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The “Silhouette” sign in urinary tract calculi. Experimental demonstration
Clin. Radiol. (1970) 21, 313-317
THE
"SILHOUETTE" SIGN EXPERIMENTAL
IN URINARY TRACT DEMONSTRATION
CALCULI.
R. E. MELHEM, A. M. HABBAL and A. P. IMAD
From the Department of Radiology, American University Hospital, Beirut, Lebanon A simple experiment is described to demonstrate the 'Silhouette' sign in urinary tract calculi. This sign is helpful in the differentiation between intraluminal and extraluminal calcifications along the urinary tract, and especially in the bladder. IT is commonly observed that radiopaque calculi within the urinary bladder (Fig. 1 and 2) or in the pelvi-calyceal system (Fig. 3 and 4) "disappear"
when these structures are filled with contrast medium, while even smaller and less opaque calcifications lying outside the urinary bladder or
FIG. 1 Fro. 2 FIO. 1.--Large punctate calcification in the pelvis, representing a large vesical calculus. FIG. 2.--Complete obliteration of the calculus after the bladder is filled with contrast medium.
FIG. 3.
FIG. 3 FIG. 4 Opaque calculus in the left kidney pelvis. F~G. 4.--Complete obliteration of calculus after the pelvis is opacified following intravenous pyelography. 313
314
CLINICAL
FIG. 5
RADIOLOGY
FIG. 6
F,G. 5.--Extra-vesical calcifications in the pelvis. FIG. 6.-- Calcifications can still be seen through the opacified bladder.
the pelvi-calyceal system remains visible through an equally opacified structure (Fig. 5 and 6). It is the purpose of this paper to present an experimental demonstration of this observation. MATERIALS A N D M E T H O D S
A. THE STONE.--Three exactly similar stones were prepared having the following properties: A homogeneous structure, a density higher than that of the liquid in which they were to be suspended and a cylindrical shape so that they could rotate on their long axis without changing their thickness in relation to the X-ray beam. For this purpose, 30 g. of melted pure bees wax
FIG. 7 View of the Experimental model from above showing the stones in relation to the bottles. The central bottle contains the stone within it.
were mixed with 40 g. of Calcium Phosphate (CA3 (PO4)2). The mixture was allowed to dry in a cylindrical mould which was continuously rolled in order to prevent settling. Three equal pieces measuring 1.5 cm. in diameter and 1.8 cm. in length and with a density of 1.3 gm./cm, z were cut. B. EXPERIMENTAL MODEL.--A water phantom and three plastic bottles were used to simulate the human body and bladder. The bottles were suspended into the water bath phantom and marked A, C, and P, denoting that the stone is suspended anterior to, in the centre of, or posterior to the bottle respectively, relative to the direction of the X-ray beam (Fig. 7). Contrast medium solutions containing 0, 1; 1.5; 2; 2.5; 3; 3.5; 4; and 5 g. of iodine (using urografin 76) per 100 ml. of water were prepared. C. TECHNICAL DATA.--After placing the stones in their respective positions in relation to the bottles in the water phantom, a radiograph was taken for each concentration of contrast medium as enumerated above. The technical factors were 84 KVP, 90 MAS and 120 cm. FFD. High speed films* were used in screen cassettes and between the phantom and film a 10 × 12 Lysholm grid was placed. The films were processed by a 7 minute automatic processing unitt under identical conditions. These films were examined visually and densitometrically. DENSITOMETRIC M E A S U R E M E N T S ~ - - T h e optical densities were determined by means of a transmis* High Speed Ansco films in Parscreen cassettes. t Kodak X-Omat Processor model M4A. :~Optical density expresses quantitatively the degree of blackening on a film and is defined in terms of the transmitted and incident light intensities so that 1 Optical Density = log10 where T = Transmitted light intensity and I = Incident light intensity
THE
SILHOUETTE
SIGN
IN U R I N A R Y
TRACT
CALCULI
315
FIG. 8 Graph relating optical density of stone and solution plotted against iodine concentration.
sion type densitometer§. The optical densities of the stones outside the bottles appear always to be less than the optical densities of the solutions in the bottle. Only the optical density of the stone inside the bottle changed with respect to the optical density of the solution, hence, densitometric measurements were carried out on the central bottle only. D E N S I T O M E T R I C RESULTS The results of the densitometric measurements are graphically represented in Fig. 8 which is a plot of the optical densities (i.e. radiological blackening) of the stone and solution, against the concentration of contrast medium in the central bottle. It is seen from the graphs that at low concentrations, the stone appears to be less dense optically (i.e. less black) than the contrast medium solution, while at high concentrations the reverse is true. It is also noted that in the middle range of contrast medium concentration the optical density of the stone becomes identical with that of the solution. This happens near a concentration of 2 g. of iodine/ 100 ml. of solution. VISUAL RESULTS If we divide the available solutions into 3 groups, we find that in the first group with iodine concentrations o f 0 . 0 ~ , 1.0~, and 1"5~o (Fig. 9), the central stones remain visible as a radiopaque density but with decreasing sharpness as the iodine concentration increases: the stones outside remain sharp. In the second group of iodine concentrations of 2.0 ~ , 2.5 ~ , and 3.0 ~ (Fig. 10), the central stone § Eel--Universal Densitometer.
FIG. 9A, B, C Decreasing visibility of the stone with increasing iodine concentrations.
is completely obliterated, while stones outside remain visible. In the third group, 3.5~, 4 . 0 ~ , and 5 ~ (Fig. 11), the central calculus becomes a negative shadow while the stones outside remain visible, though not as well as when the iodine concentration is lower.
316
CLINICAL
Fro. 10A, B, C
RADIOLOGY
FIG. llA, B, C
Virtual obliteration of stone (inside the bottle) in the middle The stone inside the bottle becomes a negative densiW at higher range of iodine concentrations. Stones outside remain visible. ~ iodine concentrations. The stones outside the bottle give a positive image, but become hidden when the iodine concentration reaches 5.0 gin. per cent.
THE SILHOUETTE SIGN IN URINARY TRACT CALCULI DISCUSSION On comparing the visual and the densitometric results, it becomes clear that the actual obliteration of the central calculus occurs over a wider range of concentrations than is seen from the graphs of the densitometric results. This suggests that actual obliteration will occur when the densities of the contrast medium and stone are approximately equal, and not only when they are exactly equal. The reason for the obliteration of the central calculus, while those outside remain visible is very likely the same as that of the silhouette sign, Felson and Felson (1950). The silhouette sign was described originally for localisation of intrathoracic lesions and may be summarized as follows: An intrathoracic lesion touching a border of the heart, aorta or diaphragm will obliterate that border on the roentgenogram. An intrathoracic lesion not
contiguous with a border of one of these structures (there is still normally aerated lung between the lesion and the cardiac border) will not obliterate those borders, although they may be superimposed. The lack of any "interphase" of different radiographic density between the contrast medium and the central calculus, while the presence of an "interphase" between the calculi outside and the contrast medium in the bottles is the major reason for the difference in visibility at different concentrations. Aeknowledgements.--The authors wish to thank Mr. S. Franji, R. T. for his technical assistance and Miss W. Jabir for typing the manuscript. REFERENCES FELSON, B. & FELSON, H. (1950). Localization of intrathoracic lesions by means of the postero-anterior roentgenograms. The Silhouette Sign. Radiology,Vol. 55, pp. 360-374.
NOTICES PLYMOUTH GENERAL HOSPITAL THEREwill be an intensive course in Radiotherapy for those intending shortly to sit the D.M.R.T. Part II examination from Thursday, 1st October until Saturday, 3rd October, 1970. Further details and application forms may be obtained from: Dr. J. M. Brindle, Radiotherapy Department, Plymouth General Hospital, Freedom Fields, PLYMOUTH, PL4 7JJ
317
21st ANNUAL CONGRESS OF COLLEGE OF RADIOLOGISTS OF AUSTRALASIA To be held in Perth 5th to 9th October 1970 Anyone interested in going contact: Dr. H. T. ApSimon, X-Ray Dept., Royal Perth Hospital, Box X2213 G.P.O., Perth, WESTERN AUSTRALIA, 6001.
THE
"SILHOUETTE" SIGN EXPERIMENTAL
IN URINARY TRACT DEMONSTRATION
CALCULI.
R. E. MELHEM, A. M. HABBAL and A. P. IMAD
From the Department of Radiology, American University Hospital, Beirut, Lebanon A simple experiment is described to demonstrate the 'Silhouette' sign in urinary tract calculi. This sign is helpful in the differentiation between intraluminal and extraluminal calcifications along the urinary tract, and especially in the bladder. IT is commonly observed that radiopaque calculi within the urinary bladder (Fig. 1 and 2) or in the pelvi-calyceal system (Fig. 3 and 4) "disappear"
when these structures are filled with contrast medium, while even smaller and less opaque calcifications lying outside the urinary bladder or
FIG. 1 Fro. 2 FIO. 1.--Large punctate calcification in the pelvis, representing a large vesical calculus. FIG. 2.--Complete obliteration of the calculus after the bladder is filled with contrast medium.
FIG. 3.
FIG. 3 FIG. 4 Opaque calculus in the left kidney pelvis. F~G. 4.--Complete obliteration of calculus after the pelvis is opacified following intravenous pyelography. 313
314
CLINICAL
FIG. 5
RADIOLOGY
FIG. 6
F,G. 5.--Extra-vesical calcifications in the pelvis. FIG. 6.-- Calcifications can still be seen through the opacified bladder.
the pelvi-calyceal system remains visible through an equally opacified structure (Fig. 5 and 6). It is the purpose of this paper to present an experimental demonstration of this observation. MATERIALS A N D M E T H O D S
A. THE STONE.--Three exactly similar stones were prepared having the following properties: A homogeneous structure, a density higher than that of the liquid in which they were to be suspended and a cylindrical shape so that they could rotate on their long axis without changing their thickness in relation to the X-ray beam. For this purpose, 30 g. of melted pure bees wax
FIG. 7 View of the Experimental model from above showing the stones in relation to the bottles. The central bottle contains the stone within it.
were mixed with 40 g. of Calcium Phosphate (CA3 (PO4)2). The mixture was allowed to dry in a cylindrical mould which was continuously rolled in order to prevent settling. Three equal pieces measuring 1.5 cm. in diameter and 1.8 cm. in length and with a density of 1.3 gm./cm, z were cut. B. EXPERIMENTAL MODEL.--A water phantom and three plastic bottles were used to simulate the human body and bladder. The bottles were suspended into the water bath phantom and marked A, C, and P, denoting that the stone is suspended anterior to, in the centre of, or posterior to the bottle respectively, relative to the direction of the X-ray beam (Fig. 7). Contrast medium solutions containing 0, 1; 1.5; 2; 2.5; 3; 3.5; 4; and 5 g. of iodine (using urografin 76) per 100 ml. of water were prepared. C. TECHNICAL DATA.--After placing the stones in their respective positions in relation to the bottles in the water phantom, a radiograph was taken for each concentration of contrast medium as enumerated above. The technical factors were 84 KVP, 90 MAS and 120 cm. FFD. High speed films* were used in screen cassettes and between the phantom and film a 10 × 12 Lysholm grid was placed. The films were processed by a 7 minute automatic processing unitt under identical conditions. These films were examined visually and densitometrically. DENSITOMETRIC M E A S U R E M E N T S ~ - - T h e optical densities were determined by means of a transmis* High Speed Ansco films in Parscreen cassettes. t Kodak X-Omat Processor model M4A. :~Optical density expresses quantitatively the degree of blackening on a film and is defined in terms of the transmitted and incident light intensities so that 1 Optical Density = log10 where T = Transmitted light intensity and I = Incident light intensity
THE
SILHOUETTE
SIGN
IN U R I N A R Y
TRACT
CALCULI
315
FIG. 8 Graph relating optical density of stone and solution plotted against iodine concentration.
sion type densitometer§. The optical densities of the stones outside the bottles appear always to be less than the optical densities of the solutions in the bottle. Only the optical density of the stone inside the bottle changed with respect to the optical density of the solution, hence, densitometric measurements were carried out on the central bottle only. D E N S I T O M E T R I C RESULTS The results of the densitometric measurements are graphically represented in Fig. 8 which is a plot of the optical densities (i.e. radiological blackening) of the stone and solution, against the concentration of contrast medium in the central bottle. It is seen from the graphs that at low concentrations, the stone appears to be less dense optically (i.e. less black) than the contrast medium solution, while at high concentrations the reverse is true. It is also noted that in the middle range of contrast medium concentration the optical density of the stone becomes identical with that of the solution. This happens near a concentration of 2 g. of iodine/ 100 ml. of solution. VISUAL RESULTS If we divide the available solutions into 3 groups, we find that in the first group with iodine concentrations o f 0 . 0 ~ , 1.0~, and 1"5~o (Fig. 9), the central stones remain visible as a radiopaque density but with decreasing sharpness as the iodine concentration increases: the stones outside remain sharp. In the second group of iodine concentrations of 2.0 ~ , 2.5 ~ , and 3.0 ~ (Fig. 10), the central stone § Eel--Universal Densitometer.
FIG. 9A, B, C Decreasing visibility of the stone with increasing iodine concentrations.
is completely obliterated, while stones outside remain visible. In the third group, 3.5~, 4 . 0 ~ , and 5 ~ (Fig. 11), the central calculus becomes a negative shadow while the stones outside remain visible, though not as well as when the iodine concentration is lower.
316
CLINICAL
Fro. 10A, B, C
RADIOLOGY
FIG. llA, B, C
Virtual obliteration of stone (inside the bottle) in the middle The stone inside the bottle becomes a negative densiW at higher range of iodine concentrations. Stones outside remain visible. ~ iodine concentrations. The stones outside the bottle give a positive image, but become hidden when the iodine concentration reaches 5.0 gin. per cent.
THE SILHOUETTE SIGN IN URINARY TRACT CALCULI DISCUSSION On comparing the visual and the densitometric results, it becomes clear that the actual obliteration of the central calculus occurs over a wider range of concentrations than is seen from the graphs of the densitometric results. This suggests that actual obliteration will occur when the densities of the contrast medium and stone are approximately equal, and not only when they are exactly equal. The reason for the obliteration of the central calculus, while those outside remain visible is very likely the same as that of the silhouette sign, Felson and Felson (1950). The silhouette sign was described originally for localisation of intrathoracic lesions and may be summarized as follows: An intrathoracic lesion touching a border of the heart, aorta or diaphragm will obliterate that border on the roentgenogram. An intrathoracic lesion not
contiguous with a border of one of these structures (there is still normally aerated lung between the lesion and the cardiac border) will not obliterate those borders, although they may be superimposed. The lack of any "interphase" of different radiographic density between the contrast medium and the central calculus, while the presence of an "interphase" between the calculi outside and the contrast medium in the bottles is the major reason for the difference in visibility at different concentrations. Aeknowledgements.--The authors wish to thank Mr. S. Franji, R. T. for his technical assistance and Miss W. Jabir for typing the manuscript. REFERENCES FELSON, B. & FELSON, H. (1950). Localization of intrathoracic lesions by means of the postero-anterior roentgenograms. The Silhouette Sign. Radiology,Vol. 55, pp. 360-374.
NOTICES PLYMOUTH GENERAL HOSPITAL THEREwill be an intensive course in Radiotherapy for those intending shortly to sit the D.M.R.T. Part II examination from Thursday, 1st October until Saturday, 3rd October, 1970. Further details and application forms may be obtained from: Dr. J. M. Brindle, Radiotherapy Department, Plymouth General Hospital, Freedom Fields, PLYMOUTH, PL4 7JJ
317
21st ANNUAL CONGRESS OF COLLEGE OF RADIOLOGISTS OF AUSTRALASIA To be held in Perth 5th to 9th October 1970 Anyone interested in going contact: Dr. H. T. ApSimon, X-Ray Dept., Royal Perth Hospital, Box X2213 G.P.O., Perth, WESTERN AUSTRALIA, 6001.