CASE REPORT Mesothelioma in Situ of the Spermatic Cord Arising from a Patent Processus Vaginalis: A Case Report Yasuyuki Kobayashi1*, Yumiko Yasuhara2, Hiroki Arai1, Masahito Honda1, Masataka Hiramatsu3, Sho Goya3 Mesothelioma is an aggressive tumor originating from mesothelial cells. Mesothelioma of the spermatic cord is a very rare disease, and the most common presentation of this disease is that of aggressive mesothelioma with no description of mesothelioma in situ. We report an extremely rare case of mesothelioma in situ of the spermatic cord arising from a patent processus vaginalis. To our best knowledge, this is the first report of this finding. The identification of a patent processus vaginalis and investigation of single-layered atypical mesothelial cells led to the final diagnosis. Keywords: atypical mesothelial cells; mesothelioma in situ; radical orchiectomy; spermatic cord tumor INTRODUCTION Mesothelioma is an aggressive tumor originating from mesothelial cells (1). Mesothelioma of the spermatic cord is a rare disease, with only 9 cases reported in detail in the English literature and none describing mesothelioma in situ (2-10). We report an extremely rare case mesothelioma in situ of the spermatic cord arising from a patent processus vaginalis. CASE REPORT An 82-year-old man complaining of a gradually enlarging swollen mass in his right inguinal area for the past three months was referred to our hospital. The right spermatic cord mass was hard, smooth, and immobile. Chest and abdominal computed tomography showed right spermatic cord swelling and no other significant findings (Figure 1). We diagnosed the patient as having right spermatic cord tumor, for which he underwent right radical orchiectomy. A spermatic cord tumor was found adhering to the surrounding tissue, and no obvious residual tumor existed intraoperatively. Macroscopically, the spermatic cord was enlarged at 7.0 × 4.0 cm and had a smooth and capsulated surface. The cut surface was creamy white, solid, thickened and poorly circumscribed (Figures 2A, B). Microscopically, the tumor was a mixture of tubulopapillary, trabecular, and solid structures (Figures 2C, D). Immunohistochemically, the tumor cells were positive for calretinin, Wilms’ tumor 1, podoplanin, glucose transporter type 1 (GLUT-1) and epithelial membrane antigen (EMA), negative for carcinoembryonic antigen, MOC-31 and Ber-EP4, and showed loss of BRCA1-associated protein (BAP1). We diagnosed the spermatic cord tumor as epithelial mesothelioma. Interestingly, a patent processus vaginalis was found lined by a single layer of mesothelial cells from the proximal end to the tunica vaginalis (Figure 3A). A single layer of atypical mesothelial cells with enlarged nuclei lined the ipsilateral side of the mesothelioma and flattened normal mesothelial cells lined the cavity on the opposite Figure 1. Abdominal CT showing the right spermatic cord swelling. Urology Journal/Vol 17 No. 6/ November-December 2020/ pp. 671-673. [DOI: 10.22037/uj.v16i7.5421 Departments of Urology, 2Diagnostic Pathology, and 3Respiratory Medicine, Kinki Central Hospital of Mutual Aid Association of Public School Teachers, Itami, Hyogo, Japan. *Correspondence: Department of Urology, Kinki Central Hospital of Mutual Aid Association of Public School Teachers, 3-1 Kurumazuka, Itami, Hyogo 664-8533, Japan Phone: +81-72-781-3712; Fax: +81-72-779-1567. E-mail: ya_su_koba@yahoo.co.jp. Received June 2019 & Accepted December 2019 Vol 17 No 06 November-December 2020 112 side (Figure 3B). Immunohistochemically, the atypical mesothelial cells were positive for GLUT-1 and EMA, negative for desmin, and showed loss of BAP1, whereas the normal mesothelial cells showed an opposite pattern (Figures 3C-D), indicating that the single-layered atyp- ical mesothelial cells were mesothelioma in situ. Final- ly, we diagnosed mesothelioma in situ of the spermatic cord arising from a patent processus vaginalis. A sec- ond surgery and adjuvant therapy were not performed because there was no obvious tumor elsewhere. He was alive without signs of disease at 2 years after surgery. DISCUSSION Mesothelioma of the spermatic cord is a rare entity; only 9 cases have been reported so far in the English Case Report 413 Mesothelioma of the Spermatic Cord-Kobayashi et al. Figure 2. (A) Macroscopic findings of the spermatic cord. The spermatic cord was enlarged (arrowheads). (B) The cut surface showed a solid and thick- ened spermatic cord (arrowheads) and no involvement of the testis and tunica vaginalis (arrows). (C) Epithelioid mesothelioma with a papillary pattern of growth. (D) Epithelioid mesothelioma with trabecular and solid patterns of growth. (C-D): Hematoxylin and eosin stain. Figure 3. (A) Cross-sections of the specimen of the right spermatic cord. (a) Mesothelioma of the spermatic cord (red line), (b) patent processus vaginalis (yellow line) and (c) vas deferens (green point). Patent processus vaginalis stained with hematoxylin and eosin (B), desmin (C) and BAP-1 (D). (B-D) Mesothelioma is present on the right side of the images. Cells on the right lining are mesothelioma in situ (arrowhead). Cells on the left lining are normal mesothelial cells (arrow). ※ = patent processus vaginalis. Vol 17 No 06 November-December 2020 672 literature (Table 1) (2-10). The patients most common- ly presented with an inguinal mass, and all 9 patients underwent surgery. Histological findings showed no descriptions of mesothelioma in situ. Mesotheli- oma arising from the peritoneum may have invaded the spermatic cord in Cases 4 and 6. Our patient be- ing alive without signs of disease at 2 years after sur- gery excluded the possibility of a peritoneal origin. BAP1 expression is detected by immunohistochemistry, which is useful for distinguishing benign and malignant mesothelial proliferations(11). BAP1 expression is detect- ed in the nuclei of benign mesothelial cells, whereas BAP1 loss is detected in the nuclei of mesothelioma cells (12). Recently, Churg et al. reported two cases of mesotheli- oma in situ. They proposed that mesothelioma in situ be defined as well-confirmed in situ lesions and be related to genomic events such as BAP1 loss(13). The single-lay- ered atypical mesothelial cells in our patient were an in situ lesion and showed loss of BAP1. Thus, they were diagnosed as mesothelioma in situ of the sper- matic cord arising from a patent processus vaginalis. REFERENCES 1. Gemba K, Fujimoto N, Kato K, et al. National survey of malignant mesothelioma and asbestos exposure in Japan. Cancer Sci. 2012; 103:483-90. 2. Kozlowski H, Zoltowska A. Mesothelioma of spermatic cord. Neoplasma. 1968; 15:97-100. 3. Arlen M, Grabstald H, Whitmore WF Jr. Malignant tumors of the spermatic cord. Cancer. 1969; 23:525-32. 4. Pizzolato P, Lamberty J. Mesothelioma of spermatic cord: electron microscopic and histochemical characteristics of its mucopolysaccharides. Urology. 1976; 8:403- 8. 5. Leiber C, Katzenwadel A, Popken G, Kersten A, Schultze-Seemann W. Tumour of the spermatic cord: an unusual primary manifestation of an epithelial mesothelioma of the peritoneum with patent processus vaginalis. BJU Int. 2000; 86:142-3. 6. Torbati PM, Parvin M, Ziaee SA. Malignant mesothelioma of the spermatic cord: case report and review of the literature. Urol J. 2005; 2:115-7. 7. Park YJ, Kong HJ, Jang HC, Shin HS, Oh HK, Park JS. Malignant mesothelioma of the spermatic cord. Korean J Urol. 2011; 52:225- 9. 8. Meng X, Guzzo TJ, Bing Z. Malignant mesotheliomas in spermatic cords: reports of two cases and a brief review of literature. Rare Tumors. 2013; 26:5:e4. 9. D'Antonio A, Mastella F, Colucci A, Silvestre G. Malignant mesothelioma of spermatic cord in an elderly man with a history of asbestos exposure. Urology. 2016; 87:e1-3. 10. Ahmed Z, Singh S, Mangal A, Mittal A. Primary malignant mesothelioma of the spermatic cord. BMJ Case Rep. 2016; pii: bcr2016214602. 11. Kinoshita Y, Hida T, Hamasaki M, et al. A combination of MTAP and BAP1 immunohistochemistry in pleural effusion cytology for the diagnosis of mesothelioma. Cancer Cytopathol. 2018; 126:54-63. 12. Wu D, Hiroshima K, Yusa T, et al. Usefulness of p16/CDKN2A fluorescence in situ hybridization and BAP1 immunohistochemistry for the diagnosis of biphasic mesothelioma. Ann Diagn Pathol. 2017; 26:31-7. 13. Churg A, Hwang H, Tan L, et al. Malignant mesothelioma in situ. Histopathology. 2018; 72:1033-8. Case Report 212Case Report 428Case Report 673 Mesothelioma of the Spermatic Cord-Kobayashi et al. Case Age Asbestos Side Symptom Tumor Operation Histologic Postoperative Follow-up Ref (Y) exposure metastasis type recurrence 1 63 NA Lt Mass in the NA NA Biphasic NA NA 2 inguinal region 2 40 NA Lt High near groin External RO, RALD NA No NED 18 Y 3 iliac lymph node 3 57 NA Rt Inguinal hernia No SR Epithelioid Local at 12 M DOD 42 M 4 Periaortic, iliac lymph nodes at 34 M 4 46 No Rt Mass in the No RA Biphasic NA DOD 8 M 5 inguinal region 5 52 NA Rt Scrotal enlargement No RA Epithelioid Local at 9 M AWD 30 M 6 Iliac lymph nodes at 30 M 6 65 Yes Lt Mass in the inguinal No RA Biphasic Local, peritoneal DOD 6 M 7 region at 3 M 7 45 No Lt Mass in the inguinal No SR Epithelioid No NED 6 M 8 region 8 80 Yes Rt Mass in the inguinal No RA Biphasic No NED 12 M 9 region 9 45 No Rt Swelling in the No RA Biphasic NA NA 10 inguinal region Our 82 No Rt Swelling in the No RA Epithelioid No NED 2 Y case inguinal region Table 1. Clinical and pathologic features of primary mesothelioma. Abbreviations: NA, not available; Lt, left; Rt, right; RO, radical orchiectomy; RALD, retroperitoneal and para-aortic lymph node dissection; SR, sper- matic cord resection; NED, no evidence of disease; DOD, dead of disease; AWD, alive with disease; Y, years; M, months; Ref, reference.