Quantitative Imaging Methods for Diagnosis and Staging of Renal Cell Carcinoma

Introduction:

Renal cell carcinoma is the most common kidney cancer. Although a serious disease, it is highly curable if detected and treated early. Regardless of when it is diagnosed, some things can be done to help relieve the symptoms and make the patient feel better during treatment.

The incidence of renal cell carcinoma is usually higher in people in the age group of 50 to 70 years. Often the kidney starts with one tumor, but it can also start with several tumors, or it can be found in both kidneys at the same time.

What Are the Various Quantitative Imaging Methods for the Diagnosis and Staging of RCC?

The various quantitative imaging methods for the diagnosis and staging of renal cell carcinoma are listed below:

• Ultrasound - It is a procedure that involves high-energy sound waves (ultrasound) bouncing off internal tissues or organs and making echoes. Echoes form an image of body tissue called a sonogram. Ultrasound is commonly requested to assess the renal ducts, but it is not as sensitive or specific as other radiological tests. Moreover, it is often difficult to accurately classify the disease locally. Renal cell carcinoma has a very different ultrasound appearance. It may appear solid or partly cystic and may be hyperechoic (brighter than normal on ultrasound), anechoic (black), or hypoechoic (appear dark grey) to the surrounding renal parenchyma. This is a relatively specific symptom but not particularly sensitive. Sensitivity improvements of up to 85 % have been reported using harmonic scanning. Contrast-enhanced ultrasound typically shows heterogeneous hyper vascular lesions in the arterial phase with initial washout in the delayed phase.

• Computed Tomography (CT) -

1. A procedure in which a series of detailed images are taken from different angles, such as the abdomen or pelvis.

2. The images are taken by a computer connected to an X-ray machine. A contrast agent can be injected into a vein or swallowed to make organs and tissues more visible. This procedure is also called computed tomography or axial computed tomography. CT is widely used for both diagnosis and staging of renal cell carcinoma. On non-contrast CT, larger lesions often indicate areas of necrosis.

3. They also show calcification. During the corticomedullary phase of contrast enhancement, 25 to 70 seconds after contrast administration, renal cell carcinoma shows variable enhancement, usually smaller than the normal cortex. Small lesions show similar enhancement and may be difficult to detect. In general, small lesions show uniform enhancement, whereas large lesions show irregular enhancement with areas of necrosis.

4. The clear cell subtype may show much greater enhancement. The corticomedullary stage is also optimal for assessing vascular anatomy, considering both renal vein involvement and arterial changes when considering partial nephrectomy. Identification by CT is important because patients with inferior vena cava involvement have a significantly worse prognosis than those with renal vein involvement alone.

5. The nephrographic phase (80 to 180 seconds) is the most sensitive phase for detecting abnormal contrast enhancement. The excretory period is less important but important in assessing the anatomy of the collection system. Abdominal biphasic imaging is recommended post-treatment for maximal detection of solid organ metastases.

• Magnetic Resonance Imaging (MRI) - A procedure that involves the use of radio waves, magnets, and a computer to create a series of detailed pictures of areas inside the body. This procedure is known as nuclear magnetic resonance tomography (NMRI). MRI is excellent for renal imaging and local tumor grading and can also suggest histological potential based on T2 differences.

1. T1: Often heterogeneous due to the presence of necrosis, hemorrhage, and solid content.

2. T2: Appearance varies by histology. The visibility of clear cell renal cell carcinoma is very intense, and papillary renal cell carcinoma shows low strength.

3. T1 C+ (Gd): Often indicates immediate arterial augmentation.

The pseudo capsule in low-grade renal cell carcinoma, oncocytoma, and renal adenoma, appears as a low-signal border between the tumor and adjacent normal renal parenchyma. MRI is also helpful for imaging renal vein and inferior vena cava (IVC) tumor thrombi and rostral extension (important in preoperative planning). The presence of thrombus enhancement can distinguish between bland and tumor-related thrombi. The use of diffusion-weighted sequencing has been investigated to help characterize small, undetermined renal lesions that may be inflammatory or malignant, both exhibiting restricted diffusion.

• Fluorodeoxyglucose (FDG)- Positron Emission Tomography (PET) Scan - This procedure is used for detection of metabolically active carcinoma. Unlike many other malignancies, FDG-PET may be of limited value in primary renal carcinoma, mainly due to the physiological excretion of FDG from the kidney and the separation of renal lesions from normal tissue. Interstitial contrast may reduce, obscure, or mask renal lesions. Some research suggests that conventional imaging is inconclusive and, in some cases, can be used effectively as an adjunct to postoperative monitoring and restaging.

• Contrast-Enhanced Ultrasound- It contains air bubbles injected intravenously as a contrast agent and can detect slow, low-flow microcirculation. Contrast agents are gas-filled microbubbles that are administered intravenously into the systemic circulation. Microbubbles have a high level of echogenicity (the ability of objects to reflect ultrasound waves). There is a difference in echogenicity between the gas within microbubbles and the soft tissue surrounding the body. Therefore, ultrasound imaging with microbubble contrast agents enhances ultrasound waves' ultrasonic backscatter (reflection), producing contrast-enhanced sonograms due to large differences in echogenicity. Contrast-enhanced ultrasound can help to image perfusion of blood in organs, measure the velocity of blood flow in the heart and other organs, and for other applications.

What Are the Risk Factors Involved in Imaging of RCC?

Exposure to the radiation used in X-rays, whether in the form of X-rays, CT scans, or fluoroscopy, only slightly increases the risk of developing cancer later in life. Sensitivity to radiation varies with age, with children being more sensitive than adults.

Conclusion:

The most preferred method for imaging renal cell carcinoma is renal computed tomography (CT). In most cases, this single test can identify and grade RCC and provide information for surgical planning. Globally, renal cell carcinoma (RCC) is the sixth most common cancer in men and the tenth most common cancer in women, accounting for 5 % and 3 % of all tumor diagnoses, respectively. Early detection through radiological imaging and correct staging of the carcinoma leads to a better condition outcome.