Aspiration cytology of pediatric solitary papillary hyperplastic thyroid nodule: Potential pitfall

Archives of Pathology & Laboratory Medicine, Dec 2001 by Khurana, Kamal K, Baloch, Zubair W, LiVolsi, Virginia A

* Context.-Solitary papillary hyperplastic thyroid nodules (SPHTNs) are frequently encountered in children and teenagers. Although the histologic features are well described, to the best of our knowledge, cytologic findings have not been resorted.

Objectives.-To review the cytologic features of histologically proven SPHTNs and to identify the potential diagnostic pitfalls in cytologic diagnosis.

Materials and Methods.-Fine-needle aspiration cytology of 3 histologically proven SPHTNs was reviewed.

Results.-Two girls and 1 boy (ages 11, 12, and 15 years) were affected. The cytologic diagnosis in all 3 cases was suspicious for papillary thyroid carcinoma (PTC). The spectrum of cytologic findings included broad flat sheets and 3-dimensional clusters with fire flares. There was mild to moderate nuclear pleomorphism and nuclear atypia. Short nonbranching papillae with transgressing vessels shown to

represent hyperplastic papillae on histologic sections were identified in all cases. The background contained giant cells, histiocytes, and watery and inspissated colloid. Although nuclear grooves were identified in occasional cells, intranuclear inclusions were absent. A cell block section (1 case) and histologic sections of SPHTNs (2 cases) were immunohistochemically negative for cytokeratin 19.

Conclusions.-Fine-needle aspiration of SPHTNs may be difficult to interpret accurately and can result in false-positive diagnosis of PTC. Although it shares several cytologic features with PTC, the presence of fire flares and short nonbranching papillae, as well as lack of intranuclear inclusions and watery and inspissated colloid in SPHTN appear to be useful features that are helpful in distinguishing SPHTN from PTC. Negative immunohistochemical staining for cytokeratin 19 is useful in excluding a diagnosis of PTC. (Arch Pathol Lab Med. 2001;125:1575-1578)

Solitary papillary hyperplastic thyroid nodules (SPHTNs) frequently occur in children and teenagers.1 These nodules are clinically solitary and may be warm or hot on radionuclide scan. Grossly, these lesions are encapsulated and often show central cystic change.1,2 Histologically, they show prominent papillae that lack the nuclear characteristics of papillary thyroid carcinoma (PTC). Increasing acceptance of aspiration biopsy for diagnosis of adult thyroid nodules has also encouraged the use of fineneedle aspiration (FNA) in diagnosis and management of pediatric thyroid nodules in recent years.3,4

Three cases of pediatric SPHTNs that were initially diagnosed on the FNA specimen as suspicious for PTC are described. To our knowledge, this is the first report describing the cytologic presentation of pediatric SPHTN.

MATERIALS AND METHODS

A search of the surgical pathology files at the State University of New York Upstate Medical University (Syracuse, NY) and the consultation files of 1 of the authors (V.A.L.) at the University of Pennsylvania (Philadelphia, Pa) revealed 3 cases in the pediatric age group with a diagnosis of SPHTN. Corresponding FNA cytology was available in all cases. The clinical data and cytologic and histologic material from all these cases were reviewed.

All FNAs were performed by an endocrinologist using a 25-- gauge needle attached to a 20-cc syringe. In all cases, the material obtained was smeared onto uncoated glass slides and either air dried or fixed in 95% ethanol for Diff-Quik or a Papanicolaou stains, respectively. The cytotechnologist provided adequacy assessment on aspirate smears at the time of performance of FNA in 2 cases. According to the guidelines of the Papanicolaou Society of Cytopathology,5 examination of FNAs of thyroid nodules was considered adequate if there were at least 5 groups of wellpreserved, well-visualized follicular cells with each group containing 10 or more cells. Material for cell block was procured by FNA in 1 case; it was fixed in 10% neutral buffered formalin, embedded in paraffin, sectioned at 4 lm, and stained with hematoxylin-eosin. The latter method also was applied to histologic samples. Immunocytochemical studies were performed in selected cases on paraffin-embedded sections by streptavidin-biotin peroxidase method.6 Antibody against cytokeratin 19 (CK-19) (mouse monoclonal; 1:40; Dako Corporation, Carpinteria, Calif) was used.

RESULTS

The Table summarizes the clinical and radiologic findings and cytologic and histologic diagnoses in each case. A cytologic diagnosis of suspicious for PTC was rendered in all 3 cases.

Cytologic Findings

In all cases, the aspirate smears were highly cellular and comprised broad flat sheets and 3-dimensional cell clusters. Diff-Quik stain revealed fire flares (flame cell change) characterized by accentuation of edges of cells with metachromatic (pink) material (Figure 1). Cells with vacuolated cytoplasm (best seen on Diff-Quik stain) with eccentrically placed nuclei exhibited atypia consisting of nuclear enlargement and pleomorphism (Figure 2). Nuclear grooves and prominent nucleoli were identified in a few cells. Papillae with transgressing vessels (characterized by capillaries passing through clusters of cells) were also identified (Figure 3). Watery colloid and sparse fragments of inspissated colloid were identified in Diff-Quik-stained slides (Figure 4). The background also contained giant cells and histiocytes. Intranuclear inclusions were not identified. A cell block section obtained in case 2 revealed papillary clusters and fragments with similar cytologic features, as noted in the aspirate smears, and these were immunohistochemically negative for CK-19 (Figure 5).