What are the etiologies of a renal (kidney) mass?

From the Guidelines

Renal masses are primarily composed of renal cell carcinoma (RCC), accounting for approximately 90% of all kidney cancers, with other etiologies including benign masses, inflammatory processes, and vascular abnormalities. The most common malignant renal mass is RCC, with other malignant etiologies including transitional cell carcinoma, Wilms tumor (primarily in children), lymphoma, and metastatic disease from other primary cancers 1. Benign renal masses include simple cysts, which are the most common renal lesion overall, angiomyolipomas (fat-containing tumors), oncocytomas, and renal adenomas. Inflammatory processes can also present as renal masses, including abscesses, xanthogranulomatous pyelonephritis, and focal pyelonephritis. Vascular abnormalities such as arteriovenous malformations and renal artery aneurysms may mimic solid masses. Congenital anomalies like polycystic kidney disease can present with multiple renal masses.

When evaluating a renal mass, imaging characteristics on CT or MRI, including enhancement patterns, presence of fat, and cystic components, help differentiate between these etiologies 1. Patient factors such as age, gender, and medical history also influence the likelihood of specific diagnoses. For example, angiomyolipomas are more common in women and patients with tuberous sclerosis, while RCC incidence increases with age and is associated with smoking and obesity. According to the most recent study 1, the primary predictors of a tumor’s biology and prognosis include pathological stage, histology, and grade, which are favorable for most patients with clinically localized disease (Stage I-II) where cancer-specific survival rates approximate 80-90% at 5-years.

Key points to consider in the evaluation and management of renal masses include:

• The majority of kidney cancers are renal cortical tumors known as renal cell carcinoma (RCC) 1
• Imaging characteristics on CT or MRI can help differentiate between benign and malignant etiologies 1
• Patient factors such as age, gender, and medical history influence the likelihood of specific diagnoses
• The primary predictors of a tumor’s biology and prognosis include pathological stage, histology, and grade 1

From the Research

Renal Mass Etiologies

• Renal cell carcinoma (RCC) is the most common kidney cancer in adults, and early and accurate imaging plays a crucial role in its detection, staging, and follow-up 2.
• The evaluation and management of RCC have evolved over the years, with most kidney tumors now being smaller, organ-confined, and suitable for nephron-sparing approaches 3.
• Computed tomography (CT) is the primary choice for imaging of renal masses, due to its high resolution, reproducibility, and reasonable cost 2.
• Magnetic resonance imaging (MRI) is considered an important alternative in patients requiring further imaging or in cases of allergies, pregnancy, or surveillance, and its use has increased due to concerns over radiation exposure 2, 4.
• Contrast-enhanced ultrasound (CEUS) is a useful method for differentiating between malignant and benign renal lesions, with comparable sensitivity, specificity, and predictive values to CT and MRI 4.

Imaging Characteristics of Renal Cell Carcinoma Subtypes

• Clear cell RCC (ccRCC) exhibits intense contrast enhancement and rapid washout pattern on CT, and appears hyperintense on T2-weighted imaging and hypointense on T1-weighted imaging on MRI 5.
• Papillary RCC (pRCC) has hypovascular features, lower contrast enhancement, and homogeneous borders 5.
• Chromophobe RCC (chRCC) has a less vascular structure and exhibits moderate contrast enhancement in the corticomedullary phase 5.
• Medullary RCC (mRCC) has invasive features and is usually diagnosed at an advanced stage, while collecting duct RCC (cdRCC) has a very aggressive clinical course 5.
• Multiloculated cystic RCC (mcRCC) contains distinct cystic areas between the septa, has a well-circumscribed structure, and generally has a low malignancy potential 5.

Comparison of Imaging Modalities

• CT and MRI have similar results in staging cases of renal cell carcinoma, but MRI may be more sensitive in detecting venous extension, metastatic adenopathy, and adjacent organ invasion 6.
• CEUS has a comparable sensitivity, specificity, and predictive values to CT and MRI in evaluating unclear renal lesions 4.