A 27 y.o. woman presented with hematuria and L flank pain.
What do you notice on her ct?
Our patient had medullary sponge kidney(MSK) on CT. Tiny stones are seen in the renal papilla where the dilated ducts of Bellini begin to collect urine for excretion. The ducts typically are not obstructed but congenitally dilated creating a sponge-like appearance. Another diagnosis in the differential is nephrocalcinosis with calcium deposits diffusely in the renal cortex and medulla.
congenitally dilated ducts of Bellini
Medullary sponge kidney can lead to calcium phosphate stones or calcium oxalate stones. 70% of MSK patients form kidney stones and 12-20% of patients who form stones have MSK. Urinary stasis occurs in the dilated collecting ducts leading to stones which can stay in the ducts or migrate distally causing a nidus for stone formation in the ureter. Our patient also has a distal stone obstructing the L kidney.
Familial clustering of medullary sponge kidney is common and it has an autosomal dominant inheritance. In a large study it was found to be either unilateral or bilateral. In addition to family history, it is possible to distinguish between nephrocalcinosis and medullary sponge kidney(MSK) although in early stages it is more difficult. Ultrasound can show echogenic material in the renal papillae where small stones form.
Differential for medullary sponge kidney includes:
Hyperparathyroidism
Hypervitaminosis D
Milk-alkali syndrome or other hypercalciuric states
Renal tubular acidosis type I
Long term treatment of stones is achieved with potassium citrate.
Urinary tract infection, hematuria and stones are the most common ways these patients come to medical attention. Progression can occur leading to renal failure requiring nephrectomy. In cases of frequent UTIs the multiple small stones can be removed surgically laparoscopically through an incision in the back.
end stage medullary sponge kidney requring nephectomy
Our patient was confirmed as having MSK on biopsy. She also had a stone in the L ureter causing obstruction. She received a stent for her obstruction and long term treatment with potassium citrate to alkalinize the urine and prevent calcium oxalate stones.
Xiang H, Han J, Ridley W, et al. Medullary sponge kidney J (2018), Medullary sponge kidney. J Med Imaging Radiat Oncol, 62: 93-94. https://doi.org/10.1111/1754-9485.40_12784
Fabris A, Anglani F, Lupo A, at al. Medullary sponge kidney: state of the art. Nephrol Dialysis Transplant 2012;28:1111.9.
Bell D, Yap J, Knipe H, et al. Medullary sponge kidney. Reference article, Radiopaedia.org (Accessed on 20 Jan 2025) https://doi.org/10.53347/rID-1653
https://kidneystones.uchicago.edu/2015/06/07/the-diagnostic-dilemma-of-medullary-sponge-kidney/
Johnson S. Medullary sponge kidney and medullary nephrocalcinosis. Journal of Diagnostic Medical Sonography 29(4):165-167