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What is medullary sponge kidney (MSK)?
Medullary sponge kidney (MSK) is a congenital disorder, meaning it is present at birth. MSK occurs when small cysts (sacs) full of fluid form within the inner area (called the medulla) of the kidneys. It is also called Cacchi-Ricci Disease.
In 70% of patients small stones form within the cysts. It also causes UTIs.
The cysts gives the medulla a sponge-like appearance. It usually affects both kidneys.
Who gets MSK?
MSK is rare. It is estimated to affect between 5 in 10,000 and 5 in 100,000 people.
The exact cause is not known, and the majority of cases do not show a family history. Though family clusters have been described (Fabris, 2013).
Men are affected by MSK more frequently than women, though women get more UTIs and are more affected by hypercalciuria (see below).
Doctors should consider MSK in all patients presenting with kidney stones, haematuria (blood in the urine) or recurrent UTIs. About 10% of people with recurrent kidney stones may have MSK.
Symptoms
Although it is a congenital disorder, the symptoms of MSK may begin at any age; Howe they usually develop during adolescence or in adults between the ages of 30 and 50 years
It may be asymptomatic – i.e. there may be no symptoms
It can be a non-predicted finding on an x-ray done for another reason
Haematuria is common and usually microscopic (>90%; only visible under a microscope). Macroscopic haematuria (<20%; blood you can see) can occur with associated infection or stone
Recurrent urinary tract infection (UTI; 30%) is a common presentation and affects more women than men
Loin/back pain, which in a few cases can be severe and intractable.
It may present with kidney stones and their complications including renal colic, haematuria, infection and urinary obstruction.
Examination There is usually nothing to find on examination.
Associated conditions
MSK is associated with a number of other congenital disorders. Some of the more common conditions include:
Congenital hemihypertrophy: this is the most frequent association. There is enlargement of a limb or one side of the body compared to the other side. 5-10% of people with congenital hemihypertrophy have MSK
Beckwith-Wiedemann syndrome: a growth disorder, which is characterised by a range of rare abnormalities, embryonal tumours (e.g. Wilms’ tumour)
Fibromuscular dysplasia: a rare non-atherosclerotic, non-inflammatory vascular disease that particularly affects the renal arteries and other vessels. It is a rare cause of renovascular disease.
Complications
Renal calculi: stones are often small and can pass spontaneously
UTI and pyelonephritis
CKD: due to recurrent infection or obstruction due to calculi
Reduced bone density. Defective bone mineralisation associated with MSK
Wilms’ tumour: children with MSK have a greater risk of developing Wilms’ tumour. This is because of the association of Wilms’ tumour with congenital hemihypertrophy and Beckwith-Wiedemann syndrome
Distal renal tubular acidosis.
Investigations
Investigation may be initiated because of recurrent UTI or renal calculi.
Radiology
Plain abdominal X-ray: may reveal nephrocalcinosis. This means alot of small stones, and looks like this:
Typical abdominal x-ray in MSK
Ultrasound scan: not very sensitive for MSK or stones, but either may be picked up coincidentally
Intravenous pyelogram (IVP; a kidney x-ray): the previous standard investigation. MSK was traditionally often picked up coincidentally on an IVP done for kidney stones. However, this test is used decreasingly due to the toxic effects of the contrast medium (x-ray dye; injected during the procedure) on the kidneys
CT scan is now be the investigation of choice for MSK, though this also involves contrast medium.
CT scan in MSK
Urine
Urine dipstick
MSU if infection is suspected
Urinary calcium: there may be hypercalciuria (high calcium level in the urine)
Urinary citrate tends to be low
Urinary pH: if distal renal tubular acidosis is present, there is inability to form an acid urine. Therefore urine pH is above 6 and there is associated hypokalaemia (low blood potassium) with a hyperchloraemic (high chloride) ‘metabolic acidosis’ (too much acid in the blood).
Other tests
U&Es, eGFR for renal function. CKD occurs in about 10% of people with MSK. Dialysis is rarely needed
Stone analysis – stones may be composed of calcium oxalate monohydrate, calcium oxalate dihydrate, calcium phosphate apatite, and uric acid.
Treatment
No treatment can eliminate the cysts in MSK. Therefore, treatment centres around treating and preventing UTIs and kidney stones:
Patient education about the usually benign nature of the condition
Complicating UTIs and pyelonephritis should be treated with antibiotics
Complicating kidney stones should be managed appropriately. This may include extracorporeal shock-wave therapy (ESWL), percutaneous surgery or ureteroscopy. In severe cases of recurrent renal stones, partial nephrectomy may be required. Rarely, total nephrectomy may be necessary in cases of severe recurrent sepsis
Investigate for other co-existing pathology, including the exclusion of malignancy if there is haematuria
Regular urinalysis and plain abdominal x-ray can help to detect infection and stones but there is no general agreement about optimum frequency. Kidney function should be monitored using U&Es and eGFR. Affected children should have surveillance for Wilms’ and other abdominal tumours
Potassium citrate administration has been shown to improve bone density. It also reduces the frequency of stone formation.
Depending on the composition of the stone, medication to prevent further stone formation is sometimes given – e.g. thiazide diuretics (for calcium stones), allopurinol (for uric acid stones) and calcium citrate (for oxalate stones).
Prognosis (outlook)
MSK is normally a benign condition that does not affect life expectancy. CKD and the need for dialysis is uncommon. Recurrent infections/stones and chronic pain cause most of the ongoing problems.
Summary
We have described what is medullary sponge kidney (MSK). We hope it has been useful.
