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AJR:159,

November

1992

CT OF EXTRAPERITONEAL

compartment a hemorrhage is in from the clinical history; conversely, anatomic localization by CT, along with assessment of other pertinent features, often allows accurate prediction of the clinical history. Urinomas are most frequently localized to the penirenal space. Abscess or infected fluid can be found in any of the compartments. Extrapancreatic fluid collections associated with pancreatitis, including well-circumscnibed pseudocysts, are most common in the anterior pararenal space, but are notorious for crossing fascial boundaries and can be found in all retroperitoneal compartments. Except for high-attenuation collections indicating an acute or subacute hematoma, some retroperitoneal fluid collections will require percutaneous aspiration for definitive diagnosis. Perirenal

Space

The perirenal space is the largest of the three retroperitoneal compartments, and on CT scans it is easily identified as a distinct space in almost all patients. Although the fat within the penirenal space is often depicted as a featureless cornponent, some anatomic textbooks mention weak trabeculae that connect the renal capsule to the renal fascia, and on CT scans Feldberg [1 4] noted linear structures within the normal penirenal fat. Kunin [1 5], however, first systematically descnibed multiple fibrous Iamellae or septa that divide the region into different compartments. Although these bridging septa are occasionally visible on CT scans of normal penirenal fat, they are more easily visualized when they become thickened by fluid or by other abnormalities. Some of these septa connect the anterior to the posterior leaves of the renal fascia, others arise from the renal capsule and extend to the fascia, and still others arise from the capsule and are arranged more or less parallel to the renal surface. Among the last group is the so-called posterior renorenal septum, a structure running from the anterolateral to the posteromedial aspect of the renal capsule (Fig. 5). With careful scrutiny, the renorenal septum can probably be detected in about 10% of abdominal CT examinations. Before the posterior renorenal septum was recognized, it was thought that subcapsular and extracapsulan hematoma would be easily distinguished on CT scans. A subcapsular hematoma was immediately contiguous to the renal panenchyma, usually flattening its normal convex border, and typically preserving a layer of perirenal fat between its peripheral edge and the nearby renal fascia. An extracapsular penirenal hematoma, on the other hand, typically preserved a layer of fat between its inner border and the edge of the renal panenchyma and was usually contiguous with the renalfascia. Kunin [1 5], however, showed that the posterior renorenal septum can confine an extracapsular hematoma and deform the renal parenchyma in a manner that can easily mimic the appearance of a subcapsular collection. Distinction of a subcapsular hematoma from an extracapsular hematoma confined by the posterior renorenal septum is usually difficult. The subcapsular location of a hematoma can be predicted with confidence only if the posterior renorenal septum is identified as a distinct structure, separated by a layer of fat from the outer border of the hematoma [16] (Fig. 6). When confined primarily to the penirenal space, acute hemorrhage is often due to blunt abdominal trauma or to a

SPACE

937

ruptured abdominal aortic aneurysm. In the pnesence of an abdominal aortic aneurysm, identification of acute hemorrhage in the penirenal space is diagnostic of aneurysmal rupture [1 1 1. Interruption of the distinct calcified on noncalcifled wall of the aneurysm is often identifiable and usually indicates the site of rupture [1 7]. Blunt abdominal trauma is another common cause of acute penirenal hemorrhage, often associated with renal contusion, laceration, on infarction. A combination of history, physical findings, and CT features often easily leads to a correct diagnosis in these two common disorders. CT features include high-attenuation material interspersed with fat in the perirenal space. With the patient supine, the blood typically assumes a dependent crescentshaped configuration within the posterior portion of this cornpartment. Like most penirenal fluid collections, the blood is usually marginated posterolaterally by the posterior renal fascia and posteromedially by the psoas muscle. The perinenal fat often has a spiculated or feathery appearance as the fluid spreads along the underlying network of septa. Spontaneous subcapsular and penirenal hematomas are uncommon but clinically important, because they often mdicate an underlying renal neoplasm. Renal cell carcinoma (Fig. 7) and renal angiomyolipoma are each the cause in about 30% of cases; the remaining cases are caused by a variety of vascular, inflammatory, cystic, and hematologic disorders [1 8]. Belville et al. [1 9] recently reported a large series of cases evaluated with CT. Initial CT examinations showed a distinct mass in 12 (67%) of the 18 cases, with CT characteristics that suggested the correct diagnosis in 1 1 cases. In the other six patients (33%), a discrete mass was not seen, and the cause of hemorrhage was not clear in five of the six. Two of the five underwent follow-up CT, which showed renal cell carcinoma in both. In the remaining three patients who had no CT follow-up, exploratory surgery showed a 1 .5-cm renal cell carcinoma in one, a 5-cm angiomyolipoma in the second, and no abnormality in the third. For patients with a spontaneous penirenal hematoma in whom a mass is not detected on initial CT, serial renal CT examinations are an alternative to exploratory surgery in order to avoid unnecessary nephrectomy in patients with benign disease or no renal disease. Such an approach, of course, necessitates follow-up studies until the hematoma is cornpletely resorbed or until a specific cause is detected and characterized. As Bosniak [1 8] has emphasized, meticulous attention to optimal CT technique is mandatory, because small renal cell carcinomas can otherwise escape detection. CT must be selectively performed using thin (5 mm or less) sections, both before and after IV injection of a bolus of contrast material. When urine continues to leak into the retropenitoneal space, an encapsulated collection of large proportion can develop. This collection is commonly termed a urinoma [20], but many other names have been used, including uniniferous penirenal pseudocyst [21 ]. Obstructive unopathy is the most common cause, but both abdominal trauma and surgical or diagnostic instrumentation also can lead to urinary extravasation. Prior reports have emphasized the frequent temporal remoteness of the cause of uninoma from its detection [20]. As ureteral obstruction is often decompressed by fomiceal rupture and pyelosinus backflow [22], it is not surprising that a uninoma

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938

KOROBKIN

ET AL.

AJR:159,

November

1992

oTir

Fig.

6.-Subcapsular

renal

hematoma.

CT

Fig. 7.-CT scan of perirenal or subcapsular renal hematoma due to a ruptured renal cell carcinoma. Rounded carcinoma (T) is similar in ap-

scan

shows that posterior renorenal septum (white arrow) is separated by a thin layer of fat from hematoma (H) and thickened renal capsule (black

pearance to adjacent hematoma

(H).

arrow).

is typically

located

in the

peninenal

space.

The

wall

of a

uninoma, formed by the surrounding renal fascia, is visibly thickened on CT, reflecting the fibrotic inflammatory process induced by a chronic urine collection [21]. A dilated renal collecting

in which

the

uninoma is confined to the penirenal space. Unenhanced will usually show a fluid collection of water attenuation,

system

is seen

in virtually

all cases

CT but

the uninoma [21 ] (Fig. 8). In these cases the contrast medium may layer within the dependent portion of the urinoma. Al-

collections. outside ruption

Infrequently,

varies, of the

urinomas

the penirenal space, caused by surgery,

they are sometimes largest perirenal fluid

accumulate

usually because instrumentation,

injuries inferior or distal to the confines

space is usually easy to detect.

all or most

efface

of the anterior

in locations

the posteromedial

of the renal fascia.

aspect

easy to identify without not

always

situated denum.

It often silhouettes

on CT and will usually

of the descending

colon.

fluid, and when present

distribute

itself

to the anterior

along

the fascia.

pararenal

space

the fluid does Fluid

is often

simply

by being

between the liver, gallbladder, kidney, The presence of gas within the night anterior

and duopanarenal

space after trauma or sphincterotomy is virtually diagnostic of a duodenal perforation (Fig. 9). We are uncertain if the presence of fluid alone, without associated gas bubbles, can result

of ureteral disor penetrating

renal fascia

Detection of fluid in the night anterior pananenal space is more subtle and difficult to identify: the anterior renal fascia is not

localized

after IV injection of contrast material, attenuation can increase progressively as urine opacified with contrast medium enters

though the size of uninomas massive, representing some

pararenal

Fig. 8.-Perirenal urinoma. Delayed CT scan 15 mm after iv injection of contrast material shows loculations of extravasated contrast material (arrowheads) adjacent to dilated right ureter (u) and in periphery of right perirenal space.

from

duodenal

injury

without

perforation,

thus

allowing

conservative management rather than surgical intervention. Because the anterior and posterior pararenal spaces converge

within

the pelvis below the cone of renal fascia, it has that pancreatitis fluid migrated infeniorly in the anterior pararenal space and then superiorly in the posterior pararenal space; this would explain the fluid commonly seen

been thought Anterior

Pararenal

Space

Unlike the peninenal and posterior anterior

pararenal

space

to identify as a distinct sites where it contains

contains

pararenal

spaces,

the

the

so little fat that it is difficult

compartment on CT except at the the alimentary tract structures or

unless it is distended by fluid. The very existence of a distinct anterior pararenal space compartment within the retropenitoneum has been challenged, largely on developmental grounds, by Dodds et al. [23], who emphasized its embryo-

collections

in the anterior

pararenal

space

are more

common on the left side, where they are almost always associated with inflammatory disease of the pancreatic tail. When

usually duodenal

found

in the

due to either injury

right

anterior

pancreatic

on perforation.

pararenal

inflammatory Duodenal

caused by peptic disease, trauma, cially endoscopic sphmnctenotomy).

space,

disease

perforation

fluid

latenoconal

disrupted resulting between

to the

by proteolytic

is

or to can be

or instrumentation (espeFluid in the left anterior

antenior

renal

enzymes

in retrorenal extension the two major layers

This produces

logic origin as an intrapenitoneal compartment. Most authonities, however, have not supported Dodds’ hypothesis [24]. Fluid

posterior to the left kidney. Raptopoulos et al. [9], however, have argued convincingly that small septal fibers, connecting fascia,

ane probably

in severe acute pancreatitis, of fluid into the potential cleft of the posterior renal fascia.

the characteristic

wedge-shaped

appearance

of the retrorenal fluid, with compression but preservation of the fat within the posterior pararenal space (Fig. 10). Thus, although it simulates fluid in the posterior paranenal space, the pancreatitis fluid posterior to the kidney actually remains

in the anterior

panarenal

space.

This

has obvious

clinical

implications if percutaneous fluid drainage is considered. Fluid within the posterior pararenal space itself, although unusual in acute pancreatitis, may occur via communication between

the anterior

and posterior

of renal fascia

tion of the extension.

pararenal

(as described

lateroconal

spaces below the cone on via enzymatic disrupallowing direct contiguous

earlier)

fascia,

AJR:159,

November

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Posterior

CT OF EXTRAPERITONEAL

1992

Pararenal

ies, and urinary bladder [5]. In a manner analogous to the renal fascia, the umbilicovesical fascia divides the anterior extraperitoneal fat into a perivesical space and a prevesical space. The penivesical space, containing the bladder, umbilical arteries, and urachus, is analogous to the perirenal space. The prevesical space, located anterior and lateral to the umbilicovesical fascia, is analogous to the anterior panarenal space. This huge potential compartment extends superiorly up to the umbilicus; posterior to the pubis it is known as the space of Retzius. At the level of the bladder dome, the umbilicovesical fascia is frequently seen on axial CT scans as it indents the contiguous anterior panietal penitoneum as part of the medial umbilical folds [5]. Auh et al. [5] have characterized extraperitoneal pelvic fluid collections as assuming a “molar-tooth” configuration (Fig. 1 1A). The “crown” portion of the molar tooth lies antenion to the urinary bladder, between the umbilicovesical fascia and transversalis fascia of the anterior abdominal wall, and displaces the bladder posteriorly. The “root” portion of the molar tooth extends posteriorly, between the fascia and either the penitoneum superiorly or the panietal pelvic fascia infeniorly. As the “roots” are frequently asymmetric, the bladder is often displaced away from the midline by large extrapenitoneal pelvic fluid collections (Fig. 11 B). The prevesical extraperitoneal compartment is directly continuous with the infrarenal retropenitoneal compartment below the cone of renal fascia. Fluid collections in this infrarenal space frequently extend into the ipsilateral aspect of the prevesical space: in this location it can be misinterpreted as being within the penitoneal portion of the pelvis [5]. Additionally, extrapentoneal fluid collections arising in the pelvis can extend, via the prevesical space, superiorly into the retropenitoneal compartments of the abdomen (Fig. 12). The prevesical space is also continuous with the rectus sheath, the presacral space, and the femoral sheath. Retropenitoneal hematoma is a significant complication of

Space

The postenion panarenal space is rarely the site of an isolated fluid collection because it contains only fat. As described earlier, it is uncommonly involved in cases of severe acute pancreatitis. It is occasionally the site of spontaneous hemorrhage in patients on anticoagulation therapy or with a bleeding diathesis, often in association with blood in other extnapenitoneal compartments. The posterior pararenal space can also be involved by extraperitoneal hemorrhage that occurs after percutaneous catheterization procedures via the femoral vessels, most commonly cardiac catheterization [8]. Blood is thought to extend superiorly from the penvasculan sheath via the prevesical extraperitoneal space to the infrarenal netnopenitoneum, and then into the posterior pararenal, anterior panarenal, or penirenal spaces. Similar extension of pus from an extrapenitoneal pelvic abscess can occur. Blood in the posterior pararenal space from a ruptured aortic aneurysm is usually overshadowed by the much larger amount in the penirenal space.

Pelvic

Extraperitoneal

Space

Assessment of fluid in the extrapenitoneal compartments of the pelvis and its differentiation from penitoneal collections is best accomplished by an understanding of the pertinent fascial planes. More complex and less well known than the more cephalic netropenitoneal counterparts, the pelvic fascia and associated compartments were comprehensively described by Auh et al. [5]. Their descriptions were based on a review of previous anatomic reports, a study of anatomic sections and cadavenic injections, and clinical observations with CT and sonography. Anterior to the penitoneum and posterior to the transversalis fascia, the umbilicovesical fascia spreads infeniorly from the umbilicus to surround the urachus, obliterated umbilical arter-

A Fig.

9.-Abscess

in anterior

pararenal

space.

CT scan shows fluid and gas bubbles (A) between duodenum, liver, and right kidney. Anterior renal fascia (arrows) forms posterior border of abscess. Intraperitoneal ascites surrounds liver.

939

SPACE

B

Fig. 10.-Retrorenal A, CT scan shows

a characteristic

extension of pancreatitis fluid. fluid (F) in left anterior pararenal space

wedge-shaped

B, Diagram shows pararenal space, C renal fascia.

=

extending

posterior

to kidney,

producing

appearance.

fluid (hatched descending

area) colon,

dissecting layers of posterior renal fascia. APS = anterior LCF = lateroconal fascia, PRF = two layers of posterior

KOROBKIN

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940

a variety offemoral vascular catheterization procedures. Trerotola et al. [8] recently described the CT findings and clinical data in 21 patients with significant hemorrhagic complications after catheterization. Hematoma was shown by CT in the following locations: retnopenitoneum (1 2/21), penitoneum (3/ 21), groin and thigh (8/21), and abdominal wall (5/21). The distribution of hematomas was explained by elaboration and extrapolation of the discussion by Auh et al. [5]. The femoral sheath, containing the femoral artery and vein, opens directly into the prevesical extrapenitoneal compartment. Blood in the prevesical space can spread superiorly and posteriorly, deep to the panietal penitoneum, into the infrarenal retroperitoneal space, and then further superiorly into the perirenal, anterior pararenal, posterior pararenal, or ileopsoas compartments. Alternatively, blood reaching the prevesical space via the femoral sheath can also ascend anteriorly just beneath the transversalis fascia to the anterior abdominal wall. The rectus abdominis and other abdominal wall muscles can be more directly involved owing to direct extension of the blood, either through the thin transvensalis fascia or along the epigastnic vessel sheaths penetrating the fascia. These speculations assume that the extraperitoneal hematomas in these patients are always due to femoral vascular injury, which then spreads to other regions via direct communication. As most of these patients are receiving anticoagulant or thrombolytic therapy, however, one could speculate that at least some of these hematomas are induced by the medications themselves and might not originate in the femoral sheath. Psoas

Muscle

The psoas muscle is a frequent site of netnopenitoneal abscesses and hematomas, and it is intimately associated with the renal fascia and the penirenal and pararenal spaces. Originating from the transverse processes of the 12th thoracic vertebra and all the lumbar vertebrae, the psoas muscle

A

ET AL.

AJR:159,

November

1992

extends infeniorly in a paraspinal location. Fusing with the iliacus muscle in the pelvis, it then passes as the ileopsoas muscle beneath the inguinal ligament to insert on the lessen trochanter of the femur [25]. Because its superior portion passes beneath the arcuate ligament of the diaphragm, the psoas muscle extends from the mediastinum to the thigh. A fascial membrane protects the psoas muscle from surrounding disease: thus the psoas muscle is sometimes referred to as a retrofascial structure. In the upper and middle portions of the abdomen, the psoas muscle marginates the medial aspect of the fat within the peninenal space. It is also contiguous, at some levels and to a lessen extent, with the posterior pararenal space. Although occasionally idiopathic, abscesses in the psoas muscle are frequently caused by direct spread of adjacent infection, usually from the spine on disk space or from the gastrointestinal tract in patients with diverticulitis, Cnohn’s disease, or complicated appendicitis [26]. Renal infections frequently extend directly into the adjacent peninenal space, and from there the infection can spread directly through the perirenal fat to involve the psoas muscle. The opposite pathway, spread of infection from a primary abscess in the psoas muscle to involve the penirenal on pananenal spaces, rarely occurs. Most infections of the psoas muscle are now caused by pyogenic organisms rather than by tuberculosis [25-27]. The psoas muscle is commonly the site of a significant retroperitoneal hematoma, especially in patients with a bleeding diathesis or who are receiving anticoagulant medications. Rarely, a ruptured abdominal aortic aneurysm can bleed directly into the psoas muscle rather than the peninenal space. Hemorrhage in the adjacent penirenal or panarenal compartments is sometimes associated with a hematoma in the psoas muscle. On CT scans, the presence of a hematoma on abscess in the psoas muscle is usually associated with diffuse enlargement of the muscle. An acute hematoma will typically have a

B

Fig. 11.-Fluid in prevesical space. A and B, Sagittal diagram (A) of lower

abdomen

and pelvis

shows

umbilicovesical

fascia,

prevesical

shows large fluid collection distending and enlarging prevesical space, producing a characteristic Auh et al. [5]. R = rectum, U = uterus, B = bladder, C, CT scan shows fluid (F) in prevesical space, margins of these collections.

C = cecum, S = sigmoid, dotted line anterior and lateral to gas-containing

=

space,

and perivesical

molar-tooth configuration.

peritoneum. bladder (B). Umbilicovesical

fascia

space.

Axial

diagram

(B)

Both diagrams modified from forms

posterior

and medial

AJR:159,

November

1992

CT OF EXTRAPERITONEAL

SPACE

941

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Fig. 12.-Extraperitoneal hematoma associated with femoral vascular catheterization and anticoagulatlon. A, CT scan shows hematoma (H) in left side of prevesical space abutting and obscuring left femoral vessels (v). Fluid (F) Is present In retrorectal presacral extension of prevesical space also. B, CT scan shows that hematoma (H) also involves left posterior pararenal space.

focal region of high attenuation to indicate the presence of fresh blood, whereas an abscess will usually show a central low-density area, especially on contrast-enhanced scans. Although uncommonly seen, gas bubbles in a psoas fluid collection are virtually pathognomonic of abscess. When an abscess in the psoas muscle is caused by direct extension of a renal abscess, the CTfindings typical of a renal and perirenal inflammatory lesion should be visible. Any neoplasm that originates in or metastasizes to the netroperitoneum can involve the psoas muscle either by blood-borne metastasis or by extension from adjacent malignant lymph nodes, and occasionally such a malignant lesion, especially if necrotic, can be indistinguishable on CT scans from an abscess or a hematoma in the psoas muscle.

10. 11. 12. 1 3. 1 4.

1 5. 16. 17.

REFERENCES 1 . Meyers MA, Whalen JP, Peelle K, Berne AS. Radiologic features of extraperitoneal effusions. Radiology 1972;104:249-257 2. Meyers MA. Dynamic radiology of the abdomen: normal and pathologic anatomy, 3rd ed. New York: Springer-verlag, 1988 3. Love L, Meyers MA, Churchill RJ, Reynes CJ, Moncada A, Gibson D.

4. 5.

6. 7.

8. 9.

Computed tomography of extraperitoneal spaces. AJR 1981;136: 781 -789 Kneeland JB, Auh YH, Rubenstein WA, et al. Perirenalspaces: CT evidence for communication across the midline. Radiology 1987;164:657-664 Auh YH, Rubenstein WA, Schneider M, ReCkler JM, Whalen JP, Kazam E. Extrapentoneal paravesical spaces: CT delineation with US correlation. Radiology 1986;159:319-328 Chesbrough RM, Burkhard TK, Martinez AJ, Burks DD. Gerota versus Zuckerkandl: the renal fascia revisited.Radiology 1989:173:845-846 Parienty RA, Pradel J, Picard JD, Ducellier R, Lubrano J, Smolarski N. visibility and thickening of the renal fascia on computed tomograms. Radiology 1981;139:119-124 Trerotola SO, Kuhlman JE, Fishman EK. Bleeding complications of femoral catheterization: CT evaluation. Radiology 1990174:37-40 Raptopoulos v, Kleinman PK, Marks 5, Snyder M, Silverman PM. Renal

18. 19.

20. 21

fascial pathway: posterior extension of pancreatic effusions within the anterior pararenal space. Radiology 1986:158:367-374 Feldberg MAM, Koehler PR, van Waes PFGM. Psoas compartment disease studied by computed tomography. Radiology 1983;148:505-512 Rosen A, Korobkin M, Silverman PM, Moore AV, Dunnick NR. CT diagnosis of ruptured abdominal aortic aneurysm. AJR 1984:143:265-268 Hopper KD, Sherman JL, Ghaed N. Aortic rupture into retroperitoneum (letter). AiR 1985:145:435-437 Vibhakar SD, Lee H, Petruschak M, Bellon EM. Aortic aneurysm presenting as psoas enlargement. J Comput Assist Tomogr 1981:5:925-928 Feldberg MAM. Computed tomography of the retroperitoneum: an anatomical and pathological atlas with emphasis on the fascial planes. Boston: Martinus Nhoff, 1983:55 Kunin M. Bridging septa of the perinephric space: anatomic, pathologic, and diagnostic considerations. Radiology 1986;158:361-365 McClennan BL, Lee JKT, Peterson RR. Anatomy of the penrenal area. Radiology 1986:158:555-557 Raptopoulos V, Cummings T, Smith EH. Computed tomography of lifethreatening complications of abdominal aortic aneurysm: the disrupted aortic wall. Invest Radiol 1987:22:372-376 Bosniak MA. Spontaneous subcapsular and perirenal hematomas (editorial). Radiology 1989:172:601-602 Belville JS, Morgentaler A, Loughlin KR, Tumeh 55. Spontaneous perinephric and subcapsular renal hemorrhage: evaluation with CT, US, and angiography. Radiology 1989:172:733-738 Healy ME, Tong 55. Moss AA. Uriniterous pseudocyst: computed tonicgraphic findings. Radiology 1984:153:757-762

Meyers MA. l.kiniferous perirenal pseudocyst: new observations. Radiology 1975:117:539-545 22. Fnedenberg RM, Moorehouse H, Gade M. Ifrmnomas secondary to pyelosinus backflow. Urol Radiol 1983;5:23-29 23. Dodds WJ, Darweesh AMA, Lawson TL, et al. The retroperitoneal spaces revisited. AiR 1986:147:1155-1161 24. Rubenstein WA, Whalen JP. Extraperitoneal spaces (commentary). AiR 1986;147:1 162-1164 25. Jeffrey RB, Callen PW, Federle MP. Computed tomography of psoas abscesses. J Comput Assist Tomogr 1990:4:639-641 26. Mendez G, Isikoff MB, Hill MC. Retroperitoneal processes involving the psoas demonstrated by computed tomography. J Comput Assist Tomogr 1980;4:78-82 27. Ralls PW, Boswell W, Henderson A, Rogers W, Boger D, Halls J. CT of inflammatory disease of the psoas muscle. AiR 1980;134:767-770 .

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942

Book

Basic Doppler 121 pp., 1991. book

This who

are

Physics. $39

is intended

familiar

By Hans-J#{248}rgen Smith

for residents,

with

B-mode

radiologists,

sonography

and but

and James

intervals.

sonographers

have

little

A. Zagzebski.

or

no

of Doppler physics, or physics in general. It is divided into

extract

two

sections:

sequential

major

basic

Doppler

Twelve of the 17 chapters the

chapters

is brief

progresses

chapter

cated tral

explanations analysis.

aliasing

and

deal

and

color

flow

imaging.

of and deals with a single basic concept. The book by chapter from first principles to more compli-

of Doppler

Numerous the

physics

with

physics,

diagrams

factors

basic

that

Doppler

signal

help

dictate

Each

processing,

clarify pulse

physics.

such

and

spec-

phenomena

repetition

frequency.

A

useful discussion of methods to prevent aliasing is included. Chapter 6 contains a brief but comprehensive discussion of Doppler signal processing. Chapters 9, 1 0, and 1 1 discuss Shannon’s sampling theory and

to

a time-domain

a time change pulses.

The

obtained

correlation

that time

Physics

from returning

method,

best matches change

Publishing,

which

echo

is correlated

pulses is is used

signatures with

the

to

from Doppler

pulse rate in order to obtain an estimation of blood-flow velocity. The potential advantages of time-domain velocity estimations include improved Other

as

WI: Medical

The pattern of reflectors

subjected

knowledge

Madison,

Review

color

potential

for

Although useful

text

Doppler

resolution

advantages

potential

real-time

volumetric

and

include flow

the design and content for

beginners,

the

entire

decreased lower

or absent

power

output

aliasing. and

the

estimations.

of this text make manuscript

is filled

it a potentially with

misspell-

tions are diagramed, and the basic working principles are explained. Scanning speed and frame rate limitations are described. The concept of dynamic focusing is presented with helpful diagrams. Color flow aliasing is presented in Chapter 16. All color flow images in this discussion were obtained by using a Doppler phantom. The final

ings, incorrect terminology, and incorrect statements. After I had read this manuscript with some concern and dismay over the apparent lack of proofreading that resulted in these incorrect and misleading statements, a two-page errata statement arrived from the publisher. The publisher has stated that it intends to append this errata sheet to the front of the text. I find this quite disturbing and think it is unfair to ask a reader to refer to an errata sheet more than 50 times during the reading of a text that is only 121 pages long. Furthermore, a beginning student of Doppler physics might not recognize an incorrect statement and therefore would not automatically know to refer to the errata sheets. Consequently, the potential reader would be forced to take the errata sheet and go through the book correcting mistakes. This is unacceptable. The authors and publisher should combine their efforts to correct all these obvious errors and come up with a second

chapter

edition.

how

it relates

to the

phenomenon

deals with the techniques blood-flow calculations. The second section, with

an introduction

time

imaging.

deals

with

which

to the

Different

of

Doppler

aliasing.

Chapter

12

and sources of error inherent in volumetric deals

transducer

the fairly

with

instrumentation

recent

and

concept

color

flow

imaging,

of B-mode signal-processing

of time-domain

begins

gray-scale

real-

configura-

correlation

as a method of estimating blood-flow velocity. This process, which is a variation of the techniques used in “color velocity imaging,” has recently been introduced in a commercially available unit. This technique

uses

an analysis

of multiple

echoes

transmitted

at very

short

Barbara Duke

A. Carroll University

Durham, NC 27710

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943

Review

Color Doppler Edward

G. Grant,12

and Ronald

Vicki

Imaging L. Schiller,1

of the Hepatic

Peter

Millener,1

Franklin

duplex

sonography

also

has

significant

draw-

backs, most of which are the result of the limited sampling ability of pulse-gated technology and the inability to provide a global display of Doppler information. Sonographic imaging of intraabdominal vessels has improved markedly with the advent of color Doppler techniques. This article reviews the use of color Doppler sonography in the evaluation of hepatic vessels. The complementary role of Doppler spectral analysis is also considered.

Evaluation of the hepatic vasculatune with Doppler sonography is performed after a thorough examination of the parenchyma of the liver. Parenchymal processes often underlie

abnormalities,

and primary

vascular

diseases

Rita

R. Perrella,1

Nagesh

abdomen. The small area of contact facilitates positioning of the transducer and intercostal access, both of which are essential if adequate Doppler angles are to be maintained. For most adults, a 3.5-MHz on lower frequency transducer

imaging may require a different transducer than is used for the Doppler examination. Positioning of the transducer varies with the vessel under study. (Specific details about techniques related to individual

are discussed

later.)

An optimum

be used for hepatic vascular imaging. Transducers of frequency are inadequate for penetration of the upper

alize extrahepatic mesentenic

veins

vessels

such as the splenic

or the hepatic

artery

The Hepatic

after

Received April 15, 1992; accepted after revision June 5, 1992. Department of Radiological Sciences, University of Califomia, Los Angeles, School Present address: Department of Radiology, veterans Affairs Medical Center, West

AJR 159:943-950,

requests

November

over the anterior

giving

of Medicine, Los Angeles,

to E. G. Grant. 1992 0361 -803X/92/1595.-0943

C American

Roentgen

or superior the

portal

Artery

courses

2

between

hepatis and the celiac axis.

increased considerably with little degrading effect on resolution. Depending on the equipment used, optimum real-time

reprint

angle

portal vein. A recent investigation [1 J has shown increased portal vein velocity after meals; postprandial scanning may be

The hepatic artery typically originates branches of the celiac axis. The common

Address

Doppler

should be maintained whenever possible. In the upper abdomen, obtaining a Doppler angle of less than 60#{176} may be difficult. Vessels are often perpendicular to the Doppler beam, and access may be limited. In some cases, scanning must be done from several directions in order to decrease the Doppler angle and optimize signal reception. Having the patient fast beforehand is not essential when the intrahepatic vasculature is evaluated, and actually may be detrimental in studies of the

abdomen by the ultrasound beam. Lower frequency transducers (2-2.25 MHz) are preferable; Doppler sensitivity is

90073.

Ragavendra,1

better for showing small portal veins or those with very slow flow. It is essential that the patient’s stomach be gas-free (either empty or fluid-filled) when attempts are made to visu-

almost

invariably have a significant effect on the parenchyma. Transducers with a sector format are best for scanning the upper

should higher

N. Tessler,1

vessels

Technique

vascular

Vasculature

Busuttil1

Duplex sonography added a new dimension to real-time sonographic imaging and can be used to characterize flow dynamics. Unfortunately,

Article

Ray Society

superior

off the gastroduodenal

as one of three major hepatic artery initially

edge of the pancreas artery,

nuns cephalad

10833 Le Conte Ave., Los Angeles, CA 90024-1721. Wilshire & Sawtelle Blvds., Bldg. 500/Wi 14, Los Angeles,

and, as

CA

944

GRANT

the proper

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bile duct

hepatic

artery

into the porta

with the portal hepatis.

In most

vein and common cases,

the

hepatic

artery lies anteromedial to the portal vein. Almost 50% of patients, however, have some form of anatomic variation or aberrant origin of the hepatic artery. Aberrant hepatic arteries typically take one of two forms: accessory or replaced. The former implies the presence of an extra hepatic artery, whereas the latter is merely a substitute for the “normal” vessel. Of the two, replaced arteries are more common, and in both cases, the anomalous origin vanes, depending on whether the right or left hepatic artery is affected. On the right, the superior mesenteric artery most commonly gives rise to the aberrant artery; on the left, the artery almost always arises from the left gastric artery. Aberrant hepatic arteries often lie dorsal to the portal vein [2]. The extrahepatic portions of the hepatic artery are often best visualized by detecting the celiac axis anterior to the aorta and following the branch that runs to the right. If the artery is located beneath the portal vein, an aberrant origin should be considered. In the porta hepatis, the common hepatic artery is easily visualized in most cases anterior to the portal vein when scanning is done from an oblique intercostal approach. Within the liver, the branches of the hepatic artery follow their attendant portal veins and are visible well into the periphery if the color Doppler technique is optimized. The hepatic artery can be distinguished from the adjacent vein

by its pulsatility,

higher

velocity

(often

displayed

in a

different shade of color), and smaller size. Spectral analysis allows absolute distinction between artery and vein and will confirm patency of the hepatic artery. The hepatic artery plays a role subordinate to that of the portal vein in parenchymal oxygenation. The portal vein supplies 70-75% of incoming blood [3]. This dual blood supply makes hepatic infarction rare in the native liver. The oxygen content of portal venous blood is usually sufficient to allow normal hepatic function even in the event of complete hepatic artery thrombosis. Abnormalities of the hepatic arteries are rarely a cause of liver disease. Enlargement of the hepatic artery, increased flow, and a tortuous “corkscrew” appearance are commonly observed in patients with cirrhosis and portal hypertension [4], but increased vascular resistance (as shown by an increased resistive or pulsatility index) has not been a useful diagnostic indicator. Because of increased dependence on the arterial system for oxygenation when portal hypertension occurs, the hepatic artery may be detected with color Doppler imaging more easily than the portal vein is. This situation can be particularly troublesome in potential liver transplant recipients in whom the patency of the portal vein must be established. In addition, with real-time sonography, ectatic hepatic arteries in patients with cirrhosis may be difficult to distinguish from dilated intrahepatic biliary radicles [5]. This problem is easily solved by using color or duplex Doppler imaging, as bile ducts produce no Doppler signal [6] (Fig. 1). The differentiation between vascular structures and dilated bile ducts may also be of value when drainage of an obstructive biliary system is considered as a possible treatment. Color Doppler imaging can be used to direct the needle to a dilated duct and avoid puncture of the adjacent vessel.

ET AL.

AJR:i59,

November

1992

Color Doppler imaging has been used to investigate arterial flow patterns in and around hepatic masses in an effort to improve the specificity of the sonognaphic examination. The flow of hemangiomas reportedly is too slow to produce a Doppler shift, and therefore they typically appear avascular. Unfortunately, metastases may also be avascular, and the two cannot be differentiated [7]. Taylor et al. [7] have reported peak systolic Doppler shifts greater than 5 kHz as being specific to hepatocellular carcinoma (HCC). Tanaka et al. [8], who used color Doppler imaging, suggested a “basket pattern” was also typical of HCC. Mann et al. [9], however, reported high-velocity flow in cirrhotic livers without hepatomas and attributed such flow patterns to the presence of small arteriovenous malformations rather than to tumor. Recent work suggests that color Doppler patterns are probably of little value in differentiating various hepatic lesions. RaIls [1 0] has shown that hemangiomas may have internal vascularity (probably the result of improvements in Doppler sensitivity) and that the patterns described by Tanaka et al. [8] as specific for HCC are commonly seen in metastases. Although

of minimal value as a diagnostic tool in hepatic masses, color Doppler imaging can be used to localize areas of significant vasculanty

if concern

exists

about

the optimum

site for biopsy.

The splenic and hepatic arteries are the most common sites for pseudoaneurysms in the abdominal vessels. These abnormalities typically occur in association with trauma or pancreatitis and may appear as a complex or cystic mass on routine neal-time examination [1 1 ]. When large, pseudoaneurysms may mimic an abscess and percutaneous puncture or drainage may be considered. In order to avoid potential catastrophe, colon or duplex imaging should be performed whenever a pseudoaneurysm is even remotely considered as part of the differential diagnosis. Unless a pseudoaneurysm is thrombosed

completely,

sufficiently

specific

The Portal

Venous

the

that a definitive

Doppler

characteristics

diagnosis

System

The portal vein and its major branches alized

in all patients

are

can be made.

by using

can be easily visu-

a night longitudinal

intercostal

approach similar to that used to display the common hepatic duct. When this approach is used, normal flow in the main portal vein is invariably directed toward the transducer and displayed in red (assuming a red toward and blue away colon scheme). Flow in the posterior branch of the night portal vein, however, is away from the transducer and should not be confused

with

that of the nearby

hepatic

veins

(also typically

displayed in blue). If a question exists, the vessel can be followed to its origin or evaluated with spectral Doppler imaging. Many significant abnormalities of the portal venous system are readily characterized by using duplex and colon Doppler imaging. Anatomic abnormalities are relatively unusual, but duplication, an anomalous course, and aneurysms have been described

[1 2, 1 3] (Fig. 2). In addition,

fistulas

may affect

the

portal venous system and involve either the hepatic artery or the hepatic veins. In both cases, fistulous lesions may be congenital or acquired. Communications between the hepatic

COLOR

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AJR:1 59, November1992

Fig.

1.-Biliary

dilatation.

Real-time

DOPPLER

tures in liver. Eariy biliary dilatation was suspected, but enlarged hepatic arteries in this patient with cirrhosis were also a consideration. Color

allows

indicates a vascular cul-de-sac.

definitive

dilated ducts and adjacent

vessels.

Fig. 3.-Hepatic artery/portal vein fistula in a patient with known fistula and multiple previous hepatic artery embolizations. At time of imaging, patient had recurrence of portal hypertension. Transverse color Doppler image through ports hepatis shows area of high-velocity, turbulent flow (straight arrow) In an artery lying posterior to portal vein. Note reversal of flow In portal vein (curved arrow). Superior mesenteric arteriogram confirmed presence of hepatic artery/portal vein fistula arising from collaterals originating from gas-

troduodenal

artery

and the portal vein tend to be symptomatic;

of the high

pressure

can be delivered hypertension.

in the artery,

large

to the portal system,

Most

hepatic

vein/portal

because

quantities

causing vein

of blood

severe portal fistulas,

on the

other hand, are asymptomatic unless they are large enough to divert the majority of portal flow and cause hepatic ischemia. Patients with this type of fistula occasionally have encephalopathy or hypoglycemia [14]. Findings

on color

both varieties

Doppler

of fistulas.

vein communications,

imaging

In patients markedly

should

be definitive

in

with hepatic artery/portal

dilated

portal

venous

struc-

tunes with abundant formation of collaterals are typical [15] (Fig. 3). Portal vein flow is often reversed and arterialized. Turbulent,

high-velocity,

color Doppler region useful

“bruit”

low-resistance

(random

arterial

color assignment

flow

with

outside

a

the

of an actual vessel) may be present [1 6]. Although a diagnostic sign, a color Doppler bruit may obscure the

vascular anatomy of the fistula and can be minimized by increasing the velocity scale or wall filter. Portal vein/hepatic vein fistulas tend to be less symptomatic than arterial lesions, as flow proceeds from one low-pressure system to another. Relatively large cystic spaces may be seen in the liver in the area of the communication. Color Doppler imaging can be used to make the diagnosis

by detecting

flow in these

spaces.

With color Doppler imaging, it should also be possible to define the attendant vascular connections [14] (Fig. 4). The portal venous system is an isolated vascular unit with relatively monophasic flow. Spectral analysis will show only minor fluctuations associated with cardiac or respiratory motion. In cases of hepatic vein/portal vein fistulas, the communication between the systemic and portal venous systems

945

VASCULATURE

vein aneurysm (arrows) extending off posterior main portal vein (P). “To-and-fro” flow pattern Is similar to that seen in pseudoaneurysms and

Doppler image through one of these areas shows no flow in one tubular structure, confirming biliary dilatation. Note obvious flow In adjacent portal vein imaging

OF HEPATIC

Fig. 2.-Sagittal color Doppler image of a patient with end-stage liver disease and documented portal hypertension shows a portal

scanning

showed numerous parallel, tubular anechoic struc-

(arrow). Color Doppler differentiation between

IMAGING

artery.

often allows the triphasic spectral pattern of the hepatic veins to be reflected back into the portal vein, producing a pattern of portal vein pulsatility. Such pulsatility is best characterized

by using spectral Doppler imaging but may color examination because of its alternating Occasionally, however, pulsatile flow may apparently normal portal vein. Some degree

be evident red/blue

on the pattern.

be detected in an of portal pulsatil-

ity is often observed in control subjects (no hepatic abnormalities), but the recent study by Duerinckx et al. [1 7] showed that a greater than two-thirds change between peak and

minimal velocity should be viewed with suspicion. As previously discussed, any anatomic communication between the systemic and portal veins, including surgically created portacaval shunts or hepatic vein/portal vein fistulas, may lead to a pulsatile portal vein. More commonly, however, clinically relevant portal vein pulsatility is associated with right-sided heart failure (increased right atrial pressure) and/or tricuspid regurgitation

[1 7, 1 8]. In such

cases,

patients

who

have

no

history of heart disease should be referred for a cardiac evaluation that includes a detailed echocardiogram with specific attention to the tricuspid value. Portal vein thrombosis (PVT) is associated

with

neoplasia

(HCC in particular), hypercoagulable states, use of oral contraceptives, and biliary atresia. Many cases occur with no apparent underlying abnormality. The signs and symptoms of PVT are relatively nonspecific and include the onset or wonsening of ascites and abdominal pain or distension. Hepatomegaly is not typical, and alterations in the results of liver function tests are not diagnostic. Color Doppler sonography is useful in the diagnosis of PVT [19]. The high negative predictive value (0.98) suggests that in patients suspected of