Ectopic decidual reaction mimicking peritoneal tubercles: a report of three cases

The extra-uterine decidual reaction of stromal cells has been well described. It is a benign, self-resolving entity;[] thus it is very important to distinguish it from the more alarming conditions it can simulate. We hereby describe three cases of ectopic decidual reaction, which during operation, resembled peritoneal tubercles. CASE REPORTS Case 1 A 34-year-old female with an uneventful antenatal period underwent an emergency caesarian section for fetal distress. Upon operating, there were multiple whitish yellow nodules on both Fallopian tubes and omentum varying in size from 1 to 4 mm, resembling tubercles. The adjacent peritoneal surfaces were hyperemic. The ovaries and uterus were unremarkable. Case 2 A 25-year-old female admitted for pregnancy-induced hypertension, jaundice and fetal distress underwent an emergency caesarian section and bilateral tubal ligation at 39 weeks of gestation. Omental yellowish nodules measuring 2-3 mm were biopsied. Case 3 A 32-year-old female with antepartum hemorrhage was diagnosed with placenta previa. At 37 weeks of gestation, a caesarian section was performed. Multiple tubercles 2-4 mm in diameter were seen on the right fallopian tube and omentum, along with adhesions in the intestine. None of these patients had a history of endometriosis. Microscopic examination In all three cases, omental and peritoneal biopsies revealed similar histomorphology. Microscopic examination disclosed submesothelial decidual cells dispersed individually as well as in nodules and plaques [Figure 1]. These cells were large with abundant eosinophilic cytoplasm, bland nuclei and single nucleoli [Figure 2]. There was no nuclear pleomorphism, hyperchromasia, or mitotic activity. The decidual foci showed many congested capillaries and mild lymphocytic infiltration. However, no epithelioid cell granulomas were observed.

Ectopic decidual reaction has been observed more commonly in the uterus, cervix, lamina propria of the fallopian tube and in ovaries, but peritoneal location is rare. Other rare sites include the appendix, omentum, diaphragm, liver, spleen, lymph nodes and renal pelvis, etc.[] Ectopic decidua is usually an incidental microscopic finding, detected in biopsies taken during caesarian sections, postpartum tubal ligations, appendectomies, or in-tubal pregnancies.[] Decidual reactions are usually asymptomatic; however, rare life-threatening events have been reported. These include hemoperitoneum,[] pseudo-acute appendicitis, pulmonary involvement,[] and obstruction in labor due to gross peritoneal deciduosis.[] An ectopic decidual reaction is an exaggerated response of the endometrium to progesterone. Zaystev, et al. proposed two theories to account for this condition. The most favored theory states that the sub-coelomic mesenchymal cells undergo a progesterone-induced metaplasia, which is usually reversible once the hormonal influence disappears.[] The second theory claims that the decidual cells are already distributed in the peritoneum. In non pregnant women, the source of progesterone is either exogenous or endogenous (secreted by corpus luteum or adrenal cortex). Deciduosis is a clinicopathologic process distinct from endometriosis. Ectopic deciduosis of the omentum has been classified into focal deciduosis (97%) and diffuse deciduosis (3%). Florid lesions may be visible during surgery as multiple, grey white, focally hemorrhagic nodules or plaques studding the peritoneal surfaces and simulating a malignant tumor. Microscopically, focal hemorrhagic necrosis and varying degrees of nuclear pleomorphism and hyperchromasia of the decidual cells may be mistaken for a tumor such as deciduoid malignant mesothelioma.[] However, the bland appearance and mitotic inactivity militate against such a diagnosis. Other differential diagnoses include metastatic signet ring cell carcinoma and metastatic melanoma. Immunohistochemically, decidual cells are vimentin and progesterone-receptor-positive and focally-positive for desmin and smooth muscle actin. Immunoreactivity for cytokeratin 5/6 and calretinin favors a diagnosis of deciduoid mesothelioma, while cytokeratin positivity supports a metastatic carcinoma. A diagnosis of metastatic melanoma is confirmed by positive S-100 and HMB-45 immunostaining.[,] This report highlights the fact that in pregnant females, ectopic decidual reactions must be considered first in all incidentally detected peritoneal nodules (during surgery), even if they resemble tubercles or metastatic tumor deposits. After histologic diagnosis, most of the lesions do not require further treatment and spontaneously involute within 4 to 6 weeks post-partum.[] Out of the few case reports of ectopic decidual reaction in Indian literature,[,] we could not find any case describing ectopic decidua as a mimicker of peritoneal tuberculosis. Source of Support: Nil Conflict of Interest: None declared.

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