LETTER
FOR
THE
EDITOR
Computerized Tomography
of the Gallbladder
Ralph J. Alfidi,
F
EW MODALITIES have captured the scientific imagination of radiology with the fervor that has accompaniedcomputerized tomography (CT). It is applicable to virtually any organ, including both the gallbladder and the biliary tract. This is not to say that the conventional oral cholecystogram will be replaced by this new (and expensive) modality. Rather, it is probably a procedure that will prove useful in the study of the nonvisualized gallbladder and in differentiating obstructive from nonobstructive jaundice. The attenuation coefficient of bile is considerably lower than that of normal liver parenchyma, so that both the normal biliary tree and the gallbladder are visible with CT. Becausethe contrast resolution of CT is extraordinarily sensitive, in certain instancesit is possibleto detect gallbladder calculi that are not apparent on conventional radiographic films. In the caseof the nonfunctioning gallbladder, both calculi and hydrops have been recognized. The calculi appear asshadowsof increased density; hydrops is demonstrated as a larger than normal low density structure. To date, all casesof cystic duct obstruction by stone have been correctly identified by CT, even though the stone itself may not be visible. Common bile duct obstruction, whether caused by carcinoma, stone, or other conditions, is recognizable by the greatly increaseddiameter of the bile ducts, appearing as larger than normal filling defects with branching pattern in the Ralph J. Alfidi, M.D.: Head, Department of Hospital Radiology, Cleveland Clinic, Cleveland, Ohio. Reprint requests should be addressed to Ralph J. Alfidi, M.D., Department of Hospital Radiology, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, Ohio 44106. o 1976 by Grune & Stratton, Inc.
Seminars in Roentgenology,
Vol.
Xi,
No.
3 (July),
1976
and Biliary Tract
M.D.
hepatic parenchyma. This effect can be enhanced by injecting ordinary urographic contrast material (eg, 100 ml of 60% Renografin@) intravenously and scanningthe liver immediately thereafter. The contrast agent increasesthe density of the liver parenchyma, exaggerating the branching filling defects. In gallstone obstruction, it hasnot always been possibleto visualize the stone itself, but at least differentiation between obstructive and nonobstructive jaundice is made. A tumor in the region of the common bile duct can be visualized by abnormal morphology in the region of the duct or head of the pancreas. Wehave found it possibleto convert transhepatic cholangiography from a “blind” procedure to a guided one if the needleintroduction is monitored with CT. This is a time-consumingprocedure but does reduce the number of needle passesthrough liver parenchyma and should decrease the incidence of complications. Presently, CT images are greatly affected by respiration and peristaltic motion. When equipment that permits extremely short scan time becomes available, image resolution should improve considerably due to elimination of motion. If three-dimensionalreconstruction of the biliary tree is achieved, there is reasonto believe that not only the obstructed gallbladder and common bile duct, but also small stones within the duct system will be visualized. It is hoped that the future will also see the development of contrast agents that will enhance the density of hepatic parenchyma considerably more than those now available, so that even minute branches of the biliary tree become perceptible. The combination of greater contrast and short scan time should considerably improve the resolution currently available.
143
FOR
THE
EDITOR
Computerized Tomography
of the Gallbladder
Ralph J. Alfidi,
F
EW MODALITIES have captured the scientific imagination of radiology with the fervor that has accompaniedcomputerized tomography (CT). It is applicable to virtually any organ, including both the gallbladder and the biliary tract. This is not to say that the conventional oral cholecystogram will be replaced by this new (and expensive) modality. Rather, it is probably a procedure that will prove useful in the study of the nonvisualized gallbladder and in differentiating obstructive from nonobstructive jaundice. The attenuation coefficient of bile is considerably lower than that of normal liver parenchyma, so that both the normal biliary tree and the gallbladder are visible with CT. Becausethe contrast resolution of CT is extraordinarily sensitive, in certain instancesit is possibleto detect gallbladder calculi that are not apparent on conventional radiographic films. In the caseof the nonfunctioning gallbladder, both calculi and hydrops have been recognized. The calculi appear asshadowsof increased density; hydrops is demonstrated as a larger than normal low density structure. To date, all casesof cystic duct obstruction by stone have been correctly identified by CT, even though the stone itself may not be visible. Common bile duct obstruction, whether caused by carcinoma, stone, or other conditions, is recognizable by the greatly increaseddiameter of the bile ducts, appearing as larger than normal filling defects with branching pattern in the Ralph J. Alfidi, M.D.: Head, Department of Hospital Radiology, Cleveland Clinic, Cleveland, Ohio. Reprint requests should be addressed to Ralph J. Alfidi, M.D., Department of Hospital Radiology, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, Ohio 44106. o 1976 by Grune & Stratton, Inc.
Seminars in Roentgenology,
Vol.
Xi,
No.
3 (July),
1976
and Biliary Tract
M.D.
hepatic parenchyma. This effect can be enhanced by injecting ordinary urographic contrast material (eg, 100 ml of 60% Renografin@) intravenously and scanningthe liver immediately thereafter. The contrast agent increasesthe density of the liver parenchyma, exaggerating the branching filling defects. In gallstone obstruction, it hasnot always been possibleto visualize the stone itself, but at least differentiation between obstructive and nonobstructive jaundice is made. A tumor in the region of the common bile duct can be visualized by abnormal morphology in the region of the duct or head of the pancreas. Wehave found it possibleto convert transhepatic cholangiography from a “blind” procedure to a guided one if the needleintroduction is monitored with CT. This is a time-consumingprocedure but does reduce the number of needle passesthrough liver parenchyma and should decrease the incidence of complications. Presently, CT images are greatly affected by respiration and peristaltic motion. When equipment that permits extremely short scan time becomes available, image resolution should improve considerably due to elimination of motion. If three-dimensionalreconstruction of the biliary tree is achieved, there is reasonto believe that not only the obstructed gallbladder and common bile duct, but also small stones within the duct system will be visualized. It is hoped that the future will also see the development of contrast agents that will enhance the density of hepatic parenchyma considerably more than those now available, so that even minute branches of the biliary tree become perceptible. The combination of greater contrast and short scan time should considerably improve the resolution currently available.
143
