hashimoto 's thyroiditis ( ht ) has a prevalence rate of 1 - 4% and incidence of 30 - 60/100000 population per year .
fine needle aspiration cytology ( fnac ) is highly sensitive in diagnosing ht , with a diagnostic accuracy rate of 92% , however , diagnosis of ht is likely to be missed in smears showing cytological evidence of hyperplasia as in grave 's disease or abundant colloid .
follicular cells that exhibit some features of papillary carcinoma and a minimum lymphoid population in the background can be a diagnostic pitfall .
sometimes there might be marked hurthle cell change with sparse inflammatory cells mimicking hurthle cell neoplasm .
a 56-year - old female presented with a swelling in front of the neck since 10 years .
it was insidious in onset and gradually progressive , initially 3 cm  2 cm to current 6 cm  5 cm .
there was no history of pain , difficulty in swallowing , change in voice and palpitation .
local examination revealed a midline solitary neck swelling , which moved with deglutination , and was non - tender .
thyroid function tests revealed normal t3 and t4 levels but increased thyroid stimulating hormone ( tsh ) . on sonography ,
fnac from multiple sites revealed high cell yield consisting of hurthle cells with delicate vascular channels running through these cells [ figure 1a ] .
pleomorphic hurthle cells had moderate to abundant cytoplasm , central to peripheral nucleus , increased nuclear - cytoplasmic ratio , binucleate forms were also noted [ figure 1b ] .
these cells were arranged in crowded three - dimensional aggregates , sheets , and in microfollicular pattern .
background showed sparse lymphocytes , scant colloid , and erythrocytes [ figure 1c and 1d ] .
cytological diagnosis of hurthle cell neoplasm , with differential diagnosis of medullary carcinoma - oncocytic variant was considered .
microphotograph of fnac smears showing ( a ) high cell yield consisting of hurthle cells with delicate vascular channels ( giemsa , 40 ) , ( b ) hurthle cells showing anisokaryosis with few binucleate forms ( giemsa , 100 ) , ( c , d ) hurthle cells arranged in cohesive clusters , microfollicular pattern and discretes , with scant colloid and sparse lymphocytes in the background ( h and e , 40 , h and e , 400 ) the patient subsequently underwent total thyroidectomy with partial neck dissection .
grossly , specimen consisted of both lobes of thyroid with isthmus . left lobe measured 6 cm  3 cm  2 cm ; cut surface was unremarkable .
surface revealed a well - demarcated grey brown to grey white nodule which measured 6 cm  5 cm with foci of colloid [ figure 2a ] .
gross photograph ( a ) cut surface of thyroid lobes showing a well - demarcated nodule in the right lobe and the left lobe was unremarkable , ( b ) microphotograph showing lymphocytic infiltration with germinal centre ( h and e , 40 ) , ( c ) thyroid follicles of varying sizes containing colloid with marked hurthle cell metaplasia ( h and e , 100 ) , ( d ) hurthle cells with eosinophilic granular cytoplasm , few binucleate forms were seen ( h and e , 400 ) microscopically , both lobes of the thyroid showed lymphocytic infiltration with germinal centres [ figure 2b ] , and thyroid follicles of varying sizes contained colloid with marked hurthle cell metaplasia [ figure 2c and 2d ] . hence diagnosis of hashimoto 's thyroiditis with marked hurthle cell change was considered .
the first report of chronic thyroiditis , struma lymphomatosa was described by hakaru hashimoto in 1912 , which bears his name .
patients usually present with a diffuse enlargement of the thyroid gland or less frequently with one or two prominent nodules .
this increase in incidence has been linked to excess iodine intake , particularly in coastal areas .
it is important to diagnose ht because patients subsequently become hypothyroid and require lifelong thyroxin supplementation .
also there is an increased risk of extranodal marginal b cell lymphoma in patients with ht .
the frequency of carcinoma in patients with ht varies between 0.5 and 23.5% which emphasizes the need for long - term follow - up .
it is also important not to over - diagnose this entity as neoplasms so that unnecessary surgery can be avoided .
ht , on fnac smears , is diagnosed by oxyphilic ( hurthle ) cells , infiltration of follicles by lymphocytes / plasma cells and the presence of moderate amount of colloid in the background .
fnac is considered superior as well as more cost - effective in diagnosing ht than antibody screening . despite its superiority fnac
sometimes an overlap in the cytomorphological features of ht with other lesions like multinodular goiter with degenerative changes , follicular neoplasm , hurthle cell neoplasm , papillary carcinoma , reactive lymphnode and lymphoma can be seen .
the false negative rate ( fnr ) is defined as the percentage of patients with benign cytology in whom malignant lesions are later confirmed on thyroidectomy .
ashcraft and van herle noted that fnr results varied in reported series from 2 - 50% and that among 1330 patients , all of whom had a histological examination , the fnr was 1.7% .
campbell and pillsbury analyzed combined data from 912 patients with benign cytological results who had a histological examination and found an fnr between 0.5% and 11.5% , with a pooled rate of 2.4% .
again , the fnr may be higher if patients with negative cytological results were followed up for months or years . in a study by boey and
colleagues , 365 patients with benign cytological results were followed for a mean of 30 months and they found two cancers .
grant and colleagues also studied 439 patients with benign cytological results who were followed up for 6.1 years and found three patients with malignancies .
the false positive rate ( fpr ) indicates that a patient with malignant fnac result was found on histological examination to have a benign lesion .
caruso and mezzaferri reported an fpr of less than 6% while campbell and pillsbury reported a rate of 1.2% . in one series they reported two cases as malignant but turned out to be hashimoto 's thyroiditis and nodular colloid goiter with focal areas of adenomatous hyperplasia .
the fpr was 3.9% which agreed with other series that ranges from 0 - 8% . in our case
the diagnosis made based on the cytology was hurthle cell neoplasm , but on histopathology it turned out to be hashimoto 's thyroiditis .
others have reported similar results , failure to demonstrate lymphocytes and to appreciate the non - neoplastic nature of hurthle cells were the causes behind the failure in these cases .
cytological features favoring a diagnosis of thyroiditis over neoplasm in a hurthle cell - rich smear include the absence of poorly organized cell clusters having nuclear pleomorphism , particularly anisonucleosis of hurthle cells .
potential pitfalls are cytologic atypia occurring in ht , abundance or scarcity of background inflammation , low cell yield , coexisting toxicity and malignancies .
but epithelial preponderance over inflammation , nuclear crowding , severe atypia and cell discohesion should raise the possibility of a neoplasm in spite of other features of ht .
fnac is a safe , sensitive and specific technique in the initial evaluation of thyroid nodules .
a correct cytological diagnosis can be achieved in the majority of cases , thus obviating the need for a surgical intervention . a careful and diligent search for various cytological features and accurate
sampling can help in reducing the number of indeterminate , false - positive and false - negative diagnoses .
 hashimoto 's thyroiditis is the second most common thyroid lesion next to goiter diagnosed on fine needle aspiration cytology ( fnac ) . 
 it is also an important cause for hypothyroidism . 
 fnac plays a significant role in the diagnosis of thyroid lesions due to its simplicity and low cost . 
 it can accurately diagnose hashimoto 's thyroidits in most patients . 
 however , a small percentage of cases may be missed due to the inherent limitations of this procedure and the varied cytomorphology of this lesion . therefore thorough cytological evaluation and an integrated approach 
 are necessary to pick up correct diagnosis and to avoid unnecessary surgery . 
 we present a 56-year - old female with solitary thyroid nodule diagnosed as hurthle cell neoplasm on fnac , but subsequent histopathological diagnosis following resection revealed hashimoto 's thyroiditis with marked hurthle cell change . 
Introduction
Case Report
Discussion
Conclusion