Role of planimetric analysis in diagnosing thyroid follicular lesions on fine needle aspiration biopsies - A study with histologic correlation

BACKGROUND: Follicular lesions represent a gray area of interpretation in fine needle aspiration biopsy (FNAB) of the thyroid, with as much as 25% inconclusive reports. We identified "predominantly follicular lesions" (PFLs) as the cytologic category most apt to take advantage of planimetric analysis to reach a more definitive diagnosis. STUDY DESIGN: Sixty-eight cases of FNAB were diagnosed as PFL among the 1,296 FNABs submitted to our institution between January 1994 and June 1995. These cases under went planimetric analysis with a Leica semiautomatic image analyzer. A smear from a colloid nodule was used as a reference slide. Nuclear areas, perimeters, form factors and maximum diameters were evaluated. Cases in which nuclear areas and maximum nuclear diameters values were found to be greater than or equal to 30% higher than the corresponding values found in the reference slide were reported to the clinician as suspicious for malignancy ("flagged" by the computer). These cases required closer follow-up with repeat FNAB within a month, ultrasound and nuclear imaging studies. Nineteen of these cases underwent surgical resection. RESULTS: Histologic reports diagnosed 9 cases of follicular carcinomas, 4 cases of follicular adenomas and 6 cases of nodular hyperplasia. When nuclear areas, perimeters and maximum diameters were all utilized, all the malignant lesions were reported correctly by the computer analysis as flagged, and all the benign lesions were reported as "not flagged." The sensitivity and specificity were 100%, and statistically significant correlations were proven. CONCLUSION: Although the above data provide strong evidence for the value of planimetric analysis in differentiating between follicular lesions, toe cannot reach definitive conclusions on the basis of such a limited number of cases. However, the results stimulated our current efforts in applying planimetry along with the evaluation of other biologic markers to a larger set of cases.