Principles in Thyroid Surgery

Atypia of Undetermined Significance or Follicular Lesion of Undetermined Significance

When cytology is read as AUS/FLUS, the mean risk of malignancy is estimated around 15% to 20%; however, notable challenges have been discussed in the literature regarding this estimate. In this setting, repeat ultrasound-guided FNA and molecular testing may be offered to aid in malignancy risk assessment. If surgery is decided upon without these further investigations, the surgery is typically a lobectomy. In the setting of repeat FNA with AUS/FLUS or suspicious molecular testing results, surgery is considered. Either a lobectomy or total thyroidectomy may be recommended as the initial treatment of choice based on clinical risk factors, specific molecular testing results, sonographic pattern, and patient preference. Rarely in this category, frozen section can confirm malignancy intraoperatively (such as with classic papillary thyroid carcinoma) and allow for conversion to total thyroidectomy if indicated. However, given the limited utility of frozen section with other diagnoses (such as follicular variant papillary thyroid cancer [PTC] and follicular thyroid carcinoma), many surgeons choose to forego frozen section intraoperatively. In any case, if lobectomy is decided upon as the initial management strategy, the patient must be counseled regarding the possible need for completion thyroidectomy.

Follicular or Hürthle Cell Neoplasm

When the needle biopsy result reveals follicular or Hürthle cell neoplasm (or suspicious for follicular or Hürthle cell neoplasm), a lobectomy without frozen section is generally offered for complete capsular histologic evaluation. The patient is counseled about the potential need for completion thyroidectomy, which occurs in approximately 20% to 30% of cases. Alternatively, molecular testing may be offered for further malignancy risk assessment. Total thyroidectomy may be considered when the lesion is more likely to be malignant, based on molecular testing results or clinical factors such as male sex or larger size of the lesion (generally > 4 cm). Initial total thyroidectomy may also be considered in patients who, based on their age, have a less favorable prognosis should a cancer be diagnosed or if there is substantial unbiopsied contralateral lobe nodularity.

Suspicious for Malignancy

Needle aspirates that read as suspicious for malignancy are most often suspicious for papillary carcinoma; the risk of papillary cancer up to 70%. These have traditionally been best treated with lobectomy with frozen section and intraoperative touch cytologic prep (see Chapter 11 , Fine-Needle Aspiration of the Thyroid Gland—The 2017 Bethesda System). If a diagnosis of papillary carcinoma can be made intraoperatively, total thyroidectomy can be offered. Biopsy of suspicious lymph nodes may be helpful for diagnosing papillary carcinoma. Alternatively, molecular testing may be considered before surgery if a positive result would lead to an altered surgical plan, such as proceeding straight to total thyroidectomy. Total thyroidectomy may be considered for nodules that have known mutations, nodules that are larger than 4 cm, or nodules in patients with a strong history of radiation exposure or familial thyroid carcinoma.

Diagnostic for Medullary Carcinoma, Anaplastic Carcinoma, or Lymphoma

An initial biopsy that is read as diagnostic for medullary carcinoma of the thyroid requires a workup to exclude pheochromocytoma, hyperparathyroidism, and radiographic evaluation for nodal disease; consideration must be made for total thyroidectomy, central neck dissection, and often unilateral or bilateral lateral neck dissection (see Chapter 26 , Sporadic Medullary Thyroid Carcinoma and Chapter 27 , Syndromic Medullary Thyroid Carcinoma: MEN 2A and MEN 2B). Blood testing for calcitonin, carcinoembryonic antigen (CEA), calcium, parathyroid hormone (PTH) and pheochromocytoma laboratory testing should be performed. Germline RET mutational analysis informs whether the patient has an inherited or a sporadic disease. With no evidence of nodal disease, total thyroidectomy with central neck dissection is considered often, with some surgeons considering lateral neck dissection depending on calcitonin levels.

With a diagnosis of anaplastic thyroid carcinoma, surgery is offered in the relatively uncommon circumstance where all gross disease can be resected; surgery is sometimes offered for palliative purposes. Given the significance of the diagnosis of anaplastic thyroid cancer, open biopsy confirmation rather than FNA alone can be considered. A common surgical procedure appropriate for anaplastic carcinoma is isthmusectomy; it can confirm tissue diagnosis and is often combined with tracheotomy if the airway is deteriorating.

Aspirates read as diagnostic for lymphoma often need to be subtyped; this frequently requires core biopsy or sometimes open biopsy/isthmusectomy (see Chapter 28 , Anaplastic Thyroid Cancer and Thyroid Lymphoma). Recommended management for thyroid lymphoma, as is the case for other lymphomas, typically involves chemotherapy and radiation rather than surgery.

The Prevalence and Favorable Prognosis of Small PTC Lesions

The first of these unique features of papillary cancers is the entity of occult or microscopic carcinoma. Such lesions are typically defined as less than 1 cm and typically as intrathyroidal. Such lesions are highly prevalent in humans and are often found incidentally during thyroidectomy performed for other lesions. The lesions occur, on average, in 8.5% of surgical specimens. When comparing data from the Surveillance, Epidemiology, and End Results Program (SEER) clinical prevalence rates to known autopsy rates of PTC, which range from 5% to 36% depending on the country, it is estimated that only 2% of existing PTC lesions in humans ever present with clinical disease. Although small occult carcinomas may metastasize to regional nodal beds in the neck, they are rarely associated with clinically significant metastatic disease or death. The favorable prognosis of small PTC lesions has been well studied. In 1960 Woolner described six patients with occult PTC diagnosed through an excisional biopsy of cervical lymph node(s) who were followed clinically (i.e. without any thyroid surgery) and found to have no progression of disease over many years. In Japan, a large prospective study of observation alone for patients with biopsy-proven papillary microcarcinomas (PMC) was performed. Among 162 patients observed, 72.3% demonstrated no local disease progression (PTC size was stable or smaller) on surveillance ultrasounds during long-term follow-up (at least 5 years) (See Chapter 21 , Papillary carcinoma observation).