Treatments: Extent of Thyroid Surgery
Including: total thyroidectomy, hemithyroidectomy and isthmusectomy, isthmusectomy
How much of the thyroid gland to remove (extent of thyroidectomy) is a strategic decision based on risks, benefits, and patient preferences. Key factors helping inform this decision include certainty of diagnosis of cancer, aggressiveness of the cancer, patient specific surgical risks,
Total thyroidectomy removes the entire grossly visible thyroid gland.
Removal of the thyroid gland (total thyroidectomy)
Total thyroidectomy is a surgical procedure to remove all thyroid tissue that can be seen. Although this involves removing the entire gland from a gross structural standpoint, it is well known that some microscopic thyroid cells typically remain behind. Patients with normal parathyroid anatomy, meaning having four glands, all in close relationship to the thyroid, may experience low parathyroid gland output following total thyroidectomy. If this occurs, it is usually temporary, with a reported rate of permanently low parathyroid hormone (hypoparathyroidism) being around 2%. Also with total thyroidectomy is the dissection of thyroid from the recurrent laryngeal nerves and the superior laryngeal nerves on each side. Temporary hoarseness after thyroid surgery is commonly related to the breathing tube placed between the vocal cords, but long-term hoarseness due to weakness of one or both vocal cords is thought to be about 2%. If that were to occur, there are procedures available to improve the voice, such as vocal cord injection medialization or medialization thyroplasty. When the entire thyroid gland has been removed, replacement of thyroid hormone is needed to prevent hypothyroidism, and this is in the form of one pill per day taken on an empty stomach.
A right hemithyroidectomy and isthmusectomy leaves the left thyroid lobe in place.
A left hemithyroidectomy and isthmusectomy leaves the right thyroid lobe in place.
Removal of part of the thyroid gland (Partial thyroidectomy)
A procedure in which less than all of the thyroid is removed is called a partial thyroidectomy. Usually, this takes the form of hemithyroidectomy and isthmusectomy. Removing only the nodule of concern, leaving all other thyroid tissue would seem to make sense, but is not done for several reasons that come down to risk and benefit. Instead, the lobe containing the nodule of concern (left or right) and the small isthmus connecting the two lobes, are typically removed in a partial thyroidectomy. (Another type of partial thyroidectomy is an isthmusectomy, discussed below.). By leaving one thyroid lobe in place and undissected, the parathyroid glands on that side and the laryngeal nerves on that side (recurrent laryngeal nerve and external branch of superior laryngeal nerve) are not at risk. Low parathyroid hormone and consequent low calcium is therefore not a risk after hemithyroidectomy. Similarly, while the one recurrent laryngeal nerve on the side of the hemithyroidectomy is at some risk, the other recurrent laryngeal nerve on the opposite side is not at risk. Therefore, weakness of both vocal cords and consequent potential for an airway problem will not happen. Further the remaining thyroid lobe may be able to produce all the thyroid hormone the body needs for the long-term. If it cannot, the diagnosis is made in the months after surgery and supplemental thyroid hormone in pill form is used.
A thyroid isthmusectomy removes only the thyroid isthmus, leaving both thyroid lobes in place.
Isthmusectomy
Uncommonly, only the segment of thyroid between the left and right lobes, the thyroid isthmus, need be removed. When this is the case, the risk of injury to either recurrent laryngeal nerve and the risk to the parathyroid glands is minimal. An example of a scenario requiring only thyroid isthmusectomy is when a thyroid nodule suspicious for cancer is present in the isthmus.
completion thyroidectomy
Completion thyroidectomy is the procedure of removing the remaining portion of the thyroid gland after a previous partial thyroidectomy. As an example, someone who previously underwent left hemithyroidectomy and isthmusectomy may subequently need the remaining right lobe removed. This example of a completion thyroidectomy could also be called a right hemithyroidectomy. Knowing the status of the recurrent laryngeal nerves prior to surgery is important in completion thyroidectomy because if the recurrent laryngeal nerve was not working after the original operation, then injury to the opposite recurrent laryngeal nerve in a completion thyroidectomy would render the patient with immobility of both vocal cords, which can cause an airway emergency or long-term problem. Regarding parathyroids, if at least one parathyroid gland on the originally operated side was preserved and functional, then the risk of low parathyroid hormone and consequent low calcium after a completion thyroidectomy is essentially nil. But, if both parathyroid glands on the side of the original operation were rendered nonfunctional, then temporary or permanent low parathyroid hormone could occur after a completion thyroidectomy. Evaluation for functionality of parathyroids on the previously operated side is not routinely performed before completion thyroidectomy; instead, the usual efforts to preserve parathyroid glands are undertaken and a patient is monitored for low parathyroid after completion thyroidectomy.
Lymph nodes and lymphatic channels are shown in green.
Removal of lymph nodes (cervical lymphadenectomy or “neck dissection”)
Thyroid cancers have the ability to spread to lymph nodes of the neck. Papillary thyroid carcinoma is especially prone to spreading to lymph nodes, whereas follicular thyroid carcinoma is less prone to spread to lymph nodes and relatively more likely to spread by blood to a tissue such as the lung. When thyroid cancer is suspected, ultrasound evaluation of the side of the neck can be undertaken to identify any suspicious neck lymph nodes. If found, typically ultrasound guided fine needle aspiration biopsy of one or more suspicious lymph nodes is undertaken. The pathologist’s reading of the needle biopsy is used in the decision-making for extent of surgery. If one or more lymph nodes on the side of the neck appears to have cancer spread to it, the surgical approach normally involves removing the entire thyroid gland (total thyroidectomy), the lymph nodes in the central neck (around the thyroid), and also the lymph nodes in the region of the known cancerous (“positive”) lymph node. This procedure, when done is skilled and experienced hands, can remove cancerous lymph nodes with maximal preservation of the important nerves, muscles, and blood vessels in the neck.
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