Operative Technique for Modified Radical Neck Dissection in Papillary Thyroid Carcinoma

June 2009
Operative Technique for Modified Radical Neck Dissection in Papillary Thyroid Carcinoma
John R. Porterfield, MD; David A. Factor; Clive S. Grant, MD
Arch Surg. 2009;144(6):567-574. doi:10.1001/archsurg.2009.89
 
ABSTRACT
Background  Papillary thyroid carcinoma is the most common endocrine malignancy. Recently, controversy has focused on the management of lymph node metastases, which represent approximately 90% of disease recurrences and may require considerable time, effort, and resources to diagnose and treat. Current intense postoperative surveillance by endocrinologists nationwide has the sensitivity to detect even minute lymph node metastases using ultrasonography, radioactive iodine scan, and thyroglobulin monitoring.福建省立医院基本外科黄东航

Objectives  To (1) present a succinct synopsis of the rationale and elements of our current surgical management strategy for papillary thyroid carcinoma and, within this context, (2) provide a detailed stepwise description of a compartment-oriented modified radical neck dissection. This description is combined with intraoperative photographs and a medical artist"s illustrations to enhance and emphasize the most important points.

Conclusions  With anatomically defined precise dissection, following the steps outlined and illustrated, a thorough lymphadenectomy can be accomplished safely, with reasonable cosmetic results, minimizing disease relapse.

•
•
Papillary thyroid carcinoma (PTC) is the most common endocrine malignancy and accounts for approximately 75% of newly diagnosed cases of thyroid cancer each year in the United States. The extent of thyroidectomy and lymphadenectomy has been surrounded by controversy since first addressed in the late 1950s by Beahrs and Woolner and Frazell and Foote. In fact, the subject of lymphadenectomy has reemerged as an important and highly contested issue in the new millennium. Microscopic regional lymph node metastases (LNM) have been demonstrated in as many as 80% of patients with PTC, but only about 35% of these patients have clinically evident nodal metastases at the time of their initial surgical procedure. While these metastatic nodes do not necessarily portend a worse prognosis at presentation, excision can minimize LNM recurrence and reoperations.

There is widespread consensus by specialty societies and recognized international experts in thyroid carcinoma that surgery is the best treatment of cervical LNM.  The current American Thyroid Association guidelines for the management of PTC include the following statement: “(R21) Preoperative neck ultrasound for the contralateral lobe and cervical (central and bilateral) lymph nodes is recommended for all patients undergoing thyroidectomy for malignant cytologic findings on biopsy.” Moreover, regarding lateral neck compartment lymph nodes, the guidelines state, “(R27) For those patients in whom nodal disease is evident clinically, on preoperative ultrasound, or at the time of surgery, surgical resection may reduce the risk of recurrence and possibly mortality. (R28) Lateral neck compartmental lymph node dissection should be performed for patients with biopsy-proven metastatic cervical lymphadenopathy detected clinically or by imaging.” Both the American Association of Clinical Endocrinologists and the American Association of Endocrine Surgeons agree that it is appropriate to remove all enlarged lymph nodes in both the central and lateral neck compartments.

Facilitated by technological advances including high-resolution ultrasonography (US) and the development of synthetic recombinant human thyroid stimulating hormone, endocrinologists nationwide have adopted a new intensive postoperative management algorithm. As a result, LNM are much more readily detected?up to 40% after traditional surgical management.

From the classic radical neck dissection removing compartments I through V, a more conservative approach evolved for PTC in which the sternocleidomastoid muscle, the spinal accessory nerve, and the internal jugular vein were preserved. This was termed a modified radical neck dissection and was recommended by Bocca and as entirely sufficient for control of cancer. He admonished that, “radicality must be conceived against the cancer, and not against the neck.” Definition of the compartments or levels of the lateral neck are included in the Table. Although a published classification of neck dissections has suggested the term selective neck dissection be applied when 1 or more lymph node groups are preserved that would normally be included in the level I through V radical neck dissection, modified radical neck dissection orfunctional neck dissection are terms still widely used to describe clearance of nodes in compartments II through V.

When lateral neck (compartments II-V) LNM are identified, the intent is to dissect the nodes thoroughly to minimize the risk of PTC disease relapse, yet proceed safely and avoid unnecessarily radical dissection. After analysis of 774 patients with PTC primarily operated on at the Mayo Clinic from 1999 through 2007, an overall surgical strategy was developed to minimize disease recurrence yet preserve the safety of thyroidectomy and both central and lateral neck dissections. Briefly described here are the rationale and results of preoperative ultrasonography, our general approach to examining lymph nodes in PTC, and a detailed description of the method for compartment-oriented lateral neck dissection. This is fully illustrated, with a series of figures that combines intraoperative photographs taken throughout a modified radical neck dissection, supplemented by medical illustrations to enhance and emphasize the important surgical anatomy and techniques.

PREOPERATIVE ULTRASONOGRAPHY

Preoperative ultrasound is valuable to detect and localize precisely nonpalpable lateral neck lymph nodes in 15% of patients. Further, even when nodes are palpable, US alters the extent of resection in 40% of patients by its ability to evaluate the entire neck. Approximately 40% to 45% of patients who have a node dissection in the central compartment prove to have positive nodes.

Two points that are important to emphasize are (1) US is rather insensitive for central nodes prior to first-time cervical explorations and (2) even if only a single node is identified by preoperative US either in the central or lateral neck, the patient may have multiple nodes involved, indicating the need for a more complete en bloc dissection.

GENERAL APPROACH TO DISSECTION OF LYMPH NODES IN PTC

First, the submental, submandibular, parotid, and retroauricular nodes are virtually never dissected in PTC. Second, the central compartment (compartment VI) in our practice is dissected routinely and completely in PTC. Third, the key lateral compartments are III, IV, and the anterior aspect of level V (posterior to the sternocleidomastoid muscle, but not formally extending the dissection to the trapezius muscle). These are the lateral compartments that we routinely dissect en bloc in PTC for LNM. If, however, by either palpation or preoperative US, positive nodes are suspected in level II, this compartment is included in the en bloc dissection. Fourth, the mediastinal nodes below the innominate artery are rarely dissected in PTC.

OPERATIVE TECHNIQUE

The operative technique is illustrated with a combination of intraoperative photographs and medical artist (D.A.F.) drawings.

INCISION PLANNING
Longer-acting muscle relaxant medications are not used to allow normal motor nerve conduction and muscle contraction throughout the neck dissection (Figure 1).

Figure 1.
Modified radical neck dissection incision, subplatysmal flaps, and dissection between sternocleidomastoid muscle (SCM) and strap muscles.

A standard collar incision is made approximately 2 finger-breadths above the sternal notch. The vertical extent of the incision coursing superiorly along the anterior border of the sternocleidomastoid muscle depends on the extent of metastatically involved lymph nodes indicated by preoperative ultrasonography. Unless metastatic nodes are defined in compartment II, the superior extent of the incision is dictated by the intent to dissect levels III, IV, and the anterior aspect of level V, as well as the patient"s body habitus. If level II nodes are dissected, the incision is significantly longer than if only the usual compartments are dissected.

Once the incision is made, the superior subplatysmal flap is dissected medially to the midline up to the thyroid cartilage and as far superiorly as necessary anterior to the carotid artery and internal jugular vein (IJV). A sharp towel clamp is used to secure the dermis of the flap to the surgical drapes at the chin.

EXPOSURE IJV AND CAROTID ARTERY
The plane between the sternocleidomastoid muscle and the strap muscles is opened by dissecting the entire medial border of the sternocleidomastoid muscle, which is retracted laterally with 2 goiter retractors throughout the dissection. The omohyoid muscle is identified, encircled, dissected superiorly and laterally, and excised, thereby exposing the IJV and common carotid artery (Figure 2).

Figure 2.
Isolation and resection of omohyoid muscle.

LNM ANTERIOR TO CAROTID ARTERY

Either at this time or later in the dissection, nodes located anterior to the IJV and carotid artery at about the level of the thyroid cartilage are excised. These nodes are often overlooked unless deliberately sought by the surgeon.

The lateral dissection is initiated approximately 2 to 3 cm superior to the clavicle, incising the fascia overlying the IJV along its lateral border. Note the blue lymph node, which has a classic appearance for metastatic PTC, with cystic fluid in the node causing the blue color (Figure 3).

Figure 3.
Initial dissection along lateral border of internal jugular vein (IJV) above level of clavicle. CCA indicates common carotid artery; SCM, sternocleidomastoid muscle.

DISSECTION OF IJV TO LOCATE FLOOR OF NECK

As the IJV is further mobilized superiorly and inferiorly, it is retracted medially and elevated anteriorly using a vein retractor. This exposes the areolar tissue behind the IJV, extending down onto the anterior scalene muscle. This space is easily entered and bluntly dissected, facilitating identification of the phrenic nerve running vertically on the anterior scalene muscle. The nerve identity may be confirmed by a gentle pinch, causing contraction of the diaphragm and a hiccup (Figure 4).

Figure 4.
Exposure of anterior scalene muscle and phrenic nerve. CCA indicates common carotid artery; IJV, internal jugular vein.

DISSECTION AND PROTECTION OF CAROTID SHEATH STRUCTURES AND THORACIC DUCT

The transverse cervical artery (a branch of the thyrocervical trunk) courses laterally across the anterior scalene muscle, anterior to the phrenic nerve, and may be a useful guide to it (Figure 5). This artery may be sacrificed if necessary, carefully protecting the underlying nerve.

Figure 5.
En bloc dissection of internal jugular vein (IJV) lymph nodes and exposure of floor of neck. ASM indicates anterior scalene muscle; BP, brachial plexus; CCA, common carotid artery; MSM, middle scalene muscles; PN, phrenic nerve; SCM, sternocleidomastoid muscle; SCV, subclavian vein; and TD, thoracic duct.

During mobilization of the IJV it should be handled gently to avoid venotomy with attendant bleeding and risk of air embolism. The remainder of the dissection is accomplished with a combination of blunt, sharp, and extensive but careful use of cautery dissection. The carotid artery and vagus nerve are identified and protected throughout the remainder of the dissection along the IJV.

As the dissection progresses inferiorly along the lateral border of the IJV, care must be taken not to dissect into the subclavian vein as it joins the IJV.

At the base of the left side of the neck, looping up a short distance behind the IJV from medial to lateral, is the thoracic duct. It descends to enter the confluence of the IJV and subclavian vein. This is very vulnerable to injury, especially if the commonly encountered, enlarged, metastatically involved nodes obscure the surgeon"s view. However, if injured in adults, the thoracic duct may be ligated without harm.

The inferior lateral compartment nodes are elevated superiorly by dissecting laterally across the base of the neck, encountering small veins that can be clipped or ligated. This fully exposes the anterior scalene muscle and, with further blunt dissection and elevation anteriorly of the nodal packet, the brachial plexus can be identified palpably and visually, coursing between the anterior and middle scalene muscles.

CERVICAL PLEXUS PRESERVATION

The packet is then retracted anteromedially as it is released from its lateral attachments. The individual nerves of the cervical plexus, which are all sensory nerves (except the phrenic nerve and ansa cervicalis), are encountered and preserved. The nodes posterior to this plexus are separated from their loose posterior attachments and delivered between the nerves (Figure 6).

Figure 6.
Cervical plexus (CP) and spinal accessory nerve dissection (extending to level II). ASM indicates anterior scalene muscle; BP, brachial plexus; CP, cervical plexus; IJV, internal jugular vein; MSM, middle scalene muscles; and PN, phrenic nerve.

SPINAL ACCESSORY NERVE LOCATION AND ORIENTATION

Superior to the cervical plexus nerves is the spinal accessory nerve that courses in an obliquely vertical course at this level. Careful use of the cautery at low power will stimulate this nerve prior to actually encountering it. Once stimulation of the trapezius is apparent, the nerve can be identified and carefully dissected superiorly without use of cautery.

Once the nodes from this level have been separated from the vessels and spinal accessory nerve, the entire packet of nodes is excised, oriented, and submitted to pathology, completing the dissection (Figure 6B and Figure 7).

Figure 7.
Dissection of level II exposing the digastric muscle (DM) and spinal accessory nerve (SAN).

RISKS AND COMPLICATIONS

The risks of modified radical neck dissection include the commonly described problems of bleeding, infection, and usual postoperative complications. Specific to the procedure are potential complications that can be characterized by anatomic groups.

NERVES
 

•Vagus (X). If the vagus nerve is injured in the neck, unilateral vocal cord paralysis will result, as the recurrent laryngeal nerve is part of the vagus at this level.

•Spinal accessory (XI). The principal disability with the XI nerve is shoulder syndrome, including weakness of the trapezius muscle with resultant reduced abduction of the shoulder, stiffness, and abnormal scapular rotation.

•Phrenic. Damage to the phrenic nerve results in unilateral elevation of the diaphragm and possible compromise to respiratory function.

•Hypoglossal (XII). A rare injury to this nerve leads to dysfunction of the tongue and deviation of the tongue to the affected side.

•Sympathetic chain. Located posterior to the carotid sheath, damage to this structure leads to Horner syndrome.

•Marginal mandibular branch of facial (VII). While damage to this nerve should be almost excluded by the extent of the dissection for PTC, its anatomic course dipping below the level of the mandible should be borne in mind. Damage causes a serious cosmetic droop of the corner of the mouth associated with drooling.

•Brachial plexus. Because of their deep location, coursing between the anterior and middle scalene muscles, injury to the these nerves should be extremely rare, but could be serious, depending on the specific nerves affected.

•Cutaneous cervical plexus. Damage to these nerves in the past has been an anticipated consequence of the operation. However, preserving these nerves can regularly be accomplished, preserving sensation to the upper and lateral chest.

 

VESSELS
 

•Carotid artery. Carotid laceration or rupture is usually associated with prior radiotherapy or markedly scarred reoperations. Stroke or fatality can result. Significant bradycardia can occur with dissection around the carotid bulb at the bifurcation.

•Internal jugular vein. Laceration or avulsion of small tributaries are bothersome but seldom serious and are usually repaired with vascular suture. The vein can be sacrificed unilaterally without serious concern. Air embolus must be prevented when patients are positioned in reverse Trendelenburg and an opening in the vein is caused.

 

LYMPHATICS
Injury to the thoracic duct can be remedied by ligation without complication in adults. However, a persistent high-volume chylous leak can be troublesome. Intraoperatively, the lymphatic fluid is nearly clear and colorless, in contrast to the milky character it becomes postoperatively after eating. A low-volume lymphatic leak may become evident in the first 2 to 4 days postoperatively, but often seals over the next few days. We had a single patient with a 300-mL daily lymphatic leak that responded promptly and dramatically with the administration of somatostatin. Similar but less prominent lymphatic trunks may be encountered just lateral to the base of the right internal jugular vein and must be managed in similar fashion to the thoracic duct.

CONCLUSIONS
Controversy regarding the appropriate management of metastatic lymph nodes in PTC is yet to be resolved. However, when the surgeon elects to proceed with dissection of the lateral neck nodes, the description above provides a compartment-oriented, thorough, cosmetically reasonable, and safe method for lymphadenectomy. The frequency of lymph node recurrence in the operative field when this technique has been used is about 5%. Reoperations often require a different strategy, but should rarely be necessary if the entire management scheme is followed.