Renal tubular ectasia is an incidental finding that is seen more commonly on intravenous pyelography (IVP), but which can also occasionally be seen on CT urography (CTU).
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Terminology
Renal tubular ectasia is also known as benign renal tubular ectasia. The term "benign" was used to differentiate it from medullary sponge kidney and the symptoms of medullary nephrocalcinosis; no tumor is associated with either condition.
Pathology
The appearance arises from congenital dilatation/ectasia of the distal tubules of the nephrons in a medullary pyramid. Some feel that the ectasia predisposes toward stone formation, but if this is the clinical case, the terms medullary sponge kidney and medullary nephrocalcinosis tend to be used instead. In the literature, there has been overlap in the use of the two terms, and some consider the two conditions to be different ends of spectrum of medullary tubular dilation.
Radiographic features
Both IVP and CTU show a similar "paintbrush" appearance to the medullary pyramid. The strands of the "brush" are mildly dilated tubules full of contrast (tubules dilated to ~0.2 mm). Unlike medullary nephrocalcinosis, renal tubular ectasia cannot be seen on a plain radiograph or a noncontrast CT.
Treatment and prognosis
No treatment or workup required. There is an association with congenital hepatic fibrosis 2, although this association may really be with medullary sponge kidney.
Differential diagnosis
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medullary sponge kidney
- the difference is predominantly one of degree, renal tubular ectasia less pronounced than medullary sponge kidney
- medullary sponge kidney also predisposes to medullary nephrocalcinosis: the distal tubules accrete calcification which predisposes to renal stone formation
- normal faint blush of contrast in the medullary pyramid
- as contrast passes through the medullary pyramid, it will cause the pyramid to "blush"/enhance, but renal tubular ectasia is greater in degree