Heterometaplastic Bone Formation In Nephrolithiasis: Critical Review Of Pathology And Pathogenetic Mechanisms

Abstract

Background: We critically analyze the incidence, presentation and histopathologic findings of heterometaplastic bone formation(HBF) in nephrolithiasis in the kidneys of patients undergoing percutaneous nephrolithitomy for stone disease. Methods: Percutaneous nephrolithitomy( PCNL) was performed on 932 patients from August 2009 to Oct.2016 by a single surgeon(1,2). In 43 cases, heterometaplastic bone formation was seen to originate from urothelium and encompassing the renal calculi. Clinical workup, radiographic imaging, treatment modalities and histopathologic features in these patients were evaluated. Result:The patients’ age ranged from 14 years to 65 years (median age 33.7 years). The male to female ratio was 4.3: 1.Heterometaplastic bone formation (HBF) encompassing the stone was identified in 69.76% in right kidney, 25.58% in left kidney and 4.65% in both kidneys . Radiographic appearance of eccentric density surrounding hypodense area was observed in 32 of 43 cases(74.41%). Histopathological evaluation showed trabecular bone with surface osteoblastic activity and intra trabecular bone marrow, haemopoietic cells and adipose tissue encompassing birefringent crystal deposits in 22 cases (51.16%). Trabecular bone in intimate proximity of woven bone and haemopoietic cell islands partially encompassing birefringent crystal deposits was observed in 17 cases (39.53%). Woven bone with mineral deposits and fibro collagenous proliferation was seen in 4 cases (9.30%).Conclusion:Although reported infrequently, HBF in nephrolithiatic deposits has a high incidence in our patients. Pathogenetic mechanisms regarding transdifferentiating renal stem cells appears tenable in such a setup and is corroborated in our study.