Mesothelioma of tunica vaginalis of "uncertain malignant potential" - an evolving concept: case report and review of the literature

Mesothelioma of Uncertain Malignant Potential (MUMP) of the Tunica Vaginalis: Proposal for Reclassification as "Complex Mesothelial Tumor of the Tunica Vaginalis"

A well-differentiated papillary mesothelial tumor (WDPMT) and malignant mesothelioma are 2 well-recognized entities arising from the testis tunica vaginalis. Another mesothelial lesion exclusively seen at this site is mesothelioma of uncertain malignant potential (MUMP)-a lesion reminiscent of WDPMT yet demonstrating variable proportions of more complex architectural patterns that could be confused with invasion. MUMP was first described in 2010 with a total of 11 cases reported to date. Herein, we describe 19 additional patients who underwent hydrocelectomy, excision, and/or orchiectomy. Novel morphologic patterns found in addition to the 2010 series include spindle cells, keloidal-type collagen, and multicystic architecture lined by bland mesothelial cells. Clinical follow-up in 9 patients for more than 1 year (1.5 to 22.5 y, median 4.5 y) revealed no evidence of disease recurrence or metastases. Despite greater architectural complexity, MUMP has (1) bland cytology; (2) merging in with WDPMT areas; (3) low mitotic rate and Ki-67 nuclear labeling index; (4) retention of MTAP and BAP1 expression; and (5) benign clinical follow-up. If these cases were malignant mesotheliomas, one would have expected at least some of the patients to demonstrate disease recurrence/progression without adjuvant therapy within the available follow-up time, particularly with limited resection in most patients. Thus, we propose that "mesothelioma of uncertain malignant potential" be renamed as "complex mesothelial tumor of the tunica vaginalis." Using the term "complex" draws a contrast with the simple cuboidal lining and simple papillary architecture seen in WDPMT. Also, labeling the lesion as "tumor" removes the stigmata of "uncertain malignant potential" and "mesothelioma" that are alarming to patients and clinicians, and potentially could unduly lead to more extensive surgery in an attempt at "complete" resection. At the same time, not definitively labeling the lesion as benign allows recommendations for follow-up.

Well-Differentiated Papillary Mesothelial Tumor of the Scrotum with Suspicious Invasion

Well-differentiated papillary mesothelial tumor (WDPMT) is a distinct form of mesothelioma with low malignant potential and is mostly found in the peritoneal cavity. It consists of mesothelial cells with papillary structure and bland cytology. We report a rare case of WDPMT with suspicious invasive foci in the tunica vaginalis. WDPMT with invasive foci is known to have a tendency for recurrence. Therefore, careful attention should be given to properly diagnosing and treating this rare entity.

Testicular/paratesticular mesothelial tumours: Uncommon histopathologic entities in a very complex anatomical site

Mesothelial tumours of the testicular/paratesticular region are uncommon, poorly characterised and difficult-to-diagnose lesions. They encompass entirely benign proliferations (adenomatoid tumour) and malignant, very aggressive tumours (mesothelioma) whose morphological features can be overlapping, highly variable and confounding. Moreover, testicular/paratesticular mesothelial tumours comprise relatively new entities with indolent behaviour (well-differentiated papillary mesothelial tumour) as well as tumours which cannot be correctly included in any of the aforementioned categories and whose classification is still controversial. The molecular profile of such tumours represents an open issue. In fact, despite the recent discoveries about the genomic landscape of mesothelial proliferations at other sites (pleura, peritoneum), testicular/paratesticular mesothelial tumours, and namely mesotheliomas, are too rare to be extensively studied on large case series and they could arguably hide relevant differences in their molecular background when compared to the more common pleural/peritoneal counterparts.The aim of this review is to provide a guide for the pathological assessment of testicular/paratesticular mesothelial tumours. Herein, we describe the most recent updates on this topic according to the latest (year 2022) World Health Organisation Classification of Urinary and Male Genital Tumours (5th edition) and current literature. The diagnostic criteria, the main differentials and the role of ancillary techniques in the diagnosis of mesothelial testicular/paratesticular tumours are discussed.

Well-differentiated Papillary Mesothelial Tumour of the Tunica Vaginalis Testis - A Rare Lesion, but one Pathologists Should Know About Two Patient Reports and a Review of the Literature

Besides malignant mesothelioma, benign mesothelial neoplasms do exist in the tunica vaginalis testis. However, histological criteria remain controversial, thus leading to diagnostic uncertainty and difficulty in their classification according to their biological behavior. In recent years, molecular markers have emerged that aid in the differentiation of benign and malignant mesothelial proliferations throughout the body. Here, we present two middle-aged men with well-differentiated papillary mesothelial tumors and a review of the literature. By now, more than a year after surgery, one patient showed no recurrence of disease after partial or complete orchiectomy without further treatment, for the second no information is available. In conclusion, well-differentiated papillary mesothelial tumors represent rare lesions in the tunica vaginalis testis, but one pathologists should know about to prevent unnecessary treatment and suffering of patients.

Well differentiated papillary mesothelial tumor: a new name and new problems

Well-differentiated papillary mesothelial tumor (WDPMT, formerly called well-differentiated papillary mesothelioma) is a morphologically distinctive lesion composed of expansile papillae with a myxoid core covered by a single layer of generally bland mesothelial cells. Whether some WDPMT are precursors of invasive mesothelioma is uncertain, and this question is confounded by shallow biopsies of ordinary diffuse mesotheliomas that have superficial areas resembling WDPMT as well as by misinterpretation of some cases of mesothelioma in situ. Genetic analyses on a very small number of published cases of peritoneal WDPMT have shown a variety of mutations/copy number losses that do not overlap at all with those that are found recurrently in invasive mesotheliomas. The newly described entity of mesothelioma in situ usually appears as a single layer of mesothelial cells that have lost BAP1 by immunostaining, but sometimes is papillary and produces a morphologic mimic of WDPMT. We propose that, at least in the peritoneal cavity where most WDPMT occur, there are two morphologically identical but functionally distinct lesions: one is true WDPMT, a process that is probably benign, and the other is papillary mesothelioma in situ with the configuration of WDPMT. For that reason immunostaining for BAP1, and if necessary MTAP or CDKN2A FISH, should always be performed on cases with the appearance of WDPMT. It is possible, but speculative, that the small number of reports in the literature which describe invasive mesothelioma arising from WDMPT are actually describing invasive mesothelioma arising from mesothelioma in situ that looks like WDPMT.

A Diagnostic Approach to Paratesticular Lesions with Tubulopapillary Architecture: A Series of 16 Serous Borderline Tumors/Low-Grade Serous Carcinoma & 14 Well-Differentiated Papillary Mesothelial Tumors and Mesothelioma

As there is limited literature on paratesticular tumors of müllerian and mesothelial origin, we reviewed archived cases of serous borderline tumors (n=15), low-grade serous carcinoma (n=1), well-differentiated papillary mesothelial tumors (WDPMT; n=2), and mesothelioma (n=12), for relevant clinicopathologic features. Molecular profiling data from the American Association for Cancer Research (AACR) GENIE registry was accessed for 8 additional patients with testicular mesothelioma. For tumors of mesothelial origin, the median age at surgical excision was 62 years, median size was 4.5 cm, and they consistently exhibited positivity for mesothelial markers (CK5/6, calretinin, WT1 and D2-40). Recurrent alterations of the NF2 gene were identified in 3 of 8 (38%) patients, and alterations of BAP1 and CDKN2A were relatively infrequent. While one patient with WDPMT had a recurrence, a second patient with WDPMT progressed to a biphasic mesothelioma two years after initial resection. For tumors of müllerian origin, the median age at surgical excision was 45 years, the median size was 2.5 cm, and these exhibited consistent positivity for ER, WT1 and PAX8. Although no recurrences were documented in patients with serous borderline tumors, a single patient with a low-grade serous carcinoma developed widely metastatic disease and died of disease-related complications. Our study emphasizes the need for close clinical follow-up in patients with WDPMT and highlights the prognostic significance of documenting invasive behavior in tumors of müllerian origin as they can have an aggressive clinical course. Finally, our results suggest that NF2 alterations may play an important role in the pathogenesis of testicular mesothelioma.

Molecular and Immunohistochemical Characterization of Mesothelioma of the Tunica Vaginalis

AIMS

Malignant mesothelioma (MM) of the tunica vaginalis (TV) is a rare and aggressive tumor, and the molecular features and staining profile with contemporary immunohistochemical (IHC) biomarkers are largely unexplored. We characterize the clinicopathologic, molecular, and IHC features of MM (N=13) and mesothelial neoplasms of uncertain malignant potential (MUMP) (N=4).

METHODS AND RESULTS

Targeted next-generation sequencing was performed on 7 MMs and 2 MUMPs. IHC was performed for MTAP, BAP1 and SOX6. 13 adenomatoid tumors were also assessed with SOX6. MM were epithelioid (7/13) or biphasic (6/13). In MM, NF2 (5/7; 71%), CDKN2A (3/7; 43%), and BAP1 (2/7; 29%) were most frequently altered. Non-recurrent driver events were identified in PTCH1 and TSC1. In contrast, none of these alterations were identified in MUMPs; however, one MUMP harbored a TRAF7 missense mutation. By IHC, loss of MTAP (2/12; 17%) and BAP1 (2/9; 22%) was infrequent in MM, whereas both were retained in the MUMPs. SOX6 was positive in 9/11 (82%) MMs, and negative in all MUMPs and adenomatoid tumors.

CONCLUSIONS

Testicular MM exhibit a similar mutational profile to those of the pleura/peritoneum; however, alterations in CDKN2A and BAP1 are less common. These findings suggest that although MTAP and BAP1 IHC are specific for MM, their sensitivity in testicular MMs appears lower. In addition, rare tumors may harbor targetable alterations in driver genes (PTCH1 and TSC1) that are unusual in MMs at other anatomic sites. SOX6 is sensitive for MM; accordingly, the presence of SOX6 expression argues against a benign neoplastic process.

Spontaneous urinary bladder perforation: An unusual presentation of well-differentiated papillary peritoneum mesothelioma

INTRODUCTION

Well-differentiated papillary mesothelioma (WDPM) is a very rare neoplasm. Most of WDPM are asymptomatic and are often incidentally detected during surgery. This report describes a case of WDPM of the peritoneum unexpectedly diagnosed in a male with a spontaneous intraperitoneal bladder rupture.

CASE PRESENTATION

A 65-year-old male presented to our Emergency Department in November 2019 with a two-day history of anuria, abdominal pain, distention, and sepsis. The CT scan reported a large amount of extra and intraperitoneal free fluid. The CT cystogram showed bladder perforations on the dome and on the left lateral wall which was repaired through exploratory laparotomy. Intraoperatively, we encountered extensive suppurative peritonitis with large fibrino-purulent exudation. The purulent perivesical peritoneum was dissected and sent for histopathological examination which unexpectedly resulted in WDPM of the peritoneum.

CONCLUSION

Although we can't affirm with certainty, this case would seem to suggest that WDPM had played a role in patient's clinical presentation. However, further research is necessary to draw stronger conclusion.

Well-differentiated papillary mesothelioma of tunica vaginalis testis of unknown malignant potential: Sonographic appearance

Paratesticular mesothelioma is a rare differential diagnosis in the presence of scrotal hydrocele. A 17-year-old boy presented with a 3-year history of progressive hydrocele. Sonography revealed a large left paratesticular mass within the hydrocele. Serum tumor markers were negative. Left hydrocelectomy was performed and pathological analysis of the epididymal mass revealed a well-differentiated papillary mesothelioma. We discuss the sonographic and pathological findings of this rare neoplasm.

Images - Well-differentiated papillary mesothelioma of the tunica vaginalis

Well-differentiated papillary mesothelioma (WDPM) is a rare mesothelial tumour occurring in the tunica vaginalis of the testicle. The pathological classification of paratesticular mesothelial tumours is controversial and continues to evolve in the literature. Diagnostic criteria of one subtype, WDPM, are histological and include the following: 1) papillary or tubular-papillary architecture; 2) bland nuclear cytology; 3) low mitotic activity; 4) lined by a single row of cuboidal cells; and 5) absence of stromal invasion.1,2 This report presents issues of diagnosis of this rare pathology with imaging from an example case.

Case Report of a Well-Differentiated Papillary Mesothelioma of the Tunica Vaginalis in an Undescended Testis With Review of Literature

Well-differentiated papillary mesothelioma (WDPM) affecting the tunica vaginalis testis is a rare tumor, and very little is known about the clinicopathological spectrum of this variant as a distinct entity. Most patients with WDPM suffer from scrotal pain or swelling, but hydrocele seems to be the most common presenting symptom. These lesions are usually not aggressive and are accompanied by an indolent clinical behavior. In this article, we report the first case known of WDPM in an undescended testis, and in addition, we review the literature for similar cases.

Mesothelioma of the tunica vaginalis testis with prominent adenomatoid features: a case report

Malignant mesotheliomas of the testis arise from the tunica vaginalis, formed from the evagination of the abdominal peritoneum into the scrotum. It is an extremely rare tumor representing 0.3% to 5% of all malignant mesotheliomas. We presented an interesting case of 68-year-old male with swelling and slightly painful in the right scrotum. Histologically, the lesion were composed of small tubular, microcystic, gland lined by flattened epithelioid cells and vague signet ring cells set in a myxofibrous stroma, which is resemblance to adenomatoid tumor. But the tumor cells showed significant atypical cytologic morphology and invaded into spermatic cord tissue, which indicated the diagnosis of malignant tumor. Immunohistochemistry study showed positive expression of CK, CK5/6, CK7, Calretinin, D2-40 and Vimentin which indicated the diagnosis of malignant mesothelioma. This case of mesothelioma should be classified as epithelial in type. To our knowledge, the mesothelioma of the tunica vaginalis testis with adenomatoid tumor-like microscopic features is very rare.

Well-differentiated papillary mesothelioma of the tunica vaginalis: a case study and review of the literature

Well-differentiated papillary mesothelioma is an uncommon tumor of the testes that usually presents as a hydrocele. Here, we present the case of one patient who did not have a history of asbestos exposure. The tumor was localized in the tunica vaginalis and was composed of three pedunculated masses macroscopically. Microscopically, branching papillary structures with focal coagulative necrosis were present. In addition to immunohistochemistry, simian virus 40 DNA was also tested by polymerase chain reaction. This report presents one case of this rare entity, its clinical and macroscopic features, and follow-up results.

A case of adenocarcinoma of the rete testis accompanied by focal adenomatous hyperplasia

Adenocarcinoma of the rete testis is very rare. There is still little knowledge about its etiology and pathogenesis. Herein, we present a case of rete testis adenocarcinoma in a 36-year-old Chinese male. The tumor was predominantly composed of irregular small tubules and papillary structures with cuboidal or polygonal cells. In peripheral area of the tumor, the remaining normal rete testis and adenomatous hyperplasia of the rete testis could also be seen, indicating the possible relationship between adenomatous hyperplasia and adenocarcinoma. In addition, the patient underwent a left hydrocelectomy because of the existence of hydrocele 3 years ago. But, it is unclear whether hydrocele and hydrocelectomy is its cause or just the early clinical presentation of the adenocarcinoma.

Primary mucinous cystadenoma of the spermatic cord within the inguinal canal

We report a hitherto not documented case of primary mucinous cystadenoma arising in the spermatic cord within the right inguinal canal of a78-year-old man. The tumor was painless, hard and mobile. A computed tomography scan on the pelvis revealed an oval shaped, low attenuation mass, measuring 5.0x2.5x2.1 cm, that was present adjacent to the vas deferens. Grossly, the excised mass was multicystic mucinous tumor, filled with thick mucoid materials. Microscopically, the cystic wall was irregularly thickened. The cystic epithelium commonly showed short papillae lined by a single layer of columnar to cuboidal mucinous epithelial cells without significant stratification or cytologic atypia. Goblet cells were also frequently present. Immunohistochemically, the neoplastic cells showed positive reaction to carcinoembryonic antigen, cytokeratin 20, CDX2, epithelial membrane antigen, and CD15. However, they were negative for PAX8 and Wilms’ tumor 1 protein. Pathological diagnosis was a papillary mucinous cystadenoma of the spermatic cord. Although mucinous cystadenoma in this area is extremely rare, it is important that these lesions be recognized clinically and pathologically in order to avoid unnecessary radical surgery.