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Address reprint requests and correspondence: David J. Terris, MD, FACS, FACE, Department of Otolaryngology and Endocrinology, Augusta University Thyroid and Parathyroid Center, Augusta University, 1120 Fifteenth St, BP-4109, Augusta, GA 30912-4060.
Substernal thyroid goiters that require surgery may pose unique challenges to thyroid surgeons based on the size and inferior extent of the disease. Consequently, there are multiple variations to the approach and additional considerations in operative planning and technique that are often required. Although there is some debate on the precise definition of substernal thyroid, for the purposes of this article it is considered to be thyroid tissue below the sternal notch or clavicle. This article aims to provide thyroid surgeons who encounter the challenges of substernal thyroid a straightforward algorithm for planning and operative techniques that have proven successful in the safe and effective management of this condition.
For the purpose of describing applicable techniques for this condition, a less restrictive definition was used in which substernal thyroid was considered to include any thyroid tissue located below the level of the sternal notch or clavicle. This article is designed to provide a stepwise guide to substernal thyroid excision, from perioperative planning and care to operative techniques and postoperative management strategies. The objective is to achieve a safe, efficient, and effective excision of thyroid glands with substernal extension with minimal recovery time, optimal esthetic results, and maximal patient satisfaction. Here, we have identified several key components in managing these patients.
Epidemiology
The incidence of substernal thyroid goiter is noted to occur in approximately 0.2%-0.5% of the population.
The reported percentage within the subset of patients undergoing thyroidectomy is highly variable ranging from 0.2%-45% in a 2010 case series depending upon the definition that is used.
The variable frequency with which substernal thyroid tissue is encountered in patients undergoing thyroid surgery highlights the importance of thorough preoperative workup and fluency in approach and technique.
Etiology or pathophysiology
Substernal thyroid tissue can be broadly classified as primary or secondary and may result from 3 different mechanisms. Primary refers to embryonic thyroid tissue that migrated and grew separately from the cervical thyroid. Primary substernal thyroid tissue receives its blood supply from intrathoracic vasculature and represents approximately 1% of patients with substernal thyroid.
The vast majority of substernal thyroid goiters are classified as secondary in origin, which refers to the presence of cervical thyroid tissue which has extended to a substernal location. Secondary substernal thyroid shares vasculature with the cervical thyroid gland. A less common etiology of secondary substernal thyroid is termed forgotten thyroid tissue, and results from tissue left behind during previous thyroidectomy.
Initial evaluation is similar to the workup for any thyroid gland pathology and includes a thorough history and physical examination, laboratory assessment including thyroid function tests, ultrasound, and usually ultrasound-guided fine-needle aspiration. History of symptoms and physical examination findings suggestive of airway or esophageal compression, or rarely superior vena cava syndrome, should raise suspicion for substernal thyroid. Inability to palpate the inferior pole, or palpation of substernal extension and tracheal deviation on examination suggest possible presence of substernal thyroid. If substernal extension is suspected, cross-sectional imaging with computed tomography or magnetic resonance imaging is useful in determining the extent of the substernal component and potential need to plan for sternotomy.
Most patients with substernal goiter should have surgery because of the risk for obstructive complications. Additional indications for excision may include malignant or indeterminate fine-needle aspiration cytology, hyperthyroidism refractory to medical management, nontoxic nodules >4 cm, progressive enlargement of multinodular goiter despite medical management, and compressive symptoms.
Once a decision has been made to proceed with surgical excision, preoperative planning is addressed. Medical comorbidities should be recognized, managed, and optimized before undertaking surgical intervention. Preoperative laryngoscopy is essential for assessment of vocal cord function, and the findings may alter the surgical approach considerably. The ability of the patient to extend their neck should be assessed as this will sometimes greatly affect the access and exposure of the mediastinum. Finally, we regularly obtain measures of calcium homeostasis before undertaking all thyroid surgery (calcium, parathyroid hormone level, and vitamin D level). Coexisting hyperparathyroidism is not uncommon and the optimal time to address it is when the thyroid compartment is already open for another indication.
Procedural description
Positioning and preparation
This description entails the perioperative and intraoperative steps for patients with substernal goiters that are amenable to transcervical excision (as seen in the imaging from Figure 1, and depicted by an artist in the drawing in Figure 2A). This will not describe the techniques for patients with advanced disease requiring sternotomy.
Figure 1Large substernal goiters such as the one demonstrated in the coronal CT image on the left (A) require careful preparation and selected intraoperative surgical strategies. Bilateral substernal extension (B) is quite rare.
For a transcervical approach with a low cervical collar incision, proper positioning of the incision is confirmed by marking the patient in the upright position before transport to the operating room. Vertical marks are placed along the incision line to facilitate the identification of a central, symmetric incision.
These maneuvers help to achieve optimal surgical exposure and ensure incisional cosmesis.
Once in the operating room, the patient is positioned with the neck in slight extension. A shoulder roll is not generally needed. Consideration is given to the use of laryngeal nerve monitoring. Nerve monitoring allows for feedback regarding nerve proximity during dissection and may be especially useful during difficult dissections.
Laryngeal nerve monitoring complements minimally invasive surgery and has become a routine adjunct to most practices. When this is utilized, the patient is transorally intubated under Glidescope guidance with a laryngeal EMG endotracheal tube under direct visualization, allowing confirmation of correct placement of the tube and surface electrodes. The neck is injected with ¼% Marcaine with 1:200,000 of epinephrine to reduce bleeding at the incision and to improve early postoperative discomfort.
Procedural technique
A low collar incision is made in the previously marked location and carried down to the strap muscles. Subplatysmal flaps are not elevated.
The strap muscles are separated in the midline and dissected off of the gland. These muscles may be horizontally transected at their midline to facilitate exposure for massive substernal goiters. The lateral and posterior extent of the gland is identified and bluntly mobilized. The middle thyroid vein is identified and divided with ultrasonic energy. The isthmus is identified in the midline and dissected off the cricothyroid muscle and anterior trachea; it may be divided to improve mobilization. The superior pole is dissected medially and laterally protecting the external branch of the superior laryngeal nerve. The upper pedicle is isolated and divided with ultrasonic energy (Figure 2B). The superior parathyroid gland is identified as the superior thyroid pole is retracted inferiorly, and preserved with its blood supply as it is dissected superolaterally.
Figure 2The vast majority of substernal goiters are amenable to a transcervical approach (A). The isolation of the superior thyroid pole and transection of the upper pedicle with advanced energy is generally performed early in the procedure and is demonstrated in this figure (B).
Attention is then directed to the substernal component of the goiter. Gentle traction combined with blunt finger dissection is applied to accomplish dissection substernally and into the thoracic inlet (Figure 3). After the inferior parathyroid gland is identified and dissected free inferolaterally with its blood supply intact, the inferior pole can be released with electrocautery or ultrasonic energy and the substernal disease is delivered into the cervical neck. The thyroid lobe is retracted out of the surgical bed enabling dissection of the recurrent laryngeal nerve (RLN), which is identified superomedially just proximal to the ligament of Berry. The tubercle of Zuckerkandl serves as an excellent landmark here, as the nerve will invariably be located just deep to the tubercle. The nerve is dissected in a retrograde direction (inferiorly). The inferior thyroid artery and all other remaining attachments at the inferior pole may be divided, and then the final nerve dissection is accomplished in an anterograde direction. Special care is given to nerve protection when dividing the ligament of Berry.
Figure 3Finger dissection of substernal thyroid goiters is a very effective technique and requires identification of the precise extracapsular plane to optimize mobilization.
When the contralateral lobe will be dissected, it is prudent to verify the electrophysiological integrity of the RLN on the first operated side. If required by the clinical circumstances, the vagus nerve may also be stimulated as it represents a more proximal verification of RLN function. If indicated, contralateral lobectomy is accomplished after establishing ipsilateral nerve function.
After meticulous hemostasis and irrigation, a large sheet of Surgicel is placed in the thyroid bed. No drain is needed. It is critical to not reapproximate the strap muscles, which otherwise may predispose to a compartment syndrome in the event of bleeding, resulting in reduced venous and lymphatic outflow, followed by airway edema and eventually obstruction. The incision is closed with 2 or at most 3 subdermal absorbable (4-0 chromic) sutures, and then skin adhesive (Dermaflex) is applied, followed by a single horizontal ¼-inch Steri-Strip (to facilitate glue removal 2 or 3 weeks after surgery). Anesthesia is instructed to undertake deep extubation in order to minimize coughing and bucking, which may lead to spikes in pulse or systolic pressure, causing increased risk of spontaneous postoperative bleeding.
When managing massive goiters, it is sometimes difficult to finger-dissect the mediastinal extension up into the cervical neck, owing largely to the volume of tissue. In these circumstances, an alternative maneuver can be used to facilitate excision of the mediastinal component. The RLN is identified in its superior-most location (just proximal to the inferior constrictor muscles) right after transection of the upper pedicle and reflection of the superior pole downward (Figure 4). This allows the ligament of Berry to be divided early in the operation, and therefore all attachments of the thyroid to the trachea may be safely released with the nerve under direct vision (Figure 5). Once this is accomplished, the thyroid becomes very mobile, and the thyroid lobe may be slid superiorly, including the substernal extension, without having to first flip it up from the chest (Figure 6).
Figure 4The recurrent laryngeal nerve may be identified just proximal to its entry to the larynx under the inferior constrictor muscled. This is the most constant location of the nerve.
Figure 5Once the nerve has been positively identified, the ligament of Berry may be safely divided along with all remaining attachments of the thyroid to the trachea, thus facilitating superior retrieval of the gland.
Figure 6Cranial delivery of the thyroid with its substernal component is very straightforward once complete lysis of the attachments to the trachea has been accomplished.
Early postoperative management is centered upon pain control and monitoring for postoperative bleeding and any signs of airway compromise. If proximal RLN stimulation yields an appropriate signal, laryngeal examination is no longer routinely performed to determine laryngeal dysfunction. Patients who undergo total thyroidectomy are prophylactically treated with a tapering regimen of oral calcium.
No postoperative calcium or parathyroid hormone levels are needed. These patients are managed on an outpatient basis and are discharged after a short stay in the recovery room to either their home or to their hotel room (if they have traveled more than 1 hour to the facility).
Conclusion
A transcervical approach may be used within the framework of modern thyroid surgical techniques to remove substernal thyroid goiters with minimal recovery time on an outpatient basis in the vast majority of patients. Adoption of methodical intraoperative techniques has proved to be invaluable in patients with substernal thyroid. Key surgical steps including isolation and control of the superior pole, mobilization of the thyroid from the anterior trachea with lysis of the ligament of Berry for counter traction along with blunt finger dissection of the substernal thyroid and laryngeal nerve monitoring combine to facilitate reproducible success in these operations. Adherence to a systematic approach, technique, and perioperative planning and care practices allows for a simplified approach to this patient population.
Disclosure
The authors report no proprietary or commercial interest in any product mentioned or concept discussed in this article.
References
Hedayati N.
McHenry C.R.
The clinical presentation and operative management of nodular and diffuse substernal thyroid disease.
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