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Int J Clin Exp Pathol 2013;6(8):1458-1466

Original Article
Urothelial eddies in papillary urothelial neoplasms: a distinct morphologic pattern with
low risk for progression

Misung Kim, Jae Y Ro, Mahul B Amin, Mariza de Peralta-Venturina, Ghee Young Kwon, Yong Wook Park, Yong Mee Cho

Department of Pathology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Republic of Korea; The Methodist Hospital,
Cornell University, Houston, TX; Cedars-Sinai Medical Center, Los Angeles, CA; Sungkyunkwan University, Samsung Medical Center, Seoul,
Republic of Korea; Hanyang University, Guri Hospital, Guri, Republic of Korea

Received May 25, 2013; Accepted July 3, 2013; Epub July 15, 2013; Published August 1, 2013

Abstract: We encountered an undescribed histologic feature of papillary urothelial neoplasms: “urothelial eddy”, which was histologically
reminiscent of squamous eddy of irritated follicular keratosis of the skin. A review of 756 patients with transurethral resection of bladder tumor
revealed 10 patients (1.3%) of papillary urothelial neoplasms with urothelial eddies. All cases were male with a median age of 65 years.
Urothelial eddies were characterized by small ovoid nests of ovoid to spindle cells arranged in an onion-skin pattern with fine cytoplasmic
processes within wide intercellular space. The cytoplasmic processes mimicked intercellular bridges but ultrastructurally were cytoplasmic
microvillous projections. They were of papillary urothelial neoplasm of low malignant potential in seven patients and low-grade urothelial
carcinoma in three patients. Nine patients presented as non-invasive tumor and one patient showed microinvasion within papillary stalks. Six
patients showed an inverted growth pattern. Their immunoprofile was more similar to that of conventional urothelial carcinoma rather than
squamous cell carcinoma: high expressions of GATA3, S100P, uroplakin III, and cytokeratin 7; and low expressions of high molecular weight
cytokeratin and p53. The Ki-67 labeling index was low (mean and median values, 2% each). During the follow-up period (mean, 88.7 months),
four patients, including the microinvasive patient, showed recurrence with the same grade and stage but neither progressed into muscle-
invasive tumor nor caused death. Our results suggest that urothelial eddy is a rare aberrant histology of papillary urothelial neoplasms with
indolent behavior and should be discriminated from squamous differentiation of urothelial carcinoma, which has a poor prognosis.

Keywords: Urothelial carcinoma, variant, urothelial eddy, indolent

Address correspondence to: Dr. Yong Mee Cho, Department of Pathology, University of Ulsan College of Medicine, Asan Medical Center, 388-
1 Pungnap-2dong, Songpa-gu, Seoul 138-736, Republic of Korea. Phone: 82-2-3010-5965; Fax: 82-2-3010-7898; E-mail: yongcho@amc.seoul.