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.