British Journal of Urology (1975). 41, 125-129
The Residual Renal Stone MANMEET SINGH, VILLIS MARSHALL
and
JOHN BLANDY
The London Hospital, London
If it is true, as is so often said, that the least fragment of stone left behind in a kidney after operation will lead to a recurrence of the calculus, then many operations for stones in the kidney are a waste of time. This has not been our clinical experience: on the contrary, the improvement in the patient’s symptoms, in the function of the kidney, and in the control of urinary infection more than outweigh the risk of. recurrence of the stone. Moreover, recurrence of stone is not inevitable when a fragment has been left behind : nor does complete removal of a stone guarantee that a stone will not recur (Singh et al., 1971, 1973). Experience gained in the course of operations on more than 120 large staghorn calculi over the course of 10 years has also made us sceptical as to the accuracy of complete clearance of a kidney, for we have often felt tiny particles of grit in the lining of the renal pelvis and calyces even when the preoperative radiograph appears to be clear, and biopsies of the kidney frequently show calcification in the renal parenchyma itself (Figure).
Figure. Biopsy of kidney showing calcification in the renal parenchyma.
Read at the 30th Annual Meeting of the British Association of Urological Surgeons in Torquay, June 1974. 47/2-~
125
126
BRITISH JOURNAL OF U R O u x i Y
We thought it would be useful to examine critically the accuracy and the range of observer error in interpretation of peroperative radiographs of the kidney, and then, armed with this information, to look again at what has happened to known fragments of stone left behind after operations for staghorn calculi. Observer Error in Preoperative Radiographs of the Kidney Method Small measured pieces from a staghorn calculus (mixed calcium magnesium phosphate and carbonate) were placed in a cadaver kidney and X-rayed. The pieces were of various sizes: the small ones were 1 x 1 mm, the larger ones 2 x 3 mm and 2 x 2 mm as measured with a micrometer screw gauge. They were placed within the kidney in 14 different combinations which were accurately charted and recorded, and X-rays were made using 2 different exposures (70 Kv 100 mA 0.3 sec and 65 Kv 100 mA 0-25 sec). The film used was the standard Kodak “kidney” contact film used in peroperative radiography. The resulting 28 films were shown to 6 experienced observers (4 surgeons and 2 radiologists) all well-used to looking at these films. The radiographs were read in a random order, and each observer marked the position and size of the calculi on a blank sheet bearing the outline and calyceal pattern of 28 kidneys.
Table I X-ray Readings 28 X-rays per person (76 stones in 28 X-rays) No. of X-rays No. of X-rays No. of X-rays Observer read correctly stones missed false positive 1 2 3 4 5
6
16 16 8 12 14 8
9 9 11 10 9 18
3 3 9 6 5 2
74 (44%)
66 (39.2%)
28 (16)
Table 11 Total Number of Stones 1. Available for diagnosis to 6 observers
2. Size distribution A - 3 x 2 ~ 2x2 2x 1 B-1x1 m m
6 x 76 = 456
264 192
Total
456
127
THE RESIDUAL RENAL STONE
Results Each observer was shown 28 films, and so 168 observations were recorded. Only 44% of the observations were correct. In 39.3% of the X-rays stones were missed and stones which were not there were marked down in 16% (Table I). Since 76 stones altogether had been “seeded” in the 28 films, the observers should have detected 7 6 x 6 = 456 stones (Table 11). In fact they missed 104 stones-all but one of them being the small 1 x 1 mm particles (Table 111). Only 37.3% of these 1 x 1 mm particles were correctly detected, but when the calculi were larger (2 x 2 or 2 x 3 mm) 99.5 % of them were correctly detected. (The difference is statistically significant P < 0,002.) Because the observer error was so great when the particles were small, it was possible to look at only the observations in the larger calculi to consider how correctly they had been positioned : 79.6 % of them were located correctly. There was no significant difference in the correctness of observations when the two different X-ray exposures were compared, nor when the first 14 observations of each observer were compared with the last. This study clearly shows that the conventional radiographic diagnosis of small calculi is only accurate when the particles are larger than 1 mm in diameter, even in the ideal circumstances of this test. In the less favourable conditions of the operating theatre, when the films are often less correctly positioned and exposed, the accuracy is likely to be even worse. Particles 1 mm or smaller in diameter are very likely to go undetected.
The Fate of the Residual Fragment of Stone Over the last 10 years 120 large branched staghorn calculi have been removed from 100 patients, 20 of them with bilateral stones (Table IV). As judged by peroperative contact X-rays and the
Table III Number of Stones Missed Category
A
2x 1 m m and bigger
B
lxlmm
103/264
Total
*
1/192
104/456
*04)05% *39*4% = 22.8%
Difference between A and B is statistically significant P < 0.002.
Table IV Extended Pyelolithotomy for Staghorn Calculi the London Hospital 1964-74
Unilateral Bilateral Total
Patients
Kidneys
80 20
80 40
100
120
128
BRITISH JOURNAL OF UROLOGY
postoperative films there was an incomplete removal of stone in 29 kidneys (24.4 %). In 6 kidneys the particles were 1 x 1 mm or less in diameter: in the other 23 the fragments were larger than 2 mm across (Table V). Residual Calculi In the 6 kidneys with the small particles less than 1 mm across, no change was seen in the followup period in 5 of them, and 1 of the kidneys became cleared entirely (as judged by successive radiographs over the years) (Table VI). In the 23 kidneys with the larger fragments there were 8 in whom the original removal had been particularly difficult, and larger and often multiple fragments had been left behind : these were the only fragments which could be seen to act as the nucleus for subsequent new stone growth. 5 of the 23 incompletely cleared kidneys subsequently got rid of the fragments which had been left behind. In 9 kidneys the residual fragments remained quite unchanged but it was interesting to note that in 2 of these 9 kidneys a new calculus formed elsewhere in the kidney but not on the original residual fragment.
Table V Staghorn Calculi-Completeness of Removal Complete removal Incomplete removal Fragments bigger than 2 x 2 mm Dust measuring 1 x 1 mm or less
91 kidneys (75.6 %) 29 kidneys (24.4 %) 23 kidneys 6 kidneys
Table M Fate of Kidneys Incompletely Cleared 8 regrowth (34.7 %) 23 kidneys with fragments *10 unchanged (43.4%) 5 passed (21.9%) 6 kidneys with dust
*
{
‘lea red
}No recurrence of stone
5 unchanged
In 2 kidneys the fragments remained unchanged but there was new stone formation.
Bilateral Staghorn Calculi These 20 patients form an interesting group. In 12 patients both kidneys were completely cleared, and have remained clear during the period of the follow up. In 8 patients only 1 of the pair of kidneys was completely cleared, so that 1 kidney acts as a control for the other. Of the 8 kidneys which were completely cleared, 4 developed a recurrent calculus, 1 became nonfunctioning, and 3 have kept clear of recurrent stone during the period of review. Of the 8 kidneys which were not completely cleared 7 developed a new stone, and in 1 the residual fragments did not grow. In the entire group of 40 kidneys 29 of them either remained clear, or the residual fragment did not grow. It should be added that few of the recurrent stones grew to be staghorn calculi.
129
THE RESIDUAL RENAL STONE
Discussion
It seems very likely that many of those kidneys which we thought were completely cleared of stone did in fact harbour tiny particles of a size which would have gone undetected by peroperative contact radiographs. Even if we could improve the radiographic technique still further, there would still be innumerable tiny foci of calcification in the renal parenchyma and collecting ducts which could act as the nidus for further stone formation. In practice our follow-up suggests that it is by no means disastrous to leave tiny fragments behind, even though it is obviously desirable to get them all out. New stones did not always form on residual fragments, and when new stones did form, it was not always on these fragments acting as nuclei. These results fully support the conventional view that it is advisable to take every reasonable precaution so as to remove calculi as completely as possible, and that leaving large bits behind is apt to be followed by a recurrence of stone. But they do not support the idea that it is futile to attempt to remove a stone unless that removal can be complete. Removing the stone does not cure the patient of stone disease, and the surgeon who sets out to remove a calculus should temper his zeal with some understanding of the natural history of the disease and the limitations of his ability to detect residual calculi. Summary A study of the observer error built in to contact preoperative radiography for renal stones shows that particles less than 2 mm in diameter are likely to be missed. The radiographic follow-up of 100 patients from whom 120 large staghorn calculi have been removed over a period of up to 10 years shows that new calculi may form in kidneys which have been completely cleared, and that residual stones do not always grow, but equally often pass spontaneously, or remain unchanged.
References SINGH,M., TRESIDDER, G . C. and BLANDY, J. P. (1971). The long-term results of removal of staghorn calculi by extended pyelolithotomy without cooling or renal artery occlusion. British Journal of Urology, 43, 658-664. SINGH,M., CHAPMAN, R., TRESIDDER, G . C. and BLANDY, J. P. (1973). The fate of the unoperated staghorn calculus. British Journal of Urology, 45, 581-585.
The Authors Manmeet Singh, FRCS, Senior Lecturer in Urology. Villis Marshall, MD, FRACS, Commonwealth Fellow in Urology. John Blandy, DM, MCh, FRCS, Professor of Urology.
The Residual Renal Stone MANMEET SINGH, VILLIS MARSHALL
and
JOHN BLANDY
The London Hospital, London
If it is true, as is so often said, that the least fragment of stone left behind in a kidney after operation will lead to a recurrence of the calculus, then many operations for stones in the kidney are a waste of time. This has not been our clinical experience: on the contrary, the improvement in the patient’s symptoms, in the function of the kidney, and in the control of urinary infection more than outweigh the risk of. recurrence of the stone. Moreover, recurrence of stone is not inevitable when a fragment has been left behind : nor does complete removal of a stone guarantee that a stone will not recur (Singh et al., 1971, 1973). Experience gained in the course of operations on more than 120 large staghorn calculi over the course of 10 years has also made us sceptical as to the accuracy of complete clearance of a kidney, for we have often felt tiny particles of grit in the lining of the renal pelvis and calyces even when the preoperative radiograph appears to be clear, and biopsies of the kidney frequently show calcification in the renal parenchyma itself (Figure).
Figure. Biopsy of kidney showing calcification in the renal parenchyma.
Read at the 30th Annual Meeting of the British Association of Urological Surgeons in Torquay, June 1974. 47/2-~
125
126
BRITISH JOURNAL OF U R O u x i Y
We thought it would be useful to examine critically the accuracy and the range of observer error in interpretation of peroperative radiographs of the kidney, and then, armed with this information, to look again at what has happened to known fragments of stone left behind after operations for staghorn calculi. Observer Error in Preoperative Radiographs of the Kidney Method Small measured pieces from a staghorn calculus (mixed calcium magnesium phosphate and carbonate) were placed in a cadaver kidney and X-rayed. The pieces were of various sizes: the small ones were 1 x 1 mm, the larger ones 2 x 3 mm and 2 x 2 mm as measured with a micrometer screw gauge. They were placed within the kidney in 14 different combinations which were accurately charted and recorded, and X-rays were made using 2 different exposures (70 Kv 100 mA 0.3 sec and 65 Kv 100 mA 0-25 sec). The film used was the standard Kodak “kidney” contact film used in peroperative radiography. The resulting 28 films were shown to 6 experienced observers (4 surgeons and 2 radiologists) all well-used to looking at these films. The radiographs were read in a random order, and each observer marked the position and size of the calculi on a blank sheet bearing the outline and calyceal pattern of 28 kidneys.
Table I X-ray Readings 28 X-rays per person (76 stones in 28 X-rays) No. of X-rays No. of X-rays No. of X-rays Observer read correctly stones missed false positive 1 2 3 4 5
6
16 16 8 12 14 8
9 9 11 10 9 18
3 3 9 6 5 2
74 (44%)
66 (39.2%)
28 (16)
Table 11 Total Number of Stones 1. Available for diagnosis to 6 observers
2. Size distribution A - 3 x 2 ~ 2x2 2x 1 B-1x1 m m
6 x 76 = 456
264 192
Total
456
127
THE RESIDUAL RENAL STONE
Results Each observer was shown 28 films, and so 168 observations were recorded. Only 44% of the observations were correct. In 39.3% of the X-rays stones were missed and stones which were not there were marked down in 16% (Table I). Since 76 stones altogether had been “seeded” in the 28 films, the observers should have detected 7 6 x 6 = 456 stones (Table 11). In fact they missed 104 stones-all but one of them being the small 1 x 1 mm particles (Table 111). Only 37.3% of these 1 x 1 mm particles were correctly detected, but when the calculi were larger (2 x 2 or 2 x 3 mm) 99.5 % of them were correctly detected. (The difference is statistically significant P < 0,002.) Because the observer error was so great when the particles were small, it was possible to look at only the observations in the larger calculi to consider how correctly they had been positioned : 79.6 % of them were located correctly. There was no significant difference in the correctness of observations when the two different X-ray exposures were compared, nor when the first 14 observations of each observer were compared with the last. This study clearly shows that the conventional radiographic diagnosis of small calculi is only accurate when the particles are larger than 1 mm in diameter, even in the ideal circumstances of this test. In the less favourable conditions of the operating theatre, when the films are often less correctly positioned and exposed, the accuracy is likely to be even worse. Particles 1 mm or smaller in diameter are very likely to go undetected.
The Fate of the Residual Fragment of Stone Over the last 10 years 120 large branched staghorn calculi have been removed from 100 patients, 20 of them with bilateral stones (Table IV). As judged by peroperative contact X-rays and the
Table III Number of Stones Missed Category
A
2x 1 m m and bigger
B
lxlmm
103/264
Total
*
1/192
104/456
*04)05% *39*4% = 22.8%
Difference between A and B is statistically significant P < 0.002.
Table IV Extended Pyelolithotomy for Staghorn Calculi the London Hospital 1964-74
Unilateral Bilateral Total
Patients
Kidneys
80 20
80 40
100
120
128
BRITISH JOURNAL OF UROLOGY
postoperative films there was an incomplete removal of stone in 29 kidneys (24.4 %). In 6 kidneys the particles were 1 x 1 mm or less in diameter: in the other 23 the fragments were larger than 2 mm across (Table V). Residual Calculi In the 6 kidneys with the small particles less than 1 mm across, no change was seen in the followup period in 5 of them, and 1 of the kidneys became cleared entirely (as judged by successive radiographs over the years) (Table VI). In the 23 kidneys with the larger fragments there were 8 in whom the original removal had been particularly difficult, and larger and often multiple fragments had been left behind : these were the only fragments which could be seen to act as the nucleus for subsequent new stone growth. 5 of the 23 incompletely cleared kidneys subsequently got rid of the fragments which had been left behind. In 9 kidneys the residual fragments remained quite unchanged but it was interesting to note that in 2 of these 9 kidneys a new calculus formed elsewhere in the kidney but not on the original residual fragment.
Table V Staghorn Calculi-Completeness of Removal Complete removal Incomplete removal Fragments bigger than 2 x 2 mm Dust measuring 1 x 1 mm or less
91 kidneys (75.6 %) 29 kidneys (24.4 %) 23 kidneys 6 kidneys
Table M Fate of Kidneys Incompletely Cleared 8 regrowth (34.7 %) 23 kidneys with fragments *10 unchanged (43.4%) 5 passed (21.9%) 6 kidneys with dust
*
{
‘lea red
}No recurrence of stone
5 unchanged
In 2 kidneys the fragments remained unchanged but there was new stone formation.
Bilateral Staghorn Calculi These 20 patients form an interesting group. In 12 patients both kidneys were completely cleared, and have remained clear during the period of the follow up. In 8 patients only 1 of the pair of kidneys was completely cleared, so that 1 kidney acts as a control for the other. Of the 8 kidneys which were completely cleared, 4 developed a recurrent calculus, 1 became nonfunctioning, and 3 have kept clear of recurrent stone during the period of review. Of the 8 kidneys which were not completely cleared 7 developed a new stone, and in 1 the residual fragments did not grow. In the entire group of 40 kidneys 29 of them either remained clear, or the residual fragment did not grow. It should be added that few of the recurrent stones grew to be staghorn calculi.
129
THE RESIDUAL RENAL STONE
Discussion
It seems very likely that many of those kidneys which we thought were completely cleared of stone did in fact harbour tiny particles of a size which would have gone undetected by peroperative contact radiographs. Even if we could improve the radiographic technique still further, there would still be innumerable tiny foci of calcification in the renal parenchyma and collecting ducts which could act as the nidus for further stone formation. In practice our follow-up suggests that it is by no means disastrous to leave tiny fragments behind, even though it is obviously desirable to get them all out. New stones did not always form on residual fragments, and when new stones did form, it was not always on these fragments acting as nuclei. These results fully support the conventional view that it is advisable to take every reasonable precaution so as to remove calculi as completely as possible, and that leaving large bits behind is apt to be followed by a recurrence of stone. But they do not support the idea that it is futile to attempt to remove a stone unless that removal can be complete. Removing the stone does not cure the patient of stone disease, and the surgeon who sets out to remove a calculus should temper his zeal with some understanding of the natural history of the disease and the limitations of his ability to detect residual calculi. Summary A study of the observer error built in to contact preoperative radiography for renal stones shows that particles less than 2 mm in diameter are likely to be missed. The radiographic follow-up of 100 patients from whom 120 large staghorn calculi have been removed over a period of up to 10 years shows that new calculi may form in kidneys which have been completely cleared, and that residual stones do not always grow, but equally often pass spontaneously, or remain unchanged.
References SINGH,M., TRESIDDER, G . C. and BLANDY, J. P. (1971). The long-term results of removal of staghorn calculi by extended pyelolithotomy without cooling or renal artery occlusion. British Journal of Urology, 43, 658-664. SINGH,M., CHAPMAN, R., TRESIDDER, G . C. and BLANDY, J. P. (1973). The fate of the unoperated staghorn calculus. British Journal of Urology, 45, 581-585.
The Authors Manmeet Singh, FRCS, Senior Lecturer in Urology. Villis Marshall, MD, FRACS, Commonwealth Fellow in Urology. John Blandy, DM, MCh, FRCS, Professor of Urology.
