Ultrasound of the urinary tract

ULTRASOUND OF THE URINARY TRACT DANIEL G. M c D O N A L D

TABLE OF CONTENTS PHYSICS AND EQUIPMENT

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ECHOGRAPHIC EVALUATION OF RENAL MASSES . . . . . . . . EVALUATION OF RENAL MASSES NONFUNCTIONING KIDNEYS . PERmENAL MASSES .

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ULTRASONIC LOCALIZATION FOR RENAL BIOPSY . . . . . . . .

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RENAL TRANSPLANTS BLADDER

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PROSTATE PRDIATRIC ULTRASOUND .

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is Radiologist at the Newton-Wellesley Hospital of Tufts University Medical School. Doctor McDonald received his M.D. degree from the State University of New York Upstate Medical Center, Syracuse, and took his radiology residency at the University of California School of Medicine, San Diego. Prior to his present appointment he served as Head of the Department of Ultrasound at the New England Deaconess Hospital. Doctor McDonald's research interests are in the areas of abdominal and cardiac ultrasound and angiography.

PHYSICS AND EQUIPMENT ULTRASOUND is any sound frequency greater than 20,000 cycles per second, and therefore it is beyond the range of the human ear. The unit of frequency is the hertz, which equals 1 cycle per second. In diagnostic ultrasound we deal with frequencies of 1 - 10 megahertz (MHz). When a sound wave strikes an interface between two media, it is reflected and refracted (Fig. 1). Reflection is the return of all or part of the sound from the interface. This ability of tissue interfaces to reflect sound is the basis of most diagnostic applications. As in optics, the angle of incidence is equal to the angle of reflection (Fig. 2). The amplitude of the reflected and the transmitted sound waves depends on the amplitude of the incident wave, the acoustic impedances of the media and the angle of incidence. The acoustic impedance of a tissue (Z) is the product of the density of the medium (p) and the velocity of the sound wave (C) within the substance. Only a small amount of energy need be reflected from an interface to provide a signal of sufficient amplitude to be detected, amplified and recorded. 2~ A "transducer" is a device that converts electrical energy to Interface

Interface

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3 Fig 1 . - S o u n d waves are reflected at the interface between substances of acoustic impedance.

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2 . - R e f l e c t e d sound waves obey the laws of optics in that the angle of incidence is equal to the angle of reflection. Thus, only those waves striking an interface at 90~ are reflected back to the transducer

sound energy and vice versa. Ultrasound transducers (Fig. 3) consist of a crystal made (~f a "piezoelectric substance" whose shape is deformed when an electrical voltage is applied to it and which generates a voltage when it is deformed by a sound wave. Thus, the same transducer acts as both a transmitter and a receiver. It transmits a short pulse of sound into the subject and then waits to receive echoes t h a t are reflected from the various interfaces within the tissue being examined. The frequency of the sound waves propagated by the transducer depends on the material and thickness of the transducer and ranges between 1 and 10 MHz in diagnostic ultrasound. As the sound wave travels through tissue, its intensity becomes lessened. This is known as attenuation of the sound wave. As the frequency increases, the rate of attenuation increases and thus the depth of penetration decreases. The rate of attenuation of sound within soft tissues in the h u m a n body is approximately 1 decibel per centimeter of tissue per megahertz (1.0 db cm -1 MHz-1). In contrast, the attenuation of sound in blood is 0.18 db cm -~ MHz-L ~ The relative intensity of two levels of sound is measured on the decibel scale. The bel is the basic unit and is logarithmic to the base 10. Since the intensity differences in ultrasound are much smaller t h a n the bel, the decibel (db) is used commonly and is

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equal to 1/loth of abel. The db equals 10 loglo (I1/I ,) where 11 and 12 are the two intensities. Thus, ifI 1 is 10 times as great as I2, it is 10 db more intense, and if I1 is 100 times more than I2, it is 20 db more intense. In measuring absorption or reflection, the reference level is the intensity of the incident beam. In order for a structure to produce a reflection of the ultrasound wave, its dimension along the sound path must be greater than a wavelength. The velocity of a sound wave equals the product of the frequency and wavelength. Since the mean value for the wave propagation velocity in h u m a n soft tissue is 1540 meters per second, the wavelength is inversely proportional to the frequency. Thus, the higher the frequency of the sound wave the smaller the object necessary to produce a reflection. Axial resolution is the separation necessary between two objects along the direction of wave propagation that will enable them to produce separate echoes. For two structures to be seen separately, their separation must be greater than the wavelength as well as more than onehalf the spatial pulse length. The spatial pulse length represents the distance from the start to the end of a burst of sound. If a frequency of 2 MHz is used, which is typical for abdominal ultra: sound, the wavelength is 0.8 millimeters and the spatial pulse length is 1.5 millimeters. Thus, the smallest detectable structure and the axial resolution equals 0.8 millimeters. Lateral resolution is the minimal separation required for two reflectors perpendicular to the sound to produce separate echoes. This is determined by the beam width, which depends on the diameter of the transducer, the shape of the transducer and the presence or absence of focusing lenses attached to the transducer: A typical focused 2-MHz transducer has a lateral resolution of 1.5 millimeters. Abdominal ultrasound utilizes pulsed ultrasound in that every 300 milliseconds the crystal receives a 10-millisecond burst of electrical energy that causes it to vibrate and emit ultrasonic waves. For the remainder of the cycle, 290 milliseconds, the crystal and transducer act as a listening device for returning echoes. Since the transducer acts as both a transmitter and a receiver, it is possible to calculate the round-trip transit time of a pulse as it travels from the transducer to a reflecting interface and back to the transducer. Since sound travels at a relatively constant speed in h u m a n tissue, 1540 meters per second, the distance between the transducer and the reflecting interface can be calculated by multiplying one-half the transit time by 1540 meters per second. The reflected echoes cause a voltage change across the transducer that is amplified and recorded on an oscilloscope in one of three ways. The A-mode (amplitude) presentation shows the reflected echoes as spikes arising from a horizontal baseline. The height of the spike is proportional to the amplitude of the echo. The distance between the transducer and the reflecting interface

is shown on the horizontal baseline as the distance between the transducer artifact spike and the spike produced at the interface. The A-mode presentation is the most basic display (Fig. 4) and is derived from the original radar and sonar instruments to show echo amplitude plotted against tissue depth. A-mode constitutes a one-dimensional analysis of the tissue in the path of the sound beam. It is an instantaneous recording that changes as the transducer moves from point to point. M-mode (motion) is used for the evaluation of moving structures. It is like A-mode in that it analyzes only the tissue directly perpendicular to the transducer at the time of the recording. The reflected echo is shown as a dot on the oscilloscope, and the intensity of the dot is proportional to the amplitude of the echo received. The tissue depth is again recorded as the horizontal distance between the echo from the transducer face and the reflecting interface. The trace sweeps from the bottom of the screen to the top of the screen at a given rate. As the invisible baseline moves up the screen, the distance between the transducer and the interface will change if the interface is a moving structure (Fig. 4). Thus, the direction and amplitude of excursion and consequently velocity of motion can be calculated. M-mode is the method of analysis used for echocardiography. It m a y be used in the abdomen to evaluate the motion of the diaphragm or pulsations within a blood vessel. B-scan refers to a composite two-dimensional image obtained while a transducer is moved across the body in a given arc. Crosssectional imaging requires the use of a scanning arm that senses the transducer position and angulation. The movable joints of this arm are equipped with angle sensors that send signals to an analog computer circuit. The computer calculates the sound beam position on the subject and positions the trace on the oscilloscope display in a corresponding orientation (Fig. 5). The reflected echoes are presented as intensity-modulated dots as in the Mmode. f

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Fig 4 . - A - m o d e display plots the echo amplitude against the distance between the transducer and the reflecting interface. B-mode depicts the echo as a dot whose brightness depends on the amplitude of the echo. M-mode is a timed exposure obtained while an invisible baseline sweeps up the screen at a fixed speed.

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Bi-stable scanning refers to the presentation of the B-scan on a storage oscilloscope. The storage oscilloscope has the disadvantage t h a t it does not show variation in echo amplitude. The amplitude of the echo signals in a typical scan of the abdomen varies over a range of 1000 to 1 or 60 db, but the standard storage cathode ray tube can produce only black and white images. It is thus an all or none phenomenon, with the amplitude of the echo being either sufficient or not sufficient to be recorded. When the gain is turned high enough to demonstrate low-level echoes from the parenchyma of various abdominal organs, reverberations are produced at the strong interfaces, and these reverberations produce noise in the over-all system t h a t cannot be distinguished from real echoes. Thus, bi-stable scanning is performed at low gain and the internal organs are clearly outlined, but little information is obtained about the homogeneity of the tissues within the organ. Newer B-scan units feature a "gray scale" format t h a t uses an electronic scan converter to store and reproduce the dynamic range of echoes into 8 or 10 shades of gray (Fig. 6). During scanning, the image is stored in the scan converter, and later it is displayed on a standard television monitor. This ability to display the dynamic range of echoes accounts for the ability of gray scale to display the echo pattern of the internal architecture of organs instead of merely outlining organs as is done in bi-stable scans. A permanent record of the scans m a y be obtained by attaching a Polaroid camera to either the cathode ray tube or the television monitor. The Polaroid camera m a y also be replaced by a 35-mm, 70-mm or 90-mm camera. More expensive recording systems are available t h a t produce a permanent picture on heat-sensitive paper or on standard radiographic film. A videotaping system can

Fig 6 . - Gray scale displays the echo as one of 8 - 1 0 shades of gray according to the amplitude of the echo.

also be attached to the unit and can be played at a later date either for diagnosis or for teaching purposes.

ECHOGRAPHIC EVALUATION OF RENAL MASSES The importance of accurately evaluating the nature of renal masses is apparent when one realizes the high incidence of asymptomatic renal masses. Asymptomatic renal masses have been reported to occur in up to 15% of patients undergoing excretory urography prior to prostatic surgery. 2s Renal masses occur in approximately 4% of patients in whom excretory urograms are obtained. Several autopsy series have revealed the incidence of renal cysts to be between 3% and 5%, with the incidence being much higher in older age groups. Although surgical exploration of all masses of the kidney formerly was believed to be obligatory, modern roentgenographic and laboratory methods now have become as accurate as surgery in assessing the nature of these lesions. The obvious goal is to diagnose correctly the nature of these renal masses at the lowest cost and the lowest mortality and morbidity to the patient. Since the mortality and morbidity of renal angiography are far less than with renal exploration, and since its accuracy compares favorably with surgery, it was widely accepted as the method of choice for investigation of renal masses. Because of the noninvasive nature of ultrasound and its ability to distinguish cystic masses from solid masses in other areas of the body,

considerable attention has been focused on the ability of ultrasound to evaluate renal masses. In the mid-1960s, A-mode ultrasound was used to evaluate the nature of renal masses identified on intravenous pyelograms. 1~ The echogram was performed by placing a transducer directly over the lesion. The lesion was localized either with fluoroscopy, by its relationship to landmarks on the patient's flank or by a series of radiographs obtained during the intravenous pyelogram with grid markers placed over the back of the patient. A totally homogeneous structure such as a fluid-filled mass, i.e.; renal cyst, is echo free in t h a t the sound waves are reflected only at interfaces between tissues of different densities. Thus, with the A-mode transducer placed directly over a fluid-filled mass, the mass is echo free at low gain and remains echo free as the gain or sensitivity is increased. If the gain is increased excessively, reverberations are produced at the periphery of the fluid and can be seen as low-level echoes arising from the periphery of the mass. A solid mass is composed of blood vessels, supporting stroma and functioning tissue and therefore has numerous interfaces from which sound waves may be reflected. A-mode analysis of a solid mass shows t h a t at low gain only the reflected echoes from the front and back wall are of sufficient intensity to be displayed. However, when the gain is increased, the lowlevel echoes are recorded at the interfaces within the interstices of the mass (Fig. 7). Extensive use of the A-mode technique in the mid-1960s produced an accuracy of more t h a n 90% in evaluating cystic masses from solid masses. ~5 The most difficult portion of the technique was the accurate localization of the mass for A-mode analysis. Therefore, as B-scanning became more prominent, investigators began to use this technique for localizing and evaluating renal masses. Because of the inability of sound to penetrate gas, B-scanning of the kidneys is routinely performed in the prone position. A series of transverse and longitudinal scans are performed to totally delineate the kidneys. The transverse scans of the kidneys are performed with 5 - 1 0 degrees of cephalad angulation. This is done because of the fact t h a t the upper pole to the kidney lies more posteriorly t h a n the lower pole, and the cephalad angulaCYST I

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Fig 7 . - A - m o d e display of a cystic mass and a solid mass. The cyst remains echo free at high gain whereas the solid mass contains echoes at high gain.

tion results in the transducer being perpendicular to the axis of the kidneys. On transverse scans, the kidneys are seen as rounded sonolucent masses with a central cluster of dense echoes. These dense central echoes arise from the renal pelvis and calices. The parenchyma of the kidney, being relatively homogeneous, is seen as a sonolucent area around the central echoes. With gray scale, the output intensity is increased to a level whereby the low-level echoes within the renal parenchyma are appreciated as a very faint shade of gray echoes. Ultrasonic sound waves are almost completely reflected from bone, and thus the prevertebral structures are not seen in prone scans (Figs. 8, A and 9, A). Before performing longitudinal scans, a crayon mark is placed at the midportion of the upper pole, middle and lower pole of the kidney. These marks then are connected, and longitudinal scans are performed parallel to this axis so that the true length of the kidney can be determined on the longitudinal scan. The kidney on a longitudinal scan is oval shaped. The lower pole is seen to lie more anteriorly than the upper pole. The longitudinal scans again demonstrate the dense central cluster of echoes from the renal pelvis and the calices in contrast to the relative sonolucent surrounding renal parenchyma (Figs. 8, B and 9, B). In some patients it m a y be difficult to outline the upper pole of the kidneys, especially the left. Frequently, the acoustic window between the iliac crest and the ribs is limited in short patients. Placing a pillow or sponge under the abdomen and placing the hands over the head spreads the ribs and increases the size of the acoustic window. In addition, the scans of the upper pole can be repeated during full inspiration and the scans of the lower pole Fig 8 . - A , a gray-scale transverse prone scan of the normal kidneys (K). The echoes from the renal pelvis and calices (P) are seen in contrast to the sonolucent renal parenchyma. (R = right.) B, a gray-scale longitudinal prone scan of a normal kidney. The row of dots seen superior to the upper pole of the kidney represents depth markers and the interval between two dots represents 1 cm in distance. (In this and all subsequent longitudinal scans, the patient's head (H) is toward the left of the picture and his feet (F) are toward the right of the picture.)

10

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Fig 9 . - A , a bi-stable transverse prone scan of the normal kidneys. B, a bistable longitudinal prone scan of a normal kidney.

repeated during full expiration. The liver lies anterior to almost the complete length of the right kidney, so the right kidney may be examined in most patients in the supine position. This is especially true of the upper pole of the right kidney. The considerable amount of bowel gas in the left upper quadrant precludes adequate scanning of the left kidney in the supine position. Lateral decubitus views frequently are adequate when the patient's condition prevents him from assuming a prone position and adequate supine scans cannot be obtained. No standard nomenclature has been adopted for the labeling of scans. However, a systematic approach should be adopted. Either the iliac crest or the most inferior point of the lowest right rib may be taken as the zero reference point for the prone transverse sections. Sections then are t a k e n at 1- or 2-cm intervals above the iliac crest or below the lowest rib and are labeled according to the distance above or below the reference point. Thus, a scan 6 cm above the iliac crest would be referred to as + 6 in our laboratory. Because the longitudinal sections are performed along an oblique axis, it is more difficult to label these scans accurately. It has been our practice to label the most medial longitudinal scan as zero. As the transducer is moved laterally, the section is labeled "L+3" when it is 3 cm to the left of the reference scan or "R+3" if the section is t a k e n of the right kidney. Renal masses over 2.5 cm can be accurately outlined with the B-scan technique. The typical renal cyst demonstrates no internal echoes, a smooth anterior wall and increased through transmission. If any of these three criteria are absent, the diagnosis of a renal cyst cannot be made with certainty. Solid lesions may show either irregular anterior walls, internal echoes or poor through transmission. With the bi-stable equipment, scans are 11

performed at both low- and high-intensity setting to t r y to define any internal echoes within the mass. In addition, confirmation of the n a t u r e of the mass t h e n is obtained by performing a standard A-mode analysis over the mass t h a t has been localized with the B-scanning equipment. Unfortunately, standard gain settings cannot be given t h a t would clearly distinguish a cystic lesion from a solid lesion. The most reliable technique is to compare the appearance of the unknown lesion with the appearance of a known reference point. Thus, a mass t h a t demonstrates internal echoes on either A-mode or B-mode before or at the same time as the normal renal parenc h y m a obviously is solid, and a mass t h a t shows no internal echoes until a gain level is reached where reverberations are seen Fig l O . - S e e text.

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within the bladder is fluid filled. Thus, a cyst should remain echo free at the time when echoes are seen within the normal kidney parenchyma. Figure 10 represents the transverse and longitudinal scans through a 5-cm mass (C) in the upper pole of the periphery of the left kidney. The mass is noted to be echo free in contrast to the multiple echoes seen within the normal renal parenchyma. The anterior wall of the mass is stronger than the wall of the opposite kidney, indicating good through transmission. The anterior wail is smooth on both the transverse and longitudinal scans. Thus, this mass demonstrates all of the characteristics of a renal cyst. (S- spleen.) Almost all renal carcinomas demonstrate internal echoes at the same or even at a lower intensity than t h a t necessary to demonstrate internal echoes within the normal kidney parenchyma. Figure 11 demonstrates a transverse scan at the level passing Fig 11. - S e e text.

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through the midportion of a mass in the upper pole of the left kidney. The left kidney is noted to be irregular in outline and enlarged as compared to the right. There a r e diffuse low-level echoes throughout the entire mass. At the right, the normal echoes from the renal pelvis and calices are clearly delineated. The longitudinal scan through the left kidney demonstrates the normal pelvic and caliceal echoes (P) displaced inferiorly by the large mass in the upper pole. This pattern is typical of a renal cell carcinoma, which this mass represented. An additional feature that one evaluates is the absorption of the sound within the mass being evaluated. Sonic absorption within a mass depends on the thickness of the boundary interface and the intrinsic factors of the specific tissues involved, i.e., their density and viscosity. Absorption is minimal for a fluid-filled mass and increases in proportion to the density of the mass. The relationship between the amplitude of the returning echoes and the density difference is dependent on the frequency of the sound waves in that it becomes more pronounced with higher frequencies. Sound is absorbed at a rate approximately 500 times higher in the normal h u m a n soft tissues than in fluid. Because of this normal absorption of sound within tissues, commercial equipment includes a time gain compensation control whereby the signal intensity may be amplified by 2 . 5 - 4.0 decibels per centimeter of tissue. Since the degree of electrical signal amplification exceeds the absorption of sound in a fluid-filled structure, the echoes from the distal wall of a cyst are displayed with greater amplitude than the echoes from the proximal wall. ~ This principle is known as increased through transmission and is demonstrated in Figure 12. Solid masses absorb sound to varying degrees depending on both their intrinsic nature and the presence or absence of a surrounding capsule. Thus, s echoes from the distal wall of a solid mass are equal to or less than the amplitude of the proximal wall. A tumor with a relatively homogeneous cellular structure m a y not exhibit any internal echoes b u t can be distinguished from a cyst because of the absence of increased through transmission. The intensity of the echoes at the anterior wall of a homogeneous mass do not appear significantly different than at the anterior aspect of the normal kidney (Fig. 13). The absorption of the sound of such a mass can be evaluated more objectively using the A-mode presentation. The heights of the spike from the proximal and distal walls of the mass are compared at a low-intensity setting. With a solid mass, the ratio is equal to or less than 1 whereas with a fluid-filled mass it exceeds 1. This ratio has been referred to as the reflection ratio ~ (Fig. 14). When a renal mass is identified as being solid, the echographer should attempt to further stage the extent of the neoplasm. Therefore, the patient is turned into the supine position and 14

Fig 1 2 . - A - m o d e display through a renal cyst demonstrates the cyst to be echo free at both low and high gain. The echoes from the far wall are much greater in amplitude than the echoes from the proximal wall.

scans are performed to evaluate the inferior vena cava and liver. The normal inferior vena cava is seen in parasagittal sections just to the right of midline. It appears as a tubular, fluid-filled structure and is free from internal echoes. The inferior vena cava distends during inspiration and Valsalva and collapses with expiration. Therefore, scans are performed during suspended inspiration. Extension of renal cell carcinoma into the vena cava has Fig 13.--A homogeneous renal cell carcinoma (T) of the lower pole of the right kidney remains echo free on both the transverse (A) and longitudinal (B) scans. The echoes from the anterior wall of the tumor are about the same intensity as those from the anterior wall of the normal left kidney as seen on the transverse scan and the normal upper pole of the right kidney as seen on the longitudinal scan.

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Fig 1 4 . - A - m o d e display through the mass (M) depicted in Figure 13 shows the reflection ratio of the mass to be less than 1, indicating the solid nature of the mass despite the fact that it is virtually echo free at high gain.

been reported to occur in 9 - 33% of cases, and can be echographically demonstrated. S~ Figure 15, A is a longitudinal scan performed 1 cm to the right of midline. The inferior vena cava (IVC) just below the diaphragm is echo free. More caudad, the cava is noted to be slightly widened and to contain a definite cluster of echoes. The cava again is free from echoes more inferior to this. A transverse scan (Fig. 15, B) through this level demonstrates the tumor (T) echoes within the inferior vena cava. The inferior venacavogram and surgery confirmed this to be t u m o r extending into the inferior vena cava. Renal carcinoma metastasizes to the liver in 1 0 - 15% of cases. The liver is best evaluated for metastatic disease with a series of longitudinal scans performed at 1-cm intervals during full inspiration. The accuracy of the present gray-scale equipment is being evaluated in several centers, and ultrasound appears to have a 7 0 - 8 0 % accuracy in the diagnosis of metastatic liver disease. Metastases to the liver are seen as solid masses within the liver, which m a y be more or less echo producing t h a n the normal liver parenchyma.

EVALUATION OF RENAL MASSES The high degree of accuracy of echography in evaluation of renal masses has altered the work-up of these masses. It is, however, not accurate enough to serve as the definitive test in the evaluation of a renal mass. Therefore, numerous systematized 16

Fig 1 5 . - S e e text.

approaches to the renal mass have been proposed recently, and these all include ultrasound as an integral part of the system. The optimal system would yield 100% accuracy in diagnosis, while limiting the number of necessary examination techniques to the minimal number and maintaining the least morbidity, inconvenience and cost to the patient. Figure 16 is a flow sheet of a diagnostic protocol t h a t we have adopted. It is quite similar to t h a t of Pollack et a l Y The goal of such a protocol is to minimize superfluous examinations and to use radionuclide imaging, nephrotomography, ultrasound, angiography and needle puncture in such a way t h a t they are complementary to one another. The vast majority of renal masses are initially identified on intravenous urograms. Urography may show either a definite or a possible mass. ~Dromedary humps," fetal lobulation, lobular compensatory hypertrophy and prominent columns of Bertin may suggest a renal mass when none is present. These are referred to as renal ~pseudotumors." All of these pseudotumors contain func17

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tioning renal cells and have been shown to accumulate 19~Hg-labeled chlormerodrin or 9~mTc DPTA because of their tendency to accumulate in the cells of the proximal renal t u b u l e s ) 6 Therefore, these pseudotumors do not produce a defect in the radionuclide image. In contrast, true renal masses do not contain functioning tissue and, therefore, produce a defect in the radionuclide image. This radionuclide technique has proved accurate in evaluating possible masses greater than 2.5 cm and, therefore, is highly valuable as the initial step in assessing equivocal urograms. On echography, true renal masses are seen as discrete masses that are distinct from the surrounding normal parenchyma. However, the echogram of a patient with a ~pseudotumor" demonstrates no evidence of a renal mass. Figure 17 is a 1-minute film from the intravenous pyelogram of a 61-year-old male referred for symptoms of prostatic hypertrophy. The prominent bump on the lateral edge of the left kidney was thought to represent a neoplasm or dromedary hump. Figure 18 is a rectilinear scan after the injection of 99mTc DPTA. This shows the ~'mass" to have functioning tissue. The echogram showed no mass. This was, therefore, dismissed as a dromedary hump. If a urogram is equivocal b u t the radionuclide image and the renal echogram are normal, the diagnostic work-up is concluded. Therefore, the diagnosis of normal variant is made. If the isotope scan is positive, the work-up then proceeds according to the ultra18

Fig 1 7 . - S e e text. Fig 1 8 . - S e e text.

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sound characterization of the nature of the mass. If no mass is identified on ultrasound, it must be assumed to be solid, and angiography is indicated. If the urogram reveals a definite mass, radionuclide imaging is omitted and ultrasound is the next diagnostic test. A mass may be characterized by ultrasound as being cystic, solid or complex. If ultrasound shows a cystic pattern, numerous investigators have shown t h a t there is approximately a 95% accuracy in saying t h a t this is a simple renal cyst. ~, 24, ~, 30 This degree of accuracy could be improved to approximately 97% or 98% by combining it with high-dose infusion nephrotomographyY The schema proposed above omits nephrotomography for several reasons. The major reason is t h a t cyst puncture is a simple, safe procedure that provides one with virtually 100% accuracy and is, therefore, believed to be the final definitive test in the diagnosis of a renal cyst. Since there is no increased risk of metastases when tumors are punctured, 44 95% accuracy seems more t h a n adequate for an initial screening procedure. Cyst aspiration may be performed under fluoroscopic or ultrasonic guidance. The fluoroscopic technique requires intravenous injection of a urographic contrast agent to localize the presumed renal cyst. Puncture under ultrasonic guidance utilizes a special transducer (Fig. 19) with a central canal through which a needle may be introducedJ s Ultrasonic puncture has the advantages that injection of contrast material is unnecessary, the physician and patient are not exposed to radiation during the puncture and Fig 1 9 . - A - m o d e and B-mode aspiration transducers are shown with a needle passing through the hollow central canal. The B-mode transducer (shown at the left) has an arm extending from the side of the transducer so that it may be attached to the scanning arm. The electrical cable of the A-mode transducer (shown at the right) comes off the side of the transducer rather than the top as on other transducers.

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the depth of the mass can be ascertained. The direction of the canal, and thus the needle, closely follows the ultrasonic beam, so if the beam is aimed at a target, the needle will strike the target. As the needle enters a fluid-filled structure, an echo is produced at the interface between the needle tip and the fluid. This allows continuous monitoring of the position of the needle within a fluidfilled mass (Fig. 20). After the ultrasound scans have demonstrated a cystic renal mass and permission for cyst puncture has been obtained from the patient and the referring physician, a mark is placed over the approximate center of the mass. The back is prepared in the typical fashion to provide a sterile field. The scanning transducer then is replaced with either a sterile A-mode or B-scan aspiration transducer. If the B-scan transducer is to be used, a sterile stocking is first placed over the scanning arm. The center of the cyst again is localized and a photo obtained to measure the depth from the skin to the center of the cyst. A needle stop then is placed on the puncture needle so t h a t the tip of the needle will be at the center of the cyst. A 20-gauge thin-walled needle with an inner stylet or a Teflon-sheathed 20-gauge needle are the needles used most frequently. The needle chosen may be 4 or 6 inches in length, depending on the distance from the top of the transducer to the center of the cyst. Although the Teflon-sheathed needle is believed by m a n y people to be less traumatic, it has the disadvantage t h a t the Teflon sheath prevents ultrasonic visualization of the needle during the puncture. The skin and subcutaneous tissues Fig 2 0 . - T h e upper tracing, A, is the A-mode display of a renal cyst with the aspiration transducer in position over the mass. The lower tracing, B, is after the needle has been inserted. The echo in the midst of the cyst represents the needle tip within the cyst.

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then are infiltrated with 1% Xylocaine. The patient is asked to suspend respiration, and the transducer is positioned over the center of the cyst. The needle then is steadily advanced through the central canal of the transducer to the required depth. A "pop" is felt as the needle enters the cyst. The inner stylet then is removed and the cyst fluid usually flows spontaneously. The needle or Teflon sheath then is connected to malleable tubing and approximately one-third to one-half of the cyst fluid is removed. The volume of fluid within the cyst is calculated prior to the puncture by assuming the cyst to be a sphere whose volume equals 4/3 ~r R 3. This can be simplified to equal V = ~/2 D3.38 The aspirated fluid then is replaced by an equal volume of a combination of air and water-soluble contrast agent such as Renografin 60. The Teflon sheath or needle then is removed and decubitus, AP and PA radiographs are obtained to evaluate the inner surfaces of the cyst (Fig. 21). Cross-table lateral, upright, Trendelenburg and oblique views m a y also be obtained if the initial films suggest any irregularity of the wall of ~he cyst: The aspirated fluid is visually assessed for color, turbidity and translucency. A small aliquot of the fluid is sent for analysis of lactic acid dehydrogenase and fat content. The remaining fluid is sent for histocytologic analysis for malignant cellsY If no fluid is aspirated from the mass, suction is applied to a syringe connected to the needle. The aspirated material is immediately smeared on slides, fixed in 95% ethyl alcohol and studied by cytology. A few ml of water-soluble material then is injected through the needle and the needle removed. Urographic contrast medium then is injected intravenously and the patient Fig 2 1 . - A , a transverse scan through a 4-cm cystic mass in the upper pole of the left kidney. B, a double contrast left lateral decubitus view after Renografin and air have been injected into the cyst. The cyst is smooth walled and contains no masses within it.

22

taken to a radiographic room, where an AP and a lateral view of the abdomen are obtained. If the injected contrast medium is seen to lie within the mass, correct needle position is confirmed and the mass is assumed to be solid. If the injected contrast medium lies outside the mass, the puncture is assumed to be inadequate and a repeat puncture attempt performed. Benign cysts contain a clear, slightly straw-colored fluid with low fat, protein and LDH content. Papanicolaou stained smears and cell block demonstrate no abnormal cells. The double contrast study demonstrates the inner lining of the cyst to be smooth. The cyst cavity is measured on the double contrast study to ensure that the aspirate is representative of the entire lesion seen on the previous urogram and echogram. This combination of findings is virtually 100% diagnostic of a simple solitary cyst. Inflammatory cysts m a y yield a clear, m u r k y or bloody aspirate with a markedly elevated LDH content and a normal or slightly elevated lipase content. The Papanicolaou smear may be classified as indeterminate as a result of the increased mitotic activity and abnormal-appearing cells. The double contrast study usually reveals smooth cyst walls. When any of the histochemical or histocytologic parameters as described above are abnormal, arteriography is recommended. An individual approach then must be taken as to whether surgical exploration is indicated. The high incidence of renal carcinoma within hemorrhagic cysts has led some people to believe that surgical exploration of a mass with a bloody aspirate is necessary regardless of all other findings. This remains a debatable point, which undoubtedly will be clarified as experience with histochemical analysis of bloody aspirates increases. Cystic or necrotic tumors usually contain a bloody or m u r k y aspirate with a high fat content and normal or slightly elevated LDH. The double contrast study demonstrates an irregular lumen with tumor nodules protruding into the lumen or grossly irregular extravasation into the tumor itself. Tumor cells usually are identifiable on cytologic examination. If the echogram demonstrates a solid mass, arteriography is recommended. If the arteriogram indicates tumor, surgery is indicated. If the arteriogram conflicts with the echogram and suggests a cyst, cyst puncture is recommended prior to completing the work-up. A complex echo pattern is one that shows good through transmission indicative of a fluid-filled mass but contains occasional internal echoes indicative of some solid elements. This pattern m a y be produced by a septated multiloculated cyst, an abscess or a necrotic tumor. In these patients, nephrotomography is performed according to the technique of Bosniak2 If the strict nephrotomographic criteria for a cyst are present, cyst puncture is performed. Otherwise, arteriography is performed. 23

A renal carbuncle also appears as a complex intrarenal mass. Although it has good through transmission, the presence of internal echoes and irregular borders distinguishes it from a simple renal cyst. Pedersen e t al. 35 have used ultrasonically guided fineneedle percutaneous aspiration to determine the infectious nature of the mass. When pus is aspirated, culture of the fluid can provide a basis for specific antibiotic treatment. Occasionally this will be adequate to treat the carbuncle and thus obviate the need for surgery. Serial scans during the course of t r e a t m e n t will help evaluate the effectiveness of the antibiotics. The virtual 100% accuracy of the cyst puncture technique as described above, combined with its low mortality and morbidity, accounts for the strong enthusiasm held for this technique. Significant complications of renal cyst puncture are .rare, and thus the procedure may be performed on an outpatient basis. Transient h e m a t u r i a occurs in less t h a n 1% of the cases. The fear of puncturing a major renal vessel precludes puncture of small peripelvic renal cysts. Pneumothorax has been reported as a complication when an attempt to puncture a small upper pole renal cyst adjacent to the diaphragm resulted in inadvertent puncture of the adjacent lung. Since the echogram is not 100% accurate, it is obvious t h a t inadvertent puncture of a renal carcinoma can occur. Some people adivse against puncture of a renal mass because of the fear t h a t this might result in rupture of the natural barrier t h a t the tissue presents to the tumor, with consequent dissemination of tumor cells along the track of the needle as it is withdrawn. This fear appears to be only hypothetical and invalid in view of the work of von Schreeb e t al. 44 They found the 5-year survival rate to be 70% in those patients who had undergone puncture of the tumor versus 38% in those patients who had not had tumor puncture. The degree of malignancy and the age groups in these two populations were not exactly comparable, so it is not valid to conclude t h a t puncture of a carcinoma improves the survival rate. It does, however, seem to indicate t h a t there are no valid grounds for supposing t h a t inadvertent puncture of a renal carcinoma decreases the survival rate, and, therefore, this does not appear to be a significant argument against cyst puncture.

NONFUNCTIONING KIDNEYS Renal ultrasound is a valuable asset in the evaluation of nonfunctioning kidneys. In patients with renal failure of unknown etiology, echography may be used as the initial screening procedure. The size of the kidneys can be evaluated readily. Initially, a series of transverse scans is performed to carefully map out the longitudinal axis of the kidney. Serial longitudinal scans then are performed along this axis to obtain the maximal length of the 24

kidney. If the kidneys are noted to be smaller than normal, the renal failure most likely is secondary to either chronic infection or vascular insufficiency of the kidney with secondary atrophy. If the kidneys are normal in size or slightly enlarged, they are evaluated for intrarenal masses as would be seen with polycystic kidney disease, metastatic disease or angiomyolipomatosis. If no masses are identified within the kidneys, the caliceal pattern is evaluated carefully. It already has been noted t h a t in normal kidneys there is a prominent cluster of strong central echoes produced by the normal renal pelvis and calices. As the renal pelvis and calices dilate with hydronephrosis, these become visible as individual fluid-filled structures. 4~ Thus, with minimal hydronephrosis, the pelvic echo pattern becomes abnormal. An echo-free area develops within the pelvic echoes and increases in size as the pelvis becomes more distended. On transverse section, the central echo pattern is either circular or C-shaped. On longitudinal section, a small, circular, echo-free area is seen in minimal hydronephrosis (Fig. 22). As the hydronephrosis becomes more severe, the sonolucent area becomes larger. On the longitudinal scan, the pelvic echoes become ovoid, with curvilinear walls surrounding the echo-free, fluid-filled, dilated renal pelvis. This pattern is difficult to distinguish from t h a t seen in renal pelvic lipomatosis. The echoes in a kidney with renal pelvic lipomatosis are oriented in an ovoid pattern around a central echoless core. 6 The sonolucent area with pelvic lipomatosis represents the fat infiltrating the pelvis and fills in at a lower output t h a n the fluid within a minimally hydronephrotic pelvis or a small peripelvic cyst. As the hydronephrosis progresses further, the kidney may appear to Fig 2 2 . - A longitudinal scan demonstrates the renal pelvis (P) as a small, ovoid, fluid-filled mass and is indicative of minimal hydronephrosis.

25

consist of multiple cystic structures with septae radiating from the pelvis. These septa delineate markedly dilated calices (Fig. 23). Eventually, when atrophy has destroyed the renal parenchyma to a thin shell, no pelvic shadow is demonstrable and the kidney takes on the configuration of a fluid-filled sac (Fig. 24). Serial studies can be performed to evaluate any progression or regression of the hydronephrosis. Thus, in patients with severe renal failure where the blood urea nitrogen level might impede satisfactory excretion of contrast medium, echography is a simple noninvasive technique for determining the presence or absence of hydronephrosis. The presFig 23.-Multiple cystic structures are seen on both the transverse (A) and longitudinal (B) scans throughout the left kidney, indicating moderately severe hydronephrosis.

26

I-I

................

Fig 2 4 . - A prone longitudinal scan to the left of midline in a 56-year-old white female with left flank pain, fever and a nonfunctioning left kidney on intravenous pyelogram demonstrates a fluid-filled mass (M) with the shape of a kidney. This indicates marked hydronephrosis with destruction of the renal parenchyma.

ence of a normal caliceal pattern in a patient with renal failure excludes the diagnosis of obstructive uropathy. For the same reasons as noted above, ultrasound is valuable in assessing the patient who has visualization of only one kidney on the excretory urogram. The differential diagnosis in such cases includes congenital absence or nonfunctioning kidney. The echogram again can evaluate the presence or absence of a kidney and its size~ As mentioned above, the presence or absence of hydronephrosis can also be evaluated. If hydronephrosis is noted, puncture of the renal pelvis can be performed under ultrasonic guidance using the aspiration transducer. Fluid then can be aspirated for cytology as well as for bacteriologic analysis. The aspirated fluid can be replaced by a water-soluble contrast medium and thus an antegrade pyelogram obtained. 4 This will outline the site and cause of the obstruction (Fig. 25). If obstruction is noted and drainage is desirable, the renal pelvis can be punctured as described above for antegrade pyelography. Using the Seldinger technique, a J guidewire then can be placed through the needle into the renal pelvis. A #6 French or #7 French polyethylene catheter then can be inserted over the guidewire and advanced into the dilated renal pelvis. The distal end of the catheter is preshaped into a pigtail and contains multiple 27

Fig 2 5 . - A n antegrade pyelogram obtained after puncture of the hydronephrotic sac seen in Figure 24 demonstrates complete obstruction of the distal left ureter secondary to recurrent carcinoma of the cervix. Pus was aspirated from the hydronephrotic sac when it was percutaneously punctured and indicated that this represented pyonephrosis. Appropriate antibiotic treatment based on culture of the aspirated fluid resulted in cessation of the fever and flank pain prior to elective nephrectomy.

side holes to facilitate drainage. The catheter then is taped to the skin and serves as a nephrostomy tube. This technique of percutaneous nephrostomy drainage can be used either as a temporary or permanent drainage procedure and is simpler t h a n a surgical nephrostomy. 41 If it is desirable to leave the tube in on a permanent basis, a larger tube can be inserted 1- 2 weeks after the initial insertion. If a nonfunctioning kidney is found to be hydronephrotic, adequate evaluation should include supine scans. These are performed from the symphysis pubis to the xiphoid in the search for a retroperitoneal mass, which might be the cause of the hydronephrosis. Transitional cell carcinomas of the renal pelvis usually are too small for detection by echography. Occasionally, however, they may be seen as a solid mass within the dilated renal pelvis. Obstructing staghorn calculi are visualized as solid masses in the renal pelvis with dilatation of the calices. The calcium within the staghorn calculus reflects all the sound so t h a t no sound pene28

trates through. Thus, the area behind the mass is echo free. This is known as acoustic shadowing (Fig. 26). When the IVP shows nonfunction of a kidney, the echogram may reveal the kidney to be enlarged, with echoes scattered throughout in a haphazard fashion. This pattern is indicative of extensive neoplastic involvement of the kidney, and may be due to either renal cell carcinoma or extensive renal metastases. With renal vein thrombosis, the kidney is also enlarged but has a normal caliceal pattern. Polycystic kidney disease may also result in nonfunction of both kidneys on intravenous pyelography. Early in the course of the disease, the echogram will disclose bilaterally enlarged kidneys, with an increased number of echoes within the renal parenchyma. Later, multiple discrete cysts may be identified within the renal parenchyma, and these cause distortion of the renal pelvis and enlargement of the kidneys. The cysts are of varying size, and there m a y be disparity in the extent of involvement of the two kidneys (Fig. 27, A). If the creatinine clearance is greater than 20 ml per minute, the diagnosis of polycystic kidney disease can be made with an equal degree of accuracy with either infusion nephrotomography or ultrasound. However, as the creatinine clearance decreases below 20 ml per minute, the degree of excretion of contrast medium usually is inadequate to diagnose polycystic disease. 46 Since echography does not depend on renal function, it is accurate in this diagnosis regardless of the degree of Fig 26.--A longitudinal scan of a nonfunctioning left kidney shows multiple cystic areas (H) throughout the kidney, indicating moderately severe hydronephrosis. In the middle of the kidney a strong cluster of echoes (C) is seen. Virtually no sound waves pass through this area, producing an acoustic shadow (Sh) behind this mass. This indicates that the cluster of echoes is coming from a calcified mass, namely, a staghorn calculus.

29

Fig 27.--A, a supine transverse scan at the level of the umbilicus demonstrates both kidneys to be enlarged and to contain multiple cystic masses (C) of various sizes. B, a longitudinal supine scan 4 cm to the right of midline demonstrates a large cyst (HC) in the posterior aspect of the right lobe of the liver. Several cysts (C) in the right kidney are also noted.

impairment of function. Supplemental supine scans are performed to evaluate the liver, pancreas and spleen for cystic disease (Fig. 27, B). Since polycystic kidney disease is a congenital disease, it is desirable to screen family members of patients with known polycystic disease. Although renal function usually is not yet impaired in these individuals, ultrasound still has several advantages over infusion nephrotomography. It does not require the injection of contrast medium, and thus the patient being screened is spared any possible morbidity or mortality that may be associated with urographic contrast media. In addition, these patients usually are children, and the avoidance of x-ray radiation is a most desirable advantage. 3O

Fig 2 8 . - A pelvic kidney (K) is seen in the right pelvis posterior to the distended bladder (B).

Renal artery occlusion, congenital hypoplasia and chronic inflammatory disease m a y result in nonvisualization of a kidney on intravenous pyelography. The echogram is nonspecific in distinguishing between these entities, and merely reveals a small kidney with a normal caliceal pattern. When no kidney is seen in the retroperitoneal area, supine scans are performed looking for an ectopic kidney. Pelvic kidneys frequently are overlooked on intravenous pyelography because of their position overlying the sacrum, and thus are misdiagnosed as unilateral nonfunction (Fig. 28). The normal caliceal pattern is preserved so that, despite the location, one can be certain that the mass is a kidney. PERIRENAL

MASSES

The term "perirenal mass" is a broad term used to encompass any mass in the vicinity of the kidney. Although not all of these 31

masses originate in or even affect the u r i n a r y tract system, they are of interest in a discussion of ultrasonic evaluation of the urinary tract because of the fact t h a t clinically they may simulate renal pathology or cause deformity of the urinary tract on intravenous pyelography. In addition, perirenal masses are difficult to diagnose with conventional radiographic procedures and frequently require more complicated invasive procedures, such as angiography. 22 The echographic evaluation includes an attempt to classify the mass as cystic or solid and to determine if the mass is renal or extrarenal in origin. Correlation of the location of the mass with the patient's history, laboratory studies and intravenous pyelogram often will enable one to reach a specific diagnosis. Examination of the perirenal region is difficult because of the presence of the spinous processes of the vertebrae medially and the ribs superiorly. These interfere with the prone scans whereas bowel gas impedes supine scans. Therefore, the scanning technique must be modified for each patient and the particular area of interest. In the evaluation of a suspected suprarenal mass, the routine prone transverse and longitudinal scans are augmented by decubitus transverse or oblique scans with a 25 ~ cephalad angle as well as supine transverse and longitudinal scans. Cystic lesions in the perirenal region include abscesses, hematomas, urine collections, adrenal cysts or pancreatic pseudocysts (Fig. 29). If immediate surgery is not performed on these perirenal fluid collections, serial scans may be used in assessing their response to treatment. In addition, percutaneous aspiration, using the aspiration transducer, may be used to determine the exact nature of the fluid within these masses. Retroperitoneal and perirenal hematomas appear as irregularly shaped sonolucent areas in the vicinity of the kidney. As the blood becomes more organized and clot formation occurs, a few internal echoes are noted. The hematoma, however, maintains good through transmission, indicating its predominantly cystic nature. If the hematoma is secondary to trauma, the underlying

Fig 2 9 . - A longitudinal prone scan of a 29-year-old male with back pain demonstrates a fluid-filled mass (PC) anterior to the upper pole Of the left kidney. A past history of pancreatitis suggested this to most likely represent a pseudocyst in the tail of the pancreas.

NT

f--

32

Fig 30. - A , a transverse prone scan of a 62-year-old white male with salmonella septicemia, vague abdominal pain and elevated BUN demonstrates a small right kidney (RK). The left kidney (LK) is also small and is displaced anteriorly and laterally by a fluid-filled mass (H), which is to the left of the vertebra (V). B, a supine transverse scan 12 cm below the xiphoid demonstrates a 5-cm aneurysm (A) of the abdominal aorta anterior to the vertebra (V) and medial and anterior to the fluid-filled hematoma (H).

33

kidney m a y demonstrate an increased number of echoes secondary to contusion. If the hematoma is secondary to a ruptured aortic aneurysm, the aneurysm can be identified on supine scans (Fig. 3O). Urinomas have a similar echographic appearance. The lack of a fall in hematocrit and the presence of extravasation on intravenous or retrograde pyelograms as well as the clinical history are used to distinguish between hematomas and urinomas (Fig. 31). Perinephric abscesses either m a y be localized, usually in the posterior perinephric area, or may displace the entire kidney. Percutaneous aspiration may be performed using the biopsy transducer. Culture of the aspirated fluid provides a specific bacteriologic diagnosis and thus dictates appropriate antibiotic therapy. In patients whose overall condition precludes surgery, the Teflon sheath of the aspirating needle may be left in place as a percutaneous drainage tube. If the fluid is too viscous to drain freely through the Teflon sheath, the Seldinger technique may be used to exchange the Teflon sheath for a # 7 o r # 8 French angiographic catheter with multiple side holes. Figure 32 is a supine cross-sectional scan of a 50-year-old diabetic white female with fever, right-sided abdominal pain and a past history of pyelonephritis. The large mass (A) is cystic in appearance and displaces the right kidney laterally away from the spine. This represented a large perinephric abscess and was drained surgically. (L = liver, K = kidney, V = vertebrae.) Fig 3 1 . - A supine transverse section 8 cm below the xiphoid in a 65-year-old white female with right upper quadrant pain 3 months after cystectomy for bladder carcinoma demonstrates the right kidney to be displaced laterally by a fluid-filled mass (U). At surgery, this mass represented a urinoma. (H = liver; A = aorta; S = spine.)

34

Fig 3 2 . - S e e text.

The differential diagnosis of a solid perirenal mass includes an adrenal neoplasm, pancreatitis, a neoplasm in the tail of the pancreas, a retroperitoneal sarcoma and lymphoma. Any of the above lesions clinically may be palpable or distort the normal kidney so that it becomes palpable and thus simulates renal pathology. The echogram is helpful in determining if the mass is renal or extrarenal in origin. When invasion of the renal capsule occurs, this distinction m a y be impossible. The normal or even hyperplastic adrenal gland is not visualized with ultrasound. However, adrenal masses greater than 3 cm can be reliably visualized and characterized as to cystic or solid? As noted above, the scanning technique is most important. The right suprarenal region is best seen on the supine scans whereas the left is best seen on decubitus scans with cephalad angulation. Solid adrenal mass lesions include benign adenomas, pheochromocytomas, adrenal carcinomas and metastases to the adrenal gland. Pheochromocytomas tend to have a very homogeneous internal texture and a well-defined capsule so that they tend to be very sonolucent (Fig. 33). They do, however, absorb sound and can be identified as solid in nature. Figure 34 is a longitudinal scan of a 55-year-old white female with a previous history of breast carcinoma and a recent history of left upper quadrant abdominal pain. On the prone longitudinal scan, the 5-cm solid mass (T) is seen above the left kidney (K). Biopsy revealed this to be a metastasis to the left adrenal gland. In children, solid masses in this area usually represent neuroblastomas. These displace the upper pole of the kidney laterally and possibly inferiorly. Retroperitoneal sarcomas and lymphomas are readily identifi35

Fig 3 3 . - A supine transverse scan 4 cm below the xiphoid in a 48-year-old female with episodic hypertension demonstrates 3 sonolucent masses anterior to the spine (so), the inferior vena cava (IVC), aorta (A) and a 3-cm left adrenal pheochromocytoma (T). (H = liver; K = kidney.)

able on supine echograms. These tend to be homogeneous solid masses with few internal echoes. When chemotherapy is elected as the t r e a t m e n t for a retroperitoneal mass, serial scans may be performed to evaluate any change in the size or echo-producing nature of the tumor mass. Although tumors tend to become more echogenic with response to treatment, 42 the number of echoes within a mass is so dependent on other factors, such as gain settings and scanning speed, t h a t it has not been found to be a practical criterion of response. If radiotherapy is elected as the treatment for a retroperitoneal mass, the cross-sectional representation of the tumor and its relationship to the kidneys and vertebrae is helpful in determining the radiation field. 12 The echogram may be performed either before or after the t r e a t m e n t field has been determined by other standard techniques. Most people prefer to perform the echogram after the estimated port margins have been marked on the patient's skin. The echogram then can determine the distance between the edge of the field and the periphery of the tumor, and the field can be appropriately altered. As the treatment progresses, serial echograms can be used to confirm the regression in tumor size, and the port may be decreased in size to conform to the size of the shrinking remaining tumor. Hypertrophy of the psoas muscle may produce either lateral deviation of the proximal ureter or medial deviation of the distal ureter, and as such may simulate a perirenal mass on the intravenous pyelogram. '~ On ultrasound, the psoas muscles are delineated as round or ovoid masses adjacent to the vertebra and contain multiple medium-intensity internal echoes. 36

Fig 3 4 . - S e e text.

Figure 35 is a supine transverse scan 8 cm below the xiphoid of a 36-year-old male with known testicular carcinoma. Intravenous pyelography suggested a right perirenal mass in t h a t the proximal right ureter was deviated slightly laterally. The echogram, however, demonstrates symmetric solid oval masses (P) adjacent to the vertebrae (V). No mass is seen in the para-aortic area. Therefore, the ureteral deviation is secondary to the psoas muscle in this muscular patient. Fig 3 5 . - S e e text.

37

ULTRASONIC LOCALIZATION FOR RENAL BIOPSY Since the initial description by Iversen 24in 1951, the technique of closed renal biopsy has been used widely. Most closed renal biopsies are performed under image intensification television fluoroscopy after the patient has received a large intravenous dose of water-soluble iodinated contrast material. This technique, however, does have several problems. First, there is a significant incidence of allergy to the urographic contrast medium. Second, it requires good renal function for visualization of the renal outline under fluoroscopic imaging. In addition, the person performing the biopsy and the patient receive radiation exposure during the course of biopsy. The radiation exposure is most important to the person performing a large number of renal biopsies in that he receives a considerable dose to his hands. Because of these problems with the fluoroscopic technique of localization, ultrasound has been advocated for the localization of the kidneys prior to closed renal biopsy. The patient is placed in the prone position, with the lower chest and upper abdomen placed on a sandbag or wedge. This prevents excessive anteroposterior movement of the kidney and makes the axis of the kidney more perpendicular to the posterior abdominal wall. The ultrasound examination consists of a series of transverse echograms at 2-cm intervals using a standard contact B-mode scanner. The medial and lateral borders at each level then are marked on the patient's back with a grease pencil or marking solution. Scans then are performed along the longitudinal axis in both full inspiration and expiration so that the upper and lower poles of the kidney as well as the excursion of the kidney can be outlined (Fig. 36). The distance from the skin surface to the lower pole of the kidney then is measured on the longitudinal echogram. The patient is left in this position, and the skin is prepared using the standard sterilization technique. A needle stop then is placed on the biopsy needle at the depth of the lower pole of the kidney as previously measured on the longitudinal echogram. The needle is inserted 1 - 2 cm superior to the full inspiration lower pole mark, and the biopsy performed in the standard manner during full inspiration. The above-described technique results in an almost 100% success rate in obtaining a good core of renal tissue. 31 Goldberg et al. TM compared the accuracy of ultrasonic localization with fluoroscopic localization. They initially localized the kidneys using ultrasound and then performed the biopsy with a standard fluoroscopic localization technique. The radiologically determined biopsy site was found to be lateral and/or superior to the site determined by ultrasound in a significant percentage of cases and, therefore, was more likely to result in bleeding or ar38

Fig 36.-The position of the kidneys is outlined on the patient's back prior to percutaneous biopsy. I represents the position of the lower pole during deep inspiration. E represents the position of the lower pole during full expiration.

teriovenous fistula. In addition to the safety factor, the ultrasound localization technique avoids the problem of allergic reactions to contrast medium, radiation exposure and poor renal function.

RENAL TRANSPLANTS Numerous studies have shown the value of serial measurements of kidney size in the assessment of transplanted kidneys. These studies have shown that an increase in length greater than 20% usually indicates rejection. 1~Since ultrasound does not have the problems of magnification error as does radiography, there has been considerable interest in the role of ultrasound in the evaluation of renal transplants. In 1970, Leopold29 first proposed the use of ultrasound for serial measurements of the transplanted kidney. Transverse scans of the lower abdomen are performed to determine the maximal width and the longitudinal axis of the kidney. The transplanted kidney, other than its location and axis, appears identical to the normal kidney. Oblique sections then are performed along the longitudinal axis of the kidney to determine the length of the kidney (Fig. 37). An A-mode measurement of the parenchyma at its thickest point is also recorded. Thus, the length, width and AP diameter of the kidney could be determined. A further advance in the ultrasonic technique of assessing transplant size was described by Bartrum e t al. 4 Transverse scans are initially performed through the lower pole, midportion and 39

Fig 3 7 . - S u p i n e (A) and longitudinal (B) scans of a normal transplanted kidney

(K) in the right iliac fossa. (U = umbilicus; P = pubis.)

upper pole of the transplanted kidney. The midpoint of the kidney then is marked on the skin at these three levels and a line is drawn connecting these points. This line represents the longitudinal axis of the transplanted kidney. A longitudinal scan then is performed along this axis. The angle of the kidney with respect to vertical is measured and the transducer is angled by this degree so that all transverse sections are at right angles to the renal axis. Serial transverse sections are made at right angles to the longitudinal axis at 2-cm intervals for the entire length of the kidney. The volume of the kidney can be estimated by several methods. In the integration technique, the areas of the serial transverse sections are mathematically integrated to give an estimate of the total volume. These areas are obtained from the Polaroid scans by hand planimetry or computer analysis of digitized contours. Three simpler techniques of estimating the volume are based 40

only on the longitudinal scans. These are known as the "area technique," the "axis technique" and the "ellipsoid technique." Bartrum et al. found the integration technique to be superior to the simpler approximations and found an R value of 0.99 with this technique. Thus, the ultrasonic volume should be within 14% of the true volume at the 95% confidence level, assuming that the examination is performed properly. Since an acute increase in the size of the transplant occurs during rejection crisis, this noninvasive ability to determine the volume is helpful in confirming the diagnosis of rejection crisis. However, this increase in volume usually is associated with changes in other parameters indicating rejection, and as such is only a confirmatory test in making the diagnosis of rejection. Perirenal fluid collections frequently develop around transplanted kidneys and can be diagnosed with ultrasound. In the immediate postoperative period, these usually represent hematomas, abscesses or urinomas (Fig. 38). Later in the postoperative period, the development of lymphoceles becomes more frequent and m a y occur in 5 - 10% of transplant patients. Any of these perirenal fluid collections can be hazardous to the function of the transplanted kidney and therefore early diagnosis is of great valFig 3 8 . - A supine scan along the longitudinal axis of a transplanted kidney demonstrates fluid (U) anterior and posterior to the upper pole of the kidney. A retrograde pyelogram demonstrated leakage of contrast medium, indicating this to be a urinoma.

41

ue. If desired, the ultrasonic transducer can be used to percuta, neously aspirate these perirenal fluid masses. 32 Aspiration of the fluid helps in distinguishing between a hematoma, urinoma or lymphocele and also determines if there is superimposed infection. The presence or absence of infection in a perirenal fluid collection can alter the surgical approach to this fluid collection. In addition, the ability of ultrasound to provide a three-dimensional image of these perirenal fluid collections, and its noninvasive nature, make ultrasound the technique of choice in performing serial examinations if immediate surgery is not contemplated. Any of these perirenal fluid collections can become large enough to compress the ureter or renal veins, and thus they may compromise the function of the transplanted kidney and simulate rejection (Fig. 39). In addition, they can compress the iliac veins with secondary pelvic thrombophlebitis, which may result in pulmonary embolism. Ureteral obstruction is another rare cause of failure of the transplanted kidney. As in the normally located kidney, the caliceal echoes of the transplanted kidney become splayed with hydronephrosis. Ultrasound has the advantage that it does not depend on renal function to make or exclude the diagnosis ofhydronephrosis. In addition, serial scans can be performed to evaluate whether the hydronephrosis is becoming more or less severe. Potential applications for ultrasonography in the evaluation of transplanted kidneys include the assessment of the parenchymal echoes. It is hoped that with advances in equipment, serial scans of the kidney will demonstrate a difference in the parenchymal echo pattern that will indicate the interstitial edema seen with early rejection. At the moment, this remains hypothetical. Rg 3 9 . - A transverse scan at the level of the apex of the distended bladder of a 26-year-old female, 1 year after renal transplant. The scan was performed after treatment for a "rejection crisis" failed to improve her renal function. A large fluid-filled mass, a lymphocele (L), is seen behind the bladder (B) and the transplanted kidney (K). The renal pelvis (P) is ovoid, indicating mild hydronephrosis. Drainage of the lymphocele resulted in prompt return of satisfactory renal function.

42

BLADDER The most widespread use of ultrasound in relation to the bladder is in the determination of bladder residue. Because of the difficulty in quantitative noninvasive estimation of residual urine in the bladder, numerous investigators have studied the value of ultrasound in this particular area. Although urethral catheterization is relatively simple, there always is the risk of introducing infection. Catheterization may also produce urethral edema with secondary outlet obstruction. The simplest ultrasound technique for evaluation of the bladder volume is measuring the distance between the anterior and posterior walls of the bladder as measured with A-mode. This one-dimensional analysis, unfortunately, shows a poor correlation to the true bladder volume. Therefore, numerous techniques have been devised using the two-dimensional B-scan pictures of the bladder. Doust et al. 13 described a technique using sagittal and parasagittal B-mode scans of the bladder. Sagittal and parasagittal scans are performed at 1-cm intervals near the midline and u intervals at the periphery of the bladder. The angulation of the scan arm remains constant so that all of the scans are parallel. Bladder volume then can be calculated by measuring the area of each B-scan with a compensating polar planimeter and applying a correction factor dependent on the length of the planimeter and the scale factor of the ultrasonic images. Each cross-sectional area then is multiplied by the distance between adjacent scans, and the total of these figures gives an estimate of bladder volume. This resulted in a high linear correlation between the calculated bladder volume and the voided volume in a series of normals. Excluding pregnant females, the true volume was found to equal the planimeter volume plus 25 milliliters. This resulted in an accuracy of plus or minus 20% in more than 90% of the cases in which the bladder volume ranged between 40 and 800 ml in volume. When this technique was used by Pedersen e t a ! . , 34 they found a poor correlation in abnormal bladders. They recorded (1) the largest sagittal diameter of the bladder obtainable with the transducer in the midline 1 cm above the symphysis, (2) a sagittal scan in the midline, (3) a transverse scan 1 cm above the pubis and (4) serial sagittal scans spaced at 1.5- or 1-cm intervals across the width of the bladder. The true bladder volume was found to correlate best with the product of the depth (D), width (W) and height (H) (Fig. 40). The linear regression equation is: volume equals depth • • • 1.39 + 40 _+ 117 milliliters. This produces a 95% confidence interval and a correlation coefficient of 0.90 and a p < 0.001. Of all of the techniques used, ultrasound is poorest in quantitating small bladder volumes. It is, however, capable of qualita43

Fig 4 0 . - A , a transverse supine scan 1 cm above the symphysis pubis shows the normal bladder to be a quadrilateral fluid-filled structure. The width (w) and depth (d) are measured on the transverse scan. B, a saggital supine scan in the midline is used to calculate the height (H) of the bladder. (P = pubis.)

tively estimating whether any significant residue is present. Since the major concern of the physician is primarily qualitative, and since the ultrasound technique is noninvasive and simple, it is a valuable technique. Interest in ultrasonic investigation of bladder tumors has been limited by the frequency of small papillomatous lesions whose size is less than the resolution of the standard equipment. In addition, the high degree of accuracy of cystoscopy and the ability to biopsy suspicious lesions noted at cystoscopy have served to limit interest in bladder echography. Barnett and Morley3 have shown that tumors of the bladder can be identified with ultrasound B-scanning. Transverse and longitudinal scans are performed in the supine position with the bladder maximally distended. On transverse scans, the normal bladder tends to have a symmetric quadrilateral shape. Tumors 44

are seen as solid masses projecting into the lumen of the bladder and their size and shape can be evaluated. The differential diagnosis includes a blood clot, bladder calculus or enlarged prostate. Figure 41 demonstrates a 2-cm solid mass (T) arising from the left posterior wall of the bladder (B) and protruding into the bladder lumen. At surgery, this was found to be a noninvasive bladder carcinoma. Kyle et al. 26 believed that echography was highly accurate in the assessment of infiltration of the wall of the bladder. They found that the normal quadrilateral shape of the bladder became distorted as the tumor penetrated into the bladder muscle and that the degree of distortion of the bladder as seen on transverse scans correlated with the degree of muscle invasion. Spread of the tumor beyond the bladder wall produced irregular echofree areas in the paravesical tissue. Most echographers agree that nonpapillomatous bladder tumors are identifiable with echography, and that extension outside the bladder into the pelvis can be diagnosed reliably. However, there is much disagreement as to the accuracy of echography in assessing bladder wall infiltration. Winterberger and Murphy 48 could distinguish between tumors that had infiltrated the submucosa only (Stage A) and those that had infiltrated the musculature (Stage B) in only 25% of their cases. However, they were unable to distinguish between lesions limited to the new musculature (Stage B) and those extending into the perivesical fat (Stage C). Gray scale echography has produced renewed interest in the echographic investigation of bladder tumors and their degree of infiltration. However, significant experience has not yet been accrued with gray scale echography for any definite conclusion to be made. Fig 41.-See text.

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PROSTATE Echography of the prostate with standard equipment has been limited to the evaluation of the volume of the prostate. Whittingham and Bishop 4~have shown that the volume of the prostate can be calculated to within 20% or 30% using ultrasonic measurements. Although this is not a high degree of accuracy, it was shown in their experience to be more reliable than rectal examination, cystoscopy, bimanual examination and contrast radiography. Supine longitudinal and transverse scans are performed with the bladder maximally distended. A 3 5 - 40 ~ caudad angulation is used for the transverse scans. The benign prostate appears as a smooth acoustically homogeneous solid mass approximating a sphere in outline. The volume of the prostate is calculated from the transverse scan showing the largest area of the prostate gland. Very large prostates appear as a bilobed structure (Fig. 42), and the volume of each lobe is separately calculated using the formula for a sphere, which is V = 6 d3Y Occasionally, the shape of the prostate m a y simulate a hemisphere, hemi-ellipsoid or cone, and the appropriate geometric formula then is used to calculate the volume. Highly nodular and irregular prostates produce the least reliable results. The echographic volume measurements of the prostate are sufficient to categorize the prostate as small, medium or large. Such categorization is valuable in determining whether removal Fig 4 2 . - A supine transverse scan just above the symphysis pubis with 35 ~ caudad angulation shows the distended bladder (B). An enlarged prostate (P) is seen as a bilobed solid mass posterior to the bladder.

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of the prostate would be best performed by open surgery or transurethral resection. Special endoscopic transducers have been developed for the transrectal examination of the prostate. When the transducer is inserted 6 - 8 cm within the rectum, the prostate can be well delineated. The normal prostate appears as a triangle-shaped mass. The hypertrophied prostate produces an enlarged, well-enclosed echo pattern. Carcinoma can be distinguished from hypertrophy with approximately an 80% accuracy. Deformity of the prostatic contour is an early sign of prostatic cancer. Most neoplastic nodules have an acoustic pattern different from the adjacent normal tissue and can be identified as a discrete mass within the prostate. Advanced carcinoma is readily diagnosed by destruction of the prostatic capsule and infiltration of the surrounding tissues, such as the bladder or seminal vesicles. 4~ If the accuracy of diagnosis with endoscopic equipment improves with advances in equipment, it undoubtedly will become used more widely.

PEDIATRIC ULTRASOUND Pediatric renal ultrasound merits special attention by virtue of the difference in patient size, cooperation and disease spectrum. It is, however, basically similar to adult echography in that the major concerns are the identification of the kidneys, masses within or adjacent to the kidneys and determination of the cystic or solid nature of these masses. Since the sound waves must traverse less tissue in children than in adults, higher-frequency transducers may be used. Thus, 3.5-MHz and 5.0-MHz transducers frequently are substituted for the standard 2.25-MHz transducer used in routine adult abdominal echography. These higher-frequency transducers result in better resolution, which is desirable, especially in view of the small size of the organs of small children. A small percentage of children will be unable to lie in a relatively still state for t h e entire ultrasonic examination; therefore, mild sedation is necessary to obtain a satisfactory examination in these children. Intravenous pyelography is routine in neonates with palpable masses because of the high likelihood that the mass will be renal in origin. Ultrasound should also be routine because it will readily determine if the mass is renal or nonrenal in origin and whether it is cystic or solid. When the intravenous pyelogram and echogram are used in conjunction, a specific diagnosis frequently can be obtained whereas each individual examination might result in only a nonspecific diagnosis. 43 When the echogram demonstrates that the palpable mass represents unilateral renal enlargement, the mass is classified as cystic or solid. In the newborn, the differential diagnosis of a cystic-appearing kidney is between a hydronephrotic or multicystic 47

kidney. Hydronephrosis in the newborn usually is a result ofureteropelvic junction obstruction and produces a characteristic echo pattern. A greater distention occurs within the extrarenal pelvis than the intrarenal collecting system. The dilated renal pelvis is seen as a large, oblong, echo-free sac that tapers inferomedially. 2~ In multicystic disease of the kidney, the involved kidney is noted to be enlarged and cystic. The normal central clumped echoes of the pelvicaliceal system are absent. Multiple lobular cystic masses are noted, with thin linear echoes between the cysts. These linear echoes represent septa between the individual cysts. Occasionally, the kidney appears as a single large cystic structure with no suggestion of internal septa. However, the dilated renal pelvis with its typical medial tapering is not demonstrated, and thus this can be distinguished from ureteropelvic junction obstruction ~ (Fig. 43). Nonvisualization of a kidney on intravenous pyelography m a y be a result of renal vein thrombosis, Wilms' tumor, renal agenesis or either of the entities discussed above. A solid echo pattern is produced when the kidney is involved with either Wilms' tumor or renal vein thrombosis. Wilms' tumor demonstrates the typical features of a solid intrarenal mass. 23 The normal calices are seen to be displaced or completely obscured by the echoes within the mass (Fig. 44). The three-dimensional measurements produced by the echogram may be used for preoperative radiation therapy planning so that optimal tumor irradiation m a y be provided at the same time as maximal protection of the normal healthy tissue is obtained. Renal vein thrombosis demonstrates the two kidneys to have a normal or slightly prominent caliceal echo pattern. The kidneys usually are slightly enlarged. There is, however, no evidence of a discrete mass or hydronephrosis. In renal agenesis, the transverse scan will demonstrate only one kidney in the normal retroperitoneal position. This kidney is larger than normal. Longitudinal scans of the pelvis in the supine position then must be performed to exclude an ectopic pelvic kidney that was not seen on the intravenous pyelogram because of its position overlying the sacrum. The echographic pattern of polycystic disease of the kidney already has been discussed. Ultrasound is as accurate as intravenous pyelography in the diagnosis of this disease, but it is a more acceptable screening test in children because of the fact that it does not require exposure of the patient to irradiation nor does it require the injection of contrast medium with its possible complications. The echographic appearance of hydronephrosis in children is the same as that in adults. Since the echographic appearance correlates with the severity of hydronephrosis, serial studies can be performed to evaluate any change of degree of obstruction. In 48

Fig 4 3 . - A , a longitudinal prone scan through a palpable left flank mass (C) in a newborn shows the mass to be cystic in nature. A normal left kidney is not seen, indicating that this cystic structure represents the left kidney. In addition, a dilated extrarenal pelvis is not seen, and, therefore, this represents multicystic disease of the left kidney. B, a longitudinal prone scan through the normal right kidney (K). (Compliments of Dr. George Leopold, University Hospital, San Diego, California.)

that there is no radiation exposure or contrast medium injected, ultrasound again has a distinct advantage over serial pyelograms. Suprapubic urinary bladder aspiration has been advocated as a means of distinguishing bacteriuria from contamination of urine obtained either by urethral catheterization or voiding. Successful bladder aspiration requires a full urinary bladder. In children too young to cooperate, this usually is evaluated by checking the diapers or by suprapubic palpation. Palpation may be difficult, and a dry diaper does not ensure a full bladder, as renal output may be diminished. A simple A-mode transducer placed on the anterior abdominal wall in the midline just above the pubis will demonstrate an echo-free zone if the bladder is filled with urine. If the echo demonstrates distention of the bladder, the distance from the skin edge to the middle of the bladder can be measured. 49

Fig 4 4 . - A , a supine transverse scan of a 2-year-old male with a mass in the right kidney on intravenous pyelogram shows the mass (T) to be highly echogenic and, therefore, a solid mass. B, a supine longitudinal scan 2 cm to the right of midline shows the solid mass (T) to be separate from the liver (L) and to compress the inferior vena cava (IVC). The normal calices are obscured by this mass, which represented a large Wilms' tumor of the right kidney. (Compliments of Dr. George Leopold, Universi{y Hospital, San Diego, California.)

Suprapubic aspiration then is performed, preferably through a sterilized aspiration transducer. If no echo-free zone is seen, the bladder is assumed to be empty, and a repeat study is performed in 1 hour. TM The determination of bladder distention can also be determined with B-mode scans of the pelvis. The A-mode technique, however, has the advantage that it can be done at the bedside. Percutaneous renal biopsy in children often is more difficult than in adults because of the small size of the kidneys. The technique of ultrasound localization as previously described in adults is highly useful in children old enough to cooperate during the closed renal biopsy procedure. 50

ACKNOWLEDGMENT I wish to thank Ms. Margo Wyner, Ms. Marcia Lavery and Ms. Debbie Glaiel for their help in the preparation of this manuscript. REFERENCES i. Asher, W. M., and Leopold, G. R.: A streamlined diagnostic approach to renal mass lesions with renal echogram, J. Urol. 108:205, 1972. 2. Baker, D. W.: Ultrasonic instruments, Semin. Roentgenol. 10:265, 1975. 3. Barnett, E., and Morley, P.: Ultrasound in the investigation of space occupying lesions of the urinary tract, Br. J. Radiol. 44:733, 1971. 4. Bartrum, R. J., Jr., Smith, E. H., D'Orsi, C. J., and Dantono, J.: Ultrasonic determination of renal transplant volume, J. Clin. Ultrasound 2:281, 1974. 5. Bearman, S. B., Hine, P. L., and Sanders, R. C.: Multicystic kidney: A sonographic pattern, Radiology 118:685, 1976. 6. Becker, J. A., Schneider, M., Staiano, S., and Cromb, E. P.: Renal pelvic lipomatosis: A sonographic evaluation, J. Clin. Ultrasound 2:299, 1974. 7. Birnholz, J. C.: Sonic differentiation of cysts and homogeneous solid masses, Radiology 108:699, 1973. 8. Birnholz, J. C.: Ultrasound imaging of adrenal mass lesions, Radiology 109: 163, 1973. 9. Bosniak, M. A.: Nephrotomography: A relatively unappreciated but extremely valuable diagnostic tool, Radiology 113:313, 1974. 10. Bree, R. L., Green, B., Keiller, D. L., and Genet, E. F.: Medial deviation of the ureters secondary to psoas muscle hypertrophy, Radiology 118:691, 1976. 11. Carlsen, E. N.: Ultrasound physics for the physician-a brief review, J. Clin. Ultrasound 3:69, 1975. 12. Cohen, W. N., and Hass, A. C.: The application of B-scan ultrasound in the planning of radiation therapy treatment ports, Am. J. Roentgenol. 111:184, 1971. 13. Doust, B. D., Baum, J. K., Maklad, N. F., and Baum, R. F.: Determination of organ volume by means of ultrasonic B-mode scanning, J. Clin. Ultrasound 2: 127, 1974. 14. Doust, V. L., Doust, B. D., and Redman, H.: Evaluation of ultrasonic B-mode scanning in the diagnosis of renal masses, Am. J. Roentgenol. 117:112, 1973. 15. Fletcher, E. W. L., and Lecky, J. W.: The radiological size of renal transp l a n t s - a retrospective study, Br. J. Radiol. 42:892, 1969. 16. Goldberg, B. B., and Meyer, H.: Ultrasonically guided suprapubic urinary bladder aspiration, Pediatrics 51:70, 1973. 17. Goldberg, B. B., Ostrum, B. J., and Isard, H. J.: Nephrosonography: Ultrasound differentiationof renal masses, Radiology 90:1113, 1968. 18. Goldberg, B. B., and Pollack, H. M.: Ultrasonic aspiration transducer, Radiology 102:187,1972. 19. Goldberg, B. B., Pollack, H. M., and Kellerman, E.: Ultrasonic localization for renal biopsy, Radiology 115:167, 1975. 20. Greene, D., and Steinbach, H. L.: Ultrasonic diagnosis of hypernephroma extending into the inferior vena cava, Radiology 115:679, 1975. 21. Hasch, E.: Ultrasound in the investigation of disease of the kidney and urinary tract in children, Acta Paediatr. Scand. 63:42, 1974. 22. Holm, H. H., Kristensen, J. K., Rasmussen, S. N., and Pedersen, J. F.: Ultrasonic diagnosis ofjuxtarenal masses, Scand. J. Urol. Nephrol. 6:83, 1974. 23. Hiinig, R., and Kisner, J.: Ultrasonic diagnosis of Wilms' tumors, Am. J. Roentgenol. 117:119, 1973. 24. Iversen, P.: Aspiration biopsy of the kidney, Am. J. Med. 11:324, 1951. 25. Kremkau, F. W.: Physical principles of-ultrasound, Semin. Reentgenol. 10: 259, 1975. 26. Kyle, K. F., Deane, R. F., Morley, P., and Barnett, E.: Ultrasonography of the urinary tract, Br. J. Radiol. 43:709, 1971. 51

27. Lang, E. K.: Co-existence of cyst and tumor in the same kidney, Radiology 101:7, 1971. 28. Lang, E. K.: Roentgenographic assessment of asymptomatic renal lesions, Radiology 109:257, 1973. 29. Leopold, G. R.: Renal transplant size measured by reflected ultrasound, Radiology 95:687, 1970. 30. Leopold, G. R., Talner, L. B., Asher, W. M., Gosink, B. B., and Gittes, R. F.: Renal ultrasonography: An updated approach to the diagnosis of renal cyst, Radiology 109:671, 1973. 31. Maxwell, D. R., and Asher, W. M.: Ultrasound localization of the kidneys for closed renal biopsy, J. Clin. Ultrasound 2:279, 1974. 32. McDonald, D. G., and Libertino, J. A.: Ultrasound in diagnosis and evaluation oflymphoceles aRer renal transplantation, Urology 7:216, 1976. 33. Miller, S. S., Garvie~ H. H., and Christie, A. D.: The evaluation of prostate size by ultrasound scanning: A preliminary report, Br. J. Urol. 45:187, 1973. 34. Pedersen, J. F., Bartrum, R. J., Jr., and Grytter, C.: Residual urine determination by ultrasonic scanning, Am. J. Roentgenol, 125:474, 1975. 35. Pedersen, J. F., Hancke, S., and Kristensen, J. K.: Renal carbuncle: Antibiotic therapy governed by ultrasonically guided aspiration, J. Urel. 109:777, 1973. 36. Pollack, H. M., Edell, S., and Morales, J. O.: Radionuclide imaging in renal pseudotumors, Radiology 111:639, 1974. 37. Pollack, H. M., Goldberg, B. B., Morales, J. O., and Bogash, M.: A systematized approach to the differential diagnosis of renal masses, Radiology 113: 653, 1974. 38. Raskin, M. M., and Roen, S. A.: Determination of renal cyst volume, Radiology 107:704, 1973. 39. Sampson, D., Winterberger, A. R., and Murphy, G. P.: The use of diagnostic ultrasound in renal transplantation, Rev. Surg. 29:77, 1972. 40. Sanders, R. C., and Bearman, S.: B-scan ultrasound in the diagnosis of hydronephresis, Radiology 108:375, 1973. 41. Stables, D. P., Holt, S. A., Sheridan, H. M., and Donohue, R. E.: Permanent nephrostomy via percutaneous puncture, J. Urol. 114:684, 1975. 42. Taylor, K. J. W., Carpenter, D. A., and McCready, V. R.: Gray scale echography in the diagnosis ofintrahepatic disease, J. Clin. Ultrasound 1:284, 1973. 43. von Micsky, L., Radkowski, M. A., Hecker, J., and Finby, N.: Optimal diagnosis of renal masses in children by combining and correlating diagnostic features of sonography and radiography, Am. J. Roentgenol. 120:438, 1974. 44. yon Schreeb, T., Arner, O., Skovsted, G., and Wikstad, N.: Renal adenocarcinoma, Scand. J. Urol. Nephrol. 1:270, 1967. 45. Watanabe, H., Kaiho, H., Tanaka, M., and Terasawa, Y.: Diagnostic application of ultrasonotomography to the prostate. Invest. Urol. 8:548, 1971. 46. Weitzel, D., Bahlmann, J., and Otto, P.: The diagnostic value of ultrasound echography in polycystic disease of the kidneys, Dtsch. Med. Wochenschr. 99: 1587, 1974. 47. Whittingham, T. A., and Bishop, R.: Ultrasonic estimation of the volume of the enlarged prostate, Br. J. Radiol. 46:68, 1973. 48. Winterberger, A. R., and Murphy, G. P.: Correlation of B-scan ultrasonic laminography with bilateral selective hypogastric arteriography and lymphography in bladder tumors, Vasc. Surg. 8:169, 1974. 49. Winterberger, A. R., Palma, L. D., and Murphy, G. P.: Ultrasound testing in human renal allografts, JAMA 219:475, 1972.

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