Scand J Urol Nephrol 12: 155-156, 1978
COMPARISON OF RADIOLOGICAL MEASUREMENT AND ACTUAL SIZE OF URETERAL CALCULI B. Otnes and H . Sandnes From the S c ~ v i o no j Urology und Depurtrnant oJ’Rudio1og.v. Univi,rsity oj Oslo, Akershus Cenirul Hospitul. Nordhyhugen, Nor\t,uy
Scand J Urol Nephrol Downloaded from informahealthcare.com by York University Libraries on 07/01/14 For personal use only.
(Submitted for publication December 15, 1977)
Ahstruct. 100 ureteral calculi were measured on X-ray films and directly on the stone after passage or removal. The largest diameters were compared. The size of the stone was radiologically overestimated for 59 stones, correct for 26 and underestimated for 15. 73 of the stones were radiologically measured within +25% of the actual size.
The radiological measurement of ureteral calculi is of interest for estimation of the probability of spontaneous passage. Stones less than 4 mm in diameter, as measured on X-ray films, have been observed to pass spontaneously in up to 91 r/r of cases, while stones 6 mm or larger have a 6 % chance of spontaneous passage ( S a n d e g M , 1956). Such estimates may serve as a rough guide to the handling of patients with ureteral calculi, although other factors such as the degree and duration of obstruction and pain or the presence of infection often assume overriding importance.
MATERIAL AND METHOD In order to evaluate the reliability of such radiological measurements we have compared the actual size of stones with measurements obtained from X-ray films in a material of ureteral calculi collected from June 1975 till October 1977. All stones obtained during this period, whether by spontaneous passage o r surgical removal, were considered for inclusion in the study. The criteria for selection were: I ) stone removed o r passed without fragmentation, 2) stone present as a definite radioopaque finding on X-ray films, 3) conviction that the stone obtained was the one actually measured on the X-ray film. The radiological measurements were done retrospectively without knowledge of the actual size of the stone. They were performed on plain films or intravenous pyelograms taken in the supine position, with the distance from X-ray tube to film being a s a rule 100 cm. T w o diameters were noted but only the larger is used in this report. The actual size of the stone was obtained from the
reports of the laboratory (Beck Analytical Services. Bloomington, Indiana, U . S . )to which the stones had been sent for crystallographic analysis. These reports include exact measurements in three diameters. with photographic corroboration showing the stone placed on millimeter paper. Only the largest diameter was used. All measurements, radiological and actual. were rounded to the nearest millimeter. Classification by shape of the stone was attempted both on the X-ray films and the actual stones, but it was found impossible to be consistent. All stones contained calcium oxalate and/or calcium phosphate. One stone consisted of triple phosphate and two had minute inclusions (less than 3 per cent) of uric acid in addition to major calcium oxalate.
RESULTS 100 stones were measured on X-ray films and the measurements compared to those reported by the analyzing laboratory. Fig. I shows the number of stones found for each given combination of actual size and radiological measurement. Twenty-six stones had the same size in actual and radiological measurements. Thirty-seven stones deviated from the actual size by one millimeter only. The maximal deviation found was 4 mm radiological overestimation of stones of which the largest diameters actually were 2, 7 and 13 mm respectively. The X-rays for stones which showed great discrepancy between actual and radiologically measured size were independently reevaluated without any significant error being found in the original registrations. When the radiologically measured diameter was markedly smaller than the largest real diameter, better approximation was regularly found to one of the other two diameters reported by the analyzing laboratory. It is apparent that overestimation was more frequent than underestimation (Fig. I ) . Fifty-nine stones were radiologically overestimated, 15 were
156
B. Ottrc’.s trntl H . Strndncs
17 16 15
I 1
No. of stones
,’
14
2 2 I /
13. 12 I
II.
10. 9. 8 7
3 I I/
2 3,22 1 6 6 b 2
1
Overestimdtron More thdn 25 ‘/i 2 5 % or k5s Correct measurement Underestimation 25 75 or les5
I
More than 25 %
!LLL-.-
Total
Scand J Urol Nephrol Downloaded from informahealthcare.com by York University Libraries on 07/01/14 For personal use only.
2
I
2 3 L 5 6 7 8 9 10 II 12 13mm Actual
20 39 26 8 7 I00
size
Fig. 1. The number of stones found for each given combination of actual size and radiological measurement. The number of stones with equal findings for the two types of
measurement is indicated by the oblique line.
underestimated. When the radiological error was calculated as percentage of the actual size (Table 1). it was found that 73 stones were measured within k25%’ of the actual size. When measured on the X-rays, 39 stones were located in the upper ureter (above the linea terminalis) and 61 in the lower ureter. The radiological error was not significantly different for stones in the two parts of the ureter. DISC U SSl ON A difference between radiological measurement and actual size of stones is not unexpected. One contributory factor must be orthograde projection of elongated stones. leading to underestimation. Another is the divergent course of X-rays from the stone t o the film with consequent overestimation.
The latter was most frequently found and is t o some extent expected by clinicians. Difficulties in distinction between the outline of the stone and acijacent bony structures o r phleboliths may account for some erroneous measurements. Although all possible care has been taken to exclude fragmented stones from this study occasional reduction in size during removal o r passage from breaking off of fragile parts of the stone may have occurred. Radiological measurement is the only clue t o the size of the stone available to the clinician. and it provides a useful but far from absolute indicator for treatment in a given case of ureteral stone. This study shows that the majority of radiological measurements are within ? 2 5 % of the actual size of stones, but there are occasional gross errors of estimation. REFERENCE SandegBrd, E. 1956. Prognosis of stone in the ureter. Actti C’hir Scand. Suppl. 219.
COMPARISON OF RADIOLOGICAL MEASUREMENT AND ACTUAL SIZE OF URETERAL CALCULI B. Otnes and H . Sandnes From the S c ~ v i o no j Urology und Depurtrnant oJ’Rudio1og.v. Univi,rsity oj Oslo, Akershus Cenirul Hospitul. Nordhyhugen, Nor\t,uy
Scand J Urol Nephrol Downloaded from informahealthcare.com by York University Libraries on 07/01/14 For personal use only.
(Submitted for publication December 15, 1977)
Ahstruct. 100 ureteral calculi were measured on X-ray films and directly on the stone after passage or removal. The largest diameters were compared. The size of the stone was radiologically overestimated for 59 stones, correct for 26 and underestimated for 15. 73 of the stones were radiologically measured within +25% of the actual size.
The radiological measurement of ureteral calculi is of interest for estimation of the probability of spontaneous passage. Stones less than 4 mm in diameter, as measured on X-ray films, have been observed to pass spontaneously in up to 91 r/r of cases, while stones 6 mm or larger have a 6 % chance of spontaneous passage ( S a n d e g M , 1956). Such estimates may serve as a rough guide to the handling of patients with ureteral calculi, although other factors such as the degree and duration of obstruction and pain or the presence of infection often assume overriding importance.
MATERIAL AND METHOD In order to evaluate the reliability of such radiological measurements we have compared the actual size of stones with measurements obtained from X-ray films in a material of ureteral calculi collected from June 1975 till October 1977. All stones obtained during this period, whether by spontaneous passage o r surgical removal, were considered for inclusion in the study. The criteria for selection were: I ) stone removed o r passed without fragmentation, 2) stone present as a definite radioopaque finding on X-ray films, 3) conviction that the stone obtained was the one actually measured on the X-ray film. The radiological measurements were done retrospectively without knowledge of the actual size of the stone. They were performed on plain films or intravenous pyelograms taken in the supine position, with the distance from X-ray tube to film being a s a rule 100 cm. T w o diameters were noted but only the larger is used in this report. The actual size of the stone was obtained from the
reports of the laboratory (Beck Analytical Services. Bloomington, Indiana, U . S . )to which the stones had been sent for crystallographic analysis. These reports include exact measurements in three diameters. with photographic corroboration showing the stone placed on millimeter paper. Only the largest diameter was used. All measurements, radiological and actual. were rounded to the nearest millimeter. Classification by shape of the stone was attempted both on the X-ray films and the actual stones, but it was found impossible to be consistent. All stones contained calcium oxalate and/or calcium phosphate. One stone consisted of triple phosphate and two had minute inclusions (less than 3 per cent) of uric acid in addition to major calcium oxalate.
RESULTS 100 stones were measured on X-ray films and the measurements compared to those reported by the analyzing laboratory. Fig. I shows the number of stones found for each given combination of actual size and radiological measurement. Twenty-six stones had the same size in actual and radiological measurements. Thirty-seven stones deviated from the actual size by one millimeter only. The maximal deviation found was 4 mm radiological overestimation of stones of which the largest diameters actually were 2, 7 and 13 mm respectively. The X-rays for stones which showed great discrepancy between actual and radiologically measured size were independently reevaluated without any significant error being found in the original registrations. When the radiologically measured diameter was markedly smaller than the largest real diameter, better approximation was regularly found to one of the other two diameters reported by the analyzing laboratory. It is apparent that overestimation was more frequent than underestimation (Fig. I ) . Fifty-nine stones were radiologically overestimated, 15 were
156
B. Ottrc’.s trntl H . Strndncs
17 16 15
I 1
No. of stones
,’
14
2 2 I /
13. 12 I
II.
10. 9. 8 7
3 I I/
2 3,22 1 6 6 b 2
1
Overestimdtron More thdn 25 ‘/i 2 5 % or k5s Correct measurement Underestimation 25 75 or les5
I
More than 25 %
!LLL-.-
Total
Scand J Urol Nephrol Downloaded from informahealthcare.com by York University Libraries on 07/01/14 For personal use only.
2
I
2 3 L 5 6 7 8 9 10 II 12 13mm Actual
20 39 26 8 7 I00
size
Fig. 1. The number of stones found for each given combination of actual size and radiological measurement. The number of stones with equal findings for the two types of
measurement is indicated by the oblique line.
underestimated. When the radiological error was calculated as percentage of the actual size (Table 1). it was found that 73 stones were measured within k25%’ of the actual size. When measured on the X-rays, 39 stones were located in the upper ureter (above the linea terminalis) and 61 in the lower ureter. The radiological error was not significantly different for stones in the two parts of the ureter. DISC U SSl ON A difference between radiological measurement and actual size of stones is not unexpected. One contributory factor must be orthograde projection of elongated stones. leading to underestimation. Another is the divergent course of X-rays from the stone t o the film with consequent overestimation.
The latter was most frequently found and is t o some extent expected by clinicians. Difficulties in distinction between the outline of the stone and acijacent bony structures o r phleboliths may account for some erroneous measurements. Although all possible care has been taken to exclude fragmented stones from this study occasional reduction in size during removal o r passage from breaking off of fragile parts of the stone may have occurred. Radiological measurement is the only clue t o the size of the stone available to the clinician. and it provides a useful but far from absolute indicator for treatment in a given case of ureteral stone. This study shows that the majority of radiological measurements are within ? 2 5 % of the actual size of stones, but there are occasional gross errors of estimation. REFERENCE SandegBrd, E. 1956. Prognosis of stone in the ureter. Actti C’hir Scand. Suppl. 219.
