I. Major blood vessels and nerves
The outside of the thyroid gland has two layers of connective tissue perithelium, the inner layer is the true capsule with a rich vascular network and the outer layer is the pseudocapsule which is part of the pre-tracheal fascia with a loose connection between the two layers of perithelium. Therefore, surgical exposure of the thyroid gland should be performed between the peritoneum with less bleeding. The thyroid suspensory ligament is formed by the thickening of the thyroid sheath over the isthmus and lateral lobes and anchors the thyroid gland to the laryngeal cartilage and tracheal cartilage. The posterior thyroid sheath of the lateral lobe is connected to the fascia of the trachea and esophagus and to the carotid sheath, where the recurrent laryngeal nerve and the inferior thyroid artery cross.
The vagus nerve exits the skull and descends posteriorly between the arteries and veins in the carotid sheath to branch to the larynx as the superior laryngeal nerve and the recurrent laryngeal nerve. The superior laryngeal nerve descends obliquely through the posterior aspect of the carotid artery and divides into two branches near the larynx: the internal and external branches. The inner branch is accompanied by the laryngeal branch of the superior thyroid artery, which innervates the sensation of the laryngeal mucosa above the vocal cords. The outer branch is accompanied by the superior thyroid artery and its branches to the cricothyroid muscle, which innervates this muscle: after the injury of the inner branch, the sensation of the laryngeal mucosa above the ipsilateral vocal cords is lost, while the injury of the outer branch causes the cricothyroid muscle to be paralyzed and the articulation is weakened and easily fatigued.
The laryngeal nerve is not bilaterally symmetrical. The vagus nerve emanates from the left side at the lower edge of the aortic arch and the right side at the lower edge of the right subclavian artery, and after it emanates, it wraps around to the lower part of the corresponding artery, then turns to the posterior medial side and enters the larynx along the groove between the trachea and esophagus. The right recurrent laryngeal nerve occasionally does not pass under the subclavian artery and goes directly to the larynx in the neck, which is called the “non-returning recurrent laryngeal nerve”. Therefore, the hoarseness of the voice mostly indicates damage to the recurrent laryngeal nerve, which is a more common and serious complication of thyroid surgery. There are more venous variants in the thyroid gland, but as long as more attention is paid during surgery, there are usually no major problems.
II. Surgical precautions
The correct position is of great significance. The exposure of the neck in the supine position is sufficient for use, but the patient’s face should be avoided to present an unpleasant bruise. The patient’s head should be flexed to the front when closing the wound.
In general, the patient’s head and neck should not be deviated to one side, so that the body surface markings of certain important anatomical structures can be obvious and intraoperative mishaps can be avoided. The collar incision is mostly used to avoid the error of too low incision and too small incision. kocher: The incision should be made from both sides of the sternocleidomastoid muscle in line with the outer edge.
The latissimus dorsi muscle should be cut at the same height as the skin incision. Subcutaneous hemostasis should be adequate.
There is much debate about the correct cut of the cervical muscles (sternocleidomastoid muscle, sternocleidomastoid muscle). It should be done on a case-by-case basis and should not be prescribed in principle. The severance of this muscle is undoubtedly of great help to the unskilled operator and can reduce the risk. There are also some goiters where the muscle must be severed even in experienced hands in order to remove it. The healing of the muscle after excision is generally smooth, and the postoperative painful swallowing should not be considered a disadvantage. On the contrary, especially in small goiter, these muscles should be preserved without hesitation.
To protect the nerve, if it is cut transversely, it should be at a higher site. A common mistake is to extensively dissect the skin and the latissimus dorsi muscle upwards with the underlying muscles. It seems that whether or not to cut the muscles should depend on whether or not it interferes with the operation. To avoid the following complications and to make the operation easier, the goiter should be dissected between the inner and outer capsules because the loose fibrous tissue between the two capsules is easy to dissect and can reduce bleeding and side injuries.
The more common complications that can occur when stripping and turning a goiter are
1. bleeding.
2. Gas embolism occurs.
3, Return N injury.
4, Parathyroid gland injury with postoperative convulsions.
5, mediastinal emphysema.
6, Thoracic duct injury, lymphatic leakage, this complication is less frequent and more serious, and should be alerted.
When turning the lower pole of the thyroid, attention should also be paid to whether the ribbed pleura is accidentally injured, which is rare.
If the trachea is injured, there are two major risks due to the interoperability of the airway and the operative field.
(1) contamination of the airway with the operative field, causing postoperative infection, which can be treated with drainage and anti-inflammatory treatment and a phase of sutured tracheal trauma.
(2) Aspiration of blood by mistake causes asphyxia or limited pulmonary atelectasis. Therefore, if the trachea is inadvertently wounded by mistake, it is appropriate to immediately occlude the wound with fingers, remove the surrounding blood accumulation, and immediately suture it; if the suture fails, a catheter can be inserted.
Postoperative drainage is usually removed in 24-48 hours, mostly with skin slice drainage. If the mass is huge and may produce a large cavity, it is appropriate to use negative pressure cannula drainage. Intraoperative prevention: strict hemostasis and elimination of dead cavity.
Postoperative: bedside placement of tracheotomy bag. There was a patient with a huge thyroid mass and after removal of the mass, the original softened tracheal wall pushed to support the subsidence and emergency tracheotomy and reoperation was performed. The patient’s life was saved due to timely resuscitation.
Postoperative danger period: within four hours, intraoperative spasm or bleeding from reopening of the blood vessel stopped by electrocoagulation produces hematoma compression. Within three days, it may be caused by coughing or eating dry or brown food. Since the area is relatively small in scope and has many important structures, a small amount of bleeding compared with the abdomen can prevent breathing or compress the A-sheath of the neck and cause life-threatening bleeding, so close monitoring should be performed within three days after surgery, especially within six hours. Using bandages to compress the operative field does not stop bleeding, but may also prevent the patient from breathing and eating and the surgeon from observing the leakage, so thick bandages are not recommended.
Ligation of the inferior thyroid artery should not be done within the surgical space, but outside it, i.e. outside the capsule (outside the fascia). Operation within the muscle capsule space is almost possible to avoid laryngeal return N injury. The ligation should be performed as far to the side as possible, as close as possible to the carotid artery, where no bleeding should be allowed. Of course, the greatest difficulty is the inability to detect this artery.
In modern operations, the thyroid artery is mostly ligated before separating the goiter.
Advantages.
1. Before separating the mass, the direct view of the operative field is clearer, and ligation of A can avoid accidental injury to N.
2. After ligation of the A, the gland shrinks and is movable, making it easy to separate.
3.Venous collapse, the gland can be clamped with hemostatic forceps without the risk of bleeding, so that the risk of air embolism can also be reduced.
During the operation, if there is slippage after ligation A, the cut off is a lot of bleeding, it is difficult to stop, and if the clamp is blindly in the blood pool, it may cause more damage.
Avoidance method: When removing the adenoma, a small piece of thyroid tissue can be retained at the upper pole along with the arterial stump. It is quite controversial whether ligation of the vessels should be done after complete separation and clear ligation or with a little tissue.