Medullary Sponge Kidney

Synonym: Cacchi-Ricci disease/syndrome

Medullary sponge kidney (MSK) is a congenital disorder that can affect one or both kidneys, or only part of one kidney. There are ectatic and cystic changes of the medullary and papillary collecting ducts.¹ The names tubular ectasia and cystic dilatation of the collecting ducts have been suggested as alternatives for this condition because the medulla does not actually appear like a sponge. It is bilateral in 70% of cases.² Cysts can be 1-7mm in diameter. Cyst formation is commonly associated with the development of small calculi within the cyst. The rest of the kidney is usually normal unless affected by complications such as pyelonephritis or obstruction secondary to renal calculi.

• Uncertain though thought to be a developmental abnormality³
• Most cases are sporadic
• Familial forms with autosomal dominant inheritance exist but are rare. Online Mendelian Inheritance in Man (OMIM) lists two types of medullary cystic kidney disease with autosomal dominant inheritance, medullary cystic kidney disease 1 and 2.^4,5 These conditions both have adult onset. There is also another form that has juvenile onset and autosomal recessive inheritance, known as familial juvenile nephronophthisis.⁶

• Estimated prevalence is 5-50 per 100,000^7,8
• May be present in as many as 20% of people with renal calculi²
• More common in women²
• Affected women are also more likely than affected men to develop calculi.²

• Although it is a congenital disorder, diagnosis is often not made until the second or third decades.
• May be asymptomatic
• Can be an incidental finding on radiological investigations performed for other reasons
• Haematuria is common and usually microscopic. Macroscopic haematuria can occur with associated infection or calculi.
• Recurrent urinary tract infection is a common presentation and affects more women than men. There may also be sterile pyuria.
• May present with renal calculi and their complications including renal colic, haematuria, infection and urinary obstruction. The stones are usually calcium oxalate and calcium phosphate.²

Medullary sponge kidney is associated with a number of other congenital disorders. Some of the more common associated conditions include:

• Congenital hemihypertrophy: this is the most frequent association. There is enlargement of a limb or one side of the body compared with the contralateral side beyond the limits of normal variation. 10% of people with congenital hemihypertrophy have MSK.²
• Beckwith-Wiedemann syndrome: the association of macroglossia, macrosomia, omphalocele, visceromegaly, MSK, hemihypertrophy, mental retardation, adrenal cortex cysts.
• Congenital hepatic fibrosis
• Congenital pyloric stenosis
• Anodontia
• Polycystic kidney disease
• Horse-shoe kidney
• Distal renal tubular acidosis
• Ehlers-Danlos syndrome
• Marfan's syndrome

Except for the possible presence of other congenital abnormalities, including hemihypertrophy, there is usually no abnormality to be found on examination.

• Renal calculi:¹ stones are usually small and can pass spontaneously
• Urinary tract infection (UTI) and pyelonephritis¹
• Renal failure: due to recurrent infection or obstruction due to calculi. Renal impairment can occur in 10% of patients.² (Please refer to separate article on Chronic Renal Failure)
• 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.^9,10,11,2
• Distal renal tubular acidosis

Investigation may be initiated because of recurrent UTI or renal calculi.

• Plain abdominal x-ray: may reveal nephrocalcinosis.
• USS: calcification may be seen on ultrasound examination.
• Intravenous urography: the gold standard investigation. There are radial linear striations in the papillae ("brushlike" patterns). Contrast media collects in the ectatic collecting ducts and is seen as "bunches of grapes" or "bouquets of flowers".²
• CT scan: this can show other associated renal abnormalities.
• Urinary calcium: there is hypercalciuria in 30 to 50%.²
• Urinary pH: if distal renal tubular acidosis is present, there is inability to form an acid urine in the distal tubule. Urine pH is above 6 and there is associated hypokalaemia with a hyperchloraemic metabolic acidosis.

• The presence of MSK does not exclude other pathology and it can co-exist with other diseases such as polycystic kidney disease.
• Sterile pyuria can be due to inadequately treated UTI or tuberculosis of the kidney.
• Haematuria requires the exclusion of malignancy of the urinary tract including clear cell carcinoma of kidney, bladder tumours or in children Wilms' tumour.

• Patient education about the usually benign nature of the condition. Fluid intake should be kept high (at least 2 litres a day) to reduce the risk of both stones and UTI. Avoidance of a high protein diet also reduces the risk of recurrent calculi.
• Complicating urinary tract infection and pyelonephritis should be treated with antibiotics.
• Complicating renal calculi should be managed appropriately.
• Investigate for other coexisting pathology including the exclusion of malignancy if there is haematuria.
• Regular urinalysis and plain abdominal x-ray can help to detect infection and renal tract calcification but there is no general agreement about optimum frequency.² Renal function can be monitored using urea, electrolytes, creatinine and eGFR. Affected children should have surveillance for Wilms' and other abdominal tumours.
• A thiazide diuretic may be used to reduce hypercalciuria and stone formation.²

• Normally a benign condition that does not affect life expectancy.
• Recurrent stones and pyelonephritis affect about 10%.
• Renal impairment can occur in 10% of patients.²