|
THYROID IMAGING WITH TREATMENT CAPABILITIES |
|
"Warm" or functionally nondelineated nodules have function equivalent to normal thyroid tissue. "Cold" nodules, either hypofunctioning or nonfunctioning, are seen as defects on the scan. The approximately 10% of nodules that are functioning are exceedingly unlikely to be malignant. "Warm" and "cold" nodules can be malignant in approximately 5 to 8% of cases. Thus, the limitation of the nuclear thyroid scan is that only about 10% of nodules are delineated as benign; hence, results are uncertain in the remaining 90%. The isotopes commonly available for thyroid imaging include 131I, 99m Tc, and 123I. Technetium scanning is quick and convenient, but results may be misleading in a small number of patients. The shortcoming is that a few technetium-identified "warm" or "hot" nodules may be hypofunctional on iodine scanning, and a few of these nodules with discordant technetium and iodine scans are malignant. 131I is clearly the most effective isotope for thyroid cancer follow-up evaluation, but for routine scanning of the thyroid, 131I exposes the patient to excessive thyroidal irradiation and should not be used. 123I scanning is recommended because it avoids the problem with technetium and also the radiation burden of 131I. A thyroid scan by any commonly used isotope does not identify the presence of a nodule but rather assesses regional uptake or function. As an initial study, it is particularly useful in evaluating asymmetric nodular goiter, hypertrophied lobes simulating nodules or masses, and substernal masses. As a secondary study, scanning is useful for patients with suppressed TSH levels. The scan may reveal an autonomous or functioning nodule. Patients with nodules found to be cytologically benign by fine-needle aspiration (FNA) biopsy would not benefit from subsequent nuclear imaging unless thyroid hormone suppression is being considered as treatment; then a nuclear scan will identify functioning nodules, for which administration of thyroid hormone could lead to thyrotoxicosis. In suspicious or nondiagnostic FNA nodules, nuclear imaging might also be diagnostically helpful. Most clinical endocrinologists have evaluated thyroid nodules for a long time with nuclear scanning, are comfortable interpreting the results, and are aware of the limitations. FNA BiopsyA major advance in the diagnosis of the thyroid nodule has been achieved with the perfection and common use of FNA biopsy. FNA biopsy is now believed to be the most effective method available for distinguishing between benign and malignant thyroid nodules. AACE advocates FNA biopsy of all thyroid nodules when the possibility of malignancy is appreciable and when the patient is a candidate for surgical or nonsurgical cancer treatment. AACE also recommends FNA biopsy even when suspicion of cancer is very high because foreknowledge of the cancer cell type aids in the planning of the surgical procedure. Several FNA biopsy series and reviews have been performed to establish the efficacy of this procedure. Members of the committee for these guidelines have reviewed these series. Mazzaferri et al. reported on 10 series with 9,119 patients: results of needle biopsy were benign in 74%, inadequate or suspicious in 22%, and malignant in 4% of those series. Gharib et al. evaluated 7 series with a total of 18,183 FNA: 69% were benign, 27% were suspicious or nondiagnostic, and only 4% were malignant. The suspicious or nondiagnostic group were approximately equally divided; of the suspicious group of nodules, 10 to 30% were ultimately malignant. Cytopathologic DiagnosesThe following benign and malignant diagnoses can be made by thyroid FNA biopsy if an adequate specimen is obtained.
Intermediate or suspicious diagnoses include the following:
The Autonomously Functioning "Hot" Thyroid NoduleFor practical purposes, autonomous thyroid nodules are never malignant. Although rare exceptions to this have been reported, FNA biopsy is seldom necessary if the nodule is known to be autonomous. All patients with toxic autonomous thyroid nodules require treatment. These toxic nodules tend to be large (>2.5 cm), and physical and laboratory features of thyrotoxicosis are present. Radioactive iodine (131I) is the treatment of choice for most patients with toxic nodules. Thyroid lobectomy is appropriate for younger patients, those with larger nodules, those whose nodules have a substantial hemorrhagic or cystic component, or any patient who prefers surgical treatment. The clinician should discuss the relative merits of these approaches and, if possible, the patient should participate in the treatment decision. Many patients with autonomous nodules and subclinical hyperthyroidism (normal thyroxine and triiodothyronine levels and suppressed TSH) should be treated at the time of diagnosis. These patients may deny symptoms, but of special concern is the older patient who should be treated more aggressively because of the cardiac implications of subclinical hyperthyroidism. Younger, healthy patients with autonomous thyroid nodules and minimally suppressed TSH levels could be monitored clinically for a finite period without treatment because a small but significant proportion of these nodules may undergo cystic degeneration or infarct; thus, the subclinical hyperthyroidism would be resolved. Clinical judgment is important in the management of these cases. When treatment is being considered, the options are similar to those for the toxic autonomous thyroid nodule. Functioning thyroid nodules with normal TSH need not be treated but are more difficult to diagnose. Thyroid hormone-suppressed nuclear imaging is useful in selected cases in distinguishing autonomous from nonautonomous nodules. In instances of ambiguity related to thyroid nodule function, FNA biopsy is indicated. Patients with these autonomous nodules should undergo follow-up and periodical reassessment. The time interval is variable. The Incidentally Discovered Small Thyroid NoduleWith carotid Doppler ultrasonography-or, less commonly, parathyroid ultrasonography-a high number of incidental thyroid nodules are being identified in older patients. This result is not surprising, when the prevalence of thyroid nodules in this group is considered. Most are 1 cm or less, partially cystic, and not palpable. Often, multiple nodules have been reported. The index of suspicion for cancer in these nodules is indeed very low, and most can be followed with no further imaging studies or biopsy. In cases of a sonographically suspicious nodule (irregularly contoured or large and nonpalpable), ultrasound-guided FNA biopsy is appropriate. Thyroid Nodules in Pregnancy and ChildhoodThyroid nodules discovered during pregnancy should be managed the same as a nodule discovered in a nonpregnant patient except that radionuclide scanning is contraindicated. FNA biopsy can be performed during pregnancy or deferred until the postpartum period if the pregnancy is advanced. If the nodule is malignant, surgical removal is relatively safe during the second trimester, or the procedure can be deferred until after the pregnancy. Clearly, most pediatric thyroid nodules are benign and can be managed medically. Surgical intervention is imperative only when the cytologic diagnosis is suspicious or malignant. |