Ultrasonic examination and manifestations of kidney cancer

B-ultrasound examination is simple and easy to perform, and does not cause pain or trauma to the examinee. It has now become one of the main items for regular health checkups in many units. More and more asymptomatic kidney cancers are discovered in this way. B-ultrasound has a high sensitivity in detecting kidney tumors and can be used as the preferred examination method. Massive echoes in the renal parenchyma are direct signs of ultrasound diagnosis of kidney cancer.

However, it should be noted that B-ultrasound images of renal cancer are non-specific, especially for tumors with a diameter of less than 2 cm or atypical sonograms. Diagnosis is difficult and requires close combination with clinical and other examination results for comprehensive analysis and judgment. On B-ultrasound images, typical renal cancer may have the following manifestations:

(1) Changes in kidney contour: When the tumor is small, the kidney contour may not change significantly. Larger tumors protrude from the kidney surface, causing the kidney contour to increase in localized size and become uneven. The kidney shape loses its normal appearance. The boundary between the tumor and the surrounding tissue is relatively clear. However, when advanced renal cancer infiltrates the surrounding tissue extensively, the boundary is often unclear.

(2) Abnormal echo of renal parenchyma: Abnormal echo masses appear in the renal parenchyma, which are round or oval in shape, with clear boundaries and a sense of sphere. The internal echo varies. Most medium-sized tumors are low-echoic, and only a few are mixed echoes or equal echoes of varying strengths. When there is bleeding, necrosis or liquefaction inside a larger tumor, an irregularly edged anechoic area will appear locally. If there is calcification, it will appear as a point or block of strong echoes with acoustic shadows. Smaller renal cancers sometimes appear as high-echo masses.

(3) The echo of the renal sinus is compressed and deformed: When the tumor grows inward and compresses or invades the renal sinus, the renal sinus may become concave, displaced, interrupted, or even unclear. In a few cases, the renal pelvis and calyx may expand and accumulate water.

(4) Abnormal changes in the blood vessels around the kidney: In the late stage of renal cancer, when the cancer tissue invades or metastasizes through the blood to the renal vein and lower limb veins, the ipsilateral renal vein or inferior vena cava will widen and become blocked, with irregular low- to medium-level dot- or mass-like echoes.

(5) Signs of renal cancer metastasis: abnormal low-echo masses in the renal hilum, retroperitoneal lymph nodes, liver, adrenal glands, and contralateral kidney.

(6) Differentiation from normal kidney variation: The hypertrophic renal column appears as a circular or elliptical low-echo area on the longitudinal section of the kidney, which is often seen in the middle and upper poles of the kidney, and resembles the echo of a renal tumor. However, careful observation reveals that the renal column is clearly demarcated from the renal sinus, and the interior is evenly distributed with tiny dot-like low-echoes. The cross-section shows that the low-echo of the renal column is continuous with the renal cortex, with no clear boundary between them. The cross-section of renal cancer has a clear boundary with the renal cortex and a distinct spherical feel. Some kidneys are abnormally lobed, causing the renal outline to bulge locally, which is often seen on the outer side of the middle and lower poles of the left kidney. In severe cases, the renal fusion is incomplete. The bulge is relatively large, but there is no boundary with the renal cortical echo, and there is no tumor configuration.

(7) Color Doppler ultrasound: It is mainly used to understand the extent of venous invasion. According to a report by Habboub et al., in the examination of 46 cases of renal cancer with venous thrombus confirmed by surgery, the accuracy of diagnosis of thrombus in the renal vein and inferior vena cava was 93%, the sensitivity was 81%, and the specificity was 98%.