Agenesis (Renal) Is a relatively rare anomaly that generally manifests as the absence of the kidney on one side and an unusually large kidney on the other side, a condition known as compensatory hypertrophy. The left kidney is more frequently missing, and the condition is more common in men than in women. A single kidney occurs in approximately 1 in 1000 individuals. It is more subject to trauma because of its enlarged size. Protection against disease in an individual with only one kidney is very important. Also known as a solitary kidney and may be associated with a variety of other congenital malformations. Before the diagnosis can be made, it is essential to exclude a nonfunctioning, diseased kidney or a prior nephrectomy. Unilateral renal agenesis results from a failure of the embryonic renal bud or renal vascular system to form. In true renal agenesis, the ureter and corresponding half of the trigone are missing also. Ultrasound or CT can demonstrate the absence of renal tissue. The absence of both kidneys, termed Potter’s syndrome or bilateral agenesis, is incompatible with life.
Calculi Are stones that develop from urine and can precipitate crystalline materials, especially calcium and its salts. If the body’s normal equilibrium is upset, these products may precipitate out of the solution. Factors that can cause this precipitation include metabolic disorders such as hyperparathyroidism, excessive intake of calcium, and a metabolic rate that causes high urine concentration. Chronic UTIs are also related to stone formation.
Men develop calculi more often than women, especially after age 30. Nearly all urinary tract calculi are calcified to some extent; however, approximately 5% of stones do not calcify. These are generally made of pure uric acid and present a more difficult diagnosis to the physician because they are one of several filling defects, including blood clots and tumors. Most stones are formed in the calyces or renal pelvis. A staghorn calculus is a large calculus that assumes the shape of the pelvicaliceal junction. Because of the calcium content in renal calculi, most are visible on an abdominal radiograph, IVU, or retrograde pyelogram. Sonography and noncontrast CT of the abdomen are often used to demonstrate stones. In many institutions, a CT “stone study” is the first modality of choice because it does not require contrast administration. It is an excellent method for differentiating abdominal or flank pain caused by renal calculi versus appendicitis or an abdominal aortic aneurysm. In addition, it can be used to detect the location of the stone and the degree of obstruction present. Stones tend to be asymptomatic until they begin to descend or cause an obstruction. Renal stones generally do not have a smooth texture and often have multiple jagged edges, causing pain as they move through the ureter. The most common site for a calculus to lodge and create an obstruction is the ureterovesical junction. Obstructions can also occur in the ureter at the pelvic brim. Movement of stones or acute obstruction results in severe, intermittent pain known as renal colic. As the stone moves along the course of the ureter toward the flank or genital regions, it is highlighted by sudden, periodic (paroxysmal) attacks, between which a constant low-grade pain is felt. Renal calculi can also cause bleeding (hematuria), fever, chills, frequent urination, and secondary infection. The physician is generally able to distinguish between biliary and renal colic because biliary colic usually causes referred pain to the subscapular area or epigastrium. The probability for recurrent calculus formation is increased as much as 50% in individuals who develop an initial renal stone, so many patients are placed on a prophylactic regimen such as diuretics, potassium alkali, and increased fluid intake to help reduce their chance of developing further stones.
In most instances the first treatment is to wait for the stone to pass normally through the urinary system in combination with the administration of antibiotics for the presence of any infection. If the stone is not passed, either lithotripsy of the stone or surgical excision of the cause of obstruction is necessary. SWL is often used to crush calculi less than 2 cm in diameter located in the renal pelvis or ureter. A percutaneous nephrolithotomy may be used to remove larger renal calculi, and ureteroscopy is necessary to remove larger stones within the ureter. Depending on the size of the stone, it may be removed with a special basket catheter or it may be crushed into smaller pieces via laser or pneumatic lithotripsy. All of these methods use fluoroscopic guidance.
In addition to the kidneys, other sites of calcification in the urinary tract include the wall of the bladder and the prostate gland in men. Calcification of the bladder wall is very rare and is usually caused by calcium deposition in a tumor extrinsic to the bladder, such as from the ovary or rectum. Rarely, it may also be on the surface of a bladder tumor. Bladder calculi often cause suprapubic pain. Prostatic calcification appears as numerous flecks of calcium of varying size below the bladder. It does not, however, correlate with either prostatic hypertrophy or carcinoma and usually is of no real significance.
Urinary tract calcifications are sometimes difficult to distinguish from other abnormal calcifications, such as gallstones, vascular calcifications, and calcified costal cartilages. To be in the kidney, the calcification must remain within the outline of the kidney on both frontal and oblique projections.
Cysts (Renal) An acquired abnormality common in adults. It is estimated that more than half of people at age 50 have renal cysts. Simple cysts may be solitary or multiple and bilateral. They are usually asymptomatic and not an impairment to renal function, but they may cause symptoms from rupture, hemorrhage, infection, or obstruction. Their pathogenesis is unknown, but obstruction of nephrons by an acquired disease may have a relationship. They are commonly found in a lower pole of the kidney and are readily demonstrated with CT, MRI and ultrasound.
Radiographically, cysts have sharply defined margins and show calyceal spreading. They can be distinguished from tumors by nephrotomography, in which a cyst shows an absence of a nephrogram phase after contrast medium injection. By contrast, tumors, the majority of which have vascularity, may show irregular opacification during the nephrogram phase. Treatment, if needed, consists of aspiration of the cyst contents. Most cysts are asymptomatic, and no treatment is needed. Simple renal cysts are the most common unifocal masses of the kidney. They are fluid filled and usually unilocular, although septa sometimes divide the cyst into chambers, which may or may not communicate with each other. Cysts vary in size, and they may occur at single or multiple sites in one or both kidneys. Thin curvilinear calcifications can be demonstrated in the wall of about 3% of simple cysts. However, this peripheral type of calcification is not pathognomonic of a benign process because malignant kidney lesions can produce a similar pattern. As a simple renal cyst slowly increases in size, its protruding portion elevates the adjacent edges of the cortex. The cortical margin appears on nephrotomography as a very thin, smooth, radiopaque rim about the bulging lucent cyst (beak sign). Although the beak sign is generally considered characteristic of benign renal cysts, it merely reflects a slow expansion of a mass and thus may occasionally be seen in slow-growing solid lesions, including carcinoma. Thickening of the rim about a lucent mass is suggestive of bleeding into a cyst, cyst infection, or a malignant lesion. Renal cysts cause focal displacement of adjacent portions of the pelvicalyceal system. The displaced, attenuated collecting structures remain smooth, unlike the shagginess and obliteration that often occur when focal displacement is caused by a malignant neoplasm.
Ultrasound is the modality of choice for distinguishing fluid-filled simple cysts from solid mass lesions. Fluid-filled cysts classically appear as echo-free structures with strongly enhanced posterior walls, in contrast to solid or complex lesions, such as tumors, that appear as echo-filled masses without posterior wall enhancement. CT is also highly accurate in detecting and characterizing simple renal cysts. On unenhanced scans, the cyst has a uniform attenuation value near that of water. After the injection of contrast material, a simple cyst becomes more apparent as the contrast material is concentrated by the normal surrounding parenchyma. The cyst itself shows no change in attenuation value, unlike a solid renal neoplasm, which always shows a small but definite increase in density.
Duplication (duplex kidney) A common anomaly that may vary from a simple bifid pelvis to a completely double pelvis, ureter, and ureterovesical orifice. The ureter draining the upper renal segment enters the bladder below the ureter draining the lower renal segment. Complete duplication can be complicated by obstruction or by vesicoureteral reflux with infection. Vesicoureteral reflux and infection more commonly involve the ureter draining the lower renal segment; obstruction more frequently affects the upper pole, where it can cause a hydronephrotic mass that displaces and compresses the lower calyces.
Most cases of congenital/hereditary anomalies of the urinary tract require no treatment. If obstruction occurs as a result of the anomaly (because of twisting or angulation of the ureter), stent placement or surgery is necessary to maintain normal urine flow. In cases of infection, which occur more frequently in renal or ureteral duplication because of vesicoureteral reflux, antibiotics are required and it is necessary to determine if there is an anatomic cause that can be corrected surgically.
Glomerulonephritis Is a nonsuppurative, (non pus forming), inflammatory process involving the tufts of capillaries (glomeruli) that filter the blood within the kidney. It represents an antigen-antibody reaction that most commonly occurs several weeks after an acute upper respiratory or middle ear infection with certain strains of hemolytic streptococci. The inflammation begins in the cortex of the kidney and in the tiny arcuate arteries that infuse the glomeruli. The major characteristic of the glomeruli is that they allow for extraordinarily high levels of water and small solutes to flow through the system. Although the kidney has an incredible capacity to cleanse the blood, glomeruli can be damaged by vascular pressure, metabolic diseases such as diabetes, and immune disorders such as lupus. More frequently, the inflammatory process is caused by a chronic autoimmune disorder. The inflammatory process causes the glomeruli to be extremely permeable, allowing albumin and red blood cells to leak into the urine (resulting in proteinuria or hematuria). Decreased glomerular filtration rate causes oliguria, a smaller-than-normal amount of urine.
The excretory urographic findings in glomerulonephritis depend on the duration and severity of the disease process and on the level of renal function. In patients with acute glomerulonephritis, the kidneys may be normal or diffusely increased in size with smooth contours and normal calyces. The kidneys appear larger, particularly during the nephrogram phase of an IVU, because of edematous accumulation. A loss of renal substance in chronic glomerulonephritis produces bilateral small kidneys. The renal outline remains smooth and the collecting system is normal, unlike the irregular contours and blunted calyces seen in chronic pyelonephritis. Ultrasound may demonstrate these findings more efficiently without contrast enhancement or radiation exposure.
Most cases of acute glomerulonephritis resolve completely, and the kidney returns to normal. In some patients, however, chronic inflammation with periods of remission and exacerbation (increased seriousness) leads to a fibrotic reaction which results in shrinkage of the kidneys with loss of renal function and the development of uremia. Before therapy is implemented, a renal biopsy may be required to determine the specific cause or to get a sample of the glomeruli to ascertain the level of disease or erosion within them. CT or sonographic guidance is provided so that a physician can obtain samples of renal tissue and send them to pathology for inspection. The biopsy samples allow the pathologist to look for the level of disease or erosion. A granular pattern develops within the glomeruli from deposits of antigens and the resulting antibodies. These microscopic deposits in the glomerulus are the gold standard for diagnosing glomerulonephritis. This condition occurs mainly in children after streptococcal infection, with most patients recovering completely. If there is an underlying antigen-antibody reaction, corticosteroids for immunosuppression would be appropriate. Infectious processes are treated with antibiotics. Treatment may also include diuretic therapy to lessen edema and its resultant pressure on the glomeruli, as well as anti-inflammatory medications. Renal dialysis may be used for severe, chronic cases.
Hydronephrosis Is an obstructive disorder of the urinary system that causes dilatation of the renal pelvis and calyces with urine. If hydronephrosis is long-standing, the resultant increase in intrarenal pressure causes ischemia, parenchymal atrophy, and loss of renal function. Although the most common cause of hydronephrosis is a calculus, it can also occur as a congenital defect or because of a blockage of the system by a tumor, stricture, blood clot, or inflammation. Patients with hydronephrosis often complain of pain in their flanks, and their urine may demonstrate blood or pus. The long-term changes of hydronephrosis are reversible if the cause of obstruction is relieved early in the process. As in most urinary system pathologies, abdominal sonography is the initial examination of choice because the kidneys do not have to be functioning properly and intravenous contrast agents are not necessary for the kidneys to be visualized on a sonogram. Additional information regarding increased vascular resistance can be ascertained using Doppler ultrasound. A spiral abdominal CT scan allows diagnosis of obstruction more than 90% of the time, so CT is quickly replacing the conventional IVU. However, a conventional IVU may be necessary to help differentiate renal cysts or stones from hydronephrosis.
Urinary tract obstruction produces anatomic and functional changes that vary with regard to rapidity of onset, degree of occlusion, and distance between the kidney and the obstructing lesion. In adults, urinary calculi, pelvic tumors, urethral strictures, and enlargement of the prostate gland are the major causes. In children, congenital malformations (ureteropelvic junction narrowing, ureterocele, retrocaval ureter, posterior urethral valve) are usually responsible for mechanical obstruction. Normal points of narrowing, such as the ureteropelvic and ureterovesical junctions, the bladder neck, and the urethral meatus, are common sites of obstruction. Blockage above the level of the bladder causes unilateral dilatation of the ureter (hydroureter) and renal pelvicalyceal system (hydronephrosis); if the lesion is at or below the level of the bladder, as in prostatic hypertrophy or tumor, bilateral involvement is the rule.
Noncontrast helical CT scanning detects mass effects, stones, or other causes of obstruction better than excretory urography. A contrast agent may be used to demonstrate renal function and the renal vascular structures if needed. In acute urinary tract obstruction, diminished filtration of urographic contrast material results in parenchymal opacification that is delayed compared with that of the nonobstructed kidney. The nephrogram eventually becomes more dense than normal because of a decreased rate of flow of fluid through the tubules, which results in enhanced water reabsorption by the nephrons and greater concentration of the contrast material. There is delayed and decreased pelvicalyceal filling because of dilatation and elevated pressure in the collecting system. The radiographic study may have to be prolonged for up to 48 hours after the administration of contrast material to determine the precise site of obstruction.
In the patient with acute urinary tract obstruction, the kidney is generally enlarged, and the calyces are moderately dilated. An uncommon but pathognomonic urographic finding in acute unilateral obstruction (usually caused by a ureteral stone) is opacification of the gallbladder 8 to 24 hours after the injection of contrast material. This “vicarious excretion” is related to increased liver excretion of contrast material that cannot be promptly excreted by the kidneys.
As an obstruction becomes more chronic, the predominant urographic finding is a greatly dilated pelvicalyceal system and ureter proximal to the obstruction. Prolonged increased pressure causes progressive papillary atrophy, leading to calyceal clubbing. Gradual enlargement of the calyces and renal pelvis with progressive destruction of renal parenchyma may continue until the kidney becomes a nonfunctioning hydronephrotic sac in which its normal anatomy is obliterated.
Whenever possible, the site of obstruction should be demonstrated. Although excretory urography with delayed films may accomplish this purpose, antegrade pyelography is often required. In this procedure, a catheter or needle is placed percutaneously into the dilated collecting system under ultrasound or fluoroscopic guidance, and contrast material is then introduced. This approach has the added advantage of providing immediate and certain decompression of a unilateral obstructing lesion.
Ultrasound is of particular value in detecting hydronephrosis in patients with such severe urinary tract obstruction and renal dysfunction that there is no opacification of the kidneys and collecting systems on excretory urograms. The dilated calyces and pelvis become large, hydronephrotic, echo-free sacs separated by septa of compressed tissue and vessels. With increased duration and severity of hydronephrosis, the intervening septa may disappear, leaving a large fluid-filled sac with no evidence of internal structure and no normal parenchyma apparent at its margins.
Nephroblastoma (Wilms’ tumor) is the most common abdominal neoplasm of infancy and childhood. The lesion arises from embryonic renal tissue, it may be bilateral, and it tends to become very large and appear as a palpable mass. A Wilms’ tumor (highly malignant) must be differentiated from neuroblastoma, a tumor of adrenal medullary origin that is the second most common malignancy in children. Peripheral cystic calcification occurs in about 10% of Wilms’ tumors, in contrast to the fine, granular, or stippled calcification seen in about half of the cases of neuroblastoma. At excretory urography, the intrarenal Wilms’ tumor causes pronounced distortion and displacement of the pelvicalyceal system. The major effect of the extrarenal neuroblastoma is to displace the entire kidney downward and laterally. Because the kidney itself is usually not invaded, there is no distortion of the pelvicalyceal system.
Ultrasound is of value in distinguishing Wilms’ tumor from hydronephrosis, another major cause of a palpable renal mass in a child. Wilms’ tumors typically have a solid appearance with gross distortion of the renal structure, which is not like the precise organization of symmetrically positioned fluid-filled spaces in hydronephrosis. Ultrasound can also demonstrate the intrarenal location of Wilms’ tumor, which is different from the extrarenal origin of a neuroblastoma.
Although it entails the use of ionizing radiation, CT can demonstrate the full extent of the tumor (including invasion of the inferior vena cava) and can detect any recurrence of the neoplasm after surgical removal. MR images can accurately differentiate Wilms’ tumor from renal or hepatic lesions. This is also extremely useful in defining the extent of the lesion and showing possible tumor thrombus within the renal vein or the inferior vena cava. Because MRI has no ionizing radiation, it is an ideal modality for follow-up evaluation after surgical removal of the tumor. Surgery, radiation therapy, and chemotherapy result in an 85% cure rate in patients with Wilms’ tumor.
Polycystic Kidney Disease is an inherited disorder in which multiple cysts of varying size cause lobulated enlargement of the kidneys and progressive renal impairment, which presumably results from cystic compression of nephrons, which in turn causes localized intrarenal obstruction. One third of patients with this condition have associated cysts of the liver, which do not interfere with hepatic function. About 10% have one or more saccular (berry) aneurysms of cerebral arteries, which may rupture and produce a fatal subarachnoid hemorrhage. Many patients with polycystic disease are hypertensive, a condition that may cause further deterioration of renal function and increase the likelihood that a cerebral aneurysm will rupture. Because patients tend to be asymptomatic during the first three decades of life, early diagnosis is made either by chance or as a result of a specific search prompted by the discovery of findings in the family history.
Excretory urography demonstrates enlarged kidneys with a multilobulated contour. The pelvic and infundibular structures are elongated, effaced, and often displaced around larger cysts, producing a crescentic outline. The nephrogram typically has a distinctive mottled or Swiss cheese pattern caused by the presence of innumerable lucent cysts of varying size throughout the kidneys. Plaques of calcification occasionally occur in cyst walls.
Ultrasound demonstrates grossly enlarged kidneys containing multiple cysts that vary considerably in size and are randomly distributed throughout the kidney. Ultrasound is also of value in screening family members of a patient known to have this hereditary disorder. In patients with bilateral kidney enlargement and poor renal function, ultrasound permits the differentiation of polycystic kidney disease from multiple solid masses.
The multiple cysts in polycystic kidney disease can also be detected on CT scans and MRI. Although most individual cysts are histologically identical to simple cysts, intracystic hemorrhage is common. Unlike simple renal cysts, which demonstrate low attenuation on CT scan, hemorrhagic cysts have high attenuation values. On MRI, a hemorrhagic cyst has a high signal intensity, unlike simple renal cysts, which have low signal intensity. A rare, usually fatal form of polycystic disease can present at birth; it involves diffusely enlarged kidneys, renal failure, and maldevelopment of intrahepatic bile ducts. The margins of the kidneys are smooth in infantile polycystic disease, unlike the irregular renal contours in the adult form of polycystic disease that are attributable to the protrusion of innumerable cysts from the kidney surface. When renal function is sufficient, excretory urography results in a striking nephrogram in which a streaky pattern of alternating dense and lucent bands reflects contrast material puddling in elongated cystic spaces that radiate perpendicularly to the cortical surface. Ultrasound shows distortion of the intraparenchymal architecture, although the individual cysts are too small to be visualized.
No cure is available. Medications are prescribed to control pain, high blood pressure, and infection related to the disease. Renal failure due to the loss of functioning kidney tissue requires dialysis, and renal transplantation may be considered.
Prostatic Hypertrophy Benign prostatic hypertrophy is a disease of the prostate that occurs with increasing age in most men. The condition is characterized by an enlargement or hypertrophy of the prostate gland. It generally involves the more central regions of the prostate, which gradually enlarge. The prostate feels ‘bulky’ on digital rectal examination. The fact that the urethra passes through the center of the prostate after exiting from the bladder is a matter of considerable clinical significance in this condition. As the prostate enlarges, it squeezes the urethra, frequently closing it so completely that urination becomes very difficult or even impossible. With time, the bladder may become hypertrophied in response to the urinary outflow obstruction. In some male patients, the obstruction becomes so severe that urine cannot be passed and transurethral or suprapubic catheterization is necessary. Despite being a benign disease, benign prostatic hypertrophy can therefore have a marked effect on the daily lives of many patients. In such cases, surgical removal of a part of or the entire gland, a procedure called prostatectomy, may become necessary.
Renal Colic A sharp, severe pain in the lower back over the kidney, radiating forward into the groin. Renal colic usually accompanies forcible dilation of a ureter, followed by spasm as a stone is lodged or passed through it.
Renal Hypertension High blood pressure resulting from aortic or renal artery atherosclerosis or from kidney disease, including chronic glomerulonephritis, chronic pyelonephritis, renal carcinoma, and renal calculi. Atherosclerosis of the renal arteries is common in persons with atherosclerosis of the aorta. The renal arteries originate from the aorta and are relatively short. Thus, aortic atherosclerosis easily spreads into the renal arteries. Because the renal arteries are much narrower than the aorta, symptoms caused by their occlusion are often more prominent. Reduced flow of blood through the renal arteries causes hypo perfusion of the kidneys, which results in reduced renal functional capacity. This renal dysfunction, combined with an increased release of renin (a hormone produced by the kidney in response to ischemia), leads to hypertension. Reduced excretion of urine and urinary sodium further aggravates hypertension, which, in turn, damages the kidneys. Atherosclerosis may thus cause irreversible (end-stage) kidney failure.
Vesicoureteral reflux Vesicoureteral reflux (VUR) is the abnormal flow of urine from the bladder back into the ureters. VUR is most commonly diagnosed in infancy and childhood after the patient has a urinary tract infection (UTI). About one-third of children with a UTI are found to have VUR. VUR can lead to infection because urine that remains in the child’s urinary tract provides a place for bacteria to grow. But sometimes the infection itself is the cause of VUR.
Vesicoureteral reflux (VUR) can cause swelling in the ureter and kidney, known as hydroureter and hydronephrosis.
There are two types of VUR. Primary VUR occurs when a child is born with an impaired valve where the ureter joins the bladder. This happens if the ureter did not grow long enough during the child’s development in the womb. The valve does not close properly, so urine backs up (refluxes) from the bladder to the ureters, and eventually to the kidneys. This type of VUR can get better or disappear as the child gets older. The ureter gets longer as the child grows, and the function of the valve improves.
Secondary VUR occurs when there is a blockage anywhere in the urinary system. The blockage may be caused by an infection in the bladder that leads to swelling of the ureter. This also causes a reflux of urine to the kidneys.
Infection is the most common symptom of VUR. As the child gets older, other symptoms, such as bedwetting, high blood pressure, protein in the urine, and kidney failure, may appear.
Common tests to show the presence of a urinary tract infection include urine analysis and cultures.
Because no single test can tell everything about the urinary tract that might be important to know, more than one of the following imaging tests may be needed:
- Kidney and bladder ultrasound
- Voiding cystourethrogram (VCUG)
- Intravenous pyelogram
- Nuclear scans
The goal for treatment of VUR is to prevent any kidney damage from occurring. Infections should be treated at once with antibiotics to prevent the infection from moving into the kidneys. Antibiotic therapy usually corrects reflux caused by infection. Sometimes surgery is needed to correct primary VUR.
Surgery is considered only when severe reflux has caused infection that can’t be controlled with antibiotics. The most common procedure to correct VUR is to sever the ureter from the bladder and then reattach it at a different angle so that urine can’t back up. In recent years, doctors have treated some cases of VUR by injecting a bulking agent into the bladder wall around the opening of the ureter where reflux happens. This procedure can be performed with a scope that reaches the inside of the bladder through the urethra, so the doctor doesn’t need to make an incision.