IMAGING FINDING IN RENAL CELL CARCINOMA – DIAGNOSIS AND STAGING
IMAGING FINDING IN RENAL CELL CARCINOMA – DIAGNOSIS AND STAGING
Dr Ivan Ađić, Dr Maja Stankov, prof. dr Nataša Prvulović Bunović
To present the defining imaging features of renal cell carcinoma in adults and the American Joint Commission on Cancer (AJCC) TNM staging system
Renal cell carcinoma (RCC) is the most common tumor to affect the kidney in adults, and it accounts for more than 80% of all primary malignant renal neoplasms. The incidence peak is between 50 and 70 years of age. These tumors can be solid, cystic or mixed, and can contain fat or calcifications. On histopathology, there are several subtypes: clear cell adenocarcinoma (which is the most common type in up to 75%), papilary (up to about 15%), chromophobe (up to 5%), unclassified (up to 5%) and collecting duct type (up to about 1%). The best imaging modality to characterize a renal mass is computed tomography (CT) or magnetic resonance imaging (MRI) with intravenous contrast. A dedicated renal protocol is performed to depict tumor size and mass type, presence or absence of macroscopic fat, tumor enhancement pattern and the presence or absence of extrarenal spread and metastases. Renal CT protocol should include a pre-contrast scan, with application of low osmolar or iso-osmolar iv. constrast material. The contrast scan should include corticomeduallary phase (at 40-70s delay) and nephrographic phase (at 100-120s delay) centered on the kidneys. An optional excretory phase scan at 7-10 minute delay is helpful to differentiate urothelial cancer from RCC and peripelvic cysts from hydronephrosis. Renal MR protocol should include axial and coronal T2W-weighted images, axial T1-weigthed in- and out-of-phase images, axial diffusion-weigthed images and axial and/or coronal T1-weighted fat-saturated pre- and post-contrast images. RCCs present as low attenuation, soft tissue masses on CT, with calcifications in up to 30%. Larger masses can have areas of necrosis. Enhancement patterns are variable, depending on the size and histological subtype but usually they enhance a similar amount or less than normal cortex on corticomedullary phase. Small lesions with indeterminate enhancement can be best depicted in the nephrographic phase. MRI can be useful for narrowing the differential diagnosis between renal tumors and its mimickers. T1 signal is most often heterogeneous, due to hemorrhage or necrosis. T2 depends on the subtype where in clear cell it is mostly hyperintense and in papillary subtype mostly hypointense. Enchancement patterns are similar as on CT scans. Diffusion weighted sequences are used to narrow down the differential diagnosis, and with small indeterminate lesions. Restriction is present in malignant tumors, but also in inflammatory lesions. Importantly an abscess will exibit greater restriction than a tumor. The differential diagnosis is broad and includes other renal tumors like adenoma, oncocytoma, angiomyolipoma as well as renal pseudotumors like complex cysts, renal abscess or renal infarct. Clinicaly RCCs can present with typical triad: hematuria, flank pain or a palpable flank mass, but only in about 10% of cases all three symptoms are found. A growing number of RCCs are incidentally found on imaging due to other, non-renal related symptoms. American Joint Commission on Cancer (AJCC) TNM staging: T0 indicates there is no evidence of a primary tumor, whereas Tx denotes that primary tumor cannot be assessed. T1 and T2 tumors are confined by the renal capsule which is an important landmark for staging. Renal masses can expand and push the capsule in T1 and T2 or invade through it in T3. T1a tumors are smaller than 4 centimetres and T1b smaller than 7 centimetres, both confined within the renal capsule. T2a tumors are greater than 7 but smaller than 10 centimetres and T2b greater than 10 centimetres, both confined within the renal capsule. T3 tumors invade the perinephic tissues or major veins but do not extend in the ipsilateral adrenal gland or beyond the perirenal fascia. T3a extends into the renal vein, renal sinus fat and renal capsule but not the perirenal fascia. T3b invades IVC below the diaphragm and T3c invades IVC above the diaphragm. T4 tumors invade the ipsilateral adrenal gland and tumor extends beyond the perirenal fascia. The retroperitoneal lymphnodes are assesed for regional nodal metastases (N status), whereas distant lymphnodes or other metastases are classified as distant metastases (M status). Nx status denotes that lymph nodes cannot be assessed, in N0 there are no regional (retroperitoneal) lymphnode metastases and in N1 there are regional lymphnode metastases. In M0 there are no distant metastases and in M1 there are distant lymphnode metastases or other metastases.
Figure 1. An exophitic tumor of the right kidney with enhancement on corticomedullary and washout on nephrogenic scan, indicated by the arrow. The enhancement is slightly lower than normal renal cortex. AJCC TNM T1b. A wellcircumscribed, T2W heterogenous lesion of the upper pole of the right kidney (in another patient), indicated by the arrow. The renal capsule is intact. AJCC TNM T1a.
Figure 2. Bilobular lesion of the left kidney, contained by the renal capsule (arrow). There is mass effect abbuting the renal vein with no infiltration (arrowhead) or tumor trombus forming. AJCC TNM T2a.
Figure 3. Mostly solid lesion of the right kidney (arrow) with cystic/necrotic foci (arrowhead). On the following postcontrast and diffusion-weigthed images, intermediate and homogeneus contrast enhancement with restriction diffusion can be seen. AJCC TNM T2a.
Figure 4. A heterogeneus mass of the right kidney, with invasion of perirenal fat and prominent collateral vein indicated by the arrowhead. Vena cava is without presence of tumor thrombus (arrows). AJCC TNM T3a. A mostly solid mass of the right kidney in another patient with heterogeneus T2W signal as well as avid contrast enhancement. Invasion of the right renal vein and vena cava below the diaphragm can be seen (arrow). A prominent retroperitoneal node is highlighted by the arrowhead. AJCC TNM T3b.
Figure 5. Mostly hypoenhancing lesion of the left kidney (indicated by the arrow) with direct invasion of the spleen and the posterior abdominal wall, which was surgically proven. AJCC TNM T4.
Figure 6. Centrally necrotic, hypoenhancing lesion of the left kidney, with invasion beyond the Gerota fascia. Multiple metastases can be seen in the right pulmonary lobe (arrowheads). AJCC TNM T4M1.
RCC is a frequently seen renal tumor in adults. Evaluation of renal masses requires a dedicated imaging protocol which allows the determination of TNM stage of RCC and the optimal treatment for the patient. Most renal masses are imaged on CT, but small or indeterminate lesions can be better charactarized on MRI. References: 1. Ng C, Wood C, Silverman P, Tannir N, Tamboli P, Sandler C. Renal Cell Carcinoma: Diagnosis, Staging, and Surveillance. AJR Am J Roentgenol. 2008;191(4):1220-32. 2. Kim H, Zisman A, Han K, Figlin R, Belldegrun A. Prognostic Significance of Venous Thrombus in Renal Cell Carcinoma. Are Renal Vein and Inferior Vena Cava Involvement Different? J Urol. 2004;171(2):588-91. 3. Ward RD, Tanaka H, Campbell SC, Remer EM. 2017 AUA Renal Mass and Localized Renal Cancer Guidelines: Imaging Implications. RadioGraphics 2018;38(7):2021–2033 4. Wang ZJ, Davenport MS, Silverman SG, et al. CT renal mass protocols v1.0. 2018 5/9/2018. https://abdominalradiology. org/wp-content/uploads/2020/11/RCC.CTprotocolsfinal-7-15-17.pdf. Accessed February 1, 2021 5. Goyal A, Sharma R, Bhalla A, Gamanagatti S, Seth A. Diffusion-Weighted MRI in Inflammatory Renal Lesions: All That Glitters is Not RCC!. Eur Radiol. 2012;23(1):272-9. 6. Davenport MS, Hu EM, Smith AD, et al. Reporting standards for the imaging-based diagnosis of renal masses on CT and MRI: a national survey of academic abdominal radiologists and urologists. Abdom Radiol (NY) 2017;42(4):1229–1240 7. Delahunt B, Cheville JC, Martignoni G, et al. The International Society of Urological pathology (ISUP) grading system for renal cell carcinoma and other prognostic parameters. Am J Surg Pathol 2013;37(10):1490–1504. 8. Shinagare AB, Krajewski KM, Braschi-Amirfarzan M, Ramaiya NH. Advanced renal cell carcinoma: role of the radiologist in the era of precision medicine. Radiology 2017;284(2):333–351.