OBJECTIVE: To determine the accuracy of cytologic interpretation in the dia
gnosis of Hashimoto's thyroiditis (HT).
STUDY DESIGN: At Ottawa Hospital from 1987 to 1994, 1,638 fine needle aspri
ation biopsies (FNABs)from thyroid were performed. HT was suggested in 184
FNAB samples taken from 157 patients. Of the 184 aspirates diagnosed with H
T, 39 had corresponding surgical specimens taken from 31 patients. A retros
pective review of these FNABs and surgical pathology slides formed the basi
s of this study.
RESULTS: In 27 (69%) aspirates, HT tons diagnosed on both the FNAB and surg
ical specimens. In 10 of 27 FNABs an associated lesion was not sampled by F
NAB. In four of these 10 aspirates some of the cellular features of HT were
misinterpreted, and the possibility of an associated neoplasm could not be
ruled out. This resulted br four false positive diagnoses. In 12 (31%) FNA
Bs from nine patients, the cytologic diagnosis of HT was not confirmed hist
ologically. These cases included five Hurthle cell adenomas and one case ea
ch of follicular adenoma, nodular goiter, macrofollicular adenoma and malig
nant lymphoma. This resulted in five false negative diagnoses.
CONCLUSION: These results support the value of FNAB in the diagnosis of HT.
The presence of hyperplastic follicular cells on FNAB samples from HT may
mimic a follicular,neoplasm and result in a false positive interpretation.
Adequate sampling of the thyroid is important, particularly when there is a
n associated lesion. The diagnosis of lymphocytic thyroiditis should not be
made when only a few lymphocytes are present. Finally, pleomorphic Hurthle
cells may be present in aspirates from Hurthle cell neoplasms and underdia
gnosed as HT, especially when they are associated with a few lymphocytes.