Fine needle aspiration cytology (FNAC) of thyroid plays a pivotal role in guiding clinical management of thyroid lesions. With advancements in radiology and radiology guided aspirations, thyroid cytology including aspirates from subcentimetric and nonpalpable lesions have set forth greater challenges to the cytopathologist. FNAC classify thyroid lesions into benign and malignant categories. However, a set of lesions are indeterminate and cannot be clearly placed into benign or malignant ends of the spectrum based on the cytological features.
The thyroid FNAC did not have a uniform reporting format in the past, leading to ineffective communication with the clinician. The Bethesda System was formulated in 2007 as a universal standard format for reporting thyroid cytology, thus conveying uniform and unambiguous information. According to this system, lesions of thyroid were classified into 6 categories (I to VI). Bethesda system also predicts the risk of malignancy as well as provides management options for each category. Among the categories, III, IV and V pose diagnostic challenge to the cytologist and are considered as “indeterminate” lesions on cytology. The revised Bethesda system in the year 2017, has retained the 6 categories and recommends incorporation of molecular testing for the indeterminate lesions at the level of cytology and thus aid in taking management decision.
Our cytology department received a total of 1113 thyroid FNACs in the year 2017. The majority of cases (70%) belonged to Category II (Benign). Indeterminate categories constituted 11% of total cases – 7%, 2%, and 2% respectively belonging to Category III, IV, and V. Follow up surgery on these categories were present in 29%, 68% and 69.5% of cases respectively with malignancy risk of 46%, 67% and 81%. Surgical intervention was based on associated clinical and radiological parameters especially in Category III lesions.
With incorporation of molecular testing at the level of cytology, we aim to reduce the indeterminate lesions and classify them towards either benign or malignant ends of the spectrum. Certain molecular markers like BRAFV600E mutations also help to predict the disease progression and aid in management. Targeted therapies can also be applied based on it in advanced disease and alleviate unnecessary surgical interventions. We at Amrita, aim to give an integrated cytology report based on morphology as well as molecular testing in relevant cases.
Dr. Anish Mohan A
Assistant Professor, Department of Pathology,
Amrita Institute of Medical Sciences, Kochi, Kerala.