Medullary spongy kidney is a congenital cystic lesion of the renal medulla characterized by pyknotic or cystic dilatation of the papillary and collecting ducts of the renal cone with infection and urinary stone formation. In the kidney specimen, spongy changes in the medulla can be seen.
Previously, spongy kidney was considered a rare disease with a 0.5% detection rate on unselected excretory urographic films. As awareness of the disease has increased, the rate of diagnosis has continued to improve. It has been suggested that spongy kidneys account for up to 25% of the etiology of kidney stones. However, it is generally believed that medullary spongy kidneys account for 5% to 11.6% of calcium-containing kidney stones.
Medullary spongy kidney is more common in men, with a male to female ratio of about 2:1, and the onset of the disease is mostly seen in 40-60 years old, accounting for more than 2/3. The disease may be hereditary, with reports of more than 2 people in the same family or several generations.
Pathogenesis of medullary spongy kidney
The spongy kidney is a congenital developmental anomaly. The papillary duct enters the calyces with a sphincter-like action, and the hypertrophy and overtightening of the tissue of this structure can cause cystic dilatation of the proximal end of the duct. The dilatation of this lesion is often more visible on excretory urography, while on the contrary it is mostly undetectable on retrograde imaging.
The mechanisms of spongy kidney stone formation may include: anatomic abnormalities that cause local urinary retention and deposition of urine salts in the cystic dilated collecting ducts or papillary ducts; complications of infection and bleeding that may promote stone formation; renal hypercalciuria in about 50% of medullary spongy kidney patients; and secondary renal tubular acidosis in some patients.
Clinical manifestations of medullary sponge kidney
The spongy kidney may have no specific clinical symptoms if there are no complications such as infection, bleeding, stone formation, etc. According to the clinical and radiological changes, the initial symptoms of patients are divided into 3 categories: clinically asymptomatic or only slightly symptomatic, showing only characteristic changes on excretory urographic films but no calcification on urograms; showing calcium deposits on urograms and patients presenting with urinary tract infections. This calcium deposition should be distinguished from primary hyperparathyroidism and renal tubular acidosis; due to chronic inflammation, renal tubular stones break out of the cone into the renal calyces and renal pelvis, producing the typical symptoms of stones.
1. Hematuria
This is the most common symptom, accounting for about 85%, and recurrent. The attack may be accompanied by back pain or discharge of fine sand-like stones at the same time. It is usually microscopic hematuria, but we can also see individual cases showing painless hematuria by the naked eye throughout.
2. Renal colic
It can be an early symptom and often occurs several times, accounting for about 50% of cases. In a few cases, the stone grows gradually in the renal pelvis or becomes lodged in the ureter, requiring surgery or lithotripsy.
3. Pyelonephritis
About 50% of patients develop pyelonephritis, which is an infection in the papillary duct, collecting duct and dilated cystic cavity within the conus, spreading to the entire urinary tract, and in severe cases, spreading to the kidney tissue around the cystic cavity and affecting kidney function.
4.Systemic symptoms
The late stage of the disease can cause damage to renal function, especially to renal tubular function, which can cause systemic symptoms, such as anemia, hypertension, edema, water-electrolyte disorder and acid-base balance disorder.
Diagnosis of medullary spongy kidney
Medullary sponge kidney is usually detected when patients present with urinary tract symptoms and urinary tract system examination, i.e. urogram or intravenous urography is performed.
1.Urogram
Multiple positive stone shadows in the kidney cone, irregular stone size and shape, as small as fine grains of sand to as large as 0.5 cm in transverse diameter. The stones are arranged in fan-shaped or dense clusters, or irregularly scattered in each cone.
2. Intravenous urography
In typical cases, the cystic cavity of the kidney cone is first filled during intravenous urography, and becomes more clearly visible when the ureter is pressurized. Retrograde urography does not show these characteristic changes. The shadows around the renal cone or calyces commonly seen on intravenous urography films are: a fan shape of contrast in the dilated collecting ducts and papillary ducts; filling of the small cystic cavity in a grape bunch pattern; or overlapping with stone shadows to form patchy shadows of uneven density; and widening of the renal calyces with a large and flattened cup.
Treatment of medullary spongy kidney
The treatment of medullary spongy kidney includes general treatment and treatment for complications, both of which are important and cannot be overlooked.
1.General treatment
Regardless of whether the patient has symptoms or not, once concluded, the patient should be advised to drink more water and adopt a low-calcium, low-oxalate diet. Patients with hypercalciuria should be treated with long-term calcium-lowering drugs, such as thiazide diuretics, and combined with potassium citrate to prevent or delay stone formation. Be careful not to do unnecessary lithotripsy treatment, as the stone is located in the renal papillary duct and cannot be expelled.
2. Treatment of complications
Complications include secondary stone obstruction and infection. When the spongy kidney stone is discharged from the papillary duct and stays and grows in the urinary tract and causes urinary tract obstruction, it contributes to the deterioration of the disease. Therefore, once secondary urinary tract stones are formed, they should be treated by lithotripsy and should not do long-term waiting. For stones that cannot be discharged on their own, extracorporeal shock wave lithotripsy should be done. Secondary urinary tract infection will accelerate the process of kidney damage, so patients with secondary infection should be given effective antimicrobial agents to control the infection. Surgery is not recommended for patients with spongy kidney stones, except in patients with unilateral lesions, and unilateral nephrectomy may be considered if it is proven that the kidney on that side has no kidney function due to secondary stones and infection.
3.Prognosis
Spongy kidney alone usually does not affect renal function, and spongy kidney stones without infection and secondary urinary tract stones also do not affect the prognosis, but once secondary stones form and cause urinary tract obstruction and secondary infection, the renal function will deteriorate dramatically. Therefore, regular follow-up and timely treatment of secondary lesions in patients with spongy kidney stones is very important.