THE JOURNAL OF UROLOGY
Vol. 116, October
Copyright © 1976 by The Williams & Wilkins Co.
Printed in U.S.A.
Original Articles ECTOPIC RENAL OSSIFICATION AS NUCLEUS OF URINARY STONES L. CIFUENTES DELATTE, J. L. R. MINON, M. SANTOS
AND
M. L. TRABA
From the Urolithiasis Laboratory, Department of Urology, Fundacion Jimenez Dfoz, Universidad Autonoma, Madrid, Spain
ABSTRACT
Areas of ectopic ossification were found in thin sections from 19 of 1,624 calculi submitted to a petrographic procedure, an incidence of 1.16 per cent. Only 8 calculi of renal, pelvic or ureteral origin with osseous tissue in its structure have been described since the first report by Phemister in 1923. The osteogenic capability of urothelium has been known for some time. Blessig was the first to find calcified tissue beneath the epithelium of the renal pelvis in rabbits, after having ligated the vascular pedicle of the kidney. 1 Sacerdotti and Frattin discovered ectopic osseous tissue when they performed a double ligature in the left renal vascular pedicle in 4 rabbits and also sectioned the vessels, leaving the kidney in situ. 2 The animals were killed 3 months later and the ischemic kidneys were removed. The kidney volume had decreased to a tenth of its previous volume in 2 animals in which calcified but no osseous areas were found. In 2 other rabbits the volume of the kidneys was reduced by two-thirds and the authors found typical osseous tissue with osseous laminae, lacunae, osteocytes and tissue analogous to that of the bone marrow. The bone formation was located mainly beneath the epithelium of the papillae and in the mucosa of the renal pelvis. 2 It is plausible that a marked ischemia causes renal atrophy with tissue calcification but the persistency of a residual blood irrigation through the ureter and the renal pelvic vessels or the establishment of a collateral circulation after ligating the main vessels would favor an active osseous metaplasia rather than a calcification. Huggins also experimented on ectopic osteogenesis and confirmed the appearance of osseous tissue after the performance of subcutaneous grafts of vesical and renal pelvic epithelium. He first observed the formation of small cysts that underwent calcification by small steps to become finally organized in typical osseous tissue. 3 In 1923 Phemister reported for the first time the finding of 3 kidney stones in connection with heterotopic renal ossification.• A thorough survey of the literature did not reveal a previous report on osseous tissue related to urinary calculi. His studies were done on 2 men, 36 and 34 years old. In the first patient he found a renal stone with osseous tissue and in the second he removed 2 concretions with zones of ossification. The 3 stones from the 2 patients were in close and direct relationship with the walls of the renal pelvis and 1 calix. In the calcified zones spongy bone, osseous marrow, connective tissue and capillaries were detected. Both patients had undergone nephrectomy and it was in the pathological examination of the operative specimens that the presence of osseous tissue was found in the stone of 1 and in the 2 calculi of the other. In the 50 years since Phemister's report there have been only 4 other reports of osseous tissue in renal and ureteral stones. •-a
Until 1971 there had been 5 reports with a total of 8 observations of bone nuclei in urinary stones. In 1973 we described another 5 stones showing inner zones of osseous tissue.• Since then we have found 14 more stones of this type, which equals 19 observations in addition to the previously reported 8 in the world literature, totaling 27 instances of bone in urinary stones. MATERIAL AND METHODS
From October 1971 to December 1974 we analyzed 1,693 stones, of which 1,018 were studied in thin sections under the polarized light microscope. 10 Another 606 stones from the collection of the late Dr. P. Cifuentes, gathered between 1914 and 1949, were also analyzed using the same procedure. Among these 1,624 stones studied by the petrographic method of thin sections we found 19 to contain osseous tissue in their inner core, an incidence of 1.16 per cent. Of these stones 16 were renal, 1 ureteral and 2 vesical, the latter of renal origin perhaps. We found 8 specimens in male patients and 11 in female patients, 1 of whom had hyperparathyroidism. The thin sections had a mean thickness of 20 mµ. Among the studied specimens 10 calculi (5 in male and 5 in female patients) were from Doctor Cifuentes' collection and 9 stones (3 in male and 6 in female patients) were removed by surgical procedures from October 1969 to December 1974. Radiologically, some appeared irregular and spongy but others had no specific characteristics. One was a curious Jack-stone located in the renal pelvis. One of the renal stones was removed from a female patient with primary hyperparathyroidism who later underwent an operation for parathyroid adenoma.
Accepted for publication November 26, 1975.
398
DISCUSSION
The osseous tissue found in urinary stones is pale and grayish-blue when observed in thin section under the microscope with crossed Polaroid. In addition to this feature typical osteocytic lacunae with thin and long canaliculi can be observed (figs. 1 and 2). These 2 traits must exist if a structure in a stone is to be accepted as typical osseous tissue. In a previous paper we reported finding structures with the same grayish-blue color under Polaroid but without lacunae in prostatic and renal stones. 11 They were similar to the preosseous acellular tissue, called aspidin by Gross 12 and studied by other authors. 13• 14 In the calcium phosphate stones of spherulitic structure certain images we call pseudo-lacunae
ECTOPIC RENAL OSSIFICATION AS NUCLEUS OF URINARY STONES
399
Fm. 1. A, thin section of renal stone as seen under crossed polaroids. Central nucleus is ectopic osseous tissue. Reduced from x 12. B, higher magnification of area of same stone shows osseous trabeculae and layer of calcium phosphate deposited upon nucleus. Reduced from x52.
are noted frequently. Occasionally, they are similar to the true osteocytic lacunae but they lack the typical canaliculi and appear also in zones of the stone in which spherulitic calcium phosphate, which does not yield the typical grayish-blue color of the osseous tissue, is present. The number of stones with pseudo-lacunae outnumbered that of stones in which we found true osseous tissue. We point out this fact to avoid confusion among those interested in the study of renal stones by the thin section method (fig. 3). Some of the stones containing osseous tissue were decalcified and again we were able to ascertain the diagnosis by histologic methods, finding an organic matrix in which the shape of osteocytic lacunae and thin canaliculi remained. Whenever a nucleus of renal ectopic ossification with a secondary stone on it is dislodged from its position in a papilla or in the wall of one of the excretor ducts of the urinary system, the osteocytes cannot survive because they are deprived of the interstitial fluid they have been receiving in living tissues. However, the lacunae remain. The finding of an osseous structure in the plane corresponding to the petrographic thin section of a renal stone only implies a factor of pure hazard. We are convinced that perhaps the proportion is more than 2 per cent of all urinary stones
since our findings were merely casual, while it might happen that in some stones the osseous structure would have been at different levels of the analyzed thin section. From the viewpoint of renal lithogenesis we should underline the possibility that a certain number of papillary calcifications similar to Randall's plaques might be ossified. A calcification formed by apatite calcium phosphate in close connection with the collagen and the papillae, in the presence of ossification inductors that seem to rise from the mucosa of the excretory ducts of the urinary system, is already a mineral phase prone to the formation of ectopic osseous tissue. The chemical analysis and the infrared or x-ray spectrography do not reveal anything in these zones other than the existence of calcium phosphate. The identification of ectopic osseous tissue is only possible by morphological methods. Those stones in which osseous structures were found, as reported before our studies, were fixed in the wall of the renal pelvis or ureter and, therefore, the existence of a lesion advocating a histopathologic study was suspected. The existence in those cases of a primitive osseous metaplasia that had served as a nucleus for the development of a true urinary stone was demonstrated. In our studies we found only calcium salts forming the stone
400
DELATTE AND ASSOCIATES
and other regions of the mucosa of the excretory ducts is an exceptional finding stand our 19 cases of osseous nuclei found by sheer hazard, thanks to the systematic use of thin sections for the study of the urinary stone structures and composition. As mentioned previously this proportion of 1.16 per cent might be lower than normal. In addition to the Randall's calcified nuclei 1 ' and those of lymphatic origin described by Carr 16 the heterotopic ossification should be included among the pathological factors that induce lithogenesis. Upon the primitive focus of ossification, which is the origin nucleus of the stone, the most commonly calculous compound we have found deposited is the calcium oxalate monohydrate, because it is a substance that precipitates more spontaneously upon a previous pathologic nucleus that has split the normal continuity of healthy urotheliurn. Whewellite or calcium oxalate monohydrate stones are found often in patients with neither hypercalciuria nor hyperoxaluria and it is assumed that they are of slow growth, contrary to those in which calcium oxalate dihydrate predominates. 17 REFERENCES
FIG. 2. A, haversian canal-like structure in osseous tissue nucleus of another stone. Reduced from x200. B, higher magnification shows osteocytic lacunae and canaliculi, and layer of calcium phosphate on top. Reduced from x 400.
FIG. 3. Pseudo-lacunae among apatite calcium phosphate spherulites in renal stone. Reduced from x300.
(primarily calcium oxalate monohydrate) but we never found uric acid or urates deposited on the primitive osseous nuclei. When pathologists become more aware of these problems more cases of stone formation on ectopic ossification zones of the renal papillae will be found. Against the commonly accepted assumption that an osseous metaplasia in the kidney
1. Blessig: Ueber die Veranderungen der Niere nach unterbindung der Nierenarterie. Virchows Arch. Path. Anat., 16: 120, 1859. 2. Sacerdotti, C. and Frattin, G.: Ueber die heteroplastische Knochenbildung: Experimentelle Untersuchungen. Virchows Arch., 168: 431, 1902. 3. Huggins, C. B.: The formation of bone under the influence of epithelium of the urinary tract. Arch. Surg., 27: 203, 1933. 4. Phemister, D. B.: Ossification in kidney stones attached to the renal pelvis. Ann. Surg., 78: 239, 1923. 5. Hellstrom, J.: Ein Fall von metaplastischer Knochenbildung in der Niere im zusammenhang mit Nierenstein. Z. Urol., 25: 401, 1931. 6. Huggins, C. B.: Bone and calculi in the collecting tubules of the kidney. Arch. Surg., 27: 203, 1933. 7. Klinger, M. E.: Bone formation in the ureter: a case report. J. Urol., 75: 793, 1956. 8. Schulman, C. C. and Weiser, M.: Formation osseuse pyelique. Acta Urol. Belg., 39: 322, 1971. 9. Cifuentes Delatte, L., Hidalgo, A., Bellanato, J. and Santos, M.: Polarization microscopy and infrared spectroscopy of thin sections of calculi. In: Urinary Calculi: Recent Advances in Aetiology, Stone Structure and Treatment. Edited by L. Cifuentes Delatte, A. Rapado and A. Hodgkinson. Basel: S. Karger, p. 220, 1973. 10. Cifuentes Delatte, L., Garcia de la Pena, E., Vela Navarrete, R. and R.-Miii6n Cifuentes, J.: Tejido oseo en calculos de! aparato urinario (cinco observaciones). Arch. Esp. Urol., 26: 457, 1973. 11. Cifuentes Delatte, L., Rapado, A., Santos, M. and Traba, M. L.: Estructuras oseas y preoseas en calculos de! aparato urinario. Rev. Clin. Esp., 131: 181, 1973. 12. Gross, W.: Die Fische des mittleren Old Red Siid-Livlands. Geo!. Palaont. Abh., 18: 123, 1930. 13. Halstead, L. B.: Aspidin, the precursor of bone. Nature, 199: 46, 1963. 14. Halstead, L. B.: Calcified tissues in the earliest vertebrates. Cale. Tiss. Res., 3: 107, 1969. 15. Randall, A.: The etiology of primary renal calculus. In: Proceedings of the VII Congress of the International Society of Urology, New York, 1939. 16. Carr, R. J.: A new theory on the formation of renal calculi. Brit. J. Urol., 26: 105, 1954. 17. Berenyi, M., Frang, D. and Legrady, J.: Theoretical and clinical importance of the differentiation between the two types of calcium oxalate hydrate. Int. Ural. Nephrol., 4: 341, 1972. COMMENT There can be little doubt that the sections presented appear to be osseous tissue of ectopic origin. This osseous tissue is located in the center of the calculi illustrated. As such, they certainly should represent ectopic bone. It would be nice to confirm the tissue as bone
Vol. 116, October
Copyright © 1976 by The Williams & Wilkins Co.
Printed in U.S.A.
Original Articles ECTOPIC RENAL OSSIFICATION AS NUCLEUS OF URINARY STONES L. CIFUENTES DELATTE, J. L. R. MINON, M. SANTOS
AND
M. L. TRABA
From the Urolithiasis Laboratory, Department of Urology, Fundacion Jimenez Dfoz, Universidad Autonoma, Madrid, Spain
ABSTRACT
Areas of ectopic ossification were found in thin sections from 19 of 1,624 calculi submitted to a petrographic procedure, an incidence of 1.16 per cent. Only 8 calculi of renal, pelvic or ureteral origin with osseous tissue in its structure have been described since the first report by Phemister in 1923. The osteogenic capability of urothelium has been known for some time. Blessig was the first to find calcified tissue beneath the epithelium of the renal pelvis in rabbits, after having ligated the vascular pedicle of the kidney. 1 Sacerdotti and Frattin discovered ectopic osseous tissue when they performed a double ligature in the left renal vascular pedicle in 4 rabbits and also sectioned the vessels, leaving the kidney in situ. 2 The animals were killed 3 months later and the ischemic kidneys were removed. The kidney volume had decreased to a tenth of its previous volume in 2 animals in which calcified but no osseous areas were found. In 2 other rabbits the volume of the kidneys was reduced by two-thirds and the authors found typical osseous tissue with osseous laminae, lacunae, osteocytes and tissue analogous to that of the bone marrow. The bone formation was located mainly beneath the epithelium of the papillae and in the mucosa of the renal pelvis. 2 It is plausible that a marked ischemia causes renal atrophy with tissue calcification but the persistency of a residual blood irrigation through the ureter and the renal pelvic vessels or the establishment of a collateral circulation after ligating the main vessels would favor an active osseous metaplasia rather than a calcification. Huggins also experimented on ectopic osteogenesis and confirmed the appearance of osseous tissue after the performance of subcutaneous grafts of vesical and renal pelvic epithelium. He first observed the formation of small cysts that underwent calcification by small steps to become finally organized in typical osseous tissue. 3 In 1923 Phemister reported for the first time the finding of 3 kidney stones in connection with heterotopic renal ossification.• A thorough survey of the literature did not reveal a previous report on osseous tissue related to urinary calculi. His studies were done on 2 men, 36 and 34 years old. In the first patient he found a renal stone with osseous tissue and in the second he removed 2 concretions with zones of ossification. The 3 stones from the 2 patients were in close and direct relationship with the walls of the renal pelvis and 1 calix. In the calcified zones spongy bone, osseous marrow, connective tissue and capillaries were detected. Both patients had undergone nephrectomy and it was in the pathological examination of the operative specimens that the presence of osseous tissue was found in the stone of 1 and in the 2 calculi of the other. In the 50 years since Phemister's report there have been only 4 other reports of osseous tissue in renal and ureteral stones. •-a
Until 1971 there had been 5 reports with a total of 8 observations of bone nuclei in urinary stones. In 1973 we described another 5 stones showing inner zones of osseous tissue.• Since then we have found 14 more stones of this type, which equals 19 observations in addition to the previously reported 8 in the world literature, totaling 27 instances of bone in urinary stones. MATERIAL AND METHODS
From October 1971 to December 1974 we analyzed 1,693 stones, of which 1,018 were studied in thin sections under the polarized light microscope. 10 Another 606 stones from the collection of the late Dr. P. Cifuentes, gathered between 1914 and 1949, were also analyzed using the same procedure. Among these 1,624 stones studied by the petrographic method of thin sections we found 19 to contain osseous tissue in their inner core, an incidence of 1.16 per cent. Of these stones 16 were renal, 1 ureteral and 2 vesical, the latter of renal origin perhaps. We found 8 specimens in male patients and 11 in female patients, 1 of whom had hyperparathyroidism. The thin sections had a mean thickness of 20 mµ. Among the studied specimens 10 calculi (5 in male and 5 in female patients) were from Doctor Cifuentes' collection and 9 stones (3 in male and 6 in female patients) were removed by surgical procedures from October 1969 to December 1974. Radiologically, some appeared irregular and spongy but others had no specific characteristics. One was a curious Jack-stone located in the renal pelvis. One of the renal stones was removed from a female patient with primary hyperparathyroidism who later underwent an operation for parathyroid adenoma.
Accepted for publication November 26, 1975.
398
DISCUSSION
The osseous tissue found in urinary stones is pale and grayish-blue when observed in thin section under the microscope with crossed Polaroid. In addition to this feature typical osteocytic lacunae with thin and long canaliculi can be observed (figs. 1 and 2). These 2 traits must exist if a structure in a stone is to be accepted as typical osseous tissue. In a previous paper we reported finding structures with the same grayish-blue color under Polaroid but without lacunae in prostatic and renal stones. 11 They were similar to the preosseous acellular tissue, called aspidin by Gross 12 and studied by other authors. 13• 14 In the calcium phosphate stones of spherulitic structure certain images we call pseudo-lacunae
ECTOPIC RENAL OSSIFICATION AS NUCLEUS OF URINARY STONES
399
Fm. 1. A, thin section of renal stone as seen under crossed polaroids. Central nucleus is ectopic osseous tissue. Reduced from x 12. B, higher magnification of area of same stone shows osseous trabeculae and layer of calcium phosphate deposited upon nucleus. Reduced from x52.
are noted frequently. Occasionally, they are similar to the true osteocytic lacunae but they lack the typical canaliculi and appear also in zones of the stone in which spherulitic calcium phosphate, which does not yield the typical grayish-blue color of the osseous tissue, is present. The number of stones with pseudo-lacunae outnumbered that of stones in which we found true osseous tissue. We point out this fact to avoid confusion among those interested in the study of renal stones by the thin section method (fig. 3). Some of the stones containing osseous tissue were decalcified and again we were able to ascertain the diagnosis by histologic methods, finding an organic matrix in which the shape of osteocytic lacunae and thin canaliculi remained. Whenever a nucleus of renal ectopic ossification with a secondary stone on it is dislodged from its position in a papilla or in the wall of one of the excretor ducts of the urinary system, the osteocytes cannot survive because they are deprived of the interstitial fluid they have been receiving in living tissues. However, the lacunae remain. The finding of an osseous structure in the plane corresponding to the petrographic thin section of a renal stone only implies a factor of pure hazard. We are convinced that perhaps the proportion is more than 2 per cent of all urinary stones
since our findings were merely casual, while it might happen that in some stones the osseous structure would have been at different levels of the analyzed thin section. From the viewpoint of renal lithogenesis we should underline the possibility that a certain number of papillary calcifications similar to Randall's plaques might be ossified. A calcification formed by apatite calcium phosphate in close connection with the collagen and the papillae, in the presence of ossification inductors that seem to rise from the mucosa of the excretory ducts of the urinary system, is already a mineral phase prone to the formation of ectopic osseous tissue. The chemical analysis and the infrared or x-ray spectrography do not reveal anything in these zones other than the existence of calcium phosphate. The identification of ectopic osseous tissue is only possible by morphological methods. Those stones in which osseous structures were found, as reported before our studies, were fixed in the wall of the renal pelvis or ureter and, therefore, the existence of a lesion advocating a histopathologic study was suspected. The existence in those cases of a primitive osseous metaplasia that had served as a nucleus for the development of a true urinary stone was demonstrated. In our studies we found only calcium salts forming the stone
400
DELATTE AND ASSOCIATES
and other regions of the mucosa of the excretory ducts is an exceptional finding stand our 19 cases of osseous nuclei found by sheer hazard, thanks to the systematic use of thin sections for the study of the urinary stone structures and composition. As mentioned previously this proportion of 1.16 per cent might be lower than normal. In addition to the Randall's calcified nuclei 1 ' and those of lymphatic origin described by Carr 16 the heterotopic ossification should be included among the pathological factors that induce lithogenesis. Upon the primitive focus of ossification, which is the origin nucleus of the stone, the most commonly calculous compound we have found deposited is the calcium oxalate monohydrate, because it is a substance that precipitates more spontaneously upon a previous pathologic nucleus that has split the normal continuity of healthy urotheliurn. Whewellite or calcium oxalate monohydrate stones are found often in patients with neither hypercalciuria nor hyperoxaluria and it is assumed that they are of slow growth, contrary to those in which calcium oxalate dihydrate predominates. 17 REFERENCES
FIG. 2. A, haversian canal-like structure in osseous tissue nucleus of another stone. Reduced from x200. B, higher magnification shows osteocytic lacunae and canaliculi, and layer of calcium phosphate on top. Reduced from x 400.
FIG. 3. Pseudo-lacunae among apatite calcium phosphate spherulites in renal stone. Reduced from x300.
(primarily calcium oxalate monohydrate) but we never found uric acid or urates deposited on the primitive osseous nuclei. When pathologists become more aware of these problems more cases of stone formation on ectopic ossification zones of the renal papillae will be found. Against the commonly accepted assumption that an osseous metaplasia in the kidney
1. Blessig: Ueber die Veranderungen der Niere nach unterbindung der Nierenarterie. Virchows Arch. Path. Anat., 16: 120, 1859. 2. Sacerdotti, C. and Frattin, G.: Ueber die heteroplastische Knochenbildung: Experimentelle Untersuchungen. Virchows Arch., 168: 431, 1902. 3. Huggins, C. B.: The formation of bone under the influence of epithelium of the urinary tract. Arch. Surg., 27: 203, 1933. 4. Phemister, D. B.: Ossification in kidney stones attached to the renal pelvis. Ann. Surg., 78: 239, 1923. 5. Hellstrom, J.: Ein Fall von metaplastischer Knochenbildung in der Niere im zusammenhang mit Nierenstein. Z. Urol., 25: 401, 1931. 6. Huggins, C. B.: Bone and calculi in the collecting tubules of the kidney. Arch. Surg., 27: 203, 1933. 7. Klinger, M. E.: Bone formation in the ureter: a case report. J. Urol., 75: 793, 1956. 8. Schulman, C. C. and Weiser, M.: Formation osseuse pyelique. Acta Urol. Belg., 39: 322, 1971. 9. Cifuentes Delatte, L., Hidalgo, A., Bellanato, J. and Santos, M.: Polarization microscopy and infrared spectroscopy of thin sections of calculi. In: Urinary Calculi: Recent Advances in Aetiology, Stone Structure and Treatment. Edited by L. Cifuentes Delatte, A. Rapado and A. Hodgkinson. Basel: S. Karger, p. 220, 1973. 10. Cifuentes Delatte, L., Garcia de la Pena, E., Vela Navarrete, R. and R.-Miii6n Cifuentes, J.: Tejido oseo en calculos de! aparato urinario (cinco observaciones). Arch. Esp. Urol., 26: 457, 1973. 11. Cifuentes Delatte, L., Rapado, A., Santos, M. and Traba, M. L.: Estructuras oseas y preoseas en calculos de! aparato urinario. Rev. Clin. Esp., 131: 181, 1973. 12. Gross, W.: Die Fische des mittleren Old Red Siid-Livlands. Geo!. Palaont. Abh., 18: 123, 1930. 13. Halstead, L. B.: Aspidin, the precursor of bone. Nature, 199: 46, 1963. 14. Halstead, L. B.: Calcified tissues in the earliest vertebrates. Cale. Tiss. Res., 3: 107, 1969. 15. Randall, A.: The etiology of primary renal calculus. In: Proceedings of the VII Congress of the International Society of Urology, New York, 1939. 16. Carr, R. J.: A new theory on the formation of renal calculi. Brit. J. Urol., 26: 105, 1954. 17. Berenyi, M., Frang, D. and Legrady, J.: Theoretical and clinical importance of the differentiation between the two types of calcium oxalate hydrate. Int. Ural. Nephrol., 4: 341, 1972. COMMENT There can be little doubt that the sections presented appear to be osseous tissue of ectopic origin. This osseous tissue is located in the center of the calculi illustrated. As such, they certainly should represent ectopic bone. It would be nice to confirm the tissue as bone
