Thyroid nodules are common lesions that present diagnostic challenges clinically. The detection of small nodules in glands that appear normal on palpation using ultrasonography (USG) highlights the prevalence and importance of nodular goiter. Although thyroid nodules are frequently observed, thyroid malignancies are rare, accounting for only 1% of all malignant tumors (1).
When a Papillary Thyroid Carcinoma (PTC) is smaller than 10 mm, it is referred to as Papillary Thyroid Microcarcinoma (PTMC), with its frequency in autopsy studies ranging from 4.7% to 9.9% (2,3). Incidental PTMC refers to the discovery of microcarcinoma in the histopathology of the thyroid in patients operated on for benign reasons. The detection rate in thyroidectomy specimens ranges from 11% to 35.3% (3,4).
There is no complete consensus in the literature regarding treatment. Some studies suggest follow-up is sufficient due to its indolent nature, while others emphasize the need for more aggressive treatment (4,5).
In this study, we aimed to present our rates of incidental papillary thyroid microcarcinoma (IPTMC) in patients identified with dominant cold thyroid nodules or nodules deemed benign by preoperative fine-needle aspiration biopsy (FNAB), and to compare our results with similar studies in the literature.
Materials and Methods
Between June 2006 and January 2010, 362 patients operated on for benign reasons were retrospectively evaluated. Clinical assessments were conducted for all patients. All patients underwent USG, laboratory tests (T3, T4, TSH), and scintigraphy when necessary. Patients with single nodules or positive/suspected FNAB results preoperatively were excluded from the study.
Patients known to have tumors preoperatively, those requiring intraoperative frozen sections based on FNAB results, or those with postoperative tumors larger than 1 cm were excluded. Patients diagnosed with multinodular goiter (MNG) and those undergoing bilateral intervention were included. Patient demographics, pathology results, treatment, and outcomes were discussed.
Results
A total thyroidectomy (TT) was performed on 347 patients, and near-total thyroidectomy (NTT) was performed on 15 patients (less than 2 g of tissue remaining). Histopathological examination revealed IPTMC in 14 patients (Table 1). Of the 14 cases, 11 had MNG and 3 had follicular adenoma preoperatively, and all were female. The mean age was 58.07 years (range 36-73). The mean tumor size was 3.7 mm (range 1-8 mm). Only one case exhibited capsule invasion, multifocality, and PTMC in three foci.
Since total thyroidectomy was performed on all 14 cases, no additional surgical intervention was planned. Suppression therapy was applied to all patients, and radioisotope therapy (RAI) was administered to only one case due to capsule invasion and multifocality. There were no mortalities. Two patients experienced transient hypocalcemia, but no other complications were noted. No family history or radiation exposure was identified. During a mean follow-up period of 27.8 months (range 10-35 months), no recurrences, distant metastases, or mortalities were observed.
Discussion
Thyroid function tests, ultrasonography, and scintigraphy are routinely used in diagnosing thyroid nodules. However, definitive differentiation between benign and malignant nodules cannot be achieved using these methods alone. FNAB, when evaluated alongside other diagnostic methods, provides more accurate information about thyroid nodule pathology.
Today, FNAB is the most valuable method for diagnosing thyroid nodules (6). Its limitations include the skill of the aspirator, the pathologist's experience, and difficulty distinguishing follicular adenomas from follicular carcinomas. Over the past decade, FNAB has become a globally accepted, accurate, and definitive diagnostic procedure. The success of FNAB in MNG may not be as high as in solitary nodules, and up to 80% of thyroid cancers may be undetected (6,7).
In a study by Tunca et al., FNAB was performed on dominant nodules larger than 15 mm under USG guidance, with a sensitivity of 71% and specificity of 96% (8). In the same study, false negatives were observed in 2 cases (3.5%) and false positives in 1 case (1.7%). In our study, all patients underwent FNAB, and despite negative FNAB results in 14 patients (4.5%), papillary microcarcinoma was found in pathology.
The incidence of IPTMC varies widely in the literature, from 6:4 male predominance to 8:3 female predominance. In our study, all cases were female, which we consider coincidental.
In recent years, TT has been preferred for patients with MNG operated on for benign reasons (10,11,12). TT or NTT can be performed with acceptable morbidity rates. This approach reduces recurrence rates and prevents the oversight of multifocal, bilateral PTMC (13). Giles et al. reported that TT and NTT significantly reduced the need for complementary thyroidectomy in incidentally detected thyroid cancers (10).
Our study supports the use of TT or NTT as the appropriate treatment option for patients with suspected MNG to avoid missing PTMC and the risks of secondary interventions.
