Florid mesothelial hyperplasia of the tunica vaginalis mimicking malignant mesothelioma: a clinicopathologic study of 12 cases

Our plain-English summary of Florid mesothelial hyperplasia of the tunica vaginalis mimicking malignant mesothelioma: a clinicopathologic study of 12 cases, by S. Lee, P.B. Illei, J.S. Han, et al (The American Journal of Surgical Pathology, 2014).

The study

• Authors: S. Lee, P.B. Illei, J.S. Han, J.I. Epstein
• Journal: The American Journal of Surgical Pathology
• Published: 2014;38(1):54-9
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The tunica vaginalis is an embryologically derived mesothelium-lined outpouching of the peritoneal cavity, which may develop neoplastic mesothelial proliferations similar to, although much less commonly than, pleural or peritoneal surfaces. We herein report our experience with 12 cases of florid paratesticular mesothelial hyperplasia, highlighting the spectrum of morphologic changes seen and the utility of fluorescence in situ hybridization analysis of homozygous deletion of 9p21 as an adjunct diagnostic tool. All cases were referred because of concern regarding the nature of the mesothelial proliferation. The median age of patients at presentation was 44.5 years (range, 16 to 71 y). Ten of 12 patients clinically presented with hydroceles (2 of which were complicated by infection or hemorrhage), 1 with "paraepididymal cyst" and 1 patient with an epididymal cyst. In contrast to the normal tunica consisting of a thin fibrous wall lined by a monolayer of flattened bland mesothelium and no significant inflammation, all of our cases were characterized by background changes of fibroblastic organization and stromal chronic inflammation. In all cases, the mesothelial proliferation within the fibrous and inflamed stroma was sparse and consisted of linear arrays of widely spaced horizontally orientated simple nonbranching elongated tubules and small solid nests and cords that were well spaced apart. There was an abrupt linear demarcation of tubules at the deep aspect of the fibrous tissue, with no evidence of definite invasion into the submesothelial tissue. Fluorescence in situ hybridization for 9p21 was negative in all 5 cases in which tissue was available for analysis. Nine patients with extended follow-up were alive (median 8 y; range, 1 to 13 y). In summary, the proliferative changes seen in reactive mesothelial hyperplasia associated with hydroceles may be florid and mimic malignant mesothelioma. In particular, the entrapment of isolated mesothelial clusters within deep fibrous tissue may be the cause of significant diagnostic difficulty. There are, however, morphologic clues such as linear arraying of widely spaced architecturally simple cell clusters that may aid in the correct identification of the benignity of these proliferations.

In plain English

This study described 12 cases of florid (very pronounced) reactive mesothelial hyperplasia, a non-cancerous overgrowth of lining cells, in the tunica vaginalis, the membrane around the testis. The cases came from one author's consultation files at The Johns Hopkins Hospital. They had been referred because of concern about the nature of the growth. Patients' median age was 44.5 years (range 16 to 71). Ten patients presented with hydroceles, 1 with a "paraepididymal cyst" and 1 with an epididymal cyst. Detailed asbestos exposure histories were not available. No case showed a visible mass. Neither dividing cells (mitotic figures) nor unequivocal invasion into deeper tissue were seen. A genetic test (FISH) for deletion of the 9p21 region was negative in all 5 cases tested. Nine patients with longer follow-up, checked only through a death index, were alive (median 8 years; range 1 to 13). The authors concluded that this reactive change can mimic malignant mesothelioma and that certain microscopic patterns may help identify it as benign. They added that the FISH test may have a supporting role, limited by low sensitivity.

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 series (clinicopathologic study) of pathology consultation cases, with FISH testing in some cases
• Who was studied: 12 patients with florid paratesticular mesothelial proliferation referred in consultation to a pathologist at The Johns Hopkins Hospital, Baltimore. Median age 44.5 years (range 16 to 71). Ten presented with hydroceles (2 complicated by infection or hemorrhage), 1 with a "paraepididymal cyst" and 1 with an epididymal cyst. Dates of the cases are not given.
• Exposure: Asbestos exposure was not studied; the authors state that a detailed history of asbestos exposure was unavailable.
• Main results:
  • In all 12 cases the mesothelial hyperplasia was an incidental microscopic finding in routine surgical specimens, and none showed polypoid, plaque-like or nodular masses on the tunica surface.
  • All 12 cases showed background fibroblastic organization and stromal chronic inflammation.
  • No case had a significant surface proliferation; 9 cases showed extensive loss of the surface lining (surface denudation).
  • In all cases the proliferation in the tissue was sparse: linear arrays of widely spaced, simple, nonbranching tubules, small nests and cords (gland:stroma ratio 1:2; gland density no more than 10 per high-power field). One case had a more complex cribriform arrangement.
  • Mitotic figures were not identified in any of the 12 cases.
  • Unequivocal invasion into fibroadipose and fibromuscular tissue was not seen in any case. In 1 case, isolated mesothelial tubules were found within superficial dartos smooth muscle bundles, without desmoplasia, and FISH for 9p21 was negative.
  • FISH for 9p21 deletion was negative in all 5 cases with tissue available for testing.
  • Nine patients with extended follow-up were alive (median 8 years; range 1 to 13 years). The other 3 cases were listed as recent.
• The authors' conclusion: The authors concluded that reactive mesothelial hyperplasia may be florid and mimic malignant mesothelioma, and that entrapped mesothelial clusters in deep fibrous tissue may cause significant diagnostic difficulty. They wrote that linear arrays of widely spaced, architecturally simple cell clusters may help identify these lesions as benign, and that frank invasion is what is diagnostic of malignancy. They also concluded that lack of 9p21 loss on FISH may have an adjunct role, limited by low sensitivity.
• Limitations the authors state:
  • Follow-up was limited to death status from the Social Security Death Index; no further follow-up information was available.
  • A detailed history of asbestos exposure was unavailable.
  • The authors did not know whether the patients had any further surgery.
  • The FISH test for 9p21 deletion has limited sensitivity. Such deletion may be less common in epithelioid than in sarcomatoid/biphasic mesothelioma, and significantly less frequent in peritoneal lesions, which the tunica vaginalis is assumed to most closely resemble.

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: Reactive Mesothelial Hyperplasia, Tunica Vaginalis, Malignant Mesothelioma, Mesothelium, Peritoneal Cavity, Paratesticular, Fluorescence In Situ Hybridization (FISH), Homozygous Deletion.

Related studies

• Value of Glut-1 and Koc markers in the differential diagnosis of reactive mesothelial hyperplasia, malignant mesothelioma and pulmonary adenocarcinoma — Ö. Üçer, A.F. Dağli, et al. (2013)
• BAP1 (BRCA1-associated protein 1) is a highly specific marker for differentiating mesothelioma from reactive mesothelial proliferations — M. Cigognetti, S. Lonardi, et al. (2015)
• Torsed appendix epididymis in an adult: misdiagnosis as tumor of tunica vaginalis on sonography — D.M. Yang, H.C. Kim, et al. (2018)
• How useful is GLUT-1 in differentiating mesothelial hyperplasia and fibrosing pleuritis from epithelioid and sarcomatoid mesotheliomas? An international collaborative study — A.N. Husain, M.K. Mirza, et al. (2014)
• Highly expressed EZH2 in combination with BAP1 and MTAP loss, as detected by immunohistochemistry, is useful for differentiating malignant pleural mesothelioma from reactive mesothelial hyperplasia — M. Yoshimura, Y. Kinoshita, et al. (2019)
• Nongynecologic metastases to fallopian tube mucosa: a potential mimic of tubal high-grade serous carcinoma and benign tubal mucinous metaplasia or nonmucinous hyperplasia — J.T. Rabban, P. Vohra, et al. (2015)

Browse more research in The American Journal of Surgical Pathology, or return to medical research.