Can misdiagnosis in pre-operative FNAC of thyroid nodule influence surgical treatment?

Pre-operative cytology in thyroid disease remains the most appropriate diagnostic test for defining the nature of a thyroid nodule before surgical excision.

We selected the most recent 825 surgical thyroid procedures performed in our institution from January 2004 to June 2007; 776 were total thyroidectomies, 23 were lobe-isthmectomies, and 26 were radical neck dissections. We distributed the data based on pre-operative cytology. Each cytological diagnosis was compared to results obtained by definitive histology. Tumors were called incidentalomas if they consisted of a neoplastic focus with a low grade of aggressiveness, as demonstrated by dimension <5 mm, non-aggressive histological subtype.

Of the 541 cases of benign disease, 417 were confirmed as benign. The other 124 cases are listed as follows: 29 follicular adenoma; 76 papillary carcinoma (35 found as incidentalomas), and 19 follicular carcinoma (3 incidentalomas). Cytology suggestive of papillary carcinoma was correct in 95.2% of cases (119/125). The 135 tumors termed "follicular neoplasm" were staged on pathology thus: 56 adenoma (41.4%), 26 carcinoma (19.2%), 13 (9.6%) absence of follicular proliferation, 38 (28.1%) papillary follicular variant, 2 (1.4%) undifferentiated cells. Medullary carcinomas were both confirmed. The "suspicious group" exhibited no malignancy on fine needle aspiration cytology (12 of 21; 57%).

Cytology has good reliability in malignant lesions. Incidental tumors occurring in benign disease have little impact on clinical and surgical management; "follicular neoplasm" posed two problems - the impossibility of identifying the nature of the tumor, as well as the newer difficulty in distinguishing papillary follicular subtype.