Resident Short Review M¨ ullerianosis of the Urinary Bladder A Rare Tumorlike Lesion Giovanni Branca, MD; Valeria Barresi, MD  M¨ ullerianosis was first described as a rare entity consisting of an admixture of cervical, tubaric, or endometrial epithelium within the lamina propria and muscularis propria of the urinary bladder. This lesion occurs mainly in the dome or posterior wall of the urinary bladder in women of fertile age. Its clinical presentation is characterized by hematuria, pelvic pain, and dysuria, nonspecific symptoms that are related to the responsive- ness of m¨ ullerian glands to hormonal stimuli. The major interest of m ¨ ullerianosis resides in its similarity, from clinical, cytologic, and histologic viewpoints, to more threatening conditions, such as neoplasias. The clinical context and the identification of periglandular endometrial stroma at histologic examination with conventional hema- toxylin-eosin stain, as well as the immunohistochemical demonstration of estrogen and progesterone receptors in the glands, are of diagnostic utility in the differential diagnosis. M ¨ ullerianosis may be responsive to gonadotro- pin-releasing hormone agonists. Surgical resection may be justified in the case of clinical symptoms refractory to hormone therapy. (Arch Pathol Lab Med. 2014;138:432–436; doi: 10.5858/ arpa.2012-0681-RS) M ¨ ullerianosis was first described by Young and Clement 1 in 1996 as a rare entity consisting of an admixture of at least 2 types of m ¨ ullerian tissues—cervical, tubaric, or endometrial—in the lamina propria and muscularis propria of the urinary bladder. At present, fewer than 20 cases of m¨ ullerianosis of the urinary bladder have been reported, 1–12 though this lesion has also been rarely observed in the ureter, 13,14 mesosalpinx, 15 inguinal lymph nodes, 16 and spinal cord. 17 The main interest of m ¨ ullerianosis of the urinary bladder resides in its potential to mimic a neoplastic lesion from clinical, cytologic, and histologic viewpoints. 10,18 Though m¨ ullerianosis is extremely rare, its correct identification is crucial for appropriate management, because patients may benefit from hormonal therapy and radical cystectomy may be avoided. CLINICAL FEATURES M¨ ullerianosis of the urinary bladder originates mainly in women of fertile age, sometimes in association with a previous history of pelvic surgery or cesarean delivery. 3–5 According to published reports, the age at diagnosis ranges between 28 and 53 years. 1–12 Because of its clinical presentation, characterized by nonspecific symptoms, such as hematuria, pelvic pain, and dysuria, 10 occurring or not occurring in association with menstruation, m ¨ ullerianosis may simulate many other pathologic conditions of the urinary tract, including neoplasias. A novel case of m ¨ ullerianosis of the urinary bladder, which we recently diagnosed, affected a fertile 50-year-old woman who complained of gross hematuria and dysuria. In this case the past clinical history was negative for pelvic surgery or cesarean section. GROSS FINDINGS A definitive gross description of m ¨ ullerianosis of the urinary bladder cannot be deduced from most of the existing reports. Indeed, in most of the cases the lesion is submitted to transurethral endoscopic resection 2,6,7 and only non– grossly descriptive fragments are sent for the histologic examination. To the best of our knowledge, the gross findings of m ¨ ullerianosis of the urinary bladder have been reported only by Guan and colleagues, 10 who described this lesion as a mass showing an internal cystic structure, with dark blue to black cysts. 10 In the remaining cases, the macroscopic aspect of m ¨ ullerianosis of the urinary bladder may be inferred only from cystoscopy, which reveals the presence of polypoid, masslike lesions ranging from 1 to 4.5 cm in size, predominantly involving the dome or posterior wall of the bladder. 10 Also in our case, cystoscopy had shown an exophytic lesion, located at the posterior bladder wall. HISTOLOGIC AND IMMUNOHISTOCHEMICAL FINDINGS AND DIFFERENTIAL DIAGNOSIS At histologic examination by hematoxylin-eosin stain, m¨ ullerianosis of the urinary bladder appears as a lesion consisting of an admixture of variably sized, bland- appearing glands that are deeply situated within the lamina propria and the muscularis propria of the urinary bladder Accepted for publication April 2, 2013. From the Department of Pathology, University of Messina, Messina, Italy. The authors have no relevant financial interest in the products or companies described in this article. Reprints: Valeria Barresi, MD, Dipartimento di Patologia Umana, Policlinico G. Martino, Pad D, Via Consolare Valeria, 98125 Messina, Italy (e-mail: vbarresi@unime.it). 432 Arch Pathol Lab Med—Vol 138, March 2014 M¨ ullerianosis—Branca & Barresi