Thyroid carcinoma

Risk of malignancy in thyroid incidentalomas identified by fluorodeoxyglucose-positron emission tomography

BACKGROUND

Thyroid tumors often exhibit increased metabolic activity, as evidenced by enhanced glucose uptake on positron emission tomography (PET) with use of (18)F-fluorodeoxyglucose (FDG). The incidence of new thyroid lesions found on routine FDG-PET has not been previously reported.

METHODS

A retrospective review of all patients who underwent FDG-PET imaging at our institution from June 1, 1996, through March 15, 2001, identified patients with a newly diagnosed thyroid lesion. Thyroid incidentaloma was defined as a thyroid lesion seen initially on FDG-PET in a patient without a history of thyroid disease. Available follow-up data were documented.

RESULTS

One hundred and two of 4525 FDG-PET examinations (2.3%) demonstrated thyroid incidentalomas. Eighty-seven of 102 patients had no thyroid histology because of other malignancies. Fifteen patients had thyroid biopsy: 7 (47%) with thyroid cancer, 6 (40%) with nodular hyperplasia, 1 with thyroiditis, and 1 with atypical cells of indeterminate origin. The average standardized uptake values were higher for malignant compared with benign lesions.

CONCLUSIONS

Thyroid incidentaloma identified by FDG-PET occurred with a frequency of 2.3%. Of the thyroid incidentalomas that underwent biopsy, 47% were found to be malignant. Given the risk of malignancy, patients with new thyroid lesions on PET scan should have a tissue diagnosis if it will influence outcome and management. Standardized uptake values may be helpful in predicting benign versus malignant histology.

Incidental focal thyroid uptake on FDG positron emission tomographic scans may represent a second primary tumor

PURPOSE

This article discusses the value of incidental thyroid uptake of fluorodeoxyglucose (FDG) on whole-body positron emission tomography (PET) scans performed in patients with cancer. This issue has been reported diversely in the literature.

MATERIALS AND METHODS

Whole-body PET scans of four patients with cancer (two of them women; age, 49 to 78 years) in whom focal thyroid uptake was visualized and subsequently correlated with thyroid carcinoma based on cytologic or histopathologic data were reviewed. The clinical outcomes of these patients were analyzed retrospectively. Maximum and average standardized uptake values (SUVs) of thyroid accumulation were recalculated in all patients.

RESULTS

Two of the four patients referred for FDG PET scans had lung adenocarcinomas, one had prostate carcinoma, and one had an unknown primary tumor. Focal thyroid uptake was visualized, with maximum and average SUVs ranging from 3.7 and 2.3 to 53 and 34, respectively. These findings were correlated with cytologic (two patients) or histopathologic data (two patients) that indicated thyroid carcinoma. In two patients, their treatment was changed and total thyroidectomy was performed; in one of them the SUVs of the focal thyroid accumulation (maximum and average values of 7.9 and 4.8, respectively) were less than the cutoff values for thyroid cancer noted in the literature. The clinical condition of the other two patients did not permit additional investigation or treatment for thyroid carcinoma.

CONCLUSION

Increased focal thyroid uptake on whole-body FDG PET scans should not be overlooked, even when it is not marked, and should prompt further investigation to rule out cancer.

Surgical management of the patient with papillary cancer

Papillary cancer is the most common thyroid cancer occurring in all age groups and is usually an indolent tumor, and patients have an excellent prognosis. The majority of patients with papillary cancer do well. It is for the small number of patients who do poorly that it is critical to carry out the appropriate initial operation. The recognized primary treatment of papillary cancer is surgical excision, and the controversy regarding lobectomy versus total thyroidectomy continues. We favor total thyroidectomy because it eradicates multicentric disease, facilitates postoperative radioactive iodine ablation, and allows thyroglobulin levels to be used as a tumor marker for follow-up. Total thyroidectomy should be done by an experienced surgeon to decrease morbidity. Otherwise a total lobectomy on the side of the nodule with subtotal removal on the opposite side is preferred to avoid serious postoperative complications.

Therapeutic implications of prognostic factors in differentiated carcinoma of the thyroid gland

Differentiated thyroid carcinoma is a relatively indolent disease. Despite the usually favorable prognosis, differentiated thyroid cancer is fatal in some patients. In the past, treatment strategies were often based upon incomplete knowledge or inaccurate assumptions regarding the significance of the presenting characteristics of the tumor and patient. More recently, several large retrospective reviews have analyzed various presenting factors and have identified those that have prognostic significance and those that do not. Significant prognostic factors are age, primary tumor size, histology, grade, local tumor extension, and M stage. N stage appears to be a significant factor in older patients but not in younger patients. Gender, focality, and a history of prior irradiation are not significant prognostic factors. Using this knowledge, patients can be grouped into low, intermediate, and high risk groups. Prognostic factor and risk group analysis has facilitated the development of more rational treatment algorithms. Low risk patients can usually be treated with lobectomy and suppression therapy. For high risk patients, total thyroidectomy and adjuvant radioiodine is advocated. Treatment for patients in the intermediate risk group should be individualized. Prognostic factor and risk group analysis makes a selective approach to differentiated thyroid cancer possible. Such an approach can spare many patients the morbidity and expense of unnecessarily aggressive treatment without compromising outcome.

Total thyroidectomy: its role in the management of thyroid disease

Of 7812 patients treated for thyroid disease in the Endocrine Surgical Unit at the Royal North Shore Hospital, 825 underwent total thyroidectomy as an initial procedure. One third of these patients (269) were operated on for malignancy and the remaining 556 were treated for benign conditions such as multinodular goitre (405), Graves' Disease (79) and thyroiditis (45). The rate of recurrent laryngeal nerve palsy was 0.5% while permanent hypoparathyroidism occurred in 0.6% of cases, the low complication rate being due to the technique of capsular dissection employed in the Unit. The number of total thyroidectomies performed as a percentage of all thyroid operations has risen from 4% in 1970 to more than 40% in 1990. The majority of this increase has been due to surgery for multinodular goitre where the proportion of patients treated by total thyroidectomy now exceeds 80%. A similar but smaller increase has been seen in an analysis of the New South Wales figures for all other public and private hospitals. It is concluded that the complication rate from total thyroidectomy can no longer be used to argue against its use as the definitive operation for malignant disease of the thyroid. Furthermore, in view of the risks of re-operative surgery, total thyroidectomy should be considered the operation of choice for most benign disease affecting the whole thyroid gland such as multinodular goitre, thyroiditis, and in a significant number of goitres affected by thyrotoxicosis.

Papillary thyroid carcinoma: occurrence and types of lymph node metastases

Fifty-seven (35.6%) of 160 patients with papillary thyroid carcinoma had lymph node metastases at the primary treatment. Children and adolescents were most frequently affected (69.2%), followed by the age group of 21-40-year olds (38.8%). Those older than 40 had the lowest incidence of lymph node metastases (29.6%; p less than 0.05). One fifth of all patients had lymph node metastases as first indication of papillary thyroid carcinoma. Two thirds of these patients were 40 years old or younger. Lymph node involvement affected the jugular vein in nearly all cases (78.8%) and the upper mediastinum as well in just under 15%. Women predominated (67.5 vs. 35.3%; p less than 0.05) if there was intrathyroidal tumor growth with lymph node metastases which occurred most frequently in the age group of 21-40-year olds. On the other hand, men had the highest incidence (67.7 vs. 32.5%; p less than 0.05) of lymph node metastases in connection with tumor growth outside the organ. Fixed lymph node metastases occurred more often in men, particularly in those older than 40 years of age. A pT4 stage (tumor growth outside the organ, 66.7%) was often present at the same time. Especially young patients had a high incidence of lymph node metastases in connection with multifocal intrathyroidal tumor growth, the lymph node metastases often being substantially larger than the mostly occult foci of thyroid carcinomas. Cystic degenerations were occasionally mistaken for cervical cysts.

Trends in thyroid cancer incidence in Sweden, 1958-1981, by histopathologic type

Time trends in the incidence of malignant neoplasms of the thyroid were examined for Sweden for the period 1958-81, 5,838 cases being studied. Autopsy-diagnosed cases were excluded. Mean annual changes in the age-standardized rates over this period were 1.9% and 1.2% for women and men, respectively, for all thyroid carcinomas combined; 4.9% and 2.1% for papillary carcinoma; 0.9% and 2.1% for follicular carcinoma; and -1.0% and -2.1% for anaplastic carcinoma. Age, period and cohort models were fitted. There was a progressive increase in papillary cancer incidence for cohorts born since 1919. This increase cannot be satisfactorily explained as an artefact of trends in classification, and probably reflects a real increase in incidence. A less marked increase was seen for follicular cancer, and there was a decline for cohorts born since 1939. While the risk of papillary and anaplastic carcinoma was lower in iodine-deficient areas, follicular cancer risk was twice as high in these areas, for men only. There was a steady decline of anaplastic cancer in both sexes after 1965, largely attributable to a decline in cohorts born since 1924.

Squamous cell carcinoma of the upper aerodigestive tract associated with well-differentiated carcinoma of the thyroid gland

The association of squamous cell carcinoma of the upper aerodigestive tract with well-differentiated thyroid carcinomas has rarely been reported in the literature. We report 10 cases illustrating this occurrence. In eight cases, the thyroid carcinoma was discovered accidentally on histological examination of a single neck node, a neck node dissection specimen, an unexpectedly found thyroid nodule, or a systematically resected thyroid lobe, all during surgical treatment of an upper aerodigestive tract carcinoma. In the other two cases, metastatic thyroid neck nodes appeared during the follow-up of a patient with an upper aerodigestive tract carcinoma. No case of upper aerodigestive tract carcinomas was found during the follow-up of thyroid cancer patients. In most cases, adequate thyroid cancer surgery was performed simultaneously or later. Prognosis was essentially determined by the upper aerodigestive tract cancer.

Operative strategy for thyroid cancer. Is total thyroidectomy worth the price?

The authors conducted a retrospective analysis with 5- to 30-year follow-up on 109 patients in order to determine the optimum management of nonmedullary thyroid cancer. Results of total thyroidectomy were compared to partial thyroidectomy, among patients well matched for prognostic indicators. No differences in cancer mortality or recurrence rates were evident. However, there were significantly more complications when total thyroidectomy was employed. In view of these results, partial thyroidectomy is recommended as the treatment of choice for nonmedullary thyroid cancer.