Discussion
A migrated metal coil placed for acute post-operative renal hemorrhage four years earlier induced stone formation in this patient with a history of recurrent nephrolithiasis. The stone and the metal coil wires formed a very robust composite, which resisted two ESWL treatments. Identification and immediate treatment of this composite stone was possible during retrograde intrarenal surgery.
The most common early complication of RAE is the post-infarction syndrome, a combination of post-interventional symptoms such as flank pain, fever, nausea and vomiting. It has been reported to occur in approximately 75% of all cases.[4]
Further complications specific to RAE have been reported to occur in 5-10% of the cases.[4,9] Complications can be classified into early and late complications. The most common early complications are groin hematoma, incomplete embolization, coil misplacement and coil migration.[4,10] Late complications are rare and are mainly related to coil migration into the collecting system.
Migration of embolization coils has been reported to occur in less then 2% of all cases.[4] Three cases of symptomatic ureteric obstruction by completely migrated metal coils after up to 1.5 years following RAE have been reported.[5–7] In all cases, the obstructing metal coil had to be removed by ureteroscopy.
It is well known that foreign bodies in the urinary collecting system can induce stone formation.[11] In the present case the foreign body inducing stone formation was a metal coil, which partly migrated into the collecting system. The history of the patient with a myelomeningocele, neurogenic bladder dysfunction, intermittent self-catheterization, recurrent urinary tract infections and right-sided pyelonephritis is suggestive for the development of infection stones. Although the stone analysis after bilateral pyelolithotomy is not available, it is likely that the initial staghorn calculi consisted, at least to some extent, of the typical infection stone material struvite. Patients with musculoskeletal anomalies are more likely to have a stone composition of struvite due to recurrent urinary tract infections.[12] However, the patient in the present case never had a pyelonephritis on the left side and the analysis of the left-sided composite stone revealed a pure calcium-oxalate/apatite composition. It has recently been shown that improved patient care in the last two decades resulted in a significant change of the predominant stone composition in these patients.[13] Nowadays, struvite stones account only for approximately 20% of all stones while stones not related to urinary tract infections such as apatite and calcium oxalate stones are found in approximately 80% of all renal stones in this patient group.[13]
The absence of recurrent infections in the left kidney and the presence of a solitary renal calculus which was adherent to the migrated metal coil support the hypothesis that the metal coil was the main trigger for the new onset of left nephrolithiasis.
To the best of our knowledge, stone formation after coil migration as a late complication of RAE has so far only been described once.[8] In this case, however, a renal calculus of 7 mm had formed around a totally migrated metal coil in the collecting system two years after RAE. The stone was treated using a pneumatic lithotripter during semirigid ureterorenoscopy. In contrast to the present case, the intraluminal metal coil was not fixed in the renal parenchyma and ESWL treatment was not performed due to low opacity of the stone.
The metal wire not only induced stone formation but also had an impact on the physical characteristics of the stone and its responsiveness to the ESWL treatment. The intra-luminal coiling material was densely integrated into the stone thereby forming a composite stone. The reinforcing characteristics of composite materials consisting of metal wires and stone or concrete (reinforced concrete) are well known and often used in construction for on-ground floors and pavements.[14] The robustness of the composite stone impeded effective disintegration and detachment of stone fragments from the metal wire, which is necessary for stone clearance after ESWL.
The close vicinity of the coils and the stone was detectable on pre-operative radiographic imaging. In retrospect, stone formation around migrated embolization coils could have been suspected earlier, particularly after the first unsuccessful ESWL treatment. However, initially, this option was not taken into consideration and f-URS was only indicated after two ESWL treatments. Retrograde intrarenal surgery seems to be the optimal treatment option in this situation. It makes direct visualization and thereby identification of the special composition of the stone possible. Furthermore, stone disintegration and removal can be combined with removal of the stone inducing foreign body.
The combination of several risk factors including a solitary kidney, recurrent stone disease and the remaining intra-parenchymal renal coil material, which might also migrate into the collecting system requires this patient to be closely followed in the future.
BMC Urol. 2013;13(29) © 2013 BioMed Central, Ltd.
