2 Case Reports in Medicine Figure 1: Low-power view of inﬁltrating malignant mesothelial tubular structures abutting the scrotal wall at the level of tunica dar- tos in close proximity of the epididymis (×40 magniﬁcation; H&E staining). Figure 3: Calretinin immunohistochemistry highlighting the mus- cle inﬁltrative properties of the neoplastic mesothelial cells in deep submesothelial lamina propria (×400 magniﬁcation; H&E staining). Figure 2: Intermediate-power view of complex, interconnect- ing pseudoglandular mesothelial proliferation spraying out into abortive tubular structures and rare isolated cells in a desmoplastic stroma. Neoplastic mesothelial cells are characterised by higher nucleus/cytoplasm ratio than normal cells and have prominent nucleoli and eosinophilic cytoplasm disposed into strands with nuclear overlapping (×100 magniﬁcation; H&E staining). paratesticular mesothelioma (Figure 1) originating from tunica vaginalis to everybody’s surprise. Neoplastic mesothe- lial cells were characterized by higher nucleus/cytoplasm ratio than normal cells, prominent nucleoli and eosinophilic cytoplasm (Figure 2). Diﬀuse expression of cytokeratin 5/6 and calretinin (Figure 3) by the tumor cells as well as the muscle inﬁltrative properties of the neoplastic mesothelial cells in deep submesothelial lamina propria conﬁrmed our diagnosis of malignant mesothelioma, which measured 3 mm on its maximum diameter. After consulting the case with medical oncology and radi- ation oncology departments, we decided to perform left rad- ical orchiectomy and hemiscrotectomy as a complementary procedure. Chest and abdominal computed tomographies (CT) as well as positron-emission tomography (PET) scans were all negative. After the second operation, he was hos- pitalized for 6 days due to the development of left hemiscrotal hematoma, which was managed conservatively. Pathological examination of the specimens removed during the second operation conﬁrmed the diagnosis of malignant paratestic- ular mesothelioma originating from the tunica vaginalis. Although he was oﬀered active surveillance, he asked for a second consultation in an urooncology center elsewhere, at which he was recommended to have a diagnostic laparoscopy to exclude any lymphatic spread after having conﬁrmed the histopathologic diagnosis of paratesticular malignant meso- thelioma by second opinion. He had the procedure where all biopsies taken from pelvic lymph nodes were found to be negative. He was then given no additional treatment. The patient is still under our close followup, and he is disease-free for 26 months. 3. Discussion Mesotheliomas are relatively rare tumors that arise from the serosal surface of the pleura, peritoneum, and pericardium. On rare occasions, they originate from the tunica vaginalis of the testis in which case they manifest as a paratesticular mass [4]. Since the ﬁrst description published by Barbera and Rubino in 1957 [5], a total of 234 cases have been des- cribed so far [4, 6]. Paratesticular mesotheliomas are rare tumors, accounting for around 0.3% to 1.4% of all cases of malignant mesotheliomas [6]. Being morphologically identical to mesotheliomas at other body parts, paratesticular mesotheliomas are known to be aggressive tumors [7–11]. They may present at any age but the peak incidence is in the sixth to eighth decades of life. Most tumours originate from the tunica vaginalis. Asbestos exposure is the main risk factor for developing malignant mesothelioma. However, a correlation between asbestos exposure and mesothelial neo- plastic proliferation could be documented in only less than half of the cases [12]. A number of other agents have been implicated in the development of malignant mesothelioma such as erionite and ﬂuoroedenite or ionising radiation with the use of thorotrast [13]. Moreover, genetic factors may play a contributive role, consistently with familial clusters in certain regions of Turkey [14]. Our patient denied any environmental, occupational, or domestic exposure to the documented etiologic factors. Moreover, his family history was unremarkable. Apart from a past medical history consistent with ex- posure to asbestos or other natural ﬁbers, preoperative