Nephrol Dial Transplant (2000) 15: 1080-1082
© 2000 European Renal Association-European Dialysis and Transplant Association
Image in Nephrology
Renal cortical nephrocalcinosis
(Section Editor: G. H. Neild)
1 Department of Nephrology and Transplantation, and 2 Department of Radiology, University Hospital Leuven, Belgium
Keywords: Alport's syndrome; cortical calcification; diagnosis; nephrocalcinosis; renal failure
Introduction
Renal cortical nephrocalcinosis is a rare condition. We report a patient with known Alport's syndrome who presents with acute on chronic renal failure, unexpectedly caused by an extreme form of cortical calcification.
Case
A 47-year-old patient presented with progressive chronic renal failure and arterial hypertension (172/110 mmHg). Serum creatinine level was 4.3 mg/dl with a calculated creatinine clearance of 23 ml/min (Cockroft–Gault formula). He had proteinuria (3.7 g/24 h) and microscopic haematuria. Parathyroid hormone (PTH) level was 157 pg/ml (normal range 3–40 pg/ml), serum phosphate 5.1 mg/dl (1.63 mmol/l), serum calcium 9 mg/dl (2.25 mmol/l).
At the age of 24 years he was noted to have mild proteinuria (0.82 g/24 h) and red blood cell casts were found in the urinary sediment. Renal function was normal at that time with a serum creatinine of 0.76 mg/dl and an estimated creatinine clearance of 146 ml/min. An intravenous urogram demonstrated symmetrical normal kidneys of 13 and 13.5 cm without calcification. Renal biopsy specimen showed typical electromicroscopic features of Alport's syndrome.
Over the following years hypertension worsened and proteinuria increased. Enalapril and subsequently carvedilol was started. Calcium and phosphorus were kept within normal range by diet and calcium carbonate; the highest Ca-P product ever measured was 46 (or 3.66 in SI units). Hypercalciuria was never diagnosed. PTH level during that time remained normal (30 pg/ml). No unprescribed calcium or vitamin D preparations had been taken.
There were multiple causes of the progression of chronic renal failure: the uncontrolled arterial hypertension, the progression of Alport's syndrome and the unexpected finding of an extreme form of renal cortical calcification.
Renal ultrasonography demonstrated a marked increase in cortical echogenicity throughout the entire cortex (Figure 1
). The medullary pyramids were spared; the renal size was normal and the renal contours were smooth. A diagnosis of cortical nephrocalcinosis was made. Plain abdominal X-ray demonstrated a symmetrical overall increase in renal opacity (Figure 2).
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Computed tomography (CT) without iodinated contrast was performed and showed a symmetrical calcification of both the septal- and basal renal cortex, confirming the diagnosis of cortical nephrocalcinosis (Figure 3
). As seen in Figure 4 the calcification is hardly detectable on T1- and T2 weighted magnetic resonance imaging (MRI) (Siemens, Vision 1.5 Tesla).
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Discussion
Renal calcification can be classified into two major groups: nephrolithiasis when the calculus is located in the collecting system; nephrocalcinosis when the calcification is located in the renal parenchyma. Nephrocalcinosis can be subdivided into a medullary and a cortical form. Causes of cortical nephrocalcinosis are listed in Table 1. The most frequent causes are chronic glomerulonephritis and acute cortical necrosis [1,2,4,6]. The aetiology of cortical nephrocalcinosis in our patient was most probably the presence of the chronic glomerulonephritis; other known causes were excluded.
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Both ultrasonography and CT can detect nephrocalcinosis earlier than plain abdominal X-ray. The latter will only be positive if the attenuation of the renal parenchyma (by CT) exceeds 100 Hounsfield Units; in this case an increased density of the kidneys will be visible on the plain X-ray film. Ultrasonography demonstrates an increased echogenicity of the renal cortex, sometimes with acoustic shadowing. CT will display punctate band or tram-line calcification in the basal and septal cortex with sparing of the medulla [5]. However, calcification is difficult to detect on MR imaging as was demonstrated in this case. Due to signal void, calcifications will appear hypointense both on T1- and T2-weighted images. Small calcifications are therefore easily missed on MR imaging [8].
In general, three different patterns are described in cortical nephrocalcinosis. Most commonly, a thin peripheral band of calcifications, often with extension into the septal cortex, is recognized. This pattern was found in this case. Two thin parallel calcified tracks (so called ‘tram-line’) represent a second type of cortical nephrocalcinosis. The least common form consists of multiple punctate calcifications with a random distribution in the renal cortex. However, none of these patterns are pathognomic and may be recognized in all causes of cortical nephrocalcinosis [8].
Notes
Correspondence and offprint requests to: D. Kuypers, Department Nephrology and Transplantation, University Hospital, Herestraat 49, B-3000 Leuven, Belgium. 
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- Arons WL, Christensen WR, Sosman MC. Nephrocalcinosis visible by X-ray associated with chronic glomerulonephritis. Ann Intern Med1955; 42: 260–282
- Palmer FJ. Renal cortical calcification. Clin Radiol1970; 21: 175–177[Medline]
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[Abstract/Free Full Text] - Manz F, Jaschke W, Van Kaick G, Waldherr R, Willich E. Nephrocalcinosis in radiographs, computed tomography, sonography and histology. Pediat Radiol1980; 9: 19–26
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- Banner MP. Nephrocalcinosis. In: Pollack HM, ed. Clinical Urography. WB Saunders Company 1990: 1768–1769
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