IMAGES IN CYTOLOGY Section Editor: Shahla Masood, M.D. Ectopic Decidua in Abdominal Washings Found Intraoperatively at Cesarean Section Carla L. Ellis, M.D., M.S., 1 Zahra Maleki, M.D., 1 and Syed Z. Ali, M.D. 1,2 * Abdominal washings are routinely performed in the intra- operative evaluation of abdominal cavity abnormalities, and are considered a highly effective diagnostic tool. We report an unusual case of a 39-year-old African American woman (para 0) at 39 weeks gestation, admitted with spontaneous rupture of membranes, moderate meconium, chorioamnionitis, and nonreassuring fetal heart tracings. At cesarean section, extensive nodular, pale-tan, and fri- able growths were noted to stud the peritoneum and involve the uterus, omentum, left adnexa, posterior cul- de-sac, and bladder peritoneum. There was no involve- ment of the liver, spleen, bowel, or diaphragm. Upper abdominal examination by palpation was unremarkable. Abdominal washings were obtained on entry, as well as omental and bladder peritoneum biopsies. A vigorous, male liveborn infant was delivered. The cytologic material was prepared by cytospin and stained with Papanicolaou stain. Microscopic examination revealed cellular smears with lose clusters of plump, round to polygonal epithelioid cells with enlarged nuclei, small to prominent nucleoli, and well-defined cell borders juxtaposed (Fig. C-1). One characteristic feature was the presence of bright pink or orange cytoplasmic coloration focally involving some of the cells and creating polychro- masia (Figs. C-1 and C-2). The latter feature resembled cytoplasmic keratinization. There was no evidence of air- drying artifact and all smears were adequately fixed and stained. Focal areas displayed cellular crowding with moderately high N/C ratios and occasional prominent nucleoli (Fig. C-2). The corresponding H and E stained cell block sections revealed sheets of large polygonal cells with bright eosinophilic glassy-appearing cytoplasm and distinct cytoplasmic borders (Fig. C-3). Ectopic decidua is defined as a histologically benign condition in which decidual cells may be found in the cervix, appendix, or areas other than the endometrium. Formation of extrauterine decidual cells of the cervix, ovary, and uterus has been well documented; however, cases of decidua formation on the peritoneal surfaces have been only sporadically described. 1 Also known as extrauterine deciduosis, ectopic decidua can be discovered incidentally in pregnancy during cesarean section, during pelvic surgery in women taking oral contraceptives, or as an asymptomatic incidental finding. When related to preg- nancy, the more accepted theory of ectopic decidua touts that it is a physiologic phenomenon related to the special- ized sensitivity of subcoelomic mesenchymal cells, which undergo progesterone induced metaplasia. A second, less accepted theory, claims that the decidual cells are already distributed in the peritoneum and are induced to prolifer- ate by progesterone secretion during pregnancy. The dif- ferential diagnosis of ectopic decidua includes peritoneal carcinomatosis, deciduoid mesothelioma, metastatic carci- noma, and metastatic melanoma. 2 The pink-tan, fleshy lesions are diffusely distributed in the peritoneum in a clinicopathologic process that appears to be distinct from endometriosis. 1 Although after histological diagnosis, most lesions do not require further treatment and sponta- neously involute within the first 4 to 6 weeks postpartum, care must be taken to monitor patients for massive post- partum intraperitoneal hemorrhage, which can be associ- 1 Department of Pathology, The Johns Hopkins Hospital, Baltimore, Maryland 2 Department of Radiology, The Johns Hopkins Hospital, Baltimore, Maryland *Correspondence to: Syed Z. Ali, M.D., The Johns Hopkins Hospital, 600 N. Wolfe Street, PATH 406, Baltimore, MD 21287. E-mail: sali@jhmi.edu Received 13 June 2009; Accepted 8 September 2009 DOI 10.1002/dc.21247 Published online 23 November 2009 in Wiley Online Library (wileyonlinelibrary.com). 740 Diagnostic Cytopathology, Vol 38, No 10 ' 2009 WILEY-LISS, INC.