Minimally Invasive Surgery of the Thyroid

Background

This article focuses on minimally invasive approaches to thyroid surgery. Please refer to other Medscape Reference articles for focused discussions of thyroid nodulesthyroid cancerbenign thyroid conditions, and conventional surgical approaches for thyroidectomy.

History of the Procedure

Minimally invasive techniques for thyroidectomy were introduced in the late 1990s and early 2000s for the surgical treatment of small thyroid nodules. These approaches were developed to minimize postoperative pain, improve cosmetic results, and potentially reduce the length of hospital stay. Two such approaches are the minimally invasive open thyroidectomy (MIT) and the minimally invasive video-assisted thyroidectomy (MIVAT). Minimally invasive approaches are currently used for both thyroid lobectomy and total thyroidectomy by some groups. [1]

An image depicting minimall invasive surgery of the thyroid can be seen below.

Identification of the recurrent laryngeal nerve duIdentification of the recurrent laryngeal nerve during video-assisted right thyroid lobectomy. A parathyroid gland is also identified.

Problem

See the list below:

  • Thyroid nodule: This is a discrete lesion of the thyroid gland that, after physical examination or ultrasound imaging, is determined to be distinct from the remainder of the thyroid parenchyma. [2]

  • Differentiated thyroid cancer: This is a papillary or follicular thyroid cancer.

Epidemiology

Frequency

The prevalence of palpable thyroid nodules is 3-7% in North America and increases up to 50% in ultrasonography or autopsy data. [3About 5% of thyroid nodules are positive for thyroid carcinoma on fine-needle aspiration (FNA).

In the United States, approximately 23,500 new cases of differentiated thyroid cancer are diagnosed yearly. [4]

Papillary thyroid cancer accounts for 75-80% of new cases of thyroid cancer; follicular thyroid cancer accounts for 10-20% of new cases. [5]

Presentation

The following are causes of thyroid nodules: [3]

  • Benign causes

    • Multinodular goiter (MNG)

    • Hashimoto thyroiditis

    • Thyroid cyst

    • Follicular adenoma

    • Subacute thyroiditis

  • Malignant causes

    • Papillary carcinoma

    • Follicular carcinoma

    • Hürthle cell carcinoma

    • Medullary carcinoma

    • Anaplastic carcinoma

    • Primary thyroid lymphoma

    • Metastasis

A patient with a thyroid nodule or differentiated thyroid cancer may present with the following:

  • Palpable thyroid or neck mass

  • Pressure symptoms such as choking, neck pain, dysphagia, hoarseness, or shortness of breath

  • Symptoms of hypothyroidism or hyperthyroidism

  • Incidental finding of thyroid nodule on neck imaging (incidentaloma)

Indications

Minimally invasive video-assisted thyroidectomy (MIVAT) is most commonly used for thyroid nodules within specific size limits and for low-stage papillary carcinoma of the thyroid (PCT). [6789The following are the most widely accepted criteria:

  • A thyroid nodule size less than or equal to 30 mm in diameter

  • Stage T1 or small T2 PCT (see Staging)

  • Total thyroid volume less than 30 mL

  • No history of thyroiditis or neck radiation

Recent studies have demonstrated that MIVAT can be safely used with patients who have histories of prior thyroiditis, prior MIVAT, and a thyroid volume up to 50 mL (see Controversies). [1011]

Relevant Anatomy

The thyroid is a bilobed gland in the midline neck that overlies the proximal trachea. The thyroid isthmus in the midline connects the 2 lobes, and a pyramidal lobe may be present. Two pairs of parathyroid glands (superior and inferior) are usually closely associated with the posterior aspect of the 2 thyroid lobes. The fascia that encapsulates the thyroid gland forms a dense consolidation at its attachment to the trachea known as the ligament of Berry.

The blood supply consists of the superior thyroid artery (STA) and inferior thyroid artery (ITA). The STA is a branch of the external carotid artery. The ITA emanates from the thyrocervical trunk and is also the main blood supply to the parathyroid glands. Venous drainage consists of the superior, middle, and inferior thyroid veins and the thyroid ima vein.

The external branch of the superior laryngeal nerve (EBSLN) courses near the superior thyroid artery adjacent to the superior pole before entering the larynx through the cricothyroid membrane. The recurrent laryngeal nerve (RLN) ascends in the tracheoesophageal groove and courses closely to the ligament of Berry prior to entering the larynx posteriorly at the cricothyroid articulation.

Contraindications

As minimally invasive video-assisted thyroidectomy (MIVAT) continues to evolve, the only absolute contraindications to this procedure are thyroid malignancy beyond low-stage papillary carcinoma and preoperative evidence of lymph node metastasis.

Nodule diameter above 35 mm and thyroid volume over 30 mL are relative contraindications because some groups have demonstrated questions about safety with larger lesions. [11]

Prior conventional thyroidectomy is considered a contraindication by most authors. Some groups consider patients candidates for completion MIVAT if a prior lobectomy was performed via a MIVAT approach. [10]

A history of prior thyroiditis is considered a relative contraindication because some groups have demonstrated that MIVAT can be safely performed in this population. 


Laboratory Studies

Serum thyrotropin (TSH) is recommended for a thyroid nodule larger than 10-15 mm. [2]

Serum thyroglobulin and calcitonin are additional tests that can be performed if other thyroid conditions or medullary carcinoma of the thyroid (MCT) are suspected.

A full thyroid-function panel that includes TSH levels and free T3 and T4 levels can be performed if a clinical suspicion of hypothyroidism or hyperthyroidism exists.

Imaging Studies

Thyroid ultrasonography (US) is the initial imaging modality of choice for suspicion of one or more thyroid nodules. [2]

CT, MRI, and positron emission tomography (PET) are adjunctive imaging modalities that can be used to assess cervical lymph node involvement for staging purposes. CT scanning and MRI can also reveal invasion of adjacent structures and airway compression and gauge the extent of substernal extension for large goiters.

Other Tests

Radionuclide scanning (thyroid scintigraphy or iodine-131 uptake scan) can be used to diagnose an autonomously functioning or “hot” nodule. Lack of uptake or “cold” nodules have a malignant risk of 5-8%. [3]

Diagnostic Procedures

Fine-needle aspiration (FNA) is the initial diagnostic procedure of choice. FNA can be performed under palpation or with US guidance. Nondiagnostic or inadequate FNA by palpation should be repeated with US guidance.

FNA is usually performed with a 27- or 25-gauge, 1.5-inch needle placed on a syringe. Once the needle has been inserted into the nodule, gentle suction is applied to the syringe; multiple passes are made within the nodule. Suction is then released prior to removing the needle from the nodule. The procedure is repeated 2-4 times and slides are prepared. Having a cytopathologist available for slide preparation to check on the adequacy of the sample is useful.

Histologic Findings

FNA results, which are diagnostic, are most commonly benign. The most common benign diagnosis is a colloid nodule. [3]

Follicular neoplasms on FNA are hypercellular, low in colloid, and show microfollicular arrangement. Hürthle cell carcinoma is a variant of follicular carcinoma with a prominence of Hürthle cells.

The most frequent malignant lesion on FNA is papillary thyroid carcinoma (PTC). Histology shows tumor cells arranged in sheets, papillary cell groups, and nuclear abnormalities.

Staging

The American Joint Committee on Cancer has devised the following staging system: [12]

  • Primary tumor (T)

    • TX: The primary tumor cannot be assessed.

    • T0: No evidence of a primary tumor is found.

    • T1: The tumor is 2 cm or less in its greatest dimension (limited to the thyroid).

    • T2: The tumor is larger than 2 cm but 4 cm or smaller in its greatest dimension (limited to the thyroid).

    • T3: The tumor is larger than 4 cm in its greatest dimension (limited to the thyroid), or a tumor with minimal extrathyroid extension is found (eg, extension to the sternothyroid muscle or perithyroid soft tissues).

    • T4a: A tumor of any size extends beyond the thyroid capsule to invade subcutaneous soft tissues, larynx, trachea, esophagus, or recurrent laryngeal nerve.

    • T4b: A tumor invades prevertebral fascia or encases carotid artery or mediastinal vessels.

  • Regional lymph nodes (N)

    • NX: The regional lymph nodes cannot be assessed.

    • N0: No regional lymph node metastasis is found.

    • N1: Regional lymph node metastasis is found.

      • N1a: The metastasis has reached level VI (pretracheal, paratracheal, prelaryngeal/Delphian lymph nodes).

      • N1b: The metastasis has reached unilateral or bilateral cervical or superior mediastinal lymph nodes.

  • Distant metastasis (M)

    • MX: A distant metastasis cannot be assessed.

    • M0: No distant metastasis is found.

    • M1: A distant metastasis is found.

Papillary or follicular thyroid cancer staging is as follows:

  • Patients younger than 45 years

    • Stage I is any T, any N, and M0.

    • Stage II is any T, any N, and M1.

  • Patients aged 45 years or older

    • Stage I is T1, N0, and M0.

    • Stage II is T2, N0, and M0.

    • Stage III is one of the following:

      • T3, N0, and M0

      • T1, N1a, and M0

      • T2, N1a, and M0

      • T3, N1a, and M0

    • Stage IVA is one of the following:

      • T4a, N0, and M0

      • T4a, N1a, and M0

      • T1, N1b, and M0

      • T2, N1b, and M0

      • T3, N1b, and M0

      • T4a, N1b, and M0

    • Stage IVB is T4b, any N, and M0.

    • Stage IVC is any T, any N, and M1.

    Treatment And Management

Surgical Therapy

Minimally invasive open thyroidectomy (MIT) is similar to conventional thyroidectomy in its surgical approach. The major difference is the length of the neck incision. A smaller incision improves cosmesis and reduces discomfort. Typically, a skin incision less than 6 cm is considered minimally invasive. The remainder of the procedure is exactly the same as is used in conventional thyroidectomy. Adaptations to this technique include transection rather than lateral retraction of the strap muscles (the Sofferman technique). [1]

Minimally invasive video-assisted thyroidectomy (MIVAT) typically involves a skin incision no greater than 3 cm that is placed slightly higher than the conventional thyroidectomy incision. Open dissection is carried out until the superior thyroid pole is encountered, after which the endoscopic video-assisted techniques are used.

Totally endoscopic techniques that include an axillary approach and the use of gas insufflation have been described, but these have not gained widespread use. Recent evidence suggests that the use of robotic technology may enhance the effectiveness of endoscopic techniques; however, these data are very preliminary.


Preoperative Details

First and foremost, the patient should meet the criteria for candidacy for MIVAT approach.

Preoperative laboratory studies should include baseline serum electrolyte levels, CBC count, coagulation panel, and pregnancy testing, if applicable.

A chest radiograph and electrocardiography should be performed as necessary.

When obtaining consent for MIVAT surgery, the possible need to convert to open, conventional thyroidectomy should always be discussed with the patient.

Intraoperative Details

The standard thyroidectomy or neck dissection set up is supplemented with a set of Miccoli instruments specially designed for MIVAT (see the first image below). A 5-mm, 29-cm long, 30° endoscope is ideal for endoscopic visualization. Harmonic scalpel scissors (Ethicon Endo-Surgery, Inc., Cincinnati, Ohio) are then used to ligate and divide the blood vessels (see the second image below).

Miccoli instrument set designed for MIVAT. Miccoli instrument set designed for MIVAT.
Endoscope and harmonic scalpel. Endoscope and harmonic scalpel.

The patient is placed in the supine position with slight neck extension (see the first image below). The neck is then prepared and draped with sterile technique. A horizontal incision is placed parallel to relaxed skin tension lines that are 3 cm or less in length (see second and third images below). The incision is placed between the sternal notch and cricoid cartilage, usually less than 1 cm inferior to the cricoid. [10]

Patient position. Note the limited neck extension Patient position. Note the limited neck extension as compared with conventional thyroidectomy.
Incision location. Incision location.
MIVAT incision length. MIVAT incision length.

Cautery is used to dissect the subcutaneous tissues until the midline raphe of the strap muscles is identified. The raphe is separated superiorly and inferiorly for a distance of about 3 cm. Anterior jugular veins can be preserved in most cases. Gentle and blunt dissection with peanuts is used to separate straps from the thyroid gland and displace them laterally. The middle thyroid vein or other vessels that are encountered at this time are clipped and divided.

Miccoli retractors are used to retract the strap muscles and soft tissues and expose the superior lobe and vascular bundle. At this point, a 30°, 5-7 mm rigid endoscope is introduced into the field to visualize the superior pole (see the image below). Three persons are required for the procedure at this point: a surgeon, a retractor, and an endoscopist.

Video-assisted dissection of the right superior poVideo-assisted dissection of the right superior pole.

The surgeon uses Miccoli spatula-shaped dissectors and aspirator dissectors to dissect the superior pole vascular bundle. Care is taken to identify and preserve the external branch of superior laryngeal nerve, which is identified medial to the superior vascular pedicle. The thyroid lobe is then retracted medially and endoscopic dissection is carried further to dissect the lateral and posterior attachments. The recurrent laryngeal nerve (RLN) is identified and preserved during this step, along with the parathyroid glands (see the image below).

Identification of the recurrent laryngeal nerve duIdentification of the recurrent laryngeal nerve during video-assisted right thyroid lobectomy. A parathyroid gland is also identified.

Once the lobe has been sufficiently mobilized, an atraumatic clamp can be used to externalize the lobe from the incision, and the remainder of the dissection can be carried out under direct vision. The isthmus is divided, and the lobectomy is complete. Total thyroidectomy is performed by repeating the same procedure contralaterally.

The wound is irrigated and complete hemostasis is ensured. The strap muscles are reapproximated. The skin is closed in layers with absorbable sutures and skin sealant. No external drainage is required.

Postoperative Details

Postoperatively, the patient should be given analgesics, antiemetics, and postoperative antibiotic prophylaxis. Any preoperative thyroid hormone supplementation should be continued.

A prospective, double-blind, randomized trial by Hong et al found repeated administration of acetaminophen 1 g IV over the initial 24 hours following thyroidectomy was easy, effective, safe, and well tolerated for pain management in patients with moderate-to-severe postoperative pain. The IV route for acetaminophen is currently investigational in the United States. [14]

For total thyroidectomy, ionized calcium and albumin levels should be checked in the recovery room and every 6-8 hours thereafter. Typically, hypocalcemia is defined as a corrected serum calcium level below 8.0 mg/dL. Early signs of hypocalcemia include perioral numbness or paresthesia and the Chvostek sign (facial spasm upon percussion of the facial nerve). Calcium supplementation may be required in some cases.

Some groups consider patients who undergo MIVAT lobectomy for same-day discharge with close follow-up.

Follow-up

The patient is seen in the office 1-2 weeks postoperatively (see the first image below), and again 6 weeks later (see the second image below). The wound healing should be assessed, and any pathology results and further treatment plans should be discussed. If the patient experiences hoarseness or shortness of breath, vocal fold movement should be assessed.

Surgical scar at 2 weeks. Surgical scar at 2 weeks.
Surgical scar at 6 weeks. Surgical scar at 6 weeks.

Complications

Complications from minimally invasive video-assisted thyroidectomy (MIVAT) are the same as with conventional thyroidectomy and occur at a similar rate. However, one study suggests surgical site infections are significantly less with the endoscopic technique. [15Complications include the following:

  • Bleeding or hematoma

  • Wound infection

  • Transient or permanent recurrent laryngeal nerve (RLN) injury

  • Transient or permanent external branch of the superior laryngeal nerve (EBSLN) injury

  • Hypocalcemia

Outcome and Prognosis

Cosmetic outcome is much better (see the images below) than that of conventional thyroidectomy. Some series have shown less postoperative pain and discomfort after minimally invasive video-assisted thyroidectomy (MIVAT) than with conventional thyroidectomy. [16The MIVAT approach has also resulted in shorter hospital stays. [11In groups with the most experience performing MIVAT, operative time is equivalent to that of conventional thyroidectomy, but a learning curve certainly exists.

Surgical scar at 2 weeks. Surgical scar at 2 weeks.
Surgical scar at 6 weeks. Surgical scar at 6 weeks.

For early papillary thyroid carcinoma (PTC), the oncologic adequacy of MIVAT is comparable with that of conventional thyroidectomy.

Future and Controversies

Around 15-20% of thyroid nodules that require surgery fit within the size criteria for minimally invasive video-assisted thyroidectomy (MIVAT). MIVAT surgery will likely gain an increasing role in this subsection of thyroid nodules.

Because MIVAT surgery is still relatively new, the following controversies exist:

Size criteria

Most groups advocate for a nodule diameter that is less than 30 mm and a thyroid volume below 30 mL. Some authors have shown that they can safely operate on a nodule size up to 40 mm in diameter and a thyroid volume approaching 50 mL.

Eligibility

Patients with a history of thyroiditis are still excluded from candidacy for MIVAT by certain groups. Some groups now include patients with Graves disease who meet size criteria, and also patients who require prophylactic thyroidectomy for RET germline mutation with normal calcitonin levels and no evidence of medullary thyroid carcinoma (MTC).

Oncologic adequacy

Excessive manipulation of the thyroid and removal of the specimen through a small incision may increase the risk of thyroid capsule rupture and the possible spillage of malignant cells. This has been disproved in at least one study. [6The adequacy of MIVAT for resection of small, low-grade parathyroid carcinoma (PTC) is also considered controversial.

External drainage

MIVAT is usually performed without external drainage. Most conventional thyroidectomy is performed with external drainage.

Outpatient surgery

The safety of MIVAT as a same-day procedure is still being studied.