Role of imaging in RCC From Diagnosis to Treatment: the Radiologist Perspective Diagnosis Staging Follow up Imaging modalities Limitations and pitfalls Duangkamon Prapruttam, MD Department of Therapeutic and Diagnostic Radiology Ramathibodi Hospital Ultrasonography Cystic or solid lesions Variable echogenic Hyperechoic (48%) Isoechoic (42%) Hypoechoic(10%) Solid lesion Small isoechoic at the pole can be misses. Must be DDx from pseudotumors. - Prominent column of Bertin - Dromedary hump - Persistent fetal lobulation - Junctional parenchymal defect Color Doppler US: similar vascularity of the pseudotumor to adjacent normal renal cortex Solid RCC Small (3 cm or less) - hyperechoic - Hypoechoic/anechoic rim = pseudocapsule and intratumoral cystic changes - RCC - Posterior acoustic shadow - AML Cystic RCC Do not fulfill all criterial of simple cyst - possibility of cystic renal carcinoma. US and CT, MR complement each other in characterization of renal lesions whose are indeterminate. 1
Cystic RCC Features suggesting a malignant cyst lesion - Thickened cystic wall - Numerous septations, thickened or nodular septations - Irregular or central calcifications - presence of flow in septations or cystic wall on Doppler imaging CT scan MC appearance: solid non-calcified lesion attenuation value > 20 HU on NCCT Enhance significantly: enhancement value > 20 HU Less intense enhance: papillary subtype These lesions accumulate contrast more slowly delayed images may be helpful in confirming enhancement Location: renal cortex, periphery near corticomedullary junction. Non-contrast: evaluate urolithiasis, acute hematoma, baseline density of renal masses. Arterial phase or coriticomedullary phase: - Evaluate arterial anatomy, 15-25 sec. - Limitation of small renal lesion small hypervascular RCC may enhance to the same degree as cortex - Maximal opacification of renal arteries and veins. - Metastasis show rapid enhancement. Nephrographic phase : - Contrast filters through glomeruli into loops of Henle and collecting tubules. - 80-180 sec. - Renal parenchyma enhanceds homogeneously. - Most valuable for detecting renal masses Delayed/excretory/urographic phase: - Begin 180 sec. - Contrast excreted into collecting system. - Evaluate involvement calices and pelvis. 2
Cystic RCC MDCT helps delineate location of mass and its relationship to collecting system and vessels. - A unilocular cystic RCC : extensive necrosis of previously solid RCC - B multilocular RCC : intrinsic multilocular growth, impossible to distinguish from multilocular cystic nephroma. - C Mural nodule in cystic RCC : tumor arising in wall of preexisting cyst. DDx of multilocular cystic renal mass : - Multilocular cystic nephroma - Complex abscess, infected cyst - Xanthogranulomatous pyelonephritis - Cystic Wilm s tumor - Organizing hematoma - Localized renal cystic disease One common pitfall in characterizing renal lesions by CT is presence of pseudoenhancement in renal cysts, due to volume averaging and beam hardening effects. - Degree of pseudoenhancement is greater in smaller renal cyst. - solid portion of cystic renal lesion > 15-20 almost always pathologic process although not always malignant - Ultrasound or MR may prove helpful. Cystic RCC vs hyperattenuation cyst Cystic renal mass : calcification Cystic renal mass : septation Bilateral synchronous multifocal RCCs Hereditary form : - von Hippel-Lindau : clear cell RCC - hereditary papillary RCC : papillary RCC. Birt-Hogg-Dube : chromophobe RCC, oncocytoma. -1.2 Sporadic form : < 5%. 3
Spontaneous perirenal hematoma - MC cause of spontaneous unilateral perirenal hemaorrhage are benign or malignant neoplasms (61%), with AML is the MC, followed closely by RCC. - Renal AML > 4cm has tendecny to bleed. - RCC : size is not a good indicator. - When initial imaging does not demonstrate the cause of renal hemorrhage, repeat imaging resolution is essential. RCC with macroscopic fat RCC containing fat mimic AML Malignant should be suspected on following criteria The combination of fat and calcification Large, irregular tumor invading perirenal or sinus fat Large necrotic tumor with small foci of fat and association with non-fatty lymph node Venous extension High soft tissue contrast Availability of non-nephrotoxic contrast agent Identification macro and microscopic fat - Macroscopic fat : AML - Microscopic fat : AML, clear cell RCC - Lipid-poor AML (5.5%) may mimic RCC. - MR: Lipid-poor AML drop SI of 42% Clear cell RCC drop SI < 20% is useful in detection and differentiation of cystic and solid renal lesions Evaluation of small renal masses, whereas CT can be problematic because of pseudoenhancement Solid renal tumors are typically isointense or slightly hypointense on T1W - Some tumors may contain hemorrhage or lipid component and show T1W hyperintensity. - Mildly hyperintense on T2W - ccrcc was predicted by signal intensity on T2W (high vs low, OR: 3.2, 95%CI 1.4-7.1) and contrast avidity (avid vs. low, OR: 4.5, 95%CI 1.8-10.8) - Variable enhancement on dynamic contrast enhanced images 4
Although some complex cysts may show higher T1 signal and lower T2 signal owing to hemorrhage, debris, or proteinaceous fluid, there should be no enhancement in cysts. MR may depict additional septa, thickening wall or enhancement. Staging RCC Currently, the most commonly used staging system is TNM system of the American Joint Committee on Cancer stage groupings. Staging RCC MRI is useful in delineating the parenchymal-tumor interface The most staging errors - perinephric extension. Intact pseudocapsule - best detected by T2W suggests lack of perinephric fat invasion Overall accuracy of MR in staging is comparable or superior to CT Vikram R et al. Radiographics 2009;29:741-754 Metastasis: Frequently to lung mediastinum bone liver Currently, size is the best quantitative imaging tumor response Immune checkpoint inhibitors pseudoprogression tumor growth with immunotherapy that regresses with time 5
With contrasted imaging, the amount of vascular tumor can be measured as an absolute or percentage change CT attenuation can also be used as an imaging biomarker more specifically designed to assess the degree of necrosis several limitations : Attenuation is also affected by contrast injection and several patient factors that make direct comparison between scans quite challenging Local tumor relapse - nephrectomy site Lung is most vulnerable site for distant metastasis Other LN, bone, brain, liver CT is modality of choice for detection local recurrence and distant metastasis. FDG PET may have a potential role in evaluation of distant metastasis, especially when findings from conventional study are equivocal and in ddx of recurrence from post-treatment change. Negative result cannot reliably rule out metastatic disease. 6