Florid cystic mullerianosis of the testis: new pathological entity originating from a peculiar Müllerian differentiation of the testicular vaginal mesothelium

Sir: The presence of cysts in the parietal layer of the tunica vaginalis of the testis is a rarity in terms of the relative high frequency of cysts of the tunica albuginea. Most reported cystic formations are single, and typically protrude towards the vaginal cavity. Histologically, most are mesothelial cysts, although lymphatic cysts have also been reported. There are two peaks of incidence, one from 5 to 8 years of age and the other from 30 to 69 years of age. Paediatric patients tend to refer with acute scrotal swelling accompanied by pain, whereas adults complain of a progressive painless scrotal enlargement. Herein we report the exceptional finding of multiple cysts in the parietal layer of the tunica vaginalis of the testis in three patients. We propose the term ‘florid cystic mullerianosis of the testis’ for this entity. It is speculated that this entity is the male counterpart of endosalpingiosis in females, given the morphological and immunohistochemical similarities of this epithelial proliferation. Endosalpingiosis appears in the fallopian tube, cervix, abdominal cavity and bladder in women, suggesting a similar histogenesis in both genders. Three cases are reported herein. Two of the cases were retrieved from the autopsy files of the Department of Pathology at La Paz University Hospital. The third case consisted of a surgical specimen sent from another hospital. Informed written consent was obtained from the three patients or their families. Due to the autopsy and/or pathological sample nature of the specimens, the procedures did not need approval by the Hospital’s ethics committee. The studies were performed according to the Declaration of Helsinki. The surgical specimens were fixed in 10% buffered formalin, and after paraffin-embedding were cut and stained with haematoxylin and eosin. Immunohistochemical studies were performed, and the following antibodies were used: cytokeratins 8, 18 and 19, markers of epithelium and mesothelium (prediluted; Dako, Glostrup, Denmark); calretinin, a marker of mesothelium and pathological Sertoli cells of the testis (prediluted; Dako); D2-40 (M2A antigen), a marker of mesothelium, lymphatic vessels and embryonic germ cells (prediluted; Dako); androgen receptor, a marker of mature Sertoli cells and Wolffian derivatives, and negative in mesothelium (1:50; Dako); oestrogen receptor, a marker of M€ ullerian derivatives (prediluted; Dako); progesterone receptor, a marker of M€ ullerian derivatives (prediluted; Dako); and CD10, a marker of stroma in M€ ullerian structures and epithelium in Wolffian derivatives (prediluted; Dako). Patient ages ranged from 47 to 81 years. Two cases showed testicular atrophy, and one case had left hydrocele of several months’ evolution that was not associated with varicocele, epididymitis or testicular tumour. Testes weight ranged from 12 to 18 g (mean 15 g). The five testes showed a small hydrocele, and no vaginal adherences were observed. The parietal layer of the tunica vaginalis was widened, showing several cysts ranging from microscopic to 5 mm in diameter. The cystic contents varied from clear to yellowish. Similar histological features were found in the parietal layer of the tunica vaginalis of the five testes studied. In the sections, the cysts were arranged either in conglomerates or in a rosary bead pattern (Figure 1A,B). They were unior multilocular. The cysts were surrounded by a thin wall of connective tissue and an epithelial lining with variable height from cuboidal to pseudostratified (Figure 1A,B). Most cysts showed both ciliated and non-ciliated epithelial lining (Figure 1B, inset), although the ciliated cells were less abundant. In some cysts, the non-ciliated cells showed cytoplasmic projections towards the lumen that gave an apocrine appearance. Those cysts with columnar or pseudostratified epithelium also showed ‘peg’ cells (basal triangular cells typical of fallopian tubes and endosalpingiosis in women) and small papillary proliferations (Figure 1B, inset). Neither atypia nor mitosis were observed. The contents of the cystic structures were of a light eosinophilic and granular material. Endometrial-like stroma or macrophages with haemosiderin were not observed. Isolated lymphocytes in the vicinity of the cystic structures were identified in only one case, a patient with HIV. The epithelial lining of the parietal layer of the tunica vaginalis was primarily a simple flat epithelium, corresponding to mesothelium. Focally, it was replaced by a tall columnar or pseudostratified epithelium with similar histological features as those described previously in the cystic structures. Regarding these areas, we observed the following: • the formation of polypoid projections toward the vaginal cavity supported by a loose connective tissue; and • the presence of invaginations deeply penetrating the parietal layer (Figure 1C).