Primary malignant mesothelioma of the tunica vaginalis presenting as hydrocele: imaging pitfalls

Our plain-English summary of Primary malignant mesothelioma of the tunica vaginalis presenting as hydrocele: imaging pitfalls, by J. Naidu, N.G. Joseph, M. Mohammed, et al (BMJ Case Reports, 2026).

The study

• Authors: J. Naidu, N.G. Joseph, M. Mohammed, V.K. Baskaradoss
• Journal: BMJ Case Reports
• Published: 2026;19(10)
• Type of article: Case report
• Read it: PubMed · Publisher · Free full text

Abstract

A man in his late 70s presented with progressive, painless scrotal swelling. The initial ultrasound was reported as a simple hydrocele, and he was scheduled for surgery. At operation, friable nodules on the tunica vaginalis were biopsied, confirming malignant epithelioid mesothelioma. Staging CT showed no pleural or peritoneal disease, supporting a primary tunica vaginalis origin. As the tunica vaginalis is an embryological continuation of the peritoneum, it is exceptionally rare for mesothelioma to arise here as a true primary rather than as a secondary spread from the peritoneum. This case highlights a rare primary malignant mesothelioma masquerading as a hydrocele, the limitations of ultrasound as a sole diagnostic tool and the importance of maintaining suspicion when operative findings are discordant with imaging.

© BMJ Publishing Group Limited 2026. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ Group.

In plain English

This case report described a man in his late 70s with several months of painless swelling on the left side of the scrotum. He had worked in an office-based job with no known exposure to asbestos. An ultrasound scan was reported as a simple hydrocele (a collection of fluid), and he was booked for surgery. During the operation, surgeons found multiple red, crumbly nodules on the tunica vaginalis, the lining around the testis, and removed them. Laboratory examination confirmed malignant epithelioid mesothelioma. A genetic test showed loss of p16, which supported malignancy, while BAP1 was preserved. When the ultrasound was reviewed afterwards, it showed subtle nodules. A CT scan of the chest, abdomen and pelvis found no pleural or peritoneal disease, and the authors took this to confirm the tumour began in the tunica vaginalis. A specialist team chose surveillance with scans every six months instead of removing the testis. The authors concluded that the case showed the limits of ultrasound alone. They stated that a single case cannot establish causation and that surveillance risks undertreatment.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: case report (single patient)
• Who was studied: one man in his late 70s with several months of progressive, painless left-sided scrotal swelling; location and dates of care not stated
• Exposure: no known exposure to asbestos; office-based job; the authors described no recognised risk factors
• Main results:
  • The preoperative ultrasound was reported as a hydrocele. Retrospective review revealed subtle mural nodularity.
  • During surgery, multiple red, friable nodules were seen on the tunica vaginalis and biopsied.
  • Histopathology of the excised nodules confirmed malignant epithelioid mesothelioma.
  • p16 (CDKN2A) testing showed loss of expression (homozygous deletion), supporting malignancy.
  • BAP1 immunohistochemistry showed preserved nuclear expression.
  • Staging CT of the chest, abdomen and pelvis showed no pleural or peritoneal thickening, masses or nodal disease.
  • The authors stated that the absence of pleural or peritoneal involvement confirmed a primary tunica vaginalis origin.
  • Radical inguinal orchiectomy was not pursued. The patient was placed under active surveillance with six-monthly CT and scrotal ultrasound.
  • The authors described this as a primary tunical mesothelioma with no recognised risk factors.
• The authors' conclusion: The authors concluded that the case emphasises the limitations of ultrasound as the sole diagnostic tool. They also suggested that surveillance may be a reasonable alternative in carefully selected patients within a specialist team setting.
• Limitations the authors state:
  • As a single case report, it cannot establish causation, identify prognostic factors or demonstrate treatment efficacy.
  • The surveillance approach requires validation through larger series.
  • Active surveillance risks undertreatment of a biologically aggressive malignancy.
  • Prognostic evidence specific to tunical disease is limited.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma, Tunica Vaginalis, Hydrocele, Ultrasound, Friable, Epithelioid, Staging, Peritoneum.

Related studies

• Pre-operative diagnosis of malignant mesothelioma of tunica vaginalis testis by hydrocele fluid cytology — S.C. Gupta, A.K. Gupta, et al. (1998)
• Papillary serous carcinoma of the tunica vaginalis testis — P. Becerra, M.A. Isaac, et al. (2000)
• Mesothelioma of the tunica vaginalis testis: a rare malignancy mimicking more common inguino-scrotal masses — P.J. Schure, K.C. van Dalen, et al. (2006)
• Malignant mesothelioma of tunica vaginalis testis: Report of a very rare case with review of the literature — E. Trenti, S.M. Palermo, et al. (2018)
• Malignant mesothelioma of the tunica vaginalis testis: report of first case with preoperative diagnosis — L. Japko, A.A. Horta, et al. (1982)
• Malignant mesothelioma of the tunica vaginalis testis: a rare case and review of literature — M. Drevinskaite, A. Patasius, et al. (2020)

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