcium. The inferior parathyroid glands are more commonly accidentally excised due to their varying anatomy. Reoperation for intrathoracic goiter poses an even higher risk of hypocalcemia.[4] Tracheomalacia is a condition in which the trachea becomes flaccid due to the development of and pressure by extra-tracheal abnormal tissue, leading to tracheal obstruction after excision of the goiter and removal of the tracheal tube; its prevalence in retrosternal goiters reaches 1.6%.[4]

Mortality following substernal thyroidectomy ranges from 0 to 15.3% in operations requiring extracervical approaches and often results from a tracheobronchial fistula or sternotomy dehiscence. Thyroid cancer and compression symptoms are related to poor outcomes. Cervical hemorrhage can occur in the first 8 hours following thyroidectomy. It is a potentially lethal complication, which results in laryngeal edema and acute airway obstruction and presents with coughing. The incidence of hemorrhage is about 4.2%. The use of a drain can help rapidly recognize this situation.[4] Other rare complications of substernal thyroidectomy include infections, pneumothorax, and the need for tracheostomy.

Clinical Significance

Substernal goiters are abnormal thyroid tissue developing primarily or, most often, secondarily into the mediastinum. Because of the existence of several different definitions, incidence rates vary between 0.2% and 45% in the literature, and thus, intrathoracic goiters can be quite common.[2] To treat this medical condition effectively, it becomes clear that a proper algorithm of diagnosis and assessment should exist, which will assist the clinicians with a precise staging of the disease and, moreover, evidence-based medical management. It also becomes clear that surgery is the gold standard. Since 2 different surgical approaches of substernal thyroidectomy and several different techniques exist, it is of great clinical significance that patients receive an ideal personalized treatment plan.

Enhancing Healthcare Team Outcomes

Substernal thyroidectomy is a major surgical procedure with a difficult diagnosis, assessment, and treatment. Several different medical specialties are involved in the management of these patients.

• Usually, the endocrinologist diagnoses patients with goiter and refers them to a head and neck surgeon.
• In case of a substernal goiter extending deep into the mediastinum, a thoracic surgeon should be involved in the procedure.
• An anesthesiologist should assess the patient preoperatively and postoperatively.
• A cardiologist and pulmonologist need to evaluate before surgery the patient’s risk for perioperative complications.
• An oncologist should be actively involved in cases oncological cases, and multidisciplinary healthcare teams should be composed.[4]

Nursing, Allied Health, and Interprofessional Team Interventions

An interprofessional team consists of nursing, anesthesia, endocrinologists, internal medicine clinicians, and surgeons to work as a team to provide the best outcomes for them. Close communication is key to the management of pre-operative, operative, and post-operative care of the patients.

Nursing, Allied Health, and Interprofessional Team Monitoring

Team monitoring is essential in the care of the patient. The entire team, including nurses, techs, and physicians of multiple specialties, must all work together to play their role in the care of the patient. Team monitoring is essential in the pre-operative, intra-operative, and post-operative care of the patient.