Minimally invasive video-assisted thyroidectomy

The description of the minimally invasive video-assisted thyroidectomy covers all aspects of the surgical procedure used for the management of thyroid nodules. Operating room set up, position of patient and equipment, instruments used are thoroughly described. The technical key steps of the surgical procedure are presented in a step by step way: dissection, ligatures, extraction/resection. Consequently, this operating technique is well standardized for the management of this condition.

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MINIMALLY   INVASIVE   VIDEO-ASSISTED   THYROIDECTOMY

Authors
Abstract
The description of the minimally invasive video-assisted thyroidectomy covers all aspects of the surgical procedure used for the management of thyroid nodules.
Operating room set up, position of patient and equipment, instruments used are thoroughly described. The technical key steps of the surgical procedure are presented in a step by step way: dissection, ligatures, extraction/resection.
Consequently, this operating technique is well standardized for the management of this condition.
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2004-06
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E-publication
WeBSurg.com, Jun 2004;4(06).
URL: http://www.websurg.com/doi-ot02en269a.htm

MINIMALLY   INVASIVE   VIDEO-ASSISTED   THYROIDECTOMY

1. Introduction
Ever since endoscopic parathyroidectomy was first reported (Gagner, 1996), video-assisted techniques have been applied to surgery of the neck. Several series (Miccoli et al., 2000; Henry et al., 1999) have documented the feasibility of these approaches for parathyroid and thyroid disease.
The first endoscopic procedures for the removal of small thyroid nodules were introduced in 1998 (Miccoli et al., 2001a; Ohgami et al., 2000; Shimizu et al., 1999). These procedures have not become widespread because the advantages of this kind of minimally invasive surgery are less evident than in abdominal surgery. This is particularly true for thyroidectomy, as the open procedure is well standardized. The major disadvantage of these minimally invasive procedures lies in the limited number of patients who can benefit from them, especially in endemic goiter areas. Moreover, the operative times and complication rates are expected to be higher at the beginning, as in every new minimally invasive procedure. Costs and technology gaps can also be deterrents to the utilization of these techniques.
2. Anatomy
• Embryology
1. First pharyngeal pouch
2. Second pharyngeal pouch
3. Epithelial cord
4. Thyroid gland
The thyroid gland begins to form around the 17th day of development between the first and the second pharyngeal pouches. The glandular primordium rapidly forms an epithelial cord, which penetrates the floor of the oral cavity and, losing its connection with the pharyngeal floor, reaches the anterior side of the trachea.
At this point, the tip of the duct bifurcates and subsequently spreads out transversely into 2 lateral lobes. In certain cases, the duct may persist partially as a thyroglossal cyst.
• Surgical anatomy
1. Right lobe
2. Left lobe
3. Isthmus
4. Pyramidal lobe
5. Capsule
6. Berry’s ligament
7. Sternothyroid muscle
8. Sternohyoid muscle
The thyroid gland consists of 2 lobes joined by an isthmus. The normal weight of the adult gland is around 20 g. Each lobe has a conical shape and measures about 2 x 3 x 5 cm. A normal thyroid is dark wine-red in color, soft, and covered by a thin capsule.
The gland is situated in the lower aspect of the neck with the isthmus crossing the trachea at the level of the second and the third tracheal ring. The posterior suspensory ligament (Berry’s ligament) attaches the gland to this structure.
The gland is covered by the strap muscles (sternohyoid and sternothyroid muscles), joined in the midline by the cervical linea alba (anterior fascia cervicalis). The medial aspect of each lobe lies over the larynx and the trachea. The esophagus is situated on the posteromedial aspect of the thyroid lobe, and the recurrent nerve runs more or less vertically along the tracheo-esophageal groove. The superior poles are in contact with the inferior constrictor muscle and the posterior aspect of the cricothyroid muscle. The inferior pole usually reaches the fourth or fifth tracheal ring. Often a remnant of the thyroglossal duct extends cranially from the isthmus and is variably developed (pyramidal lobe).
• Blood supply
1. External carotid artery
2. Superior thyroid artery
3. Superior laryngeal nerve
4. Inferior thyroid artery
5. Thyrocervical trunk
6. Inferior laryngeal nerve
7. Inferior parathyroid gland
8. Superior parathyroid gland
9. Superior thyroid vein
10. Middle thyroid vein
11. Inferior thyroid vein
The gland receives its arterial blood supply from the superior and inferior thyroid arteries. The superior thyroid artery originates from the external carotid artery. It descends along the surface of the inferior constrictor of the pharynx and enters the upper pole of the thyroid on its anterior superior surface. In about 10% of cases, a branch of this artery feeds the superior parathyroid gland. The external branch of the superior laryngeal nerve runs very close to the branches of the superior thyroid artery, even though this relationship is quite variable.
The inferior thyroid artery is a branch of the thyrocervical trunk; it passes behind the common carotid artery and jugular vein, toward the cricoid cartilage. At the level of the gland, the artery loops downward and medially and enters the middle aspect of the lobe. It divides into several terminal branches. This artery and its branches have a very close relationship with the inferior laryngeal nerve. A branch of the inferior thyroid artery usually feeds the inferior parathyroid gland; in most cases, the inferior thyroid artery supplies also the superior parathyroid gland. A thyroid artery (thyroidea ima artery) is rarely present: it arises from the innominate artery and enters the isthmus.
The venous drainage is more variable than the arterial supply. The superior thyroid vein is closely related to the superior thyroid artery and drains into the internal jugular vein. Middle thyroid veins vary in number and pass from the lateral border of the lobe into the internal jugular vein. The inferior veins are separate from the inferior thyroid arteries and drain the inferior lobes into the internal jugular or innominate veins.
• Lymphatic drainage
1. Central compartment
2. Lateral compartment
3. Innominate vein
4. Trachea
5. Carotid
The lymphatic drainage of the thyroid gland is very extensive. The surgeon has to consider 2 main zones of lymphatic drainage: central compartment (periglandular space) and lateral compartment. The carotid sheet separates the 2 compartments.
The central compartment includes the prelaryngeal, pretracheal, and paratracheal-esophageal groups. The strap muscles constitute the anterior boundary of this compartment. There is a large connection between the 2 compartments and the 2 sides due to the existence of a capsular network, which is in communication with the deep lymphatic vessels. The central compartment is delimited by the innominate vein inferiorly, by the trachea medially and by the carotid laterally.
• Laryngeal nerves
• Superior
1. Superior laryngeal nerve
2. Superior thyroid pole
3. Middle constrictor muscle
4. External branch of superior laryngeal nerve
5. Internal branch of superior laryngeal nerve
6. Cricothyroid muscle
The external branch of the superior laryngeal nerve is in close contact with the superior thyroid vessels and the superior thyroid pole. The superior laryngeal nerve arises from the vagus nerve and descends to lie on the middle constrictor muscles. At this level, it divides into external and internal branches. The external branch continues inferiorly and innervates the cricothyroid muscle. This muscle produces tension of the vocal cord; injuries of the external branch may thus lead to the compromise of higher-pitched vocal sounds. In 6% to 18% of cases (Berti et al., 2002), the external branch of the superior laryngeal nerve runs with or around the superior thyroid artery or its branches and so is susceptible to injury during surgical dissection. In almost 20% of cases (Berti et al., 2002), it is not situated in the surgically accessible area around the superior pole of the thyroid gland and cannot be visualized during conventional surgery; with the endoscope, optical magnification and the 30° angle allows for exposure of the entire anterior surface of the cricothyroid muscle. Thus its preparation is easily achieved during video-assisted procedures; in case its course makes its visualization impossible, the superior thyroid artery should be ligated selectively and very close to the capsule of the thyroid.
• Inferior
1. Inferior laryngeal nerve
2. Vagus nerve
3. Right subclavian artery
4. Aortic arch
The inferior laryngeal nerve arises from the vagus nerve and supplies all muscles of the larynx except the cricothyroid muscle. On the right side, the nerve surrounds posteriorly the subclavian artery. On the left side, the nerve passes around the aortic arch. Both nerves run cranially and medially, toward the cricoid cartilage where it enters the larynx. The inferior laryngeal nerve is not a single strand but usually splits into several branches (to the esophagus, trachea, thyroid), and anastomoses with other nervous structures (superior laryngeal nerve, sympathetic system, contralateral nerve). The relationship between the inferior thyroid artery and the inferior laryngeal nerve is very variable. The latter may pass anteriorly, posteriorly or between the branches of the artery. In less than 1% of cases (Henry et al., 1988), the nerve does not recur on the right side and originates directly from the vagus on the neck, reaching the larynx running more or less transversely. This variation is determined by a vascular anomaly during embryonic development, resulting in an aberrant subclavian artery (arteria lusoria), originating directly from the aortic arch on the left of the left subclavian artery and passing transversely posterior to the esophagus. This anomaly is exceptional on the left side and happens in cases of situs viscerum inversus and associated vascular anomaly.
3. Indications
Careful selection of patients is the only guarantee of a good outcome for this procedure. Only a minority of cases are eligible for a video-assisted approach to the thyroid (Miccoli et al., 2001a). An important limit is, at present, the volumes of both the nodule and the gland to be operated on. The lobe has to be removed without disrupting its capsule because of the necessity of an accurate histologic evaluation, as these nodules are often suspected for a carcinoma (either follicular or papillary). Other limits of this technique are manifest in the presence of adhesions that can make dissection difficult to carry out. This can happen in redo surgery and also when a thyroiditis is discovered, unveiled both by increased thyroid antibodies and ultrasound aspects.

General indications:
- thyroid nodules less than 30 mm at their widest point;
- thyroid gland volume less than 20 mL, as estimated by ultrasound;
- no history of thyroiditis;
- no previous neck surgery or irradiation.
It is debated whether “low-risk” papillary carcinomas are suitable for minimally invasive procedures. There is no doubt that a total thyroidectomy can be easily performed with median access, but the presence of lymph nodes should be carefully excluded by means of a neck ultrasound preoperative examination. At our institution, video-assisted thyroidectomies have been performed over the last 2 years for “low risk” small papillary carcinomas and preliminary follow-up has been very encouraging (Miccoli et al., 2002b).
Both postoperative serum thyroglobulin and radioiodine scintigraphy are comparable to those of patients operated on by means of traditional techniques and this is proof of an excellent oncological resection for video-assisted thyroidectomy as well.
4. Preop period
Principal requirements

Blood tests: to ascertain the euthyroidism at the time of the operation and exclude the presence of thyroiditis.

Ultrasonography: to assess gland volume and nodule size, to exclude the presence of suspicious lymph nodes.

Fine needle aspiration biopsy (FNAB): to assess the type of nodule (benign, malignant, suspicious).
5. Operating room set-up
• Patient
- supine position without neck hyperextension;
- conventional neck preparation and draping;
- a sterile drape covering the skin.
• Team
1. The surgeon is on the right side of the table.
2. The first assistant is opposite the surgeon.
3. The second assistant is at the head of the table.
4. The scrub nurse is on the left of the first assistant.
• Equipment
1. Double screen (optional)
2. Ultrasound generator
6. Instrumentation
1. Forward-oblique telescope 30°, diameter 5 mm, length 30 cm
2. Suction dissector with cut-off hole, with stylet, blunt, length 21 cm
3. Atraumatic forceps, very fine, serrated, working length 12.5 cm
4. Conventional tissue retractor
5. Tissue retractor, double-ended, length 12 cm
6. Clip applier for vascular clips (5 mm)
- straight scissors, length 12.5 cm
- elevator, 2 mm wide, blunt, length 19 cm
- ultrasonic scalpel
7. Dissection
• Skin incision
A 15 mm horizontal incision is made 2 cm above the sternal notch.
The midline opening is a critical point as it should be incised on a bloodless plane; any minimal bleeding at this point prevents the surgeon from continuing the procedure.
The surgeon should use the electrocautery with its blade protected with a thin film of sterile drape.
• Preparation
Subcutaneous fat and platysma are carefully dissected to avoid bleeding. The cervical linea alba is divided longitudinally over 3 to 4 cm. The strap muscles on the affected side are then gently retracted with a small retractor. A second retractor is placed directly on the thyroid lobe, which is retracted medially and lifted up. The dissection of the lobe from the strap muscles is completely achieved through the skin incision by gentle retraction and using conventional instruments.
The 2 small retractors maintain the operative space. A 30° 5 mm endoscope is inserted through the skin incision. Under endoscopic vision, the dissection of the thyrotracheal groove is completed with small 2 mm instruments: atraumatic spatulas in different shapes, spatula-shaped aspirator, atraumatic forceps, and scissors.
• Tip
1. Spatula-shaped aspirator
Washing and cleaning the operative field is very simple because there are no trocars in this procedure and water can be injected directly with the syringe: its aspiration is greatly facilitated by the use of the spatula-shaped aspirator. This helps the surgeon to continue operating through the spatula and aspirate smoke and liquids without introducing extra instruments into the incision.
8. Ligatures
• Ligature/middle vein
1. Middle thyroid vein
The first vessel to be ligated is the middle thyroid vein, when present, or the small veins between the jugular vein and the thyroid capsule. Hemostasis is achieved by means of small 3 mm conventional vascular clips or by ultrasonic scissors.
This step helps in the preparation of the thyrotracheal groove, where the recurrent nerve will be searched for later on.
• Ligature/upper pedicle
1. Superior thyroid artery
2. Superior thyroid vein
3. Thyroid gland
4. Posterior fascia
The upper pedicle must be carefully prepared, until optimal visualization of the different branches is achieved.
The thyroid lobe is retracted downward by the retractor. After exposing the upper pole, the spatula is used to separate the larynx from the vessels and retract them laterally. The vessels are then selectively ligated either by conventional vascular clips or by ultrasonic scalpel and cut.
The tip of the ultrasonic scalpel must be carefully checked while ligating the upper pedicle as it reaches high temperatures that can damage the larynx and even the pharynx if applied to the walls for too long.
The external branch of the superior laryngeal nerve can be easily identified during most of the procedure once the different components of the upper pedicle have been prepared.
The external branch of the superior laryngeal nerve is much easier to identify during the endoscopic procedure than during the standard procedure. If this nerve is not clearly visible before the division of the upper pedicle, dissection of its elements is mandatory, particularly of the artery because it is very likely that the nerve runs parallel and in contiguity to the artery. If the surgeon decides to use an ultrasonic scalpel, the pedicle should not be coagulated “en bloc” but selectively, isolating each element. This generally avoids any injury to the nerve, which usually becomes visible once the artery has been ligated.
• Visualization/dissection
1. Parathyroid gland
2. Vascular pedicle
3. Recurrent laryngeal nerve
4. Posterior fascia
After retracting the thyroid lobe medially and lifting it up, the fascia can be opened by gentle spatula retraction. The recurrent laryngeal nerve generally appears at this point, lying in the thyrotracheal groove and posterior to the Zuckerkandl tuberculum (posterior lobe), which is an excellent landmark.
In conventional surgery, the recurrent nerve is generally prepared at its emergence from the thoracic outlet, but this area can be difficult to visualize with the endoscope while the middle part of the thyroid gland is clearly visible and nerve dissection is ideal.
Also, both parathyroid glands are generally easily visualized because of the endoscope magnification. Their vascular supply is preserved by selective ligature of the branches of the inferior thyroid artery. Hemostasis is achieved during dissection by vascular clips or ultrasonic scalpel, when dealing with large vessels or small vessels close to the nerve. In this way, the recurrent nerve and the parathyroid glands are dissected and freed from the thyroid gland.
The surgeon should always remember to keep the inactive blade of the ultrasonic scalpel posteriorly oriented during the division of the artery to avoid jeopardizing the nerve, which always lies posterior to it and is very sensitive to heat transmission.
9. Extraction/resection
• Extraction and resection
After removing the endoscope and the retractors, the surgeon carefully pulls out the upper portion of the gland using conventional forceps. Gentle traction over the lobe allows for complete exteriorization of the gland.
The operation is now conducted as in open surgery under direct vision. The lobe is freed from the trachea by ligating the small vessels and dissecting Berry’s ligament. It is very important to check the laryngeal nerve once again at this point to avoid its injury before the final step.
• Removal of the lobe
The isthmus is then dissected from the trachea and divided. After completely exposing the trachea, the lobe is finally removed by the conventional open technique.
• Wound closure
Drainage is not necessary. The space is filled with a hemostatic substance. The linea alba and platysma are closed with an absorbable suture. The skin is closed either by subcuticular suture or by skin glue.
10. Conclusion
Postoperative management
Patients receive fluids intravenously on the day of the operation. They are allowed to drink but not to eat. They receive antibiotic therapy and analgesics if necessary. The day after, serum calcium is evaluated in case of total thyroidectomy. Direct laryngoscopy is performed 3 months after the operation. The scar does not necessitate any medication, because the skin glue covers and protects the scar. Patients are generally discharged the day after the operation.

Conclusion
If the eligibility criteria are respected, minimally invasive video-assisted thyroidectomy is a safe operation that can be performed in an acceptable operative time. Complication rates are not higher than in open surgery, and following a short learning period, operative times are not much longer (Miccoli et al., 2002a).
Total thyroidectomy is feasible through the same central access. This allows the treatment of bilateral pathologies as well as diseases where an ablation of the entire gland is advocated; this is the case with low risk differentiated carcinomas where the radicality of the resection is exactly the same as in open surgery. We have already evaluated whole body scintigraphy (WBS) and serum thyroglobulin (sTg) dosage in these patients in a previous series (Miccoli et al., 2002b). The results were comparable to those of traditional surgery both in terms of radioactive iodine (I131) uptake and sTg levels. It thus demonstrates that an adequate resection can be achieved in this kind of carcinoma, so frequently occurring in young females particularly concerned about the operation’s cosmetic outcome.
It is also important to stress that even when a contralateral lobectomy might be necessary after histology has proven the presence of such a malignancy, re-operation can be done through the same incision. This is the main reason we prefer this approach, which is characterized by a unique central incision.
The greatest limit for MIVAT is the volume of the thyroid gland to be treated. Large multinodular goiters appear not to be eligible for minimally invasive neck surgery, both because the operative space is too small to allow surgical maneuvers and because of the impossibility of retrieving them through these tiny skin incisions.
Finally, the greatest caution must be used when dealing with serious malignancies; medullary carcinomas and even high-risk differentiated carcinomas constitute an absolute contraindication, also because of the frequent presence of lymph node involvement in these tumors (Dralle et al., 1994).
In terms of possible advantages there is little doubt that the cosmetic result is far better, and reduced tissue dissection minimizes postoperative pain.
MIVAT also proves to be a safe procedure when performed in different surgical settings (Miccoli et al., 2002a). It has proven to be a valid therapeutical option as long as indications are strictly followed, because some advantages in terms of cosmetic result and postoperative pain can be demonstrated (Miccoli et al., 2001b).
11. Reference