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A 50-year-old man presents with renal colic and an intravenous pyelogram demonstrates "clumps" of
contrast medium limited to the medulla. Multiple small stones are also seen. Blood chemistries
are all within normal limits. What is the most likely explanation for these findings?
A. Adult polycystic renal disease
B. Horseshoe kidney
C. Infantile polycystic renal disease
D. Medullary sponge kidney
E. Renal dysplasia
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MMM...THIS SOUNDS FAMILIAR...THIS Q...WHERE R THESE FROM?
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samomcos tooo fast answ d
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Explanation:
The correct answer is D. This is a classic presentation for medullary sponge kidney, which has
a male predominance and typically presents at 40-60 years of age. Histologically, medullary
sponge kidney shows multiple small cysts lined by columnar or cuboidal epithelium localized to
the medullary collecting tubules. The cysts can contain laminated concretions of calcium
phosphates. Renal failure is rare in patients with medullary sponge kidney and the pathogenesis
for the lesion has not been clarified. The rare uremic medullary sponge kidney is distinguished
from the more common form by occurrence in 20-30 year-olds, salt-losing nephropathy, and
progression to renal failure.
The kidney of adult polycystic disease (choice A) is massively enlarged and filled throughout
with round cysts of varying sizes. Adult polycystic kidney disease often presents with
hypertension rather than renal failure or stones.
Horseshoe kidney (choice B) involves fusion of the upper or lower (most common) pole of the
kidney. It is fairly common (as high as 1:500), and is typically an incidental finding at
autopsy.
8
Infantile polycystic kidney (choice C) produces a small kidney with round medullary cysts and
"radiating" linear cortical cysts.
Renal dysplasia (choice E) can also cause cystic change in a kidney, but typically involves
only the medulla and cortex of part of the kidney.
