模擬腎轉移癌的散發性副睪乳頭狀囊腺瘤

沈毓明、潘岳

彰化基督教醫院泌尿外科

Sporadic Epididymal Papillary Cystadenoma Mimicking Metastatic RCC

Yu-Ming Shen, Yueh Pan

Division of Urology, Department of Surgery, Changhua Christian Hospital

Introduction

Papillary cystadenoma of the epididymis (PCE) is an exceptionally rare epithelial tumor arising from the efferent ductules. It is frequently encountered in the setting of von Hippel–Lindau (VHL) disease, particularly when bilateral, yet sporadic unilateral cases have also been documented. The tumor’s clear-cell morphology and cystic-papillary pattern often resemble metastatic renal cell carcinoma (RCC), leading to potential diagnostic pitfalls. As management strategies differ significantly between these entities, an integrated approach combining imaging and immunohistochemical assessment is essential. We present a case of unilateral, non–VHL-associated PCE that clinically and microscopically mimicked metastatic RCC, emphasizing the diagnostic reasoning and postoperative evaluation confirming its benign nature.

Case presentation

A 64-year-old man with hypertension noticed a firm, non-tender nodule in the left scrotum during self-examination. Physical assessment revealed a localized epididymal mass, and ultrasound demonstrated a 1.4 cm well-circumscribed lesion with heterogeneous echotexture and preserved testicular contour. Excision through a scrotal approach was performed. The specimen measured 2 × 1.4 × 1 cm, revealing a yellowish, partially cystic cut surface. Microscopic analysis showed papillary and tubular structures lined by cuboidal cells with clear cytoplasm and uniform nuclei, without necrosis or atypia. Immunostains were positive for CK7, PAX8, and CA IX, with focal AMACR reactivity, while CD10 and RCC markers were negative. These findings supported PCE. Abdominal computed tomography ruled out renal or visceral lesions. Seven-month surveillance imaging confirmed no recurrence or systemic involvement, consistent with a sporadic, localized benign tumor.

Discussion

PCE represents a benign neoplasm of mesonephric origin and constitutes the second most frequent epididymal tumor after adenomatoid lesions. Although approximately one-third of cases occur in patients with VHL disease, most unilateral lesions develop sporadically. The lesion typically presents as a slow-growing, painless paratesticular mass and may be incidentally discovered during imaging for unrelated conditions. Because of its striking histologic similarity to metastatic clear-cell RCC—both sharing glycogen-rich clear cytoplasm and papillary growth—accurate diagnosis requires a combination of morphologic and immunophenotypic evaluation.

Typical immunoprofiles of PCE include CK7, EMA, and PAX8 positivity with variable CA IX expression and negative staining for CD10 and RCC markers. In contrast, metastatic RCC usually shows diffuse CD10 and CA IX positivity with absent CK7. Correlation with renal imaging is therefore indispensable to exclude metastatic disease.

Surgical excision is curative, and recurrence is exceedingly rare, usually attributed to incomplete removal. Bilateral cases or those in young patients should prompt genetic testing for VHL mutations. In older adults with unilateral lesions and unremarkable systemic evaluation, additional molecular workup may be unnecessary.

This case highlights that sporadic unilateral PCE can mimic malignancy both radiologically and histologically. Awareness of its benign nature and distinct immunohistochemical signature is crucial for urologists and pathologists to prevent unnecessary orchiectomy or oncologic therapy. Comprehensive but judicious evaluation ensures both diagnostic certainty and optimal patient outcomes.

Conclusion

Papillary cystadenoma of the epididymis is a benign tumor that may closely simulate metastatic RCC. Recognition of its distinctive histopathologic and immunohistochemical profile, supported by renal imaging, enables accurate diagnosis. Complete excision offers an excellent prognosis, and extensive genetic or systemic investigation is unnecessary in sporadic unilateral cases.

Figure 1. A well-defined heterogenous epididymal lesion.