Renal Cell Carcinoma

2% of sporadic renal cell carcinomas (RCCs) are bilateral, and 16-25% of sporadic RCCs are multicentric in same kidney

Exophytic: Projects from cortical surface, distinct from parenchyma

Most are hypervascular (not papillary RCC)

Rarely, small areas of fat attenuation (-80 to -120 HU)

• Combination of fat and calcification suggests RCC, not renal angiomyolipoma (AML)

Renal venous (23%) and inferior vena cava (IVC) tumor extension (7%)

Metastases (most to least common): Lung, liver, bone, adrenal, opposite kidney, and brain

Cystic RCC: Enhancing, smooth or nodular septa

Multiphase CT

• Mandatory: Nonenhanced and parenchymal phase

• Optional: Corticomedullary, excretory phases

Multiphase MR

• T1WI: Typically low signal intensity (SI)

• T2WI: High to heterogeneous SI due to necrosis

• Post contrast: Heterogeneous due to areas of viable, hypervascular tumor and necrosis

Renal oncocytoma

Renal AML

Renal transitional cell carcinoma

Renal metastases and lymphoma

Renal abscess

Complex renal cysts (Bosniak classification types II and III)

Clear cell (70%), papillary (10-15%), granular cell (7%), chromophobe cell (5%), sarcomatoid (1.5%), collecting duct (< 1%)

Marked variability among tumors by histopathology

• Accurate distinction relies on molecular and cytogenetic markers

Renal cell carcinoma (RCC)

Malignant tumor arising from renal tubular epithelium

Location

• 2% of sporadic RCCs are bilateral; 16-25% of sporadic RCC are multicentric in same kidney

• Renal cortex is most common location

Morphology

• Usually solid mass, but occasionally cystic

Other general features

• ~ 50% found incidentally on imaging

NECT

• Heterogeneous mass ± cystic components

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    High attenuation (hemorrhage)

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    Low attenuation (≤ 20 HU) due to necrosis or cystic component

• Pseudocapsule may result from hyperattenuating rim

• Contour deformity due to exophytic tumors

• Rare calcifications (< 10% of cases)

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    Mostly amorphous & internal

• Rare, small areas of fat attenuation (-80 to -120 HU)

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    Usually due to enveloping perirenal or sinus fat

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    Dedifferentiated renal cell carcinoma (RCC) → fat and calcification

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    Fat + calcification suggests RCC > angiomyolipoma (AML)

• Cystic RCC

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    Uni- or multilocular cystic mass with thick wall

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    Calcification of septa or tumor capsule

CECT

• Enhancement (attenuation value ↑ by ≥ 20 HU compared to NECT)

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    < renal parenchyma on nephrographic and pyelographic phases

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    Small mass may be missed on corticomedullary phase

• Heterogeneous enhancement (necrosis)

• Exophytic: Projects from cortical surface, distinct from parenchyma

• ± lucent zone surrounding mass (pseudocapsule)

• ± infiltrating mass may simulate urothelial carcinoma

• ± subcapsular or perinephric hemorrhage

• ± invasion of renal veins or inferior vena cava (IVC)

• Direct extension to adjacent muscles (e.g., diaphragm, psoas, quadratus lumborum, erector spinae) & viscera (i.e., colon, liver, pancreas, spleen)

• Metastases to local lymph nodes (≥ 1 cm) or viscera

• Metastases (most to least common): Lung, liver, bone, adrenal, opposite kidney, and brain (often hypervascular)

• Cystic RCC: Enhancing, smooth or nodular septa

T1WI

• Typically isointense (~ 60%) to hypointense

• ↑ signal intensity (SI) if internal hemorrhage (methemoglobin)

T2WI

• Clear cell RCC: Typically ↑ SI

• Papillary RCC: Typically ↓ SI

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    Appears same as AML with minimal fat

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    Papillary RCCs often have pseudocapsule

T1WI C+ FS

• Enhancement is usually < normal renal tissue

Hypointense band/rim on T1WI (25%) and T2WI (60%)

In/out of phase

• Clear cell RCC can lose SI on out-of-phase images

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    Tumor cells may contain intracellular lipid

• Loss of signal on out-of-phase sequence cannot be reliably used to differentiate RCC from AML