Generally, the risk of a serious complication with thyroid surgery is about 1%. Thyroidectomy is major surgery usually performed under general anesthesia. It is attended with risks that include, but are not limited to, bleeding, infection, and heart or lung problems related to anesthesia. These are common to many major surgical procedures. Our purpose is to discuss the risks of surgery that are unique to thyroid surgery. These risks involve the voice and the parathyroid glands.
With removal of one lobe of the thyroid gland (thyroid lobectomy) the primary risk is to the voice. About 10-15% of patients experience a variable degree of temporary subjective voice change after thyroidectomy. This is typically described as a “frog in the throat” or “cracking “ of the voice or a “weak” voice. These changes are temporary and last a few days to a few weeks. They are attributed to swelling of the muscles in the area of the dissection and /or inflammation and swelling of the voice box (larynx) related to the dissection in the area, or trauma from the breathing tube placed at surgery.
More serious voice changes may occur. These are related to injury to nerves that control the larynx. These changes may be permanent. The risk of permanent voice injury with thyroidectomy is about 1%. During the surgery, we monitor the function of the nerves, but even with these techniques injuries can still occur. There are two nerve pairs we need to consider.
The External Branch of the Superior Laryngeal Nerve
The external branch of the superior laryngeal nerve (EBSLN) runs along the upper part of the thyroid gland on both sides. These nerves go to muscles that fine tune the vocal cords. If they are injured the voice quality is usually fairly normal but creating high pitched sounds may be difficult. Singing might be affected. Initiating the swallowing process may be a problem. Some patients may not notice these problems because the consequences of EBSLN injury can subtle. Because the voice changes with this nerve injury can be hard to detect the exact injury rate with surgery is difficult to know. It is thought to be less than 2%.
The Recurrent Laryngeal Nerve
The second nerve and by far the most important is the recurrent laryngeal nerve (RLN). This nerve runs up from the patient’s chest in the groove between the swallowing tube ( esophagus) and the breathing tube (trachea). It is the main nerve that controls the vocal cord. There is a RLN on each side for each vocal cord. These nerves run along the underside of the thyroid gland.
If this nerve is injured the vocal cord on that side will not work. The voice quality is frequently significantly compromised. The voice is severely hoarse with a slightly high pitched, breathy quality. Yelling, singing and voice modulation are compromised. In our patients the risk of permanent RLN injury is significantly less than 1%. Temporary RLN injury is about 1%. If we think a nerve injury has occurred and the patient is not having a great deal of trouble, then we don’t recommend any intervention and wait for it to get well on its own. This may take 3-4 months. If it is not better after that period then a referral to a voice specialist is made. There are procedures that can be done to improve the voice quality but intervention too early can make the situation worse. Patience is very important.
The issues discussed above describe single nerve injuries that can occur with either removal of one side of the thyroid (thyroid lobectomy) or total thyroidectomy. With total thyroidectomy, nerves on both sides may be placed at risk. If both RLNs are injured during a total thyroidectomy then both vocal cords could be paralyzed. If this happens the airway could be compromised. It is possible that this compromise could be so severe that a tracheostomy could be required. This is a surgical opening in the trachea through which the patient breaths. This complication is extremely rare. We have never had a patient require a permanent tracheostomy in our practice.
The Parathyroid Glands
The second area of concern is the parathyroid glands. Parathyroid glands are of concern primarily with total thyroidectomy. The parathyroid glands are 4 small glands that sit behind and adjacent to the thyroid gland. There are two parathyroid glands on each side. These glands make a hormone that controls the calcium level in the blood. Specifically, the hormone causes elevation of the calcium level. Too little hormone leads to a low calcium level.
When the thyroid is removed these glands need to be left in place. Usually this is easy to do but sometimes these glands can be damaged or even inadvertently removed. If one or two of these glands are compromised there are no functional issues, however with a total thyroidectomy it is easy to appreciate how all 4 glands could be placed at risk. If all 4 glands are injured then the calcium level could run low. If it goes too low, significant problems could develop, including seizures. If low calcium develops after total thyroidectomy it is treated with oral calcium supplements. This condition of low calcium after thyroidectomy is called hypoparathyroidism. The risk of permanent hypoparathyroidism following total thyroidectomy in our patients is less than 1%. Patients with hypoparathyroidism have to take significant calcium supplements several times each day along with vitamin D to keep their calcium levels in the appropriate range.
While permanent hypoparathyroidism is very uncommon, temporary dysfunction of these glands may occur after total thyroidectomy. This is difficult to predict. Therefore, all patients who undergo a total thyroidectomy are carefully watched for low calcium after surgery and all are sent home on calcium supplements temporarily. Vitamin D is also given. This helps the patient absorb the calcium. Most patients are on these supplements 2-3 weeks, while the “stunned” parathyroid glands recover. The calcium level is monitored and the supplements are weaned as the glands start functioning again. During this time we want the patient to take only the supplements we prescribe. Once we are sure the parathyroids are working, we have the patient resume any calcium supplements they may have been taking pre-op.
We don’t consider post-op hypoparathyroidism to be permanent unless the patient is still requiring calcium supplements and vitamin D six months post-op. As with voice issues, patience is important in dealing with this problem.
Hypoparathyroidism is not an issue after simple thyroid lobectomy because only 2 glands are placed at risk. The 2 glands on the opposite side are enough to keep the calcium level normal even if both parathyroids on the side of thyroid lobectomy are injured.