[416] Thyroid Follicular Lesion of Undetermined Significance: A Single Center Experience

MJ Horne, D Chhieng, C Theoharis, K Schofield, D Kowalski, AJ Adeniran. Yale University School of Medicine, New Haven, CT

Background: The Bethesda 2007 Thyroid Cytology Classification defines follicular lesion of undetermined significance as a heterogeneous category of cases that are not convincingly benign nor sufficiently atypical for a diagnosis of follicular neoplasm or suspicious for malignancy. Others are placed in this category because of non-specific patterns, or compromising factors such as low cellularity, poor fixation or obscuring elements. In our institution, we refer to these cases as "indeterminate", and they are further sub-classified into two: 1) Low cellularity with predominant microfollicular architecture and absence of colloid (INa) and, 2) Nuclear features not characteristic of benign lesions (nuclear atypia) (INb). We reviewed these indeterminate cases seen over a period of eighteen months to document the follow-up trend using this 2-tier classification.
Design: A search of the cytology records was performed for the period between January 2008 and June 2009. All thyroid FNA cases were reviewed and the ones diagnosed as indeterminate were identified. Correlating follow-up FNA and/or surgical pathology reports were reviewed. The percentage of cases showing a malignancy was calculated.
Results: One hundred and seventy one indeterminate cases were identified, representing 2.8% of the 6205 thyroid FNA cases examined during the time under review (104 INa, 64 INb and 3 with both features). Records of follow-up procedures were available in 104 (61%) cases. Of the 59 cases of INa with follow-up, 35 (59%) had repeat FNA and 24 (41%) had surgical resection. In contrast 73% of cases of INb had surgical resection while only 27% had repeat FNA alone. Malignancy was identified in 20% of all indeterminate cases. This was disproportionately more in the INb (56%) compared to the INa (7%) cases. The benign diagnoses were predominantly hyperplastic nodules (goiter) in both groups, while Hashimoto's thyroiditis was more prevalent in the INb group.
Conclusions: A diagnosis of "low cellularity with predominant microfollicular pattern in the absence of colloid" (INa) does not carry the same implication as that of "nuclear features not diagnostic of benign lesions" (INb). The INb category needs a more aggressive follow up than the INa category and may justify an immediate referral for lobectomy. Despite the vague morphologic criteria for this diagnostic category, the indeterminate rate remains relatively low and falls within the NCI recommendation (<7%).
Category: Cytopathology

Tuesday, March 23, 2010 9:30 AM

Poster Session III # 90, Tuesday Morning


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