Types of Thyroid Surgery
The thyroid gland, shaped like a butterfly, sits just below the skin and several thin muscle layers in the lower part of the neck (Figure 1). It’s attached to the deeper neck structures (trachea and voice box) and elevates when we swallow.
From the angled view (Figure 2), one can see the parathyroid glands, and the recurrent laryngeal nerve (RLN) adjacent to the breathing tube and beneath the voice box. The RLN is the nerve that goes to the voice box and the vocal cords and controls the movement of the vocal cords. The parathyroid glands and the RLN are all behind the Thyroid gland (Figure 3). The lymph nodes are mostly behind and below the thyroid gland in the lower neck. They are also around the RLN and parathyroid glands, making the parathyroid glands hard to identify at times.
Types of Thyroid Surgery
Options for surgical management of thyroid cancer as defined by the American Thyroid Association Guidelines include total thyroidectomy, subtotal thyroidectomy, hemi-thyroidectomy, and completion thyroidectomy. All the surgeries discussed are done on a routine basis at the CENTER; when patients qualify, minimally invasive techniques are performed.
Total thyroidectomy Total Thyroidectomy entails complete removal of all thyroid tissue from the bilateral thyroid beds including tracheal attachments (Figure 4).
In most thyroid cancer cases a total thyroidectomy is indicated for several reasons:
1. Some thyroid cancers present with more then one cancer in the thyroid gland itself, there can be a few separate cancers of the same type on each side of the thyroid (multi-focal).
2. By removing the entire thyroid, radioactive iodine treatment (RAI) can be given; without the gland being present the RAI will concentrate in the any microscopic cancer cells that maybe left behind after surgery.
3. Lastly, after surgery a blood test can be done to check for a specific thyroid protein (thyroglobulin) that is produced by both normal thyroid gland and thyroid cancer. With the thyroid gland being removed, if this protein starts to appears in the blood again, then it means that the cancer has returned. This is a very important monitoring tool.
Subtotal thyroidectomy Subtotal Thyroidectomy allows for a remnant of the thyroid at the tracheal attachments to remain while removing the majority of the gland. This type of surgery leaves a small portion of the thyroid gland at the area of the recurrent laryngeal thereby decreasing the risk of injury, however it also may leave a small portion of thyroid gland that could have thyroid cancer within it; therefore, a subtotal thyroidectomy is generally not used for thyroid cancer treatment, but rather for removal of a goiter (enlarged thyroid gland that does not have cancer within it).
Hemi-thyroidectomy Hemi-thyroidectomy, also known as thyroid lobectomy, leaves one lobe or side of the thyroid by removing only the side of the thyroid that has the mass or tumor in it, as well as the pyramidal lobe (the small tongue-shaped portion of the gland in the middle at the junction between the two sides of the thyroid). The advantage of hemi-thyroidectomy is that half of the thyroid gland remains, and therefore the person, in most, cases wont need to take thyroid hormones. Additionally, because the other side of the thyroid is untouched, there is no risk to the other recurrent laryngeal nerve or the other two parathyroid glands (we only need one parathyroid gland to work properly for the body to function normally). A hemi thyroidectomy is mostly indicated for either removing a very large mass that is not cancerous on one side, or to see if a mass that appears suspicious is a cancer (if the needle biopsy (FNA) is not able to clearly give us an answer).
Completion thyroidectomy Completion thyroidectomy, is done when a patient has previously undergone a hemi-thyroidectomy, and was found to have cancer on the side that was removed. Therefore they have to return to the operating room to remove the rest of the thyroid gland to complete the thyroidectomy. Dense scarring may form after the first surgery (hemi-thyroidectomy), and then the surgery becomes more challenging for the surgeon and puts the patient at increased risk of RLN and parathyroid injury. Surgeons experienced in re-operative surgery are best prepared both for this surgical challenge as well as to minimize risk to the patient. Completion thyroidectomy is optimally performed within two weeks of the initial surgery to avoid the formation of dense scarring.
Hemi-thyroidectomy Versus Total Thyroidectomy
The decision between total thyroidectomy over hemi-thyroidectomy for Well Differentiated Thyroid Cancer (WDTC or Papillary & Follicular thyroid cancers) has been the subject of repetitive study, and controversy.
Early experience at Memorial Sloan Kettering Cancer Center (MSKCC) identified that in patients with WDTC, age > 45 years, metastatic disease (spread to other parts of the body), lesions > 4 cm, and histology were factors associated with a decreased 20-year overall survival of 43%. Spread to lymph nodes was not a significant factor. Yet, a more recent outcome analysis of the Surveillance, Epidemiology, and End-Results (SEER) database demonstrated that lymph node status did significantly affect the outcome.
Nevertheless, when type of surgical intervention was compared over the same 20-year period, MSKCC found similar survival for patients with low risk lesions – defined as age younger than 45 years, tumors < 4 cm in size, low-grade histology, absence of distant metastasis (no spread to other parts of the body), and absence of extrathyroidal extension (invasion outside of thyroid) – treated with total (99%) versus hemi- (100%) thyroidectomy. Thus, the MSKCC approach is to stratify patients into risk groups to determine surgical approach: hemi-thyroidectomy for low risk, total thyroidectomy for intermediate risk, and total thyroidectomy with Radioactive Iodine therapy (RAI) for high-risk patients.
The overall disadvantage of hemi-thyroidectomy is that postoperatively, patients cannot have RAI if needed. Hay, et al from the Mayo Clinic compared low and high-risk patients based on both recurrence and survival rates over a 20-25 year period. They found that although low risk patients had similar survival rates independent of surgical approach, recurrence rates increased significantly in patients undergoing hemi-thyroidectomy (Graph 1) In high-risk patients, both a recurrence and survival advantage was detected with total thyroidectomy. Thus, based on recurrence risk, all patients with PTC would benefit from total thyroidectomy.
Several papillary thyroid cancer features have been identified as independent risk factors associated with a worse outcome, suggesting that hemi-thyroidectomy is inadequate therapy. Although some patients with a history of ionizing radiation exposure may present with only a small, single nodule, total thyroidectomy is the appropriate therapy. These patients are 30-40% more likely to harbor malignancy and as many as half have multifocal disease. Patients with nodules 4 cm or greater seem to harbor malignancy more frequently than FNA confirms. In these patients, the false negative rate is 34%, and 40% of indeterminate lesions later prove to be malignant. Also, the worsened prognosis observed in patients with locally advanced lesions, positive margins, and high-risk histologic WDTC variants – tall cell, columnar cell, and diffuse sclerosing – are indications for aggressive therapy that includes total thyroidectomy. Patients > 45 years are known to have a higher recurrence rates, suggesting that near-total or total thyroidectomy is the treatment of choice.
Central compartment neck dissection (CND) involves the removal of the lymph nodes in the area deep and beneath the thyroid glands (Figure 5). This may be done on one side or both. Indications for a CND are complicated and involve an in-depth discussion with your physician.
Lateral compartment neck dissection (LND) involves the removal of Lymph nodes in the remainder of the neck to the side of the thyroid from the collarbone up to just underneath the jaw. LND is indicated when abnormal lymph nodes are found on the side of the neck on exam or ultrasound (Figure 6).
If during thyroid surgery a parathyroid gland is found to have insufficient blood flow to it, therefore leading the surgeon to believe that it will not function, then the gland may be removed and cut into very small pieces and then placed in a small pocket made in the muscle of the neck. This is done so as to have the blood vessels from the muscle to grow into the parathyroid pieces and allow it to begin to work properly. Auto-transplanted glands start to work after about a month.
Upper Aero-digestive Tract Invasion
Aero-digestive tract invasion (ATI) means involvement of the breathing tube (trachea) or the swallowing tube (esophagus) by the tumor. ATI by well-differentiated papillary and follicular thyroid carcinoma has been reported in a very small percentage of thyroid cancer cases. Medullary thyroid cancer, although more aggressive, rarely presents with ATI. In contrast, ATI is a frequent clinical presentation in anaplastic carcinoma. This type of invasion by the tumor can cause trouble with breathing and swallowing.
Cancers that involve the trachea and esophagus must be removed. In most cases this means partial removal of a small portion of the trachea or esophagus. Rarely, large portions need to be removed and reconstructed (Figure 7). It is imperative that the operating surgeon is not only familiar with the types of cancer involvement but also well versed in techniques of both complex surgical resection and reconstruction of these structures.
Complications Recurrent Laryngeal Nerve (RLN) Injury – The RLN controls the movement of the vocal cords. The nerve travels from the brain all the way down the neck into the chest and loops back up into the neck and courses behind the thyroid gland to enter the voicebox. Injury to the nerve can occur during thyroidectomy. This would cause the vocal cord on the side of injury to stop moving, which would cause the person to become hoarse; the person could still talk but would just be hoarse. If discovered at the time of surgery, then the nerves can be reattached. The incidence of RLN is very low, but is very minimal in the hands of expert thyroid surgeons.
EMG Laryngeal Monitoring EMG Laryngeal Monitoring is a monitoring system for the vocal cord nerves (RLN’s) that allows the surgeon to assess the function of the nerve during surgery. Additionally, if the nerve is not easily found due to cancer involvement of the nerve, or if the patient has had an operation before and there is dense scarring, this monitoring system can help the surgeon find the nerve and confirm that it is working.
Parathyroid Injury– The parathyroid glands are extremely small and can be easily mistaken for fat or lymph nodes. The blood vessels that feed the gland are also very small and can be easily cut or disrupted. The parathyroid glands, therefore, can be easily removed by mistake, or have their blood vessels cut which would cause them not to function. The chance of this happening is low, but it is a possibility that can be minimized in the hands of an experienced surgeon. Additionally, with experience the surgeons become better at recognizing which parathyroid glands don’t have enough blood flow, at which point, that particular gland can be transplanted in the muscle so that it can start to work (auto-transplantation).
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