| Disease | Renal papillary adenoma |
| Epidemiology | Papillary adenomas are common. They have been reported in 7% of nephrectomy specimens and 10-40% of autopsy kidneys. In autopsy series, the lesions are more common in older patients (10% of patients <40 years; 40% in those >70 years) and in patients with end stage kidney disease. Papillary adenomas may be found more frequently in resected kidneys with papillary renal cell carcinoma, and in patients with hereditary RCC, renal vascular disease, end-stage renal disease or acquired cystic kidney disease. |
| Clinics | Most renal papillary adenomas are discovered incidentally at nephrectomy for another disease. However, with better imaging more tumors may be identified preoperatively. Multiple, bilateral papillary adenomas are referred to as renal adenomatosis. |
| Pathology | The current World Health Organization (WHO) classification of kidney tumors defines renal papillary adenomas as unencapsulated epithelial tumors lesions with a tubulo-papillary architecture measuring ≤ 15mm and of low nuclear grade (Eble et al., 2016). The tumors morphologically resemble PRCC with papillary to tubulopapillary architecture and CK7 expression. By definition, cytologic aypia and necrosis are absent (Fig. 1). |
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| Figure 1: Histologically, papillary adenomas resemble low grade papillary RCC, but are < 15 mm in greatest dimension. |
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| Treatment | Although very little is typically done for small renal masses <2.0 cm, a core biopsy can be obtained to confirm the diagnosis of a papillary adenoma detected by imaging. Subsequent treatment options would typically include observation and cyoablation; surgery is less for papillary adenomas and is typically reserved for carcinomas. |
| Evolution | It has been proposed that renal papillary adenomas are precursor lesions of papillary renal cell carcinoma. In addition to the epidemiologic association with PRCC (see above), papillary adenomas and PRCC show similar immunohistochemical expression of alpha-methylacyl-coenzyme A racemase ( AMACR ). Interestingly, papillary adenomas arising in the setting of acquired polycystic kidney disease do not show AMACR expression, suggesting a different biological mechanism for these neoplasms. |
| Prognosis | Excellent for this benign lesion. Renal papillary adenomas theoretically have no metastatic potential. |
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| Papillary adenoma. |
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