Nephrocalcinosis: re-defined in the era of endourology

Abstract

Nephrocalcinosis generally refers to the presence of calcium salts within renal tissue, but this term is also used radiologically in diagnostic imaging in disease states that also produce renal stones, so that it is not always clear whether it is tissue calcifications or urinary calculi that give rise to the characteristic appearance of the kidney on x-ray or computed tomography (CT). Recent advances in endoscopic imaging now allow the visual distinction between stones and papillary nephrocalcinosis, and intrarenal endoscopy can also verify the complete removal of urinary stones, so that subsequent radiographic appearance can be confidently attributed to nephrocalcinosis. This report shows exemplary cases of primary hyperparathyroidism, type I distal renal tubular acidosis, medullary sponge kidney, and common calcium oxalate stone formation. In the first three cases--all being conditions commonly associated with nephrocalcinosis--it is shown that the majority of calcifications seen by radiograph may actually be stones. In common calcium oxalate stones formers, it is shown that Randall's plaque can appear as a small calculus on CT scan, even when calyces are known to be completely clear of stones. In the current era with the use of non-contrast CT for the diagnosis of nephrolithiasis, the finding of calcifications in close association with the renal papillae is common. Distinguishing nephrolithiasis from nephrocalcinosis requires direct visual inspection of the papillae and so the diagnosis of nephrocalcinosis is essentially an endoscopic, not radiologic, diagnosis.

Fig. 1

Pre-operative KUB in patient with primary hyperparathyroidism. Arrows indicate regions that appear to be nephrocalcinosis

Fig. 2

a Endoscopic image of left lower pole calcifications in patient with primary hyperparathyroidism. b Endoscopic view of relatively normal papilla in the upper pole of the left kidney in the same patient

Fig. 3

Post-operative KUB following bilateral PCNL in this patient with primary hyperparathyroidism demonstrating complete removal of all renal calcifications

Fig. 4

Pre-operative KUB in patient with Type 1 distal RTA

Fig. 5

Endoscopic views in a patient with Type 1 distal RTA. a Close-up view during procedure, demonstrating large calyceal stone and smaller stones protruding from dilated duct of Bellini (arrowheads). b Lower power image following removal of calyceal stones in the same patient, demonstrating only finely stippled scattered calcifications remaining

Fig. 6

Post-operative KUB in same patient with distal RTA. Almost all the X-ray dense material visible in Fig. 4 has been removed, demonstrating that the finely stippled calcification seen in Fig. 5b is not apparent on plain X-ray

Fig. 7

Pre-operative KUB findings in patient with MSKD

Fig. 8

Intraoperative images demonstrating the typical endoscopic findings in MSKD. a Deformations in calyceal spaces appear as a web of openings within the kidney. b Higher power view where laser fiber is shown incising the tissue of a cystic cavity where stone material is present

Fig. 9

Post-operative KUB following left PCN in this same patient with MSKD

Fig. 10

High-resolution CT images following left PCNL in common calcium oxalate stone former. Calcifications confirmed to be Randall's plaque by second-look nephroscopy