Details of thyroid surgery

1. Positioning the patient

Fig.1: Inflatable shoulder pillow in positionThe patient is placed flat (supine) on the operating table and the neck extended which helps to pull the thyroid up from the root of the neck. A supportive bolster is placed behind the shoulder blades and the head is supported in a ring, to maximise access (Fig. 1). The operating table is tilted 5-10 degrees head up, which reduces the venous pressure in the neck. 

The earth and return leads for the intraoperative nerve monitor should be inserted away from the operative field, and the NIM machine should be tested to ensure correct functioning prior to starting the operation.

2. The Incision

Fig.2: Line of minimally invasive thyroid incisionThe line of the incision is marked with a pen before the surgery (Fig. 2), and should be placed in a skin crease if possible, approximately 3-5cm in length, and 2-3cm above the suprasternal notch. 

3. Exposing the Thyroid

Fig.3: Raising the upper subplatysmal flapThe initial incision is made through the skin, subcutaneous tissues and platysma muscle. A plane is then developed superiorly between the platysma muscle and other underlying tissues (Fig. 3). It is best to develop this plane laterally first because the platysma is more obvious in the lateral neck. Similar development of the subplatysmal plane then is performed in the lower neck down to the suprasternal notch.

After this plane has been opened up, the wound is held open with a self-retaining Joll's retractor. The thyroid is then exposed by separating the strap muscles in the midline. The easiest way to find the midline is to look low in the neck where the strap muscles separate from each other.  

The left and right strap muscles are separated right up to the thyroid cartilage, and then it is useful to open the plane between the anterior and posterior strap muscles on the side of the operation, to aid mobility and to allow the sternothyroid muscle to be divided easily if necessary. Once this is done the sternothyroid muscle can be dissected away from the thyroid.

4. Mobilisation of the Thyroid

Fig.4: After opening the superior 'window' the external branch of the SLN is visible (green arrow), separated from the superior thyroid artery (blue arrow)The first step is to open up the plane lateral to the lobe, with a peanut swab, dividing any middle thyroid veins with the Ligasure thermal sealing device. This blunt dissection should be done as far as is possible at this stage, to gain maximum mobility of the lobe and allow it to begin to rotate out of the neck.

Attention can then be turned to the superior pole of the thyroid, which needs to be separated from the cricothyroid muscle, by opening up a ‘window’ between them (Fig. 4).

When these superior thyroid artery branches are retracted laterally, the external branch of the superior laryngeal nerve is often visible, and needs to be preserved. This nerve is responsible for tightening the vocal cords during shouting, or while singing high notes.

The superior thyroid arteries and veins are ligated close to the thyroid pole (usually with the Ligasure device in my hands, although ligaclips or harmonic scalpel can also be used). Hand ties have largely been superseded nowadays, and are unnecessarily risky.

As the superior pole comes free, smaller vessels can be ligated with the Ligasure close to the gland, but care must be taken to preserve the upper parathyroid gland, which is often hiding at the back of the superior pole.

5. Finding the Recurrent Laryngeal Nerve

Fig.5: Recurrent laryngeal nerve (arrowed) as it enters larynx with thyroid rotated awayOnce the superior pole is free it is time to look for the recurrent laryngeal nerve, which must be found before proceeding further. It is important to visualise the nerve, usually by identifying it low in the neck and following its course into the larynx. No structure should ever be divided until the recurrent laryngeal nerve has been identified (Fig. 5). The intraoperative nerve monitor can aid detection and dissection of the RLN, and should be available in every case.

The intraoperative nerve monitor is particularly valuable in thyroid cancer surgery, especially nodal dissection, reoperative surgery for benign and malignant disease, large goitres and retrosternal goitres, Graves' disease and other forms of thyroiditis, bilateral surgery, and surgery on the side of the only functioning RLN.

The recurrent nerve has a fairly constant relationship to the tubercle of Zuckerkandl, a lateral or posterior projection from the lateral lobe of the thyroid. The tubercle varies in size but in 93% of cases the recurrent laryngeal nerve runs under the tubercle in a fissure between the tubercle and trachea.  

Fig.6: Non recurrent laryngeal nerve (arrow) passing from lateral side directly towards the larynx; the thyroid is retracted to the right of pictureIf the nerve cannot be identified on the right side, then a non-recurrent nerve must be considered (Fig. 6).

This occurs in 1 in 100 cases, where instead of the RLN coming up the tracheo-oesophageal groove, the nerve comes from directly lateral, parallel to the inferior thyroid artery.

Care must be taken, especially on the right side not to ligate any structure coming in this direction until the RLN has been identified definitively. If there is any doubt, then the intraoperative nerve monitor can be particularly valuable in sorting things out.

There are a number of technical and patient factors that need to be taken into account to help avoid RLN injury: 

1. predicting problems
-thyroiditis, redo surgery, cancer surgery and node dissection increase the risk

2. meticulous surgical technique
- last 2cm of RLN near the ligament of Berry is most at risk
- avoid excessive tension, mechanical trauma & thermal spread when dividing ligament of Berry
- functioning RLN should be preserved unless clearly invaded

3. use of intraoperative nerve monitoring (NIM)
- beware variants of RLN: bifid nerve, non-recurrent nerve
- NIM is useful, as just the observation of an intact nerve can be misleading on its own
- NIM adds electrical information: identifies the nerve, maps it out, predicts postoperative function, and it allows the staging of an operation if there is loss of signal

6. Thyroid Resection

When mobilising the lower pole of the thyroid, finding the front of the trachea is a good first step to orientate the anatomy, then the veins can be divided.

Only the terminal branches of the inferior thyroid artery (on the thyroid gland itself) should be ligated to preserve the blood supply of the parathyroids. The lower parathyroid should be found and preserved where possible, but if there is doubt about its viability it can be auto-transplanted, with a high chance of graft take.

The final part of the gland mobilisation usually takes place at the ligament of Berry, a tough, fibrous attachment of the thyroid to the trachea. It is also a particularly vulnerable spot for injury to the recurrent laryngeal nerve, which is intimately related to the ligament, and often surrounded by tiny arterial and venous branches, which must always be controlled first.

Usually enough space can be gained by sweeping the nerve laterally as the lobe is mobilised, which will reveal these annoying small vessels. They can usually be controlled with the Ligasure, but if there is not enough distance from the nerve then ligaclips will usually suffice. If these vessels are not controlled first, they will often bleed quite vigorously and obscure the final centimetre of the nerve, allowing potential injury during efforts to stop the bleeding.

After the lobe has been fully mobilised, the vessels ligated and divided with the Ligasure, and the recurrent laryngeal nerve identified, the thyroid is ready for resection, using the diathermy to remove it from the tracheal fascia. If a hemithyroidectomy is being done, then the isthmus is divided at the edge of the contralateral lobe (i.e taken with the specimen) using the Ligasure. Removal of the isthmus every time prevents a prominent cut edge of the isthmus being felt by the patient, or you, as a persistent nodule in a thin neck.

7. Closure

The final and essential step is to secure haemostasis prior to closure. Placing the patient in a head-down position with the anaesthetist performing a pseudo-Valsalva manoeuvre, to raise the patient’s venous pressure, allows a thorough check for any bleeding. Drainage of the wound is usually not necessary but a rule of thumb is that if you think it might be necessary to drain the wound then do so.  The wound is closed in layers, firstly apposing the strap muscles and then the platysma, before closing the skin.