Occult papillary microcarcinoma of the thyroid-apotential pitfall of fine needle aspiration cytology?

H R Harach, E Saravia Day, S B Zusman

AbstractThe use of fine needle aspiration cytologydetected papillary carcinoma in twopatients with multinodular goitremeasuring 07 cm and 0-9 cm indiameter, respectively. Like most of thecases from previous large series, thetumours progressed slowly as shown byabsence of enlarged glands on surgicalexploration and no clinical signs ofmetastasis after two and five years offollow up. This study shows that aspira-tion cytology can detect a virtuallyharmless occult papillary carcinomathat will oblige patients to have surgery.

This very occasional "pitfall" of fineneedle aspiration should not precludethis well known beneficial method frombeing used in the management of thyroiddisease.

Fine needle aspiration (FNA) cytology is an

accurate and selective method for diagnosingthyroid disease. Its application reduces theneed for surgery with the attendant risks topatients, and it is cost effective.' 2 Occultpapillary carcinomas of the thyroid occur

frequently in systematic necropsy studies andmay also be discovered incidentally duringsurgery for an unrelated thyroid lesion.7These tumours may present clinically withregional metastases, but their prognosis isexcellent and not life threatening.3'6 7 Wereport two patients with occult papillary car-

cinoma of the thyroid incidentally detected byFNA that, in our opinion, led to virtuallyunnecessary surgical intervention.

Pathology Service,Dr A OnativiaEndocrinology andMetabolism Hospital,Salta, ArgentinaH R HarachS B Zusman

Department ofSurgery, Dr AOnativiaEndocrinology andMetabolism Hospital,Salta, ArgentinaE Saravia DayCorrespondence to:Dr H Ruben Harach,Department of Pathology,University of Wales Collegeof Medicine, Heath Park,Cardiff CF4 4XN

Accepted for publication23 October 1990

Case reportsTwo female patients aged 43 and 25 years,respectively, presented with a lump in theneck. After palpation multinodular goitre was

diagnosed. A thyroid scintigram showedirregular radioiodine uptake in nodular areas

from both lobes. Routine laboratory analysesand studies of thyroid function were withinthe normal ranges. Thyroid FNA was per-formed on both patients. The right thyroidlobes were chosen because they showed thedominant nodules as described in our

previous study.2 Smears showed epithelialcells individually and arranged in sheets andclusters containing nuclei that were irregularin shape. They also showed overlapping,prominent nucleoli, and sometimes nuclear

cytoplasmic inclusions and grooving (figs 1and 2). A cytological diagnosis of papillarycarcinoma was made and the patients under-went subtotal thyroidectomy.

Frozen sections of thyroid were cut at 3-5 mm intervals and showed multiple, welldemarcated colloid nodules of various sizes.The right lobes from both thyroids alsoshowed a whitish hard 0 9 cm nodule anda 0 7 cm cystic lesion, respectively, thathistologically corresponded to papillarymicrocarcinomas of the thyroid. Surgicalexploration of bilateral cervical lymph nodesshowed no abnormalities.Diagnoses of multinodular goitre and

papillary microcarcinoma were confirmed on

permanent sections from both patients. Oneof the tumours was mainly composed oftrabeculae and microfollicles (fig 1); the cystictumour showed mainly papillary and follicularstructures (fig 2). In both cases the neoplasticcells showed irregular and sometimes palenuclei, prominent nucleoli, some nuclearcytoplasmic inclusions and grooving (figs 1

and 2). The capsule of the cystic carcinomashowed an occasional psammoma body, as

well as haemorrhagic changes and an inflam-matory reaction probably due to the needlepass (fig 2). The patients were well and free ofdisease five years and two years after diagnosis.

DiscussionA histological diagnosis of papillary micro-carcinoma according to the WHO classificationwas made in both cases as the tumours were

smaller than 1 cm in diameter.8 Nucleargrooves and cytoplasmic inclusions are diag-nostic cytological variables that have also beendescribed in aspirates from clinically manifestpapillary carcinomas.9 The term occultpapillary carcinoma is also used for tumourssmaller than 1 5 cm in diameter,356 butnowadays it is preferred for tumours with no

clinical signs'" as in our cases.The cytological features of clinically evident

papillary carcinomas smaller than 1-5 cm indiameter have been described." A fortuitousfinding of an occult focus (probably larger than1 cm) of a multicentric papillary carcinoma byFNA has been reported. Thyroid scan re-

evaluation showed this to be a cold nodule.'2The two occult papillary carcinomas inciden-tally detected by FNA would not have beendetected by thyroid scintigraphy due to theirsmall size. This is not unexpected as theprevalence of these tumours is high in sys-tematic necropsy studies"5 with an incidence

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Harach, Saravia, Day, Zusman

Figure 1 Papillarymicrocarcinoma withdominant trabecularcomponent infiltrating thethyroid capsule(haematoxylin and eosin).Inset: aspirate showingneoplastic cells withirregular nuclei containingprominent nucleoli,grooving (large arrow)and cytoplasmic inclusion(small arrow)(Papanicolaou).

of up to 36%, a figure much lower than wouldbe expected if thyroids had been examinedonly histologically.5 Most occult papillary car-cinomas are smaller than 1 cm in diameter buttheir size range is not comparable in differentseries because the sections have beenexamined by different workers.5Whether these tumours would have become

clinically manifest is not known. They were

intrathyroidal as no lymph node disease wasfound during surgical exploration and noclinical signs of metastases were presentduring the two to five years of follow up. Mostoccult papillary carcinomas found by accidentare confined to the thyroid according to largesurgical and necropsy series.367 13 14 Theprevalence of regional micrometastases was16% in a series of systematic lymph node

Figure 2 Cysticpapillary microcarcinomawith dominant papillarycomponent. At theinterface between tumourand surrounding thyroidtissue there are twohaemorrhagic lakes with ahistiocytic reaction,possibly as a consequenceof traumatic needle pass(haematoxylin and eosin).Left inset: neoplastic cellswith irregular nucleishowing prominent nucleoliand grooving (arrows)(Papanicolaou). Rightinset: nuclear cytoplasmicinclusion in a neoplasticcell close to a cluster ofnon-neoplastic cells (May-Grunwald-Giemsa).

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Occult papillary microcarcinoma

dissections.'3 Papillary carcinomas up to1 5 cm in diameter with regional lymph nodesmetastases, as well as clinically manifest largerintrathyroidal papillary carcinomas, havean excellent prognosis and are not lifethreatening.367 13 15 Distant metastases fromoccult papillary carcinomas are practicallynon-existent, as shown in a large necropsyseries'3 and, when clinically manifest, aresometimes unremarkable.""'8

In conclusion, FNA may eventually detect aharmless occult papillary microcarcinoma thatwill unavoidably lead to surgery as happenedin our cases. In our series this "pitfall"occurred twice in 1758 aspirates (0-1%) whichshould not interfere with the known beneficialuse of FNA cytology in the management ofthyroid disease.'2

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