Genitourinary System and Retroperitoneum





Anatomy and Imaging Techniques


The urinary system may be imaged in a number of ways. The initial studies of choice for many suspected clinical problems are shown in Table 7.1 . Historically, the most common radiographic method was intravenous injection of an iodine-based contrast agent followed by a series of radiographs (intravenous pyelogram [IVP]). IVP has been replaced by computed tomography (CT) scanning, with or without intravenous contrast (CT urogram). The normal anatomy is shown in Fig. 7.1 . The other common initial imaging modality is ultrasound.



TABLE 7.1

Initial Imaging Studies for Common Clinical Genitourinary Problems












































































































































































Clinical Problem Imaging Study
Acute onset flank pain; suspected ureteral calculus CT of abdomen and pelvis without contrast
Recurrent nephrolithiasis US with plain x-ray or low-dose CT
Gross hematuria (painless) CT of abdomen and pelvis with and without contrast (CT urography)
Hematuria with known renal parenchymal disease US of kidneys and bladder
Microscopic hematuria after recent vigorous exercise, presence of infection, or present or recent menstruation No imaging recommended
Acute pyelonephritis in a complicated patient CT with and without IV contrast
Acute pyelonephritis (uncomplicated) Imaging not usually appropriate
Recurrent urinary tract infection Cystoscopy; CT if nonresponding or high-risk patient
Cystitis (uncomplicated and no underlying risk factors in a female) No imaging
Recurrent lower tract infection (complicated, patients who are nonresponders or have underlying risk factors) CT of abdomen and pelvis with and without contrast
Abscess CT with and without IV contrast
Blunt or penetrating abdominal injury with suspicion of multisystem injury or macroscopic hematuria CT of abdomen and pelvis with IV contrast
Suspected renal mass CT with and without IV contrast or MRI; if renal insufficiency present, begin with duplex Doppler US
Renal cell carcinoma (initial staging) CT of abdomen with and without contrast and chest x-ray
Renal cell carcinoma (follow-up) Chest x-ray, CT of abdomen and pelvis with contrast (MRI is an alternative)
Renal failure (acute or chronic) US of kidneys and bladder
Hydronephrosis US
Renal transplant dysfunction US with duplex Doppler
Obstructive voiding symptoms US of kidneys and bladder
Bladder rupture or pelvic penetrating trauma CT cystography or x-ray of pelvis and retrograde cystography
Urethral obstruction or tear X-ray of pelvis and x-ray retrograde urethrography
Bladder cancer Cystoscopy, CT with IV contrast for regional and distant disease
Suspected renovascular hypertension CT angiography or MR angiography; if significantly decreased renal function, US of kidneys with duplex Doppler
Acute-onset scrotal pain without trauma; suspected testicular torsion Doppler US
Testicular or scrotal mass or trauma Doppler US
Testicular malignancy staging CT of abdomen and pelvis with contrast and chest x-ray or chest CT with contrast
Hematospermia (persistent associated symptoms or age > 40 years) US of transrectal prostate; imaging not needed for asymptomatic, transient, age < 40 years, with no other symptoms
Pelvic or adnexal mass (nonpregnant female) US of pelvis, transabdominal, Doppler, and/or transvaginal
Pelvic pain (female) US of pelvis, transabdominal and transvaginal; CT of abdomen and pelvis with contrast if nongynecologic cause suspected
Cervical cancer
Screening or size < 2 cm No imaging
≥ 2 cm MRI with and without contrast
Ovarian cancer (screening) Not recommended for general population
Ovarian cancer (high risk or symptoms) US, transvaginal
Endometrial cancer
Low grade No imaging
High grade MRI or CT
Uterine fibroids (initial, enlarging, painful, or bleeding) Pelvic US
Suspected benign prostatic hypertrophy (BPH) Imaging not recommended unless medications fail or hematuria is present
Suspected prostate cancer (no previous biopsy) PSA measurement and transrectal US (TRUS)-guided biopsy
Suspected prostate cancer (negative TRUS biopsy) Multiparametric MRI of pelvis with and without contrast and MRI-targeted biopsy
Prostate cancer (intermediate or high risk) active surveillance MRI of pelvis, with and without contrast
Prostate cancer posttreatment, rising PSA level NM whole-body bone scan
Infertility (female) No imaging until after physical examination, determination of hormone levels, US for ovarian evaluation, MRI of pelvis for endometriosis, hysterosalpingography for suspected tubal occlusion
Pregnancy
Assessment of fetal well-being (low risk pregnancy) Imaging not indicated
Suspected multiple gestation US
Abnormal antenatal testing US for biophysical profile
Acute pelvic pain (female reproductive age group) US
Vaginal bleeding
First trimester Transabdominal or transvaginal US correlate with β-hCG level
Second and third trimesters Transabdominal US (endovaginal US if inconclusive and no evidence of open cervix, bulging amniotic sac, or ruptured membranes)
Premenopausal (first study) US, transvaginal
Postmenopausal (first study) US, transvaginal
Adrenal mass incidentally discovered See text

CT , Computed tomography; β -hCG , beta-human chorionic gonadotropin; IV , intravenous; PSA , prostate-specific antigen; MRI , magnetic resonance imaging; US , ultrasound.



Fig. 7.1


(A) Computed tomography urogram. Normal anatomy is shown in the coronal plane. (B) Axial image without intravenous contrast. (C) Axial image with contrast in venous phase with vessels, kidneys, and liver brighter than muscle. (D) Axial image with contrast in the renal pelvis (excretory phase).

IVC , Inferior vena cava.


Often, a plain x-ray image of the abdomen (sometimes referred to as a KUB [kidney, ureter, and bladder]) is available. You should examine this carefully, looking for abnormalities in the skeleton, soft tissue margins of the liver, spleen, and psoas regions, the gas pattern in the bowel, and calcifications. Of particular interest are those calcifications that project over or overlie the region where you expect to find the kidneys, ureters, and bladder.


The kidneys should be examined for size, shape, position, and axis. The length of kidneys on a radiographic study is typically about 11 to 13 cm. On an ultrasound examination, they are smaller, only about 10 to 11 cm in length. Intravenous contrast being excreted during a CT examination causes the kidneys to enlarge 1 to 2 cm in length. Normally, the left kidney is somewhat higher than the right; the long axis of the kidneys should be tilted slightly inward, with the superior pole of the kidney being more medial than the lower pole. Look for uniform thickness of the cortex relative to the calyces of the collecting system. The shape of the kidneys should be relatively smooth in outline, although occasionally a slight lump is seen on the lateral margin of the kidneys. The lateral lump is sometimes referred to as a dromedary hump or column of Bertin. Although this is a common variant, you cannot exclude a cyst or neoplasm if a major difference is found between the thickness of the cortex between the calyces and the outer margin of the kidney or if one portion of the cortex is focally thicker than another. Often a renal ultrasound is the most cost-efficient and innocuous way of resolving this problem.


On the CT scan, a dark area normally surrounds the collecting system of the kidneys, which represents fat in the hilum of the kidney. Look carefully at the calyces to make sure that they are sharp and pointed, not blunted, at their outer corners, and examine the renal pelvis and ureters for any intrinsic or extrinsic defects. The ureters should course inferiorly and medially from the kidneys and anterior to the psoas muscles at the L3 to L5 level. On the anteroposterior projection, the ureters typically are most medial and project over the lateral aspect of the transverse processes at L3, L4, and L5. As the ureters pass over the sacrum, they deviate laterally and then enter the bladder from the posterolateral aspect.


Renal ultrasound is a simple, noninvasive examination ( Fig. 7.2 ). Remember that all ultrasound images are referred to as slices and that the easiest view of the kidney to understand is the longitudinal view. The right kidney is easily visualized by transmitting sound through the right lobe of the liver. Because bowel and stomach gas prevents ultrasound transmission, the left kidney is usually visualized from the patient’s back. The kidney is bean-shaped and has bright central echoes because of the fat surrounding the collecting system. Ultrasound is typically ordered to exclude hydronephrosis or evaluate renal size or suspected renal cysts.




Fig. 7.2


Normal Renal Ultrasound.

(A) A longitudinal view of the right kidney was obtained by passing the sound beam through the right lobe of the liver. The kidney is seen behind this, outlined by the markers. The central bright echoes (arrow) in the kidney are due to fat around the collecting system. (B) Normal variant column of Bertin (arrows) , which is the prominence of the renal cortex near the midpole of the kidney.


CT is often used as the initial imaging test for suspected renal cell carcinoma, complicated renal or ureteral stones, or trauma. Magnetic resonance imaging (MRI) or CT may be used in cases of renal cell carcinoma to exclude renal vein or inferior vena cava thrombus. Nuclear medicine techniques are used when function or other parameters must be quantitated. Indications for radioisotope techniques include the evaluation to determine whether a dilated collecting system is obstructive or nonobstructive and to detect renovascular hypertension.


Intravenous contrast medium is heavier than urine and layers posteriorly in the bladder when the patient is supine. The anterior and lateral bladder walls are usually not well seen. Consequently, if you wish to see the entire internal surface of the bladder, a Foley catheter can be placed directly into the bladder, the urine drained, and the bladder refilled with contrast material. This procedure is called a cystogram . On a cystogram, images of the bladder are obtained in several different projections. A cystogram can also be performed with CT. When the catheter is removed, the patient may be asked to void, and fluoroscopic images are then taken. In male patients, this gives a good demonstration of the urethra ( Fig. 7.3 ). The male urethra also can be studied in a retrograde fashion by inserting a small tube in the tip of the penis and injecting the contrast material. This is usually done only in cases of suspected urethral trauma or stricture.




Fig. 7.3


Normal Voiding Urethrogram.




Kidneys


Congenital Abnormalities


Congenital abnormalities of the urinary tract occur quite frequently, and you should be aware of the most common variants. Embryologically, the ureter buds and grows superiorly from the bladder to meet and connect with the renal parenchyma. The ureter can divide as it ascends, causing a person to have two partially duplicated or completely separate collecting systems for one kidney. If complete ureteral duplication is found, the ureter that supplies the upper half of the kidney often becomes obstructed ( Fig. 7.4 ). If the upper pole of the kidney is completely obstructed, all that is visualized is the normally draining lower pole collecting system, and it looks like a drooping lily. You should also be aware that the duplicated ureter that supplies the upper pole may often have an ectopic insertion into the bladder, urethra, or vagina.




Fig. 7.4


Duplicated Collecting System of Left Kidney.

An image from a urogram shows a normal right collecting system and ureter. On the left is a completely duplicated collecting system. As happens frequently with duplicated systems, the collecting system to the upper pole is dilated and obstructed.


A number of other anomalies occur in the course of the normal embryologic ascent of the kidneys out of the bony pelvis. These anomalies include one kidney rising normally and the other kidney remaining in the pelvis. Remember, it is rare to have a unilateral kidney, and thus if you see only one kidney in its normal position, you should look elsewhere for an ectopic kidney ( Fig. 7.5 ). Another common variant is fusion of the inferior aspect of both kidneys (a horseshoe kidney). This is relatively easy to identify because the axis of the kidneys is abnormal, with the superior aspect of the kidneys tilted outward instead of inward ( Fig. 7.6 ).




Fig. 7.5


Pelvic Kidney.

In this young woman, a questionable mass was felt in the pelvis during a routine gynecologic examination. (A) A transverse contrast-enhanced computed tomography scan of the upper abdomen reveals only the left kidney (K) . The liver (L) is seen, but no right kidney is identified. (B) Continuing the scan down into the pelvis shows that the right kidney is ectopic.

Ant , Anterior.



Fig. 7.6


Horseshoe Kidney.

(A) On this urogram, the inferior aspects of the right and left kidneys are joined (arrows) . Note the abnormal axis of both the right and left collecting systems, with the upper portion tipping outward from the spine instead of tipping slightly inward. (B) On an axial computed tomography scan, the isthmus can easily be seen anterior to the aorta and inferior vena cava.


Renal Cysts


Renal cysts are quite common, and their incidence increases with age. Most persons older than 60 years have one or more simple renal cysts. These are often found incidentally on ultrasound or CT scans ordered for other reasons. Ultrasound is a good and inexpensive initial test to characterize a renal cyst. The margins of a benign simple cyst should be well defined, and increased echoes should be seen on the posterior aspect of the cyst because of good transmission of sound through the fluid in the cyst ( Fig. 7.7A ). If a cyst has septa or internal echoes on ultrasound, a short-term follow-up ultrasound or CT scan is usually ordered to exclude a cystic neoplasm.




Fig. 7.7


Renal Cysts.

(A) A longitudinal ultrasound image shows the normal liver and renal parenchyma with a cyst in the upper pole of the right kidney. Notice that no (white) echoes appear within the cyst and increased transmission of sound occurs through the fluid of the cyst, producing a posterior enhanced echo pattern (arrows) characteristic of a simple cyst. (B) Renal cysts are common incidental findings on computed tomography scans. In this case, there are two simple low-density cysts (short arrows) . There is also a hyperdense lesion (long arrow) , which needs further workup to exclude an inflammatory process, complex cyst, or neoplasm.


On a CT scan, renal cysts are typically hypodense relative to the renal parenchyma; however, occasionally they can be hyperdense due to blood or protein content (see Fig. 7.7B ). Hyperdense renal cysts should not enhance more than about 10 Hounsfield units after contrast administration and should have a smooth outline and be internally homogeneous.


Currently renal cysts or cystic masses are classified according to the Bosniak criteria. Bosniak I lesions are benign cysts that are round or oval with a thin wall, no septations, Hounsfield CT units of 0 to 20, and no enhancement with intravenous contrast. Follow-up is not usually needed. Bosniak II lesions are the same but with a few septations, a few thin calcifications, or both. These are often followed up in 6 to 12 months, but both Bosniak I and II lesions have a very small chance of being malignant. A Bosniak III lesion has any or all of the following: a thick wall, calcifications, Hounsfield density of 0 to 20, and no enhancement of nodules. These lesions have about a 60% chance of being malignant. Bosniak IV lesions have a thick wall, thick septations, coarse calcifications, Hounsfield density of more than 20, and enhancement with intravenous contrast. All these lesions should be considered to be malignant and require further workup.


Polycystic renal disease presents a difficult imaging problem. In the adult form of this heritable disorder, often progressive renal failure occurs. A CT scan will demonstrate very lumpy kidneys, but the cysts may not be well defined because hemorrhage often is found within the cyst. Cysts also are usually identified in the liver and sometimes in the pancreas ( Fig. 7.8 ).




Fig. 7.8


Adult Polycystic Disease of the Liver and Kidneys.

(A) A computed tomography scan through the upper abdomen shows the liver with multiple low-density areas throughout due to cysts within it. (B) A transverse scan obtained slightly lower shows markedly deformed and enlarged kidneys bilaterally. Note that some of the cystic areas within the left kidney are of low density (white arrow) and some of the cysts are of higher density (black arrow) . This makes it very difficult to exclude a malignancy in this patient.

K , Kidney; Sp , spleen.


Hematuria


Hematuria can be traumatic or nontraumatic and visible or microscopic. Microscopic hematuria is defined as three or more red blood cells (RBCs) per high-power field (HPF) on microscopic evaluation of urinary sediment from two of three properly collected urine specimens. In cases of trauma and visible hematuria, a CT scan is indicated. In cases of trauma, microscopic hematuria, and little suspicion of injury to other organs, many physicians do not do any imaging but rather wait 48 hours to see if the hematuria clears. Young women with a clinical picture of simple cystitis and other patients whose microscopic hematuria completely and permanently resolves after rest or therapy are unlikely to benefit from imaging.


Of patients with nontraumatic visible hematuria, about 25% have cancer, 25% have infection, and 15% have calculi. About 5% of patients with nontraumatic microscopic hematuria (5 RBCs/HPF) have a urologic cancer. Obviously, the presence of unilateral flank pain suggests calculi, discussed later. If RBC casts are seen in urine with associated proteinuria, a renal biopsy is usually performed. Neither CT nor an ultrasound examination can completely exclude a urologic malignancy because CT and ultrasound are poor for detection of small urothelial tumors and evaluation of bladder tumors. The best evaluation of painless nontraumatic hematuria often begins with cystoscopy and possibly retrograde pyelogram at the same time. If this is negative, a CT scan is indicated.


Renal Stone Disease


Calcification can occur within the substance of the kidney or within the collecting system. Calcification within the substance of the kidney (nephrocalcinosis) may be cortical (near the periphery of the kidney) or medullary (near the ends of the calyces). Cortical calcification can be due to chronic glomerulonephritis, cortical necrosis, or acquired immunodeficiency syndrome (AIDS)-related nephropathy. Medullary calcification may be idiopathic or caused by papillary necrosis, medullary sponge kidney, or other hypercalcemic states (including hyperparathyroidism and osteoporosis; Fig. 7.9 ).




Fig. 7.9


Nephrocalcinosis.

A plain x-ray of the abdomen shows multiple calcifications (arrows) within the left kidney, located near the ends of the calyces (medullary) rather than in the cortex. This patient had medullary sponge kidneys.


The vast majority of renal calculi are radiopaque and appear dense (or white) on a routine x-ray ( Fig. 7.10A ). Occasionally, renal stones become very large and essentially fill the collecting system of the kidney. These are referred to as staghorn calculi (see Fig. 7.10B ). If calculi are radiopaque, overlie the kidneys, or are within the course of a ureter, they are usually fairly easy to see. Sometimes it can be difficult to visualize a small stone in the region where the ureter passes anterior to the sacrum. Remember that a large number of vascular calcifications occur low within the bony pelvis and to the sides of the bladder. These phleboliths typically can be recognized because they are round, have a lucent (dark) center, and are more lateral and lower in the pelvis than the normal course of the ureter.




Fig. 7.10


Renal Calculi.

(A) On a plain radiograph of the abdomen, a single calcification is seen in the right upper quadrant (arrow) . This is a right renal calculus. Renal calculi should be suspected any time a calcification is seen within the renal outline or along the expected course of the ureter (dotted lines) . (B) In a different patient, a plain radiograph of the abdomen shows a calcification conforming perfectly to the collecting system of the left kidney. This is referred to as a staghorn calculus .


The most common clinical presentation of stone disease is intense flank pain with hematuria. If the patient is having a first presentation of renal stone disease, a spiral noncontrast CT scan is indicated, even if no calculus is seen on the plain x-ray of the abdomen. Only about 50% of renal calculi are seen on a plain film, whereas detection with CT is about 95%. CT scanning is exquisitely sensitive for the detection of even tiny calcifications and provides additional detail about other potential causes of pain, and the size of the stone can be accurately measured. Ultrasound can visualize large renal stones and hydronephrosis but is poor for the detection of small renal or any size ureteral stones ( Fig. 7.11 ).




Fig. 7.11


Renal Calculi.

(A) On an ultrasound image, a bright echo (arrow) is seen in the renal cortex as a result of a stone. A stone must be relatively large to be reliably diagnosed with ultrasound. (B) An axial computed tomography (CT) image from another patient shows a tiny 2-mm nonobstructing stone (arrow) . CT is the most sensitive method for the detection of calculi.


If a history of renal stones is known, imaging is not always needed. Imaging may be reserved for patients who have pain uncontrolled by medication, those with continued flank pain for more than 5 days, those who have continued hematuria 2 weeks after passing a stone, those with microscopic hematuria for more than 1 month, and those who have acute flank pain and are known to have a solitary kidney or pelvic tumor.


The size of a stone is inversely proportional to its passage. A stone 5 mm or smaller has a 68% probability of spontaneous passage, whereas a 10-mm stone is very unlikely to pass spontaneously. Stones typically become lodged in the ureter at the ureteropelvic junction, iliac vessels, or ureterovesicular junction.


On a CT urogram, obstruction of the ureter by a stone may cause delayed visualization of the affected kidney and ureter. When it is visualized, the ureter is usually dilated and the renal calyces are blunted. On delayed images, whereas the normal kidney is completely clear of contrast, the affected kidney and ureter will be seen retaining contrast. Delayed images are often necessary to determine the exact level of the ureteral obstruction.


Usually a kidney with an acute problem due to renal calculi will have associated perirenal edema in the adjacent soft tissues ( Fig. 7.12A ). Benign age-related perinephric stranding is usually bilateral and occurs mostly in persons older than 55 years. If a stone is lodged in the distal ureter, a dilated proximal ureter can often be seen (see Fig. 7.12B ). Sometimes on a CT scan it is difficult to differentiate ureteral calculi from atherosclerotic vascular calcifications or vascular phleboliths. One way is to look for a soft tissue rim around the calculus (see Fig. 7.12C ). Phleboliths are most common in the lower pelvis below the middle portion of the femoral heads, whereas the ureters almost always enter the bladder at a more cephalad level.




Fig. 7.12


Obstructing Left Ureteral Calculus.

(A) On this noncontrast computed tomography scan, at the level of the kidneys there is stranding (arrows) around the left kidney but not around the right kidney. (B) At a lower level, a dilated left ureter is seen (arrow) , and at the level of the bladder (C), a calculus is seen at the left ureterovesicular junction (arrow) . The small rim of soft tissue around the calculus helps distinguish it from a phlebolith.


Occasionally, the back pressure caused by an obstructing ureteral stone can rupture a renal calyx or renal pelvis. When this occurs, extravasation of urine and contrast outside the kidney into the perirenal space is seen. When an obstructing lesion of the ureter is present, the urologist may perform cystoscopy and then place a little tube into the distal ureter and inject contrast (retrograde pyelogram). The ureter, renal pelvis, and calyces are usually visualized. Because pressure is being exerted during the injection, minimal blunting of the calyces is normal under these circumstances. A retrograde pyelogram is useful for looking at small lesions within the collecting system, such as a transitional cell carcinoma. Occasionally, air bubbles will be inadvertently injected along with the contrast, which may give the appearance of filling defects. The key to differentiating these entities is that tumors will not move around on different views; many calculi also have sharp or geometric borders ( Fig. 7.13 ). Air bubbles move and are completely round.




Fig. 7.13


Ureteral Calculi on a Retrograde Pyelogram.

A cystoscope has been put in the bladder, and the orifice of the left ureter catheterized. Contrast is then injected retrograde. Multiple lucencies can be seen within the collecting system of the left kidney (arrow) . The fact that these defects are not round but have sharp corners indicates that they are calculi and not inadvertently injected air bubbles.


Renal Failure


Imaging is indicated in patients with unexplained oliguria or new onset of renal insufficiency or failure (serum creatinine level > 2 mg/dL). Many imaging studies of the kidneys rely on normal function. The most common clinical question is whether renal failure is due to obstruction or to medical renal disease. Because the intravenous contrast material used for a CT or MRI scan can reduce renal function, the imaging examination of choice for acute or chronic renal insufficiency is ultrasonography. Normally, the cortex of the kidney has the same ultrasound echo density as the liver or has fewer echoes than the substance of the liver. In cases of medical renal disease, more echoes are found within the renal cortex than within the liver. This is probably the result of fibrosis and scarring ( Fig. 7.14 ). For the use of intravenous contrast with a CT or MRI scan, an estimated glomerular filtration rate (eGFR) of 60 mL/min per 1.73 m 2 or greater is acceptable, an eGFR of 30 to 60 mL/min per 1.73 m 2 usually requires hydration of the patient, and a value of less than 30 mL/min per 1.73 m 2 is a significant contraindication.




Fig. 7.14


Medical Renal Disease.

Ultrasound is often performed in patients with renal failure to differentiate between hydronephrosis and renal parenchymal disease. Patients with renal parenchymal disease usually have smaller than normal kidneys. In this longitudinal ultrasound image of the right kidney, note that the parenchyma of the kidney has more echoes or is whiter than that of the liver at the same depth. Normal renal parenchyma will have a number of echoes equal to or lower than those of the liver. (See Fig. 7.26 for an ultrasound image of hydronephrosis.)

K , Kidney.


Pyelonephritis and Renal Infections


The clinical findings of pyelonephritis include fever, flank pain, and pyuria. Most patients with pyelonephritis have no discernible findings on imaging studies. Imaging studies are usually not warranted in an uncomplicated patient unless there are repetitive episodes or there is persistent worsening pain after 3 days of appropriate antibiotic therapy. CT scanning with and without intravenous contrast is appropriate in patients who are complicated (e.g., have diabetes, are immunocompromised, had prior renal surgery or history of stones). Sometimes, in patients who have severe acute pyelonephritis, enough edema of the renal parenchyma is present that the swelling causes compression of the calyces or renal pelvis, and there is poor visualization of the collecting system on a CT urogram. Occasionally, with acute pyelonephritis, focal areas of edema can be seen. The real purpose of ordering CT scans in these cases should be to look for a renal parenchymal or perirenal abscess.


In patients with chronic pyelonephritis, the kidney is usually shrunken and has an irregular outer margin. Typically, the cortex also is thinned. The irregularities of the outer cortical margin are fairly characteristic, with dimpling or scarring directly over a calyx. If there is dimpling or a defect in the margin of the kidney between two calyces, it is more likely to be the result of a focal infarct.


Persons with diabetes are particularly prone to an unusual form of acute pyelonephritis called emphysematous pyelonephritis . In these patients, gas is generated by the bacteria within the parenchyma of the kidney. Usually the kidney is nonfunctional, and a dark radiating striated gas pattern is seen where you would normally expect to find a kidney ( Fig. 7.15 ).




Fig. 7.15


Emphysematous Pyelonephritis.

This condition most commonly occurs in persons with diabetes. (A) On a pyelogram, nonfunction of the affected kidney is seen, in this case on the right (arrows) . (B) A more detailed view of the right upper quadrant shows radiating dark thin lines of gas within the parenchyma of the right kidney (outlined by dashed line ).


Occasionally, inflammatory abnormalities can cause enlargement of both kidneys, particularly in acute glomerulonephritis. The differential diagnosis for bilaterally enlarged kidneys includes bilateral obstruction, leukemia, glycogen storage diseases, lymphoma, and polycystic disease, as well as a number of other entities ( Fig. 7.16 ).




Fig. 7.16


Acute Glomerulonephritis.

A urogram in this child demonstrates markedly enlarged kidneys bilaterally. The injected contrast has made the kidneys visible, but the kidneys are unable to excrete the contrast.

K , Kidney.


Infections of the kidney can progress to the stage at which the kidney is essentially nonfunctional. In an entity known as xanthogranulomatous pyelonephritis , a nonfunctional kidney is seen, with some calcification visible within it ( Fig. 7.17 ). The kidney is removed surgically. However, on the basis of any imaging study, it is difficult to differentiate xanthogranulomatous pyelonephritis from a renal tumor.




Fig. 7.17


Xanthogranulomatous Pyelonephritis.

(A) On a pyelogram, no function is seen in the left kidney, although some evidence of calcification is noted (arrow) . (B) In a different patient with the same condition in the right kidney, a computed tomography scan again shows nonfunction, with areas of low density and calcification (arrow) . With any imaging modality, it is very difficult to differentiate this condition from a neoplasm.

Ant , Anterior; K , kidney.


Renal tuberculosis can affect the kidneys, ureter, and bladder; the infection typically begins in the kidneys, and you should look there first. In the early stages, narrowing or amputation of the infundibulum is seen between a renal calyx and the renal pelvis. In late stages, a nonfunctional shrunken kidney with clumps of calcification is found. A number of fungal infections can affect the kidney in diabetic and immunosuppressed patients. Fungal infections often cause large fungal clumps or balls within the collecting system that can obstruct the kidney ( Fig. 7.18 ).


Feb 19, 2020 | Posted by in GENERAL RADIOLOGY | Comments Off on Genitourinary System and Retroperitoneum
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