1

Introduction

Increasing use of fine-needle aspiration (FNA) for diagnosis of thyroid nodules has become standard and often the primary diagnostic criterion for operative management. Although decisions for surgical resection are often clear, follicular patterned nodules cause a diagnostic dilemma and are risk stratified according to the likelihood of malignancy. Indeterminate nodules have commonly been divided into follicular lesions and follicular neoplasms. As there are controversies regarding the classification of follicular patterned lesions on histologic specimens , this proves even more difficult with cytology. Diagnosis is based on findings such as high cellularity, lack of colloid, microfollicules, nuclear atypia or enlargement, and syncytial clusters . Unfortunately none of these alone are very sensitive or specific and can be seen frequently with both benign non-neoplastic lesions and carcinoma . Attempts have been made to standardize the classification and reporting of thyroid FNA to allow for effective risk stratification and communication between pathologists and clinicians. However, it has been shown that there is still a significant lack of inter- and intraobserver reproducibility for thyroid FNA. One study found that over half of follicular lesions and neoplasms had discrepant cytologic diagnosis when compared among two pathologists .

The most commonly used current diagnostic classifications come from the 2007 National Cancer Institute (NCI) Bethesda System for Reporting Thyroid Cytopathology and the 2009 American Thyroid Association (ATA) guidelines . The Bethesda system classifies thyroid FNAs in one of six diagnostic categories: non-diagnostic, benign, follicular lesion of undetermined significance/atypia of undetermined significance (FLUS/AUS), follicular neoplasm/suspicious for follicular neoplasm (FN/SFN), suspicious for malignancy, and malignant . The ATA guidelines use comparable diagnostic criteria as well. Accompanying these are accepted malignancy rates associated with each diagnosis which are used by surgeons for operative decision-making and preoperative counseling. The malignancy rates for indeterminate thyroid FNAs at our institution empirically seemed to be higher than these “accepted” values, and we sought to validate this hypothesis.

2

Materials and methods

After IRB approval was obtained from Wayne State University, patients were identified by using CPT codes for any type of thyroidectomy performed by Wayne State University head and neck otolaryngology faculty from 2000 to 2012. Of the 570 patients who underwent thyroidectomy, 362 were identified who had an accompanying preoperative thyroid FNA report. Exclusion criteria included a lack of adequate documentation from either cytology or final histopathology, outside pathology which was not internally reviewed, other non-thyroid pathologies such as squamous cell carcinoma, and FNA on the opposite lobe of surgical resection. Cytology reports were categorized into the most appropriate diagnostic criteria. Reports with unclear or conflicting terminology were not used. For our purposes we regarded “follicular lesion of undetermined significance”, “atypia of undetermined significance”, “suspicious for follicular lesion”, “cellular follicular lesion” and “Hurthle cell lesion” to be regarded as “follicular lesion”. Diagnoses of “suspicious for follicular neoplasm”, “suspicious for neoplasm”, and “Hurthle cell neoplasm” were regarded as “follicular neoplasm”. Both Hurthle cell lesions and neoplasms were included since they carry a similar malignancy rate as those without Hurthle cell features in the literature and in our series.

2

Materials and methods

After IRB approval was obtained from Wayne State University, patients were identified by using CPT codes for any type of thyroidectomy performed by Wayne State University head and neck otolaryngology faculty from 2000 to 2012. Of the 570 patients who underwent thyroidectomy, 362 were identified who had an accompanying preoperative thyroid FNA report. Exclusion criteria included a lack of adequate documentation from either cytology or final histopathology, outside pathology which was not internally reviewed, other non-thyroid pathologies such as squamous cell carcinoma, and FNA on the opposite lobe of surgical resection. Cytology reports were categorized into the most appropriate diagnostic criteria. Reports with unclear or conflicting terminology were not used. For our purposes we regarded “follicular lesion of undetermined significance”, “atypia of undetermined significance”, “suspicious for follicular lesion”, “cellular follicular lesion” and “Hurthle cell lesion” to be regarded as “follicular lesion”. Diagnoses of “suspicious for follicular neoplasm”, “suspicious for neoplasm”, and “Hurthle cell neoplasm” were regarded as “follicular neoplasm”. Both Hurthle cell lesions and neoplasms were included since they carry a similar malignancy rate as those without Hurthle cell features in the literature and in our series.

3

Results

Charts from 570 patients who underwent thyroidectomy were reviewed. Of these, 362 were identified who also had an FNA report associated with the site of resection. The malignancy rates for lesions that were rated as benign, atypical follicular lesions, follicular neoplasm, suspicious for malignancy, and malignant were 13%, 46%, 49%, 83% and 97%, respectively. Additionally, the rate of malignancy for indeterminate nodules (those of atypical follicular lesion or follicular neoplasm) was 47%. These findings are much higher than the ATA and NCI quoted risk of malignancy. When micro-carcinomas were excluded, the malignancy rates were 3%, 38%, 40%, 80% and 97% respectively. Additionally, the rate of malignancy for indeterminate nodules when micro-carcinomas were excluded was 38%. These rates are still significantly higher for the atypical follicular lesions and follicular neoplasms, but they are similar to ATA and NCI criteria for suspicious for malignancy and malignancy categories ( Table 1 ).

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