Diagnosis: Clear cell renal cell carcinoma (RCC) – Stage I
Discussion: Clear cell RCC (formerly known as “conventional” RCC) is the most common type of RCC (65-80%), and its cells are composed of lipid and glycogen-laden clear cytoplasm (Fig. 10). Clear cell RCC originates from the renal cortex with an expansile growth pattern. Multicentricity/bilaterality is rare (<5%). 3p deletion is usually seen with this entity, and clear cell RCC is part of the von Hippel-Lindau syndrome.
Fuhrman Grading System correlation with prognosis has been reported:
1: Small, round, uniform nuclei without nucleoli
2: Larger nuclei with nucleoli and irregularities
3: Even larger nuclei and nucleoli and obvious irregularities
4: Bizarre, multilobed nuclei with heavy clumps of chromatin
Cystic degeneration occurs in 4-15% of RCCs. Clear cell RCC can be predominantly cystic. Clear cell RCC, especially sarcomatoid and rhabdoid types, is associated with a poorer prognosis than either papillary (prevalence = 10-15%) or chromophobe (prevalence = 4-11%) types.
Robson Staging:
I – Confined to capsule (95% five-year survival rate after radical nephrectomy)
II – Invading perinephric fat, but confined within Gerota’s fascia
IIIA – Invading the IVC or renal vein
IIIB – Regional lymph node involvement
IIIC – Venous and lymph node involvement
IV – Invading adjacent viscera/distant metastases (excluding ipsilateral adrenal
gland)
MR Findings: Varies depending on intratumoral hemorrhage (hyperintense on T1 and T2, if subacute/chronic; hypointense on both, if chronic) and necrosis (nonenhancing central homogeneity/hypointensity on the T1; and moderate to high signal intensity on the T2 data sets).
T1: Similar to renal parenchyma.
T2: Increased signal intensity.
In/Opposed Phase: Loss of signal intensity on opposed phase imaging within the solid portions corresponds to cytoplasmic fat in 60% of tumors.
T1+C: Heterogeneous enhancement (arterial phase).
Differential:
Papillary RCC: Bilateral/multifocal possible; BasophilicType I (homogenously hypointense on T2 imaging, homogenous mild enhancement, and heterogeneous if hemorrhage/necrosis); Eosinophilic Type II (complex/heterogeneous due to hemorrhage/necrosis, enhancing papillary projections, and fibrous capsule).
Chromophobic RCC: Solid and sometimes with cystic component, but necrosis uncommon. MR characteristics similar to clear cell RCC.
Oncocytoma: Spherical/well-defined; bilateral/multicentric possible; central scar (low T1 and high T2 signal with delayed enhancement) in 54% of cases; variable MR appearance, but usually lower signal on T1 compared to the renal parenchyma and higher signal on T2 with heterogeneous enhancement.
Collecting duct and renal medullary carcinomas are very aggressive.
References:
1. Pedrosa, Ivan, et al. “MR Imaging of Renal Masses: Correlation with Findings at Surgery and Pathologic Analysis.” Radiographics 2008; 28:985-1003.
2. Prasad, S.R., et al. “Common and Uncommon Histologic Subtypes of Renal Cell Carcinoma: Imaging Spectrum with Pathologic Correlation.” Radiographics 2006; 26:1795-1810.
3. Semelka, Richard C. Abdominal-Pelvic MRI. John Wiley & Sons, NY, Second Edition; 2006.
