Introduction
Thyroid cancer is a curable disease with increasing incidence and treatment strategies. This corresponds with the widespread use of screening modalities and improved health care availability. With more cases being detected in early stages, the incidence of invasive thyroid cancer is relatively low, ranging from 5% to 25%. Despite the low incidence, invasive thyroid cancer has significant prognostic implications, with nearly half of deaths from thyroid cancer being attributable to local disease, typically due to airway obstruction and bleeding. Extrathyroidal extension (ETE) in well-differentiated thyroid cancer is a surrogate indicator for loss of normal cellular architecture and poor prognosis. However, in contrast to invasive anaplastic thyroid cancer, tumors of papillary or follicular histology with ETE often retain a favorable prognosis and can successfully be managed surgically. Invasive thyroid cancer is a challenging surgical problem that requires complete preoperative evaluation, comprehensive surgical planning, and often a multispecialty surgical team to manage the wide range of surgeries that are required for complete tumor extirpation while minimizing morbidity.
Key Learning Points
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Patients with a high risk of invasive thyroid cancer should be identified and have cross-sectional imaging preoperatively.
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ETE into muscle or other connective tissue may be adequately treated with wide local excision.
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The recurrent laryngeal nerve (RLN) should be resected if invaded and preoperative assessment revealed ipsilateral paralysis. Conversely, efforts should be made to spare the nerve if preoperatively it was determined to be functional.
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Shave resection may be acceptable for limited invasion into the larynx, trachea, and esophagus but with increased rates of local recurrence.
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Transmural invasion into the viscera of the neck typically requires more aggressive margin-negative resection.
Preoperative Period
History
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History of present illness
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Evaluate onset, growth, and pain.
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Rapidly growing tumors may represent a more aggressive histology and behavior.
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Pain or stiffness in the neck may be a feature of invasion.
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If a diagnosis of malignancy has not yet been confirmed, index of suspicion must be high for goiters with an aggressive clinical history.
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- b.
Is there a history of voice changes?
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Complaints of voice changes are often the earliest symptom of invasion and should alert the surgeon to evaluate further for laryngotracheal or nerve invasion.
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Voice change is not very sensitive for detecting vocal fold paralysis.
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- c.
Does the patient have complaints of dysphagia, dyspnea, cough, or hemoptysis?
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May represent intraluminal invasion of neck viscera
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However, may also be secondary to compression as in benign goiters
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Absence of symptoms does not make invasion less likely, because the majority of invasive thyroid cancers are asymptomatic.
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Is there a history of previous thyroid cancer?
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Recurrent cancer in the original thyroid bed has a high risk of invasion
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Risk Factors
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Age
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There is a higher incidence of ETE in older patients with thyroid cancer.
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Size of the mass
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Primary cancer >4 cm have increased incidence of invasion
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Histology
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Papillary thyroid carcinoma is the most common histologic type.
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ETE is often associated with subtypes such as insular, tall cell, and trabecular carcinomas.
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Anaplastic or poorly differentiated cancers are nearly uniformly invasive but have a different decision-making tree due to their poor prognosis
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Past medical history
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History of previously treated thyroid cancer
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Central neck recurrence after thyroidectomy is often invasive due to anatomic proximity, as well as disruption of natural tissue planes.
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Physical Examination
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Complete examination of the head and neck
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Examine the thyroid for fixation to underlying structures and overlying skin and assess movement with swallowing.
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Palpate the neck to evaluate for lymph node metastases.
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Assessment of cranial nerves
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Laryngeal function should be routinely assessed.
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Voice assessment is required in all patients being seen for thyroid cancer.
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Best practice includes visualization of the larynx because laryngeal paralysis often does not produce noticeable voice changes.
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Mirror laryngoscopy or flexible laryngoscopy should be used to document vocal fold mobility.
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Preoperative ipsilateral vocal fold paralysis is highly predictive of invasive thyroid cancer, and these patients should receive advanced cross-sectional imaging.
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Diagnostic Studies
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Fine-needle aspiration (FNA)
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FNA is an important initial diagnostic tool for workup in the evaluation of thyroid tumors.
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Regional metastases and recurrent masses should be biopsy-proven prior to surgical treatment.
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Laboratory studies
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Of limited clinical value in evaluating the extent of invasive thyroid cancer
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Rising thyroglobulin or thyroglobulin antibodies may indicate recurrent or metastatic disease.
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Imaging
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Ultrasound
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Performed routinely for all thyroid cancer evaluations
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May identify invasion into surrounding structures, although studies have shown a wide range of sensitivity and specificity
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Operator dependent
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May be useful for surgical planning if performed by the operating surgeon
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Computed tomography (CT) and magnetic resonance imaging (MRI)
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Should be done for all patients suspected of invasive thyroid cancer
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CT and MRI have similar rates of sensitivity and specificity in detecting extent of tumor and invasion.
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CT is rapid, widely available, and easily read by most surgeons.
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Use of iodinated contrast may interfere with postoperative radioactive iodine (RAI) treatment for up to 6 to 8 weeks and should be used judiciously.
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- c.
Positron emission tomography (PET)
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May identify metastatic or recurrent disease in radioiodine negative tumors
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Evaluation of distant extent of disease ( Fig. 82.1 ) may alter treatment decisions at the primary site.
Fig. 82.1
PET evaluation of primary and distant sites, showing hypermetabolic activity in the right thyroid.
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Indications
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Surgical resection remains the hallmark of treatment for thyroid cancer, invasive or otherwise.
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Optimal resection should result in negative margins with wide resection of tumor and involved structures
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Structures with low morbidity on resection such as strap muscles
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Preoperative nerve infiltration causing dysfunction
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Transmural invasion of larynx, trachea, or esophagus
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Shave resection may provide similar survival with decreased morbidity.
- a.
Partial-thickness invasion into larynx, trachea, or esophagus
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Nerve encasement with normal preoperative function
- a.
Contraindications
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Morbidity or surgical sequelae of resection unacceptable to patient
- 2.
Major organ resection should be avoided, if possible, in the case of incidental finding of invasion if patient has not been counseled preoperatively.
- 3.
Limiting morbidity and surgical risk in widely metastatic or unresectable, poorly differentiated thyroid carcinoma
Preoperative Preparation
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Discussion/informed consent with patient regarding treatment goals and extent of resection
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Many studies fail to demonstrate survival difference between aggressive and conservative surgery.
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Local control rates vary and conservative surgery may require repeated surgery and eventual salvage.
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The surgeon should be prepared for the wide range of surgical resections and reconstructions that may be required.
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When transmural invasion is suspected, reconstructive options should be available, including microvascular surgery and thoracic surgery support.
- a.
Operative Period
Anesthesia
- 1.
Surgery for invasive thyroid cancer generally requires general anesthesia with endotracheal intubation.
- 2.
Thyroid cancer with limited extension could theoretically be done with sedation and local anesthesia, but this is not typical.
- 3.
Esophageal temperature probe or nasogastric tube (NGT) placement is helpful to easily identify the esophagus intraoperatively, as well as use for stenting and feeding in the case of esophagectomy or pharyngectomy.
Positioning
- 1.
Neck should be placed in slight extension with shoulder roll
- 2.
Reverse Trendelenburg or elevated head of bed to promote venous drainage away from the neck
Perioperative Antibiotic Prophylaxis
- 1.
Major head and neck surgery warrants a preincisional antibiotic dose, typically a first-generation cephalosporin for gram-positive coverage.
- 2.
If upper aerodigestive tract breach is expected, coverage for anaerobic bacteria should be added with metronidazole or clindamycin.
Monitoring
- 1.
Intraoperative laryngeal nerve monitoring may be used.
- a.
Utility and benefit in routine thyroidectomy are controversial.
- b.
May provide information regarding functional status of the nerve intraoperatively in the case of surgery of invasive disease and may help to guide extent of surgery and treatment of the contralateral side
- c.
Should not substitute direct identification and preservation by the surgeon
- a.
Instruments and Equipment
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Basic open neck surgery instruments
- a.
Thyroid or neck dissection sets
- b.
Fine-tipped dissectors or McCabe dissection for nerve dissection
- a.
- 2.
Vascular instruments should be available or open if vascular involvement is suspected.
Key Anatomic Landmarks
- 1.
RLN
- a.
The right RLN course is often more tangential due to its course around the subclavian artery when compared with the left side.
- b.
The RLN enters the larynx just deep to the inferior laryngeal constrictor, behind the cricoarytenoid joint, where it is closely associated with branches of inferior thyroid artery.
- c.
RLN invasion is most common at its entry into the larynx due to its relative fixed position.
- d.
The expected position of the RLN may be distorted in cases of thyroid malignancy.
- a.
- 2.
Larynx
- a.
Invasion occurs through direct extension through the thyroid and cricoid cartilage or via the paraglottic space around the lateral edge of the thyroid cartilage ( Fig. 82.2 ).
Fig. 82.2
CT imaging demonstrating laryngeal invasion into the left paraglottic space from around the lateral edge thyroid cartilage.
- b.
Extension into the hypopharynx may occur through the piriform sinus, which is closely associated with the lateral edge of the thyroid cartilage.
- a.
- 3.
Trachea
- a.
Invasion occurs from direct extension from the thyroid or paratracheal lymph node metastases.
- b.
Adherence and superficial invasion into the peritracheal fascia and perichondrium occur first.
- c.
Transmural invasion typically occurs between the cartilaginous rings with feeding vessels that traverse the soft tissue.
- 1)
Often has submucosal spread before intraluminal extension ( Fig. 82.3 )
Fig. 82.3
Grading of tracheal invasion from thyroid cancer.
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