Markschwammniere

Medullary sponge kidney is a congenital malformation of the kidneys with:

• malformation of the terminal collecting tubes in the medullary pyramids and papillae
• Formation of medullary cells

The medullary sponge kidney affects 75% of both kidneys (Herold 2021).

The extent of the changes in the kidney can be used to assess the risk of symptomatic nephrolithiasis:

• Grade 1: In this case, 1 calyx is found unilaterally. The risk is 0.09 episodes / year.
• Grade 4: More than 1 calyx is affected bilaterally. The risk is then 0.34 episodes / year (Kuhlmann 2015).

The incidence of medullary sponge kidney is 1: 5,000 (Herold 2021), and that of asymptomatic is 1: 200 (Hegele 2015).

This is a congenital disease. The mode of inheritance is unknown (Keller 2010). According to Hofmann (2005), less than 5% of families are affected. It is suspected that changes in the flow properties in the tubules promote stone formation (Kasper 2015).

Complaints in medullary sponge kidney usually appear in the 4th or 5th decade of life in the form of recurrent urinary tract infections or nephrolithiasis with hematuria, colic, pyuria, etc. (Risler 2008).

The diagnosis is often made as an incidental finding on i. v. urogram or CT. Symptoms may include:

• recurrent nephrolithiasis
• recurrent urinary tract infections
• symptoms of chronic renal insufficiency (rare) (Hegele 2015)

In the past, the diagnosis was made by i.v. urography. Nowadays, this is usually done by CT, although this shows a lower sensitivity (Kasper 2015).

Sonography:

• Hyperechogenic papillae presentable (Hegele 2015).
• Nephrolithiasis
• Nephrocalcinosis (Herold 2021)
• dorsal sonic effacement phenomenon may exist depending on the extent of calcifications
• the medullary pyramids appear speckled and interspersed with brilliant echoes (also called "Christmas tree phenomenon") (Hofmann 2005)
• Calcification in the tips of the papillae (Herold 2021)

CT:

• radial radiation emanating from the calyxes
• radiopaque stones grouped in affected calyxes
• widened pyramids
• cysts arranged like clusters in the area of the papillae (represent dilated collecting tubes) (Keller 2010)

i. v. pyelography: The ectatic collecting tubes are filled with contrast medium and the outflow is delayed. In advanced stages, calcifications occur along the collecting tubes (Hegele 2015). Nowadays, however, i. v. pyelography is rarely used for diagnosis. CT has taken its place (Kasper 2015).

Hypercalciuria (Herold 2021).

Histologically, papillary dilated collecting tubes are found in the area of the medullary pyramids, from which cysts with a diameter of approx. 1 mm - 8 mm originate. These cysts are connected to the draining urinary system and may contain blood, leucocytes, cell detritus etc.. Calcifications or nephrocalcinosis can often be detected (Risler 2008).

• Medullary cystic disease (MCD) (Hofmann 2005)
• distal tubular acidosis
• primary hyperparathyroidism (Kuhlmann 2015)

Differential diagnosis of bilateral calcifications

• Hyperparathyroidism
• vitamin D intoxication
• Sarcoidosis
• Tuberculosis
• multiple myeloma
• Milk-alkali syndrome (Hegele 2015)

Renal insufficiency due to nephrocalcinosis (Herold 2021)

In patients with nephrolithiasis, 3 % - 5 % have medullary sponge kidney, and in those with calcium stones the proportion rises to as much as 20 % (Kuhlmann 2015).

Medullary sponge kidney also occurs in patients with hemihypertrophy syndrome, in whom the risk of developing a Wilms tumor is increased. In this case, regular sonographic controls are necessary (Hofmann 2005).

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