Study Questions

A common laboratory test used for renal disease is BUN. What does this abbreviation stand for, and how does this test work?

The blood urea nitrogen (BUN) is the concentration of urea nitrogen in blood, which is the end product of cellular metabolism. Urea is formed in the liver and carried to the kidneys through the blood, to be excreted in urine. Impairment of renal function and increased protein catabolism result in BUN elevation in relation to the degree of renal impairment and rate of urea nitrogen excreted by the kidneys.

What does the presence of hemoglobin in the urine signify?

The presence of hemoglobin in urine occurs whenever there is extensive damage or destruction of the functioning erythrocytes. This condition is injurious to the kidney and can cause acute renal failure.

Where is the junctional parenchymal defect most commonly found, and what is its appearance on sonographic examination?

A junctional parenchymal defect is a triangular echogenic area in the upper pole of the renal parenchyma that can be seen during normal sonographic scanning. The defect results from the normal extensions of the renal sinus in cases in which there is distinct division between the upper and lower poles of the kidney. The kidneys develop from the fusion of two embryonic parenchymatous masses referred to as renunculi. In cases of partial fusion, parenchymal defects occur at the junction of the renunculi and are best demonstrated on sagittal scans.

What is the definition of a parapelvic cyst? Describe its sonographic appearance.

A parapelvic cyst arises in the renal hilum but does not communicate with the collecting system. Sonographic findings include no septations and irregular borders because of compression of adjacent renal sinus structures. The parapelvic cyst may obstruct, but the peripelvic cyst does not. Symptoms are infrequent and can cause pain, hypertension, and obstruction. The sonographer can differentiate from hydronephrosis by trying to connect them centrally.

Describe the clinical signs and symptoms that a patient with renal infection or disease process may have.

A patient with renal infection or disease process may experience any of the following symptoms: flank pain, hematuria, polyuria, oliguria, fever, urgency, or generalized edema.

Describe the sonographic appearance of a simple renal cyst.

A simple renal cyst generally is believed to represent a retention cyst that occurs secondary to tubular obstruction, vascular occlusion, or focal inflammation. It may occur in as many as 50% of adults >50 years of age. The sonographer should be careful not to confuse cysts with renal pyramids. Sonographic findings include no internal echoes, acoustic enhancement, clear demarcation of back wall, and a spherical or slightly ovoid shape. Low-level echoes within real cysts are the result of one of the following: artifacts, infection, hemorrhage, or a necrotic cystic tumor. The technique used is high gain or reverberation from the wall.

What is the effect of AIDS on the kidneys? How does it appear on sonographic examination?

AIDS is a highly contagious disease. The virus destroys T cells and then replicates rapidly within the body. It affects many organs within the body. Patients experience various symptoms. An echogenic parenchymal pattern is present on sonographic examination. Cortical echogenicity is increased. Kidneys are normal-sized to enlarged.

What type of reversible renal failure may result from medical conditions or pathophysiologic mechanisms? Describe the sonographic characteristics.

Acute renal failure (ARF) is a common condition that is the result of medical disease or pathophysiologic mechanisms that can be reversible. The sonographic scan shows bilateral enlarged kidneys with hyperechoic pyramids; this can revert to normal appearance. The differential consideration includes nephrocalcinosis. In pediatric patients the renal pyramids are very echogenic, without shadowing. The calculi may be too small to not cause dilation and shadowing. As renal function improves, the echogenicity decreases. This can occur in the medulla or cortex. If this reverses, this is probably ATN.

Describe the sonographic technique and considerations that should be made before evaluation of a renal mass.

Before the sonographic examination for the evaluation of a renal mass, a complete review of the patient's chart and previous diagnostic examinations should be made by the sonographer. Many patients may have already had a previous imaging study, such as an intravenous pyelogram, CT, or MRI study. These films should be obtained before beginning the sonographic study to tailor the examination to answer the clinical problem. The sonographer should evaluate the films for the shape and size of the kidney, determine the location of the mass lesion, look for distortion of the renal or ureter structure, and look for the presence of calcium stones or gas within the kidney.

What is the distinction between a simple renal cyst and an atypical cyst?

Atypical renal cyst sonographic findings include echoes within, septae, and mural nodules or calcifications. (1% to 3% of cysts calcify with rimlike calcification. Usually they are benign, although up to 20% are malignant.) An atypical cyst with low-level echoes may represent hemorrhage. Computed tomography (CT) or magnetic resonance imaging (MRI) may help define texture.

Describe Bertin's column. How can the sonographer confuse this variant with a renal mass?

Column of Bertin is a prominent invagination of the cortex located at varying depths within the medullary substance of the kidneys. This area is normal cortex. The column may be the fusion of two septa into a single column that is twice the normal thickness. The column is most exaggerated in patients with complete or partial duplication. Sonographic features of a renal mass effect produced by a hypertrophied column of Bertin are as follows: a lateral indentation of the renal sinus, a clear definition from the renal sinus, or a maximum dimension that does not exceed 3 cm. In addition, there is contiguity with the renal cortex, and the overall echogenicity is similar to the renal parenchyma.

What are the causes of false-positive hydronephrosis?

Dilation of the renal pelvis does not always mean obstruction is present. Several other factors may cause the renal pelvis to be dilated, such as reflux, infection, high flow states (polyuria), postobstruction atrophy (once obstruction is relieved, the obstruction can remain), or pregnancy dilation (the enlarged uterus can compress the ureter; usually occurs more on the right). There are many conditions that may mimic hydronephrosis, such as extrarenal pelvis, parapelvic cysts, reflux, transient diuresis, congenital megacalices, papillary necrosis, renal artery aneurysm (which may be distinguished by color Doppler), or an arterial-venous malformation (which also may be distinguished by color Doppler). Localized hydronephrosis may be secondary to strictures, calculi, or focal masses (transitional). A duplex system can be obstructed because of the ectopic insertion of a ureter. In females it can insert below the external urinary sphincter and cause dribbling. In patients with a false-negative hydronephrosis, several techniques may be used to help distinguish the dilated renal pelvis from another condition. In patients with retroperitoneal fibrosis or necrosis, the sonographer should give a fluid challenge to see if the renal pelvis dilates. In patients with distal calculi, no obstruction may be seen unless the calculi have been there for several days. A staghorn calculus can mask an associated dilation.

The horseshoe kidney has several distinguishing features on sonographic examination. What are they?

Fusion anomalies of the kidneys include crossed renal ectopia and a horseshoe kidney, which is the most common. In a patient with a horseshoe kidney, there is fusion of the polar regions of the kidneys during fetal development that almost invariably involves the lower poles. Usually this condition is associated with improper ascent and malrotation of the kidneys, usually in a lower retroperitoneal position. The renal pelvis and ureters are more ventrally located. These kidneys usually lie closer to the spine than normal kidneys. The inferior poles lie more medially. The isthmus of the kidney lies anterior to the spine and may simulate a solid pelvic mass. Pathologic conditions associated with this are pyelocaliectasis, anomalous extrarenal pelvis, and urinary calculi.

What is the significance of hematuria?

Hematuria is the appearance of red blood cells in the urine and may indicate early renal disease. An abundance of red blood cells in the urine may suggest renal trauma, calculi, or pyelonephritis; or glomerular or vascular inflammatory processes such as acute glomerulonephritis and renal infarction. Leukocytes may be present whenever there is inflammation, infection, or tissue necrosis originating from anywhere in the urinary tract.

How can the sonographer be sure the diagnosis of hydronephrosis is correct?

Hydronephrosis may be specific, with many sonographic findings. The dilated pyelocalyceal system appears as a separation of the renal sinus echoes by fluid-filled areas that conform anatomically to the infundibula, calyces, and pelvis. The renal sinus and parenchyma become compressed with progressive obstruction, and in end-stage hydronephrosis, only multiple cystic spaces may be seen. Whenever hydronephrosis is seen, the ureters and bladder are scanned because dilation of these structures is indicative of obstruction of the ureterovesical junction or of the urethra. A localized hydronephrosis occurs as a result of strictures, calculi, focal masses, or a duplex collecting system.

What should the sonographer look for in a patient with a pelvic kidney?

If the kidney is not seen in the normal position in the renal fossa, the retroperitoneum and pelvis should be scanned. Most true ectopic kidneys are located in the bony pelvis and may be malrotated. The pelvic kidney may simulate a solid adnexal mass. It may be associated with other abnormalities, such as vesicoureteral reflux and anomalous extrarenal pelvis.

How does a renal infarction appear on sonographic examination?

Infarcts within the renal parenchyma appear as irregular masses somewhat triangular in shape along the periphery of the renal border. The renal contour may be somewhat lumpy in appearance. Remember that contour lobulations in the pediatric patient may be normal, except for the dromedary hump variant. In the adult patient, the renal contour should be smooth. The irregular area may appear to be slightly more echogenic than the renal parenchyma in the patient with a renal infarct.

Name the most common primary sites of tumor metastases to the kidney.

Metastases to the kidneys is a relatively common finding at autopsy; however, it may also occur while the patient is alive. The most common primary sites of tumor spread are malignant melanoma; lymphoma; and carcinoma of the lungs, breast, stomach, cervix, colon, or pancreas.

The most common tumor of childhood is Wilms' tumor. Describe the clinical findings the sonographer should consider in the evaluation of a Wilms' tumor.

Nephroblastoma, or Wilms' tumor, is the most common solid renal mass found during childhood. Its incidence is rare in the newborn, with a peak incidence in the second year of life. Half of the tumors occur before the affected child's third birthday. The tumor may recur, so careful follow-up of the patient is important. Most of the cases present with a palpable abdominal mass. Other clinical findings may include abdominal pain, anorexia, nausea and vomiting, fever, or gross hematuria. Venous obstruction may result, with findings of leg edema, varicocele, or Budd-Chiari syndrome. The tumor may spread beyond the renal capsule and invade the venous channel, with tumor cells extending into the IVC and right atrium, with eventual metastases into the lungs. The tumor may be multifocal in a small percentage of patients.

What is the most common renal tumor?

Renal cell carcinoma is the most common of all renal tumors, comprising 85% of kidney tumors. The frequency of occurrence in males is two times that of females. The peak incidence usually does not occur until the sixth or seventh decade of life.

Why does sinus lipomatosis produce such an echogenic renal image?

Sinus lipomatosis is a condition characterized by the deposition of a moderate amount of fat in the renal sinus. The degree of proliferation of fibrofatty tissue varies. The renal sinus is composed of fibrous tissue, fat, lymphatic vessels, and renal vascular structures. On normal kidneys, this central zone appears as a bright area. In sinus lipomatosis, the abundant fibrous tissue may cause enlargement of the sinus region and increased echogenicity.

Describe the staging of renal cell carcinoma.

Staging of renal cell carcinoma: • Stage I: confined to kidney • Stage II: spread to perinephric fat, but within Gerota's fascia • Stage III: spread to renal vein, IVC, and regional lymph nodes • Stage IV: invasion of neighboring structures; distant metastases

What are the clinical symptoms of a renal abscess?

The clinical symptoms are acute onset of symptoms including fever, a palpable mass, elevated WBC count, and elevated pyuria.

What are the clinical symptoms of renal cell carcinoma?

The clinical symptoms are erythrocytosis, leukocytosis, red blood cells in urine, pyuria, and elevated LDH.

What are the clinical symptoms of a renal subcapsular hematoma?

The clinical symptoms are hematuria and a decrease in hematocrit.

What are the clinical symptoms of chronic renal failure?

The clinical symptoms are increased concentration of urea in blood, high urine protein excretion, high BUN, increased creatinine, and the presence of granulocytes.

What are the clinical symptoms of renal cystic disease?

The clinical symptoms include flank pain, hematuria, proteinuria, white blood cells in urine, and elevated protein.

What is a dromedary hump, and where is it commonly found?

The dromedary hump is a cortical bulge that occurs on the lateral border of the kidney, typically more on the left. In some patients it may be so prominent that it looks like a neoplasm. It probably is the result of pressure on the developing fetal kidney by the spleen. The echogenicity is identical to the rest of the renal cortex.

Describe the duplex collecting system and its appearance on sonographic examination.

The duplex collecting system is a common normal variant that can be seen. Usually the sonographer cannot tell if it is complete or incomplete because it is difficult to see the ureters well. The duplex kidney usually is enlarged and has smooth margins. The central renal sinus appears as two echogenic regions separated by a cleft of moderately echogenic tissue similar in appearance to the normal renal parenchyma. The pelvis of the lower pole usually is larger than the upper pole.

What is the sonographic appearance of an extrarenal pelvis?

The normal renal pelvis is a triangular-shaped structure. Its axis points inferiorly and medially. An intrarenal pelvis lies almost completely within the confines of the central renal sinus. This is usually small and foreshortened. The extrarenal pelvis tends to be larger, with long, major calyces. On sonography the renal pelvis appears as a central cystic area that is either partially or entirely beyond the confines of the bulk of the renal substance. Transverse views are best to see continuity with the renal sinus.

Where are the renal arteries located, and what is the best view to image them?

The renal arteries are located on the posterolateral aortic wall. The renal arteries are best seen with the patient in the supine and lateral decubitus positions. The right renal artery extends from the posterolateral wall of the aorta to enter the central renal sinus. On the longitudinal scan, the right renal artery can be seen as a circular structure posterior to the inferior vena cava (IVC). The right renal vein extends from the central renal sinus directly into the IVC. Both vessels appear as tubular structures in the transverse plane. The renal arteries have an echo-free central lumen with highly echogenic borders that consist of vessel wall and surrounding retroperitoneal fat and connective tissue. They lie posterior to the veins and can be demonstrated with certainty if their junction with the aorta is seen. The left renal artery flows from the central renal sinus directly to the posterolateral wall of the aorta. The left renal vein flows from the central renal sinus anterior to the aorta and posterior to the superior mesenteric vein to join the IVC. It is seen as a tubular structure on the transverse scan. It may be referred to as the nutcracker phenomena, that is, aorta-left renal vein-superior mesenteric artery.

What is the sonographic appearance of the renal medulla?

The renal medulla consists of hypoechoic pyramids disbursed in a uniform distribution separated by bands of intervening parenchyma that extend toward the renal sinus. The pyramids are uniform in size and triangular in shape and distribution. The apex of the pyramid points toward the sinus, and the base lies adjacent to the renal cortex. The arcuate vessels lie at the base of the pyramids. The pyramids are located at the junction between the more peripheral renal cortex and the central sinus.

Name the three distinct segments of the kidney.

The supine scan shows three distinct segments of the kidney: a poorly echoic medullary zone that consists of numerous anechoic, triangle-shaped renal pyramids, a moderately echogenic renal cortex, and a highly reflective central renal sinus. The renal capsule and perinephric fat have a distinct layer of very reflective echoes that differentiate a normal right kidney from the liver (or left kidney from the spleen). The thickness of this very reflective echogenic zone varies in relation to the amount of perinephric fat deposited around the kidney.

Discuss polycystic renal disease.

There are two kinds of polycystic renal disease: infantile and adult. Infantile is autosomal recessive. In utero the fetus has enlarged kidneys that are echogenic on sonographic examination. The fetus develops renal failure and pulmonary hypoplasia which is not compatible with life.. In juvenile polycystic disease, there is bile duct proliferation, periportal fibrosis, portal hepatic varices, and nephromegaly. Adult polycystic disease is autosomal dominant. Adults are affected later in life. Renal failure is not as severe upon the onset. An adult patient usually develops hypertension in the 30- to 40-year age range. Patients may have spontaneous bleeding in cysts and pain. Enlarged kidneys are replaced by cysts. The renal sinus is obliterated. Associated abnormalities include circle of Willis intracranial aneurysm (20% of patients), liver cysts (30% to 50% of patients), and splenic or pancreatic cysts (10% of patients).

What is the natural course of a renal infection, and how do these infections affect the kidneys?

There is a spectrum of severity. The disease can progress from pyelonephritis to focal bacterial nephritis to an abscess. An abscess can be transmitted through the parenchyma into the blood. Most renal infections stay in the kidney and are resolved with antibiotics. A perirenal abscess occurs from a direct extension.

Describe the condition of pyonephrosis. What are its causes and sonographic findings?

This condition occurs when pus is found within the obstructed renal system. It is often associated with severe urosepsis and represents a true urologic emergency that requires urgent percutaneous drainage. It usually occurs secondary to long-standing ureteral obstruction from calculus disease, stricture, or a congenital anomaly. The sonographic findings include the presence of low-level echoes with a fluid debris level. The sonographer should be aware that an anechoic dilated system can occur; a sonographic-guided aspiration or computed tomography may have to be done.

Discuss the findings in a multicystic dysplastic kidney.

This disease is a nonhereditary renal dysplasia. It is the most common palpable abdominal mass found in neonates. It is unilateral, with an enlarged nonfunctioning kidney. The kidney can be small and calcified in adults. Multiple cysts of varying size with no normal parenchyma are often seen. The sonographer must be able to separate it from renal hydronephrosis. Other findings include ureteral atresia, a contralateral ureteropelvic junction (33%), and atretic renal artery.

Describe nephrocalcinosis and its sonographic findings.

This disease process shows very echogenic pyramids with or without associated shadowing. Renal stones are very echogenic, with shadowing posterior. The patient may have a fever; this may indicate infection with hydronephrosis. When searching for renal stones, the sonographer should scan along the lines of the renal fat. Usually the stones are small and may not shadow.

Describe the composition of an angiomyolipoma of the kidney.

This is an uncommon benign renal tumor composed mainly of fat cells. It is intermixed with smooth muscle cells and aggregates of thick-walled blood vessels. There may be hemorrhage in the tumor itself or in the subcapsular or perinephric spaces. On sonographic examination, a focal, solid hyperechoic mass is typical of an angiomyolipoma. There are two primary patterns of occurrence, the most common being the tumor that is solitary, nonhereditary, and found in women who are between 20 and 50 years of age. The other is one of multiple tumors with bilateral renal involvement found in teenagers who have tuberous sclerosis.

Describe the urinalysis laboratory test and discuss when it is used.

This urinalysis laboratory test is essential for the detection of urinary tract disorders in patients whose renal function is impaired or absent. Most renal inflammatory processes introduce a characteristic exudate for a specific type of inflammation into the urine. The presence of an acute infection causes hematuria, pus, or red blood cells in the urine.

What renal abnormalities are found in patients with tuberous sclerosis?

Tuberous sclerosis is an autosomal-dominant lesion that is associated with multiple renal cysts and multiple and bilateral renal angiomyolipomas.

Describe the appearance of renal cell carcinoma as seen on sonographic examination.

When found, it usually presents as a solid, hypoechoic parenchymal mass, frequently with areas of hemorrhage and necrosis. Renal cell carcinoma is not usually echogenic unless calcification is present. Occasionally renal cell carcinoma may appear predominantly as a cystic or complex mass on sonography. Irregular tumor calcification can be seen in a small number of affected patients. Any calcified mass within the kidney will cause the sonographer to think of tumor; one should define the extent of involvement by scanning the renal veins, IVC, and right atrium of the heart. Color flow Doppler is useful to image the renal vein to observe flow rate. A low velocity may be seen if a lot of tumor obstruction is present. There is an increased incidence of renal cell carcinoma in patients with von Hippel-Lindau disease or those on chronic dialysis. Tumors tend to be multiple and bilateral, and there is an increased incidence of adenomas. The tumor appears bilateral in 0.1% to 1.5% of patients.