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Malignant mesothelioma of the tunica vaginalis testis

Department of ¹ Diagnostic Radiology, ² Urology and ³ Pathology, Chi-Mei Foundation Medical Center, 901 Chung Hwa Road, Yung Kang, Tainan, Taiwan, Republic of China

	Abstract

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Malignant mesothelioma of the tunica vaginalis is rare, and is usually not diagnosed until surgery is undertaken. Reports on the ultrasound features of this tumour are limited. We present an unusual case with ultrasound features mimicking an adenomatoid tumour.

	Introduction

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Malignant mesothelioma is an uncommon tumour arising in body cavities lined by mesothelium. The majority of these tumours are found in the pleura, peritoneum and less frequently pericardium. As the tunica vaginalis is a layer of reflected peritoneum, mesothelioma can occur in the scrotal sac. The non-specific symptoms, broad age distribution and lack of tumour markers make pre-operative diagnosis of malignant mesothelioma of the tunica vaginalis difficult and indeed most of the reported cases were diagnosed at histology. Although ultrasound is considered the imaging modality of choice in evaluation of scrotal tumours, to date, reports on the ultrasound features of mesothelioma arising from tunica vaginalis are limited.

	Case report

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A 41-year-old man visited the outpatient department with a 1-year history of a left scrotal mass. Initially, the scrotal mass had been ignored but as the scrotum became progressively enlarged, medical help was sought.

Physical examination revealed a large tender mass occupying the left hemiscrotum. The right testis was normal. No lymph nodes were palpable in the inguinal regions. The transillumination test was positive. A "bulging" mass suspected to be due to inguinal hernia was also seen at right inguinal region.

The past history was insignificant, the patient denied any trauma or infectious history to the scrotum. The patient also denied any exposure to asbestos in the past. Laboratory results including testicular tumour markers, alpha-feto-protein and beta human chorionic gonadotropin were normal.

High resolution ultrasound using a 10 MHz linear transducer (GE LOGIQ 500; General Electric Medical Systems, Milwaukee, WI) showed a 2.1 cm x 1.3 cm hypoechoic mass with areas of colour Doppler flow demonstrated at left epididymal head (Figure 1). A moderate volume hydrocele was also found. Both testicles were normal in size and echopattern with no focal nodules detected. A minor varicocele was found in the left scrotum.

View larger version (121K): [in this window] [in a new window]   Figure 1. Colour Doppler ultrasound demonstrates a well-defined hypoechoic nodule (arrow) occupying the left epididymal head, with a few areas of colour flow demonstrated. The left testis (T) was intact with no focal nodule detected. A hydrocele is also present.

Histology showed that the left epididymis was intact, the mass excised during the operation was a paratesticular tumour arising from the tunica vaginalis. Microscopically, the tumour was a well differentiated papillary mesothelioma consisting of complex papillary fronds lined by cuboid bland-looking nuclei with moderate amount of eosinophilic cytoplasm. Numerous foamy histiocytes were seen in the fibrovascular stroma (Figure 2). Immunohistochemistry of this tumour was positive for cytokeratin and vimentin, but negative for carcinoembryonic antigen, consistent with mesothelioma.

View larger version (154K): [in this window] [in a new window]   Figure 2. Photomicrograph showing papillary fronds covered by bland-looking epithelial cells and aggregates of foamy histiocytes in the right hand side (haematoxylin and eosin stain, 200 x ).

	Discussion

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Malignant mesothelioma of the tunica vaginalis is a rare primary tumour that occurs in a broad age range, with the highest incidence between 55 years and 75 years [1]. Although trauma, herniorrhaphy and long term hydrocele [2] have been considered as the predisposing factors for development of malignant mesothelioma, the only well established risk factor is asbestos exposure [1, 3].

The ultrasound features of mesothelioma of the tunica vaginalis testis have not been widely reported. Hydrocele, either simple or complex is present and may be associated with: (1) well organized soft tissue fronds of mixed echogenicity (a hypoechoic centre surrounded by a hyperechoic rim) which extends into the hydrocele [4]; (2) multiple extratesticular nodular masses of increased echogenicity arising from the scrotal wall [5]; and (3) focal thickening of the tunica vaginalis testis with presence of nodularity [6]. The present case differs from the usual presentation; the mesothelioma demonstrated in our case consisted of a well-defined, slightly lobulated mass occupying the left epididymal head mimicking an epididymal tumour, and differentiation from the most common epididymal tumour, adenomatoid tumour was difficult.

Adenomatoid tumour, also known as benign mesothelioma, occurs in a younger age group, usually in the 3rd to 4th decades. The ultrasound features of an adenomatoid tumour may be variable and usually consists of a well-defined round shaped nodule having variable echogenicity ranging from hypoechoic to hyperechoic. The adenomatoid tumour is mostly located in the epididymal tail. As this is a benign tumour, surgical excision is unnecessary unless it is large enough to cause discomfort to the patient. However for patients with mesothelioma, surgical intervention is necessary as this is an aggressive tumour.

Patients with malignant mesothelioma of the tunica vaginalis frequently have a progressively enlarging hydrocele, and rapid re-accumulation of fluid after aspiration raises the suggestion of malignancy [7]. However fluid cytological analysis is frequently negative. Bruno et al [6] suggested direct ultrasound guided fine needle aspiration of the solid masses rather than fluid from the hydrocele, however this is still subject to sampling error. Unlike the more common adenomatoid tumour, which is usually well-defined and round in shape, the present case demonstrated an oval and slightly lobulated mass. Surgery was therefore performed, due to the uncertainty of the diagnosis.

Wolanske and Nino-Murcia [7] described the first colour Doppler ultrasound features of mesothelioma with decreased vascularity in the tumour compared with normal testicular parenchyma, consistent with the present case who also revealed relative hypovascularity of the tumour.

Even though ultrasound may not be able to differentiate a malignant paratesticular tumour from the more common benign tumour the role of ultrasound cannot be ignored in clinical practice. Besides determining whether a lesion is cystic or solid it is also helpful in differentiating whether the lesion is a neoplasm or infectious process, hence avoiding unnecessary surgical intervention. The low cost of ultrasound, absence of ionizing radiation, convenience and ready availability, renders ultrasound the imaging modality of choice in the evaluation of intrascrotal, extratesticular mass compared with the other imaging modalities such as CT or MRI. In conclusion, malignant mesothelioma of the tunica vaginalis is a rare neoplasm, whenever a paratesticular mass is seen in the epididymis, the possibility of mesothelioma should be included in the differential diagnosis even when there is no history of asbestos exposure such as in the present case. As these tumours may mimic adenomatoid tumours, fine needle aspiration of the tumour may be contributory in making a pre-operative diagnosis in these patients. This is important as it affects the surgical approach and the patient's prognosis. However, when a lobulated mass rather than a round shape is encountered, surgical intervention is recommended.

Received for publication October 6, 2003. Accepted for publication December 17, 2003.

	References

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3. Jones MA, Young RH, Scully RE. Malignant mesothelioma of the tunica vaginalis: a clinoco-pathologic analysis of 11 cases with review of the literature. Am J Surg Pathol 1995;19:815–25.[Medline]
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6. Bruno C, Minniti S, Procacci C. Diagnosis of malignant mesothelioma of the tunica vaginalis testis by ultrasound-guided fine-needle aspiration. J Clin Ultrasound 2002;30:181–3.[Medline]
7. Wolanske K, Nino-Murcia M. Malignant mesothelioma of the tunica vaginalis testis: atypical sonographic appearance. J Ultrasound Med 2001;20:69–72.[Medline]

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