Renal Cell Carcinoma Imaging: Practice Essentials, Radiography, Computed Tomography (2024)

The preferred method of imaging renal cell carcinomas is dedicated renal computed tomography (CT). In most cases, this single examination can detect and stage RCC and provide information for surgical planning. ^{[1, 2, 3]} Worldwide, renal cell carcinoma (RCC) represents the sixth most frequently diagnosed cancer in men and the 10th in women, accounting for 5% and 3% of all oncologic diagnoses, respectively. ^[4] In the United States, there are approximately 65,000 new cases and almost 15,000 deaths from RCC each year. It most often occurs in patients aged 55 years or older (average age, 64 yr). ^[5] One fourth to one third of patients present with metastatic disease. In only approximately 2% of cases are bilateral tumors seen at presentation. Because of improvements in diagnostic tests such as CT and MRI, the incidence of RCC has increased, with the most common type of RCC being clear cell carcinoma. ^[6]

(See the images below.)

Risk factors include increased age; male sex; smoking; cadmium, benzene, trichloroethylene, and asbestos exposure; excessive weight; chronic dialysis use; and several genetic syndromes (familial RCC, hereditary papillary RCC, von Hippel–Lindau syndrome, and tuberous sclerosis). ^{[7, 8]}

RCCs can be staged by using the American Joint Committee on Cancer TNM (Tumor, Node, Metastases) classification, as follows:

• Stage 1 RCCs are 7 cm or smaller and confined to the kidney.

• Stage 2 RCCs are larger than 7 cm but still organ confined.

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• Stage 3 tumors extend into the renal vein or vena cava, involve the ipsilateral adrenal gland and/or perinephric fat, or have spread to local lymph nodes.

• Stage 4 tumors extend beyond the Gerota fascia, have spread to local or distant nodes, or have distant metastases.

Guidelines

The American College of Radiology (ACR) Appropriateness Criteria for RCC staging recommends contrast-enhanced multiphasic CT scanning of the abdomen as the diagnostic modality of choice for staging a primary renal tumor. MRI of the abdomen is a suitable substitute when contrast-enhanced CT is contraindicated. If the status of the renal veins and IVC cannot be determined on CT, contrast-enhanced multiphasic 3-D MR venography can be performed. CT of the chest should be used to detect pulmonary metastasis in patients with large or locally advanced tumors. Chest radiography may be sufficient in patients with small primary tumors. In patients with suspicion of metastatic disease based on symptoms, other sites of metastases, or abnormal laboratory findings, brain MRI and bone scans can be performed. ^[9]

The National Comprehensive Cancer Network (NCCN) guidelines for kidney cancer recommend the following as part of the initial workup ^[10] :

• Abdominal/pelvic CT or abdominal MRI with or without contrast, depending on renal insufficiency

• Chest imaging

• Brain MRI, if clinically indicated

The NCCN guideline recommends abdominal MRI to assess suspected tumor involvement in the inferior vena cava, or as an alternative to CT for renal mass detection and staging in cases where the use of contrast is contraindicated because of allergy or renal insufficiency. ^[10]

The American Urological Association (AUA) guideline for the management of the clinical T1 renal mass recommends a high-quality cross-sectional CT or MRI, first without and then with intravenous contrast if kidney function is adequate. The objectives are as follows ^[11] :

• Rule out angiomyolipoma radiographically if possible

• Evaluate for locally invasive features

• Study the involved anatomy

• Determine the status of the uninvolved kidney and its vasculature

Imaging modalities

Although a variety of examinations (ultrasound [US], magnetic resonance imaging [MRI], angiography) can be used in the workup of patients with suspected RCC, the preferred method of imaging is dedicated renal computed tomography (CT). In most cases, this single examination can be used to detect and stage RCC and to provide information for surgical planning without additional imaging. ^{[1, 2, 3]}

Noninvasive cross-sectional imaging (CT, MRI, US) has replaced angiography in the workup of patients with known or suspected RCC. Advances in CT angiography and magnetic resonance angiography have diminished the need for preoperative conventional angiographic mapping of the renal vasculature prior to nephron-sparing or minimally invasive surgery. Angiography is still occasionally used if the origin of a tumor (eg, renal vs adrenal) is not certain. In these patients, selective injection of the renal and adrenal arteries, as well as additional vessels, may be necessary.

High resolution, reproducibility, reasonable preparation and acquisition time, and acceptable cost allow CT to remain as the primary choice for radiologic imaging. MRI is an important alternative in patients requiring further imagingand in cases ofallergies, pregnancy, or surveillance. Because of concern over radiation exposure, there has been a trend toward more use of MRI. ^{[12, 13]}

Kutluhan et al reported that renal capsular invasion and perirenal fat invasion are reliable signs of locally advanced RCC in both CT and MRI ^[14]

Preliminary studies have reported a promising role for positron emission tomography (PET)/CT with radiolabeled molecules targeting prostate-specific membrane antigen (PSMA)in patients with RCC. ^[15]

A systematic review, by Vogel et al, of 40 studies with a combined 4354 patients compared CT, MRI, positron emission tomography (PET)/CT, and ultrasonography for diagnosing and staging RCC in adults. For CT, median sensitivity and specificity were 88% and 75%, respectively, and for MRI, 87.5% and 89%. Staging sensitivity and specificity for CT were 87% and 74.5%, while MRI showed a median sensitivity of 90% and specificity of 75%. Contrast-enhanced US had a median diagnostic sensitivity of 93% and mediocre specificity, and the diagnostic performance of unenhanced US was poor. ^[16]

Oliva et al compared the characteristics on MRI of papillary renal cell tumors and clear cell tumors and noted that they had a similar appearance and signal intensity ratio on T1-weighted images, but on T2-weighted images, most papillary tumors were hypointense and most clear cell tumors were hyperintense. A tumor T2 signal intensity ratio of 0.66 or less had a specificity of 100% and a sensitivity of 54% for papillary tumors. ^[17]

A meta-analysis, by Chiarello et al, of 13 studies involving 275 papillary RCC lesions and 758 other renal masses that used MRI to differentiate papillary RCC from other renal lesions found moderate sensitivity and excellent specificity of quantitative enhancement in the corticomedullary phase (sensitivity of 79.6% and specificity of 88.1%). ^[13]

Taouli et al compared diffusion-weighted MRI with contrast-enhanced MRI to diagnose renal lesions. They found that although diffusion-weighted images can be used to characterize renal lesions (eg, differentiate solid tumors from oncocytomas and characterize histologic subtype), such images are less accurate than contrast-enhanced images. The area under the curve (AUC), sensitivity, and specificity of diffusion-weighted imaging were 0.856, 86%, and 80%, respectively, whereas the AUC, sensitivity, and specificity of contrast-enhanced MR imaging were 0.944, 100%, and 89%, respectively. ^[18] MRI findings correlate well with aggressive histology in the progression of RCC. ^[19]

In the few patients in whom CT findings are equivocal, MRI or US can be useful. Some studies have suggested a use for contrast-enhanced Doppler US for lesions that show equivocal enhancement at CT. Angiography is rarely used in the workup of suggested RCC, but it can provide information about the origin of the tumor in troublesome cases. Patients with a hereditary predisposition for RCC should be periodically examined by using dedicated renal CT.

(See the renal cell carcinoma images below.)

According to Guzzo et al, multidetector CT with 3-Dmapping is effective in accurately characterizing the level of venous thrombus in patients with renal cell carcinoma. When excluding patients with segmental venous involvement only, the concordance rate between multidetector CT and pathologic findings was 84%, and multidetector CT predicted the level of tumor thrombus in 26 of 27 patients (96%). The investigators noted that in patients with renal cell carcinoma in whom multidetector CT fails to detect tumor thrombus, it is unlikely that a tumor thrombus will be found at surgery that would change the surgical approach. ^[1]

After studying 298 cases of RCC and oncocytoma using preoperative multiphasic multidetector CT, Young et al concluded that this approach can assist in discriminating clear cell RCC from other forms of RCC. ^[20]

Radiogenomics is a field of translational radiology that aims to associate a disease's radiologic phenotype with its underlying genotype, thus offering a novel class of noninvasive biomarkers with diagnostic, prognostic, and therapeutic potential. ^{[21, 22]}

Dual-energy CT (DECT) can be used to measure iodine and calcium concentrations and increase the iodine signal to help differentiate pathologic processes and clarify the internal structure of mass lesions. DECT can also potentially reduce the radiation dose by applying virtual noncontrast images, eliminating the need for precontrast CT. ^[23]

Limitations of techniques

The primary limitation of CT is the characterization of hypoattenuation in masses smaller than 8-10 mm, in which pseudoenhancement may be a problem. In these cases, US may be of some use in characterizing the lesions as cysts. In addition, spread to regional lymph nodes in the absence of lymph node enlargement can be missed. If contrast material cannot be intravenously administered, CT is a poor choice for evaluating renal masses. MRI should be performed instead.

The primary limitations of US include problems related to incomplete staging (bones, lungs, regional nodes) and to the detection of small non–contour-deforming masses. In addition, large patients are not good candidates for US because of technical difficulties in obtaining adequate images.

MRI is limited by patient cooperation because MRI is more sensitive to motion artifact than CT. However, advances in techniques for limiting motion, as well as techniques that allow free breathing, may obviate these limitations. However, MRI is still more expensive and less readily available than CT. Furthermore, patients with pacemakers, certain types of medical implants, or severe claustrophobia are excluded from undergoing MRI.

Pregnancy

When RCC is suggested in a pregnant patient, US should be considered first for imaging, especially in the first trimester. CT also can be useful, and the radiation exposure to the fetus is justifiable, especially if the clinical picture is confusing; any fetal damage is unlikely at the radiation doses typically used. The dose should be kept to a minimum by increasing the pitch and decreasing the microamperes and avoiding scanning the pelvis if possible. MRI is good for detecting, characterizing, and staging renal masses and avoids the exposure to ionizing radiation; however, intravenous gadolinium contrast cannot be used.

The use of the most appropriate and accurate diagnostic method (contrast-enhanced CT or MRI) and the most appropriate treatment of the mother is most likely to result in long-term benefit to the fetus. Nephrectomy can be performed with the least morbidity to the mother and fetus in the second trimester and is probably preferable to leaving a malignancy untreated throughout pregnancy.

Contrast agent allergy

If contrast enhancement is needed, actions can be taken to decrease the risk of an adverse reaction in patients with an allergy to iodinated contrast material. The patient can be premedicated with steroids and histamine blockers. Use of low-osmolar contrast may also help.

In patients who have had previous life-threatening reactions, the use of iodinated contrast material should be avoided.

Renal insufficiency

In patients with renal insufficiency, avoiding or limiting intravenous iodinated contrast material and ensuring adequate hydration is best if the creatinine levels are above 2 and if the patient is not receiving long-term dialysis. Poor renal function also results in failure to opacify the kidneys and collecting system, limiting evaluation of the kidneys. In patients with renal insufficiency, MRI is an excellent alternative to CT.

Another consideration in patients with abnormal renal function not yet requiring dialysis is that nephrectomy will likely result in dialysis dependence. In these patients, accurate diagnosis and staging is imperative and is probably best accomplished by using contrast-enhanced MRI.

In patients already undergoing dialysis, iodinated contrast material does not need to be avoided, and in fact, CT is preferable to MRI because of the small but documented risk of nephrogenic systemic fibrosis (NSF).