Cellular swirls and cellular swirl-like structures are not restricted to papillary thyroid carcinoma

Recently, besides the presence of papillae and typical nuclear features (e.g., grooves and pseudoinclusions), a peculiar architectural feature known as “cellular swirls” has been recognized as an additional criterion for diagnosing papillary thyroid carcinoma (PTC) in fine needle aspirates. Cellular swirls are defined as concentrically organized aggregates of tumor cells in which many of the most peripherally situated cells have ovoid rather than round nuclei that are oriented perpendicular to the radius of the swirl (Fig. 1A). Although their reported sensitivity for PTC is low (17%), they have not been found in benign thyroid lesions. Therefore, in the thyroid gland, cellular swirls appear to be highly specific to PTC. Furthermore, cellular swirl-like structures with some but not all the features of cellular swirls have also been described in PTC. They also appear to be specific for PTC, and may even more prominent in the aspiration smears than the characteristic swirls. Therefore, swirl-like structures may also be a useful feature in the diagnosis of PTC. The potential diagnostic value of cellular swirls and/or cellular swirl-like structure in other papillary lesions arising from other organs has not been investigated previously. In contrast to high grade urothelial carcinoma, the sensitivity of urinary cytology for the diagnosis of low grade papillary urothelial neoplasms (LGPUN) is very low (overall sensitivity of 26% for LGPUN versus >95% for high grade urothelial carcinoma). Although the presence of papillary fragments with fibrovascular cores is diagnostic of LGPUN, they are rare. The other architectural and cytological diagnostic criteria, including cell clusters with irregular edges, increased nuclear/cytoplasmic ratios, irregular nuclear borders, and cytoplasmic homogeneity, although specific when combined together, are also not sensitive for LGPUN. Therefore, additional diagnostic features may be helpful to recognize LGPUN on cytology. To the best of the author’s knowledge, cellular swirls or similar structures have not been described in LGPUN. Following the observation of cellular swirl-like structures (Fig. 1B) in a bladder washing specimen from a case of low-grade papillary urothelial carcinoma, the author analyzed 15 additional bladder washing specimens to evaluate if cellular swirls or similar structures could also be helpful for the diagnosis of LGPUN on cytology. For each case, the diagnosis of noninvasive low-grade papillary urothelial carcinoma was confirmed on histology. In the 15 cases subsequently analyzed, no convincing cellular swirls or cellular swirl-like structures were found. Therefore, in contrast to PTC, this peculiar architectural feature does not appear to be helpful as an additional diagnostic criterion for LGPUN on cytology. Furthermore, cellular swirls were also subsequently observed in benign mesothelial cell clusters from normal peritoneal washing specimens (Fig. 1C). This suggests, in fact that they may not be linked to tumors with a papillary architecture such as PTC, but that they may rather represent nonspecific areas of incipient infolding within flat sheets of cells, whether neoplastic or not. Division of Clinical Pathology, Geneva University Hospital, 1211 Geneva 14, Switzerland *Correspondence to: Dr. Marc Pusztaszeri, Service de Pathologie Clinique, Hopitaux Universitaires de Geneve, 1 rue Michel-Servet, 1211 Geneve 14, Switzerland. E-mail: Marc.Pusztaszeri@hcuge.ch Received 28 November 2012; Revised 11 October 2013; Accepted 9 January 2014 DOI: 10.1002/dc.23108 Published online 00 Month 2014 in Wiley Online Library (wileyonlinelibrary.com).