Abstract
Ultrasonography (US) is the most sensitive imaging method for detecting cervical metastases after thyroidectomy for papillary thyroid carcinoma (PTC) and is superior to diagnostic whole-body scan (DxWBS) (1,2). Although US is known to be operator dependent, no study to our knowledge has evaluated the impact of this on the sensitivity of US to detect lymph node metastases. Therefore, a prospective study was performed.
Patients with PTC seen by me in a 1-year period and who had total thyroidectomy followed by remnant ablation with 5.5 GBq 131I were studied if they had complete tumor resection, their posttherapy WBS showed no ectopic uptake, they were at high risk for local recurrence because >10 lymph nodes were affected (3), their clinical examination was normal, and they had negative tests for antithyroglobulin (Tg) antibodies at 6 months after ablation. The study was approved by the Ethics Committee of Santa Casa de Belo Horizonte and written informed consent was obtained from all subjects.
Fifty-two patients (36 women and 16 men; age: 16–78 years, median: 48 years) were included. The first US (US-1) was carried out at a diagnostic imaging center, where only radiologists performed the examination. The request form indicated that this was to look for lymph node metastases from PTC in a patient with a high risk of local recurrence. The examiners were unaware that their readings were part of a study. The reports were grouped as follows: (a) normal US when lymph nodes were not noted in the report or said not to be visualized; (b) US showing “reactive or inflammatory lymph nodes”; (c) US read as “lymphadenopathy whose etiology has yet to be defined,” without suggestions regarding their etiology; (d) US read as “suspicious lymph nodes or lymph nodes compatible with malignancy.”
A second US (US-2) was performed within a maximum interval of 15 days by a professional considered to be a radiologist par excellence by the author (although with only 5 years of experience in thyroid US). He also was unaware that his readings would be used in the study and patients were explicitly asked to omit information that they had undergone a previous US. US-1 and US-2 were performed with a linear multifrequency 10-MHz transducer. Patients with the “c” and “d” US readings had fine needle aspiration cytology (FNAC) (cytology and Tg measurement in needle washout fluid). Finally, a DxWBS was performed using standard protocol in all patients.
Twenty-one patients had a “normal” US-1 result but US-2 identified “suspicious” lymph nodes that were metastatic in two of these patients. US-1 revealed “reactive or inflammatory lymph nodes” in 23 patients, but US-2 led to their reclassification or identified additional “suspicious” lymph nodes that corresponded to metastases in 4 of these patients. All eight patients in whom US-1 showed “suspicious lymph nodes or lymph nodes whose etiology has yet to be defined” were also classified as “suspicious” upon US-2. After US-1, only eight patients required investigation (FNAC) and six cases of metastases were diagnosed. After US-2, 16 patients required investigation and 12 cases of metastases were diagnosed. A review of the images and reports of the six patients with metastases detected only by US-2 was requested from the radiology center, but there was no change in the initial conclusion.
This study showed that, at least in one institution, up to 50% of the sensitivity of US for cervical metastasis might be different among operators even when all were told that the patients were at high risk and all examiners operated in a specialized, high-volume setting. All affected lymph nodes discovered only by US-2 measured >5 mm and therefore required further workup (FNAC). No lymph nodes were detected by DxWBS, and stimulated Tg was <10 ng/mL in five or six patients. As a consequence, other imaging methods were not indicated and the detection of these metastases by other means was therefore unlikely.
This study calls attention to the fact that the sensitivity of US in the detection of cervical metastases of PTC might be compromised by up to 50% depending on the examiner, and that metastases not detected by US of lower sensitivity would not be diagnosed otherwise when following current recommendations. There are obvious limitations in this study such as the fact that it involved only one institution. We believe that standardized ultrasonographic characteristics that define lymph nodes as suspicious (4) may minimize differences between operators, but larger studies are needed and these should be the basis for well-established recommendations.