Understanding the Function of Your Kidneys. Your physician may request that you drink a minimum amount of liquid before the procedure, such as 24 ounces of water or more. You might be asked to hold your bladder for the test.
If you must void before the ultrasound, you may need to drink water while in the waiting room to maintain a full bladder. But there could be case-by-case instances where your doctor asks you to modify your diet leading up to the ultrasound. Wear comfortable clothing. The technicians must use a gel on your skin, which aids in the conduction of the sound waves. Sometimes, the technician will ask you to remove your clothing and wear a hospital gown instead. Consider leaving your jewelry or other valuable items at home.
Allow 30 to 60 minutes for the completion of the kidney ultrasound. Make sure you follow any additional instructions your healthcare provider gives you. The technician will have you lie on your stomach to locate the kidneys during the ultrasound. As mentioned earlier, the technician will apply a gel to your skin to facilitate the transmission of the sound waves and obtain an image.
The clinician will place a transducer on your skin over the particular areas of interest or concern. You may be asked to hold a position for a few moments, or, you might be asked to adjust your position for a clearer image. This sound is perfectly normal. If your bladder is being scanned, you might need to take some images with a full bladder , void, then have additional images taken with an empty bladder.felcicongeschmi.tk
Ultrasound: Renal (Kidneys, Ureters, Bladder)
When the kidney ultrasound is over, the technician will wipe the gel off or your skin. Afterward, you likely can get dressed and leave. Your physician will contact you with the results and any additional steps you may need to take. A Word From Verywell. Was this page helpful? Thanks for your feedback! Sign Up. What are your concerns? Article Sources. Johns Hopkins Medicine.
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Kidney Ultrasound. The right kidney is often found more caudally and is slimmer than the left kidney, which may have a so-called dromedary hump due to its proximity to the spleen. The kidney is surrounded by a capsule separating the kidney from the echogenic perirenal fat, which is seen as a thin linear structure.
The kidney is divided into parenchyma and renal sinus. The renal sinus is hyperechoic and is composed of calyces, the renal pelvis, fat and the major intrarenal vessels. In the normal kidney, the urinary collecting system in the renal sinus is not visible, but it creates a heteroechoic appearance with the interposed fat and vessels. The parenchyma is more hypoechoic and homogenous and is divided into the outermost cortex and the innermost and slightly less echogenic medullary pyramids. Between the pyramids are the cortical infoldings, called columns of Bertin Figure 1.
In the pediatric patient, it is easier to differentiate the hypoechoic medullar pyramids from the more echogenic peripheral zone of the cortex in the parenchyma rim, as well as the columns of Bertin Figure 2. The length of the adult kidney is normally 10—12 cm, and the right kidney is often slightly longer than the left kidney.
The adult kidney size is variable due to the correlation with body height and age; however, normograms for pediatric kidney size are available. Cortical thickness should be estimated from the base of the pyramid and is generally 7—10 mm. If the pyramids are difficult to differentiate, the parenchymal thickness can be measured instead and should be 15—20 mm Figure 3. The echogenicity of the cortex decreases with age and is less echogenic than or equal to the liver and spleen at the same depth in individuals older than six months.
In neonates and children up to six months of age, the cortex is more echogenic than the liver and spleen when compared at the same depth. Doppler ultrasonography of the kidney is widely used, and the vessels are easily depicted by the color Doppler technique in order to evaluate perfusion. Applying spectral Doppler to the renal artery and selected interlobular arteries, peak systolic velocities, resistive index, and acceleration curves can be estimated Figure 4 e.
Figure 2. Normal pediatric kidney. Figure 3. Measures of the kidney. Masses are seen as a distortion of the normal renal architecture. Most renal masses are simple cortical renal cysts with a round appearance and a smooth thin capsule encompassing anechoic fluid. Cysts cause posterior enhancement as a consequence of reduced attenuation of the ultrasound within the cyst fluid Figure 5. The simple cyst is a benign lesion, which does not require further evaluation. Complex cysts can have membranes dividing the fluid-filled center with internal echoes, calcifications or irregular thickened walls.
In advanced stages of this disease, the kidneys are enlarged with a lack of corticomedullary differentiation Figure 7. Figure 5. Simple renal cyst with posterior enhancement in an adult kidney. Figure 6. Complex cyst with thickened walls and membranes in the lower pole of an adult kidney. Figure 7. Advanced polycystic kidney disease with multiple cysts. A solid renal mass appears in the US exam with internal echoes, without the well-defined, smooth walls seen in cysts, often with Doppler signal, and is frequently malignant or has a high malignant potential.
RCCs are typically isoechoic and peripherally located in the parenchyma, but can be both hypo- and hyper-echoic and are found centrally in medulla or sinus. The lesions can be multifocal and have cystic elements due to necrosis, calcifications and be multifocal Figure 8 and Figure 9.
RCC is associated with von Hippel—Lindau disease, and with tuberous sclerosis, and US has been recommended as a tool for assessment and follow-up of renal masses in these patients. However, US is not the primary modality for the evaluation of solid tumors in the kidney, and CT is the first choice modality.
Nevertheless, hemorrhagic cysts can resemble RCC on CT, but they are easily distinguished with Doppler ultrasonography. Other malignant tumors in the kidney are transitional cell carcinoma and squamous cell carcinoma, which arise from the urothelium and are found the renal sinus, as well as adenocarcinoma, lymphoma and metastases, which can be found anywhere in the kidney Figure Benign solid tumors of the kidney are oncocytoma and angiomyofibroma.
Oncocytoma has a varying ultrasonic appearance, but may have a central scar or calcification as a hallmark.
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Angiomyofibroma are often found in patients with tuberous sclerosis. They are composed of fat, smooth muscle tissue and vascular elements. The echogenicity is governed by the composition of these elements, but the lesion is often hyperechoic Figure 11 and Figure Benign tumors are difficult to separate from malignant tumors using US. Thus, solid renal masses found on US are difficult to classify and should be further evaluated with CT.
In special cases of cystic or solid renal masses, additional US guided biopsy or drainage is performed to identify the histologic tumor type before a decision on surgery is made. Figure Solid tumor in the renal sinus seen as a hypoechoic mass, later found to be lymphoma. The '1' and '2' on the US image are reference points used for CT fusion not shown.
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Angiomyolipoma seen as a hyperechoic mass in the upper pole of an adult kidney. Patient with tuberous sclerosis and multiple angiomyolipomas in the kidney. One of the primary indications for referral to US evaluation of the kidneys is evaluation of the urinary collecting system. Enlargement of the urinary collecting system is usually related to urinary obstruction and can include the pelvis, the calyces and the ureter. Hydronephrosis is seen as an anechoic fluid-filled interconnected space with enhancement within the renal sinus, and normally, the dilated pelvis can be differentiated from the dilated calyces.
Several conditions can result in urinary obstruction. In both adults and children, masses, such as abscesses and tumors, can compress the ureter. In children, hydronephrosis can be caused by ureteropelvic junction obstruction, ectopic inserted ureter, primary megaureter and posterior urethral valve Figure In the latter, both kidneys will be affected.
In adults, hydronephrosis can be caused by urolithiasis, obstructing the outlet of the renal pelvis or the ureter, and compression of the ureter from, e. Under normal conditions, the ureter is not seen with US. However, in, e. The hydronephrosis is typically graded visually and can be divided into five categories going from a slight expansion of the renal pelvis to end-stage hydronephrosis with cortical thinning Figure The evaluation of hydronephrosis can also include measures of calyces at the level of the neck in the longitudinal scan plane, of the dilated renal pelvis in the transverse scan plane and the cortical thickness, as explained previously Figure 16 and Figure If the fluid in the dilated collecting system has echoes, pyonephrosis should be excluded by clinical exam, blood analysis and, in special cases, puncture or drainage.
Hydronephrosis can also be caused by non-obstructive conditions, such as brisk diuresis in patients treated with diuretics, in pregnant women and in children with vesicoureteral reflux.
What to Expect at a Kidney Ultrasound
End-stage hydronephrosis with cortical thinning. Hydronephrosis with dilated anechoic pelvis and calyces, along with cortical atrophy. Even though US has a lower sensitivity and specificity than CT for the detection of kidney stones urolithiasis , US, if available, is recommended as the initial imaging modality in patients with renal colic and suspected urolithiasis. US has no risk of radiation, is reproducible and inexpensive, and the outcome is not significantly different for patients with suspected urolithiasis undergoing initial US exam compared to patients undergoing initial CT exam.
Hyperechoic stones are seen with accompanying posterior shadowing. Additional twinkling artifacts below the stone can often be seen using Doppler US. Large stones filling the entire collecting system are called coral stones or staghorn calculi and are easily visualized with US Figure Stones in the ureters are usually not visualized with US due to the air-filled intestines obscuring the insonation window. However, ureteral stones near the ostium can be visualized with a scan position over the bladder.
An exam of the ureteric orifices and the excretion of urine to the bladder can be performed by inspecting the ureteric jets in the bladder with color Doppler US. Centrally-located stone with posterior shadowing.