Robert Robert

M. Liddell, M. Varnell,

MD MD

#{149} Richard #{149} William

L Baron, MD #{149} Jon P. Shuman, MD

Normal Intrahepatic CT Depiction’ Visualization of intrahepatic bile ducts (IHBDs) at computed tomography (CT) has previously been considered evidence of biliary obstruction. The authors have found that hepatic CT enhanced with contrast material and with the use of ceramic scintillation detectors allows frequent visualization of normal IHBDs. One hundred patients without imaging, laboratory, or clinical evidence of hepatobiliary or pancreatic disease were prospectively examined to assess the frequency of visualization, location, and size of IHBDs. IHBDs were visualized in 40% of the patients and had an average size of 2.0 mm in the central part of the liver and 1.8 mm in the peripheral part of the liver. Ducts were seen in the right lobe more often than in the left lobe. There was no statistically significant relationship between visualization of IHBDs and patient age. Demonstration of IHBDs on current CT scanners is a normal finding and does not indicate biliary obstruction. Index terms: Bile ducts, Bile ducts, CT, 765.1211 phy (CT), technology Radiology

.

anatomy, Computed

Bile

P

MD

REVIOUS

material either does not demonstrate normal intrahepatic bile ducts (IHBDs) or only depicts the intrahepatic distal right and left hepatic ducts just proximal to the common hepatic duct (1-5). Therefore, visualization of peripheral IHBDs at CT has been considered to be indicative of biliary dilatation, which leads to the evaluation of suspected obstructive jaundice. In our experience, the recent addition of synthetic ceramic scintillation detectors to our CT scanners has improved spatial resolution and lowcontrast detectability. In patients with normal biliary tracts, this improvement has allowed the visualization of focal low-attenuation structunes, adjacent to portal venous radides, in the expected locations of IHBDs. We designed a prospective study to demonstrate the frequency of IHBD visualization and to assess the size and distribution of IHBDs.

ization of low-attenuation cent to portal vein radicles. tenuation

structures

IHBDs. within the

AND

From January 160 consecutive

5 through patients

CT

was

scanner

performed

with

April referred

examinations,

27, 1989, for ab-

without

known hepatobiliary ease, were prospectively fling

METHODS

or pancreatic examined. on

HiLight

a GE

9800

ceramic

disScanCT

scintilla-

tion detectors (GE Medical Systems, Milwaukee). Consecutive dynamic scans at

10-mm intervals with 5-mm collimation were obtained during rapid intravenous bolus of 60 mL of Conray (iothalamate meglumine;

Squibb,

New

at 1.5 mL/sec, followed mL/sec. Scanning was kVp ning

Brunswick, NJ) by 90 mL at 1.0

performed

and 140 mA, with a 2-second time for most patients. The

at 120 scankilovolt

peak was increased to 140 kVp for large patients. At the conclusion of each examination, images were reviewed without magnification at both wide and narrow window settings and assessed for visual-

were

anatomy

of the

assumed

interlobar

hepatic and portal veins lobe was not evaluated. was arbitrarily classified within a zone extending 2 cm

to be

inferior

to,

and

fissure

and

(5). The caudate A “central” duct as being that 2 cm superior to,

within

a 2-cm

axial

radius of the bifurcation of the portal vein, but the tubular area of low attenuation

left

adjacent

to the

portal

veins

distal right tial volume

proximal

(which

and left averaging

na

for

a central

ripheral The in

an

ducts visualized

right

may

hepatic from

portal fat) was excluded. duct was any duct not duct.

and

represent ducts or adjacent

parpen-

A “peripheral” meeting the cniteThe

number

of pe-

in each lobe was counted. IHBDs were measured

anteropostenior

dimension

with

electronic calipers on magnified (X2.5) images. Each scan was reviewed later by two of the investigators for consensus on each measurement and on the exact location of each duct. Of the original 160 consecutive patients, 48 were excluded due to hepatobiliary fied cal

PATIENTS

structures adjaThese low-at-

We identified each duct as being the right or left lobe by evaluating

or pancreatic on the initial

following

dominal

‘From the Department of Radiology, University Hospital, SB-OS, University of Washington School of Medicine, 1959 NE Pacific St. Seattle, WA 98195. From the 1989 RSNA scientific assembly. Received February 1, 1990; revision requested March 9; revision received April 23; accepted April 25. Address reprint requests to R.L.B., Department of Radiology, PresbyterianUniversity Hospital, DeSoto at O’Hara Sts, Pittsburgh, PA 15213. RSNA, 1990

a

Ducts:

reports have stated that thin-collimation, dynamic computed tomography (CT) enhanced with bolus administration of contrast

765.92. tomogra-

1990; 176:633-635

E. Ekstrom,

the

charts

abnormalities CT scans.

Six

CT examinations,

of the

patients

with

identimonths

the

medi-

visualized

IHBDs were reviewed or referring physicians were contacted to determine if hepatobiliary or pancreatic disease had developed. Ten patients were excluded from further analysis because they developed clinical, laboratory, or imaging evidence of hepatobiliary or pancreatic disease. Two patients were lost to follow-up; thus, 100 patients were included in the study group. The study population included 61 men and 39 women, with a mean age of 52 years (range, 18-88 years). In the 40 patients

in

clinical

and

whom

IHBDs

were

visualized,

biochemical follow-up studies at 6 months or more were available in 26 patients; 10 of these patients also underwent follow-up CT examinations that helped confirm a normal biliary tract. Ten patients underwent clinical and biochemical follow-up at 3-6 months, two of

Abbreviation:

IHBD

=

intnahepatic

bile

duct.

633

whom also aminations biliary

tract.

underwent that helped Four

follow-up confirm

patients

died

CT exa normal 1-2

months following the CT examination, without clinical or biochemical evidence of biliary tract disease (autopsy confirmation was obtained in one of these patients). A standard one-way analysis-of-variance software package (StatView-II; Abacus Concepts, Berkeley, Calif) was used for statistical analysis.

RESULTS IHBDs were visualized in 40 of the 100 patients (Figs 1, 2). The overall mean diameter of visualized peniphera! ducts was 1.8 mm (range, 1.0-3.0 mm) and that of central ducts was 2.0 mm (range, 1.0-3.0) (Table). The mean diameter of the visualized penipheral right lobe ducts was 1 .9 mm and was slightly larger than that of the peripheral left lobe ducts (7.7 mm). In the 40 patients with visualized IHBDs, central and peripheral ducts were visualized in 24, peripheral ducts only were visualized in 14, and central ducts only were visible in two. In the 26 patients in whom the central ducts were visualized, the central ducts in the right lobe only were seen in 19, the central ducts in the left lobe only in one, and central ducts in both lobes in six. In the 38 patients in whom peripheral IHBDs were seen, both the right and left lobe ducts were visualized in 31, only right lobe ducts in five, and only left lobe ducts in two. When separate ducts were present, we evaluated the number visible in each lobe. In the right lobe, four or more peripheral ducts were seen in 25 patients, while one to three penipheral ducts were visible in 1 1 patients. In the left lobe, four or more peripheral ducts were seen in eight patients, while one to three penipheral ducts were visible in 25 patients. There was no statistical correlation between visualization of IHBDs and patient age. Also, although the size of the common bile duct is known to increase with age (6), we found no correlation of the size of IHBDs with age.

DISCUSSION Except for the distal right and left hepatic bile ducts, visualization of low-attenuation structures adjacent to intrahepatic portal veins on CT scans has previously been considered evidence (1,2,5).

634

Our

of biliany study

#{149} Radiology

obstruction shows that

with

1.

2.

Figures in

the

1, 2. right

(1) CT scan and

left

lobes

enhanced of the

with liver.

contrast

Multiple

material

seen adjacent to portal venous radicles. (2) CT scan strates peripheral (arrow) and central (arrowhead) within a 2-cm zone of the portal venous bifurcation. scan obtained 1 cm inferionly.

Central

and Peripheral IHBD

Visualized

Central and peripheral Peripheral only Central only *

Duct

demonstrates

low-attenuation

peripheral

structures

enhanced with contrast IHBDs. A central duct The portal bifurcation

IHBDs

(arrowheads)

are

material demonis defined as being was present on a

Size No. of Patients

Central Duct Size (mm)* 1.9 (1.0-2.8)

24 14 2

Numbers are means. Ranges in panentheses. No range included because size was same

...

Peripheral Duct Size (mm)* 1.8 (1.0-3.0) 1.7 (1.0-3.0)

3.Ot

...

in both patients.

current CT technology, IHBDs were visualized in 40% of patients who did not have biliany disease. Recognition of this finding is important to prevent unnecessary evaluation for suspected biliary obstruction. Fat or lymphatic ducts could theoretically cause areas of low attenuation adjacent to intrahepatic portal veins. However, fatty connective tissue does not extend into the liver parenchyma beyond the proximal portal veins (7). The normal intrahepatic lymphatic vessels are too small to allow visualization with CT (8). Obstructive intrahepatic lymphedema could cause areas of low attenuation adjacent to portal veins, but these typically appear on both sides of a portal vessel (8,9) rather than on one side of a portal vein, as in our cases. Therefore, we conclude that the juxtaportal low-attenuation structures identified in the periphery of the liver represent normal intrahepatic bile ducts. In the 40 patients with IHBDs demonstrated at CT, the frequency and location of duct visualization

varied (Table). More IHBDs were seen in the right lobe than in the left. This is likely due to the larger anatomic size of the right lobe compared with that of the left lobe (10). This disparity may also be secondary to scanning being performed in the supine position, which causes the more dependent right ducts to be slightly larger than the left. This latter hypothesis may be supported by the finding that the ducts in the right lobe, when visualized, were slightly larger than those seen in the left lobe. We

are

uncertain

why

IHBDs

were

not visualized in all patients. In addition, although multiple peripheral ducts were visible in many patients, only scattered peripheral ducts were seen in some. The reasons for these disparities are not clean, but they could be due to sampling error, a suboptimal bolus of contrast material in some patients, minimal decreased liven attenuation from nonuniform fatty liver infiltration, or other unknown factors. It is well known that fatty liver infiltration can make it dif-

September

1990

ficult to detect even an abnormally dilated biliary tree within the liven parenchyma (11). In our experience, the detection of IHBDs in a significant number of healthy patients is related to the ceramic scintillation CT detectors. The technical advantages of these rareearth-oxide detectors include a higher absorption efficiency compared with that of xenon gas detectors and

a higher scintillation efficiency compared with that of cadmium tungstate detectors. The small detector size also improves spatial resolution because more elements fit into the detector array. Smaller spacing between detectors improves geometric efficiency as well (GE Medical Systems product data B791OLA/LE; Milwaukee: GE Medical Systems, 1988; 1-5). These technical improvements

lead

to increased

spatial

detectability,

(low-attenuation) likely to be

Volume

176

detected

bile-filled IHBDs are more against the back-

#{149} Number

mm) also increases visualizing these In conclusion,

CT technology

3

the likelihood structures. recent advances

allow

4.

S.

in

6.

7.

of

strucportal likely to findings as eviU

8.

9.

2.

3.

Benland

ducts.

Philadelphia:

Liver and biliary tract. In: Lee JKT, Sagel SS, Stanley RJ, eds. Computed body tomography. 2nd ed. New York: Raven, 1989; 593-660. Simeone JF. The biliary ducts: anatomy and exam technique. In: Taveras JM, Fernucci JT, eds. Radiology: diagnosis-imaging-intervention. Philadelphia: Lippincott, 1989; 1-13. Friedman AC, Sachs L. Gallbladder and biliary tract embryology and anatomy. In: Friedman AC, ed. Radiology of the liver, biliary

tract,

more:

Williams

pancreas

Stanley

and

& Wilkins,

RJ.

spleen.

1987;

10.

11.

1983;

ed.

Philadelphia:

Saunders,

1975;

688-725. Koslin BD, Stanley RJ, Berland LL, Shin MS. Dalton SC. Hepatic penivascu!an lymphedema: CT appearance. AJR 1988; 150:111-113. Manincek B, Banbien PA, Becker CD, Mettler D, Ruchti C. CT appearance of impaired lymphatic drainage in liven transplants.

L, Lee JKT,

Saunders,

242-245. Wu CC, Ho YM, Chen CY. Effect of aging on common bile duct diameter: a neal-time ultrasonographic study. JCU 1984; 12:473475. Bloom W, Fawcett DW. The liven and gallbladder. In: A textbook in histology. 10th

References 1.

Pedrosa CS, Casanova R, Rodriguez R. Computed tomography in obstructive jaundice. I. The level of obstruction. Radiology 1981; 139:627-634. Koehler RE, Stanley RJ. Computed tomography of the gallbladder and bile ducts. In: Benk RN, Fenrucci JT, Leopold GR, eds. Radiology of the gallbladder and bile

of

visualization

1.0-3.0-mm low-attenuation tures adjacent to intrahepatic veins. These structures are be IHBDs. Therefore, these should not be misconstrued dence of biliary obstruction.

resolution

and increased low-contrast detectability. The improved spatial detail allows smaller structures (eg, IHBDs) to more likely be resolved on CT scans. Because of the improved low-

contrast

ground of higher-attenuation liver. It had been our experience with older CT equipment that normal intrahepatic bile ducts were rarely detected. It is certainly possible that the technologic advances of other manufactuners may also allow visualization of normal intrahepatic bile ducts. The use of thinner collimation (5

AJR

1986;

147:519-523.

Edmondson HA, Peters RL. Liver. In: Kissane JM, ed. Anderson’s pathology. 8th ed. St Louis: Mosby, 1985; 1096-1104. Quint LE, Glazer GM. CT evaluation of bile diology

ducts

in patients 1984;

with

fatty

liven.

Ra-

153:755-756.

Balti-

305-332.

Radiology

#{149} 635