[412] Morphologic Pitfalls of Hashimoto's/Lymphocytic Thyroiditis on Fine Needle Aspiration and Strategies To Avoid Overdiagnosis

AM Harvey, LD Truong, DR Mody. Methodist Hospital, Houston, TX; Weill Cornell Medical College, New York, NY

Background: There has been an emphasis on identifying papillary carcinoma or lymphoma within a background of Hashimoto's/lymphocytic thyroiditis (H/LT). However, misdiagnosing a neoplasm on fine-needle aspiration (FNA) of a thyroid with only H/LT and how to avoid this pitfall have not been adequately addressed.
Design: This study aimed to identify specific cytomorphologic features that may lead to the overdiagnosis of neoplasm in a background of H/LT. We found, within a five year period, nine cases in which thyroid FNAs were classified as suspicious or positive for malignancy/neoplasm, but the subsequent thyroidectomy specimens showed only H/LT. The cytologic features of these nine cases (Group I) were compared to eight control cases (Group II) from the same time period, in which the thyroid FNAs were also diagnosed as “suspicious or positive”, but the tumors were confirmed against a background of H/LT on the thyroidectomy specimens (2 follicular adenomas and 6 papillary carcinomas). FNAs from both groups were re-evaluated for cytologic features commonly referred to in the cytology literature that may facilitate a correct diagnosis.
Results: Features most commonly leading to an overdiagnosis of papillary carcinoma in Group I were: pale, powdery or open nuclear chromatin, occasional nuclear grooves or holes, high cellularity with a microfollicular pattern, and a paucity of background lymphocytes. One helpful feature for differentiating H/LT from neoplasms was the presence of lymphocytes intimately infiltrating follicular groups. This likely overlooked feature was noted in most cases, even when background lymphocytes were scanty. In contrast, FNAs of true papillary carcinoma in Group II tended to display multiple typical cytologic features of papillary carcinoma in multiple cell clusters. These clusters were either devoid of infiltrating lymphocytes, or displayed only rare lymphocytes at their periphery. A microfollicular pattern with paucity of background lymphocytes was the major pitfall in cases diagnosed as suspicious for follicular neoplasms.
Conclusions: Features suspicious for papillary or follicular neoplasm are often seen in FNA of H/LT, leading to unnecessary surgery. Awareness of this diagnostic pitfall and recognition of differentiating cytologic features should avert the misdiagnosis.
Category: Cytopathology

Tuesday, March 23, 2010 9:30 AM

Poster Session III # 96, Tuesday Morning

 

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