Hydronephrosis N13.3

Posterior urethral valves (a cause of hydronephrosis) were first described by Margagni in 1715 (Coen 2006).

There are different names for hydronephrosis in the literature.

Historically, hydronephrosis was equated with the presence of an associated loss of renal function in addition to the presence of obstruction of the urinary tract (Geiger 2003).

Kuhlmann (2015) describes hydronephrosis as the dilatation of the renal pelvis due to obstructive nephropathy. The dilation of the renal calices is referred to as hydrocalix (Kuhlmann 2015).

In the German-speaking world, Hegele (2015) understands this to mean urinary stasis in the area of the renal pelvis with accompanying degenerative changes in the renal parenchyma.

In English-speaking countries, "hydronephrosis" is understood to be a temporary or permanent dilatation of the renal pelvis or the renal pelvic caliceal system (Hegele 2015).

• Congenital hydronephrosis (Entezami 2002):
  • intrinsic obstruction (most common form)
  • extrinsic obstruction
  • secondary obstruction

Acquired hydronephrosis:

• unilateral: It results from stenosis above the urinary bladder.
• Bilateral: This is found with stenosis in or below the urinary bladder (Kasper 2015).
• partial / complete
• acute / chronic (Kuhlmann 2015)

Staging hydronephrosis:

• Grade I:

There is enlargement of the renal pelvis, possibly also of the calices. The organ itself is not enlarged.

• Grade II:

In addition to the changes mentioned under grade I, there is enlargement of the organ.

• Grade III:

In addition to the above-mentioned changes, there is also a narrowing of the parenchymal rim.

• Grade IV:

The kidney presents itself as a so-called hydronephrotic cul-de-sac kidney. The parenchyma is without function. A single cavity or calyces dilated as a cluster are found (Debus 2012).

Staging according to Beetz et al:

• Grade I:

The parenchyma is of normal width, the pyelon is dilated, the transverse diameter is above the 95th percentile, the calyces are not dilated.

• Grade II:

The parenchyma is normal in width, the pyelon and calyces are dilated, the calyx necks are slightly dilated, the papillae tips are preserved, the fornix angle is acute.

• Grade III:

The parenchyma is narrowed, there is marked renal caliceal dilatation, the calices themselves are plumped with flattened papillae and obtuse fornix angle.

• Grade IV:

Here the parenchyma is considerably narrowed, the renal pelvic calices are extremely dilated, the calices are broadly rolled out, the boundary between pyelon and caliceal system is partially to completely abolished (Schäfer 2016).

Congenital hydronephrosis accounts for approximately 75% of renal malformations diagnosed prenatally. The incidence is 1: 200 to 1: 1,000 births. The sex ratio in ureteropelvic stenosis is 4: 1 male / female. ureterovesical stenosis also affects more male newborns, exact figures are not available. In about 70 % hydronephrosis occurs unilaterally (Entezami 2002).

Congenital hydronephrosis occurs predominantly spontaneously, but may also be associated with over 70 different syndromes (Entezami 2002).

In the congenital form, > 60% involve the left kidney and up to 10% involve both kidneys (Steinmüller2011).

Acquired hydronephrosis has an incidence of 1: 1,250 and the male sex is affected twice as often (Steinmüller 2011).

Hydronephrosis due to ovarian vein thrombosis occurs with an incidence of 1: 3,000 pregnancies (Manski 2019).

• Congenital hydronephrosis(Entezami 2002):
  • mostly spontaneous onset
  • a teratogenic effect is found in:
    • diabetes mellitus
    • Benzodiazepines
    • Cocaine
    • thalidomide
• Acquired hydronephrosis:
  • In the context of other diseases such as:
    • stenosis due to enlargement of the prostate, nephrolithiasis, pyonephrosis, intramural obstruction, tumors in the area of the urinary tract
    • acquired neurogenic bladder
    • renal hypertension (Häring 2011)
    • pyelonephritis
    • schistosomiasis (Herold 2021)
    • vesicoureteral reflux
    • urogenital tuberculosis
    • Ovarian vein thrombosis
    • aortic aneurysm
    • pronounced nephrogenic diabetes insipidus (Lentze 2014)
  • Z. n. Radiatio
  • iatrogenic during surgery in the genital area, rectum, etc.
  • extrauterine pregnancy (Manski 2019)
• by drugs such as:
  • Anticholinergics
  • Opiates
  • alphamimetics (Kasper 2015)

The pathophysiology of hydronephrosis of the adult or acquired in older children is fundamentally different from the congenital form.

• Congenital hydronephrosis:

The glomerular and tubular surface area of the kidney in the newborn is only about, 10% of that of an adult kidney, and the glomerular filtration rate (GFR) is 20%-30% of that of an adult. In the first 10 days of life, the GFR increases rapidly and is then approx. 1 - 2 ml / kg bw / h. The adult value is only reached at the age of 10. The adult value is not reached until the age of 2 years.

In congenital hydronephrosis, the disproportion between urine production and removal leads to an enlargement of the renal pelvis in the sense of accommodation. By autoregulation, renal blood flow and urine production adapt to the restricted outflow possibilities. By decreasing renal blood flow and GFR, a balance between urine production and outflow is established.

The pressure in the renal pelvis is not usually increased, even with prolonged dilatation. This only occurs after an imbalance and the resulting overdistension. The incipient reduction in kidney function need not be progressive (Steinmüller 2011).

• Acquired hydronephrosis:

The pathophysiology of acquired hydronephrosis has only been partially elucidated. Unilateral complete obstruction performed in animal experiments leads to an increase in intraluminal and intranephronal pressure with dilatation of the corresponding nephron segments. GFR decreases to 16% within 3 weeks.

There is also

• Increase in intrapelvic pressure
• upregulation of the renin-angiotensin system
• vascular resistance increases
• renal blood flow decreases (Kuhlmann 2015).

Initially there is edema of the interstitium, later there is fibrosis of the interstitium with scarring and atrophy. These changes are initially seen only in the papillae and renal medulla, and later in the renal cortex.

The increase in angiotensin- II supports an inflammatory response and leads to an accumulation of fibroblasts. Over time, this process leads to chronic kidney damage (Kasper 2015).

Congenital hydronephrosis is usually asymptomatic (Steinmüller 2011).

In older children or in adults, symptomlessness can sometimes also be observed, so that the diagnosis is made incidentally.

In the remaining cases, the following symptoms may exist:

• failure to thrive in children
• Abdominal pain (this occurs only in acute obstruction; the slowly developing dilatation of the cavity system is painless [Kuhlmann 2015]).
• Nausea
• Vomiting
• Hematuria
• arterial hypertension
• frequent urinary tract infections
• pyelonephritis
• anemia
• nephrolithiasis (Steinmüller 2011)

In the case of a sonographic suspicion of hydronephrosis, a CT scan should be performed in addition to the sonography to clarify the aetiology and to localise the obstruction precisely. If further questions arise, retrograde or antegrade urography is recommended (Kasper 2015).

Sonography: Sonography is the primary diagnostic test in cases of hydronephrosis. Hereby are found:

• central lightening
• radial arranged ectatic calyces
• the parenchyma between the calyces may appear as thin as a septum (Hofmann 2005)

In congenital hydronephrosis can be well visualized prenatally sonographically as dilatation of the renal pelvis (Entezami 2002).

Computed tomography: A CT is diagnostically meaningful in the case of, for example, sonographic suspicion of nephrolithiasis (here - without contrast medium - not only the congestion is shown as in sonography, but also any concrements that may be present), tumorous changes, blood clots, retroperitoneal fibrosis, rejected papillae, etc. (Debus 2012). (Debus 2012).

Micturition cystourethrography: If there is a suspicion of vesicoureteral reflux, micturition cystourethrography with installation of contrast media into the bladder and subsequent sonographic imaging of the reflux is recommended (Debus 2012).

X-ray micturition cystourethrography: In boys, X-ray micturition cystourethrography is recommended for the detection of anomalies of the urethra (especially in the case of urethral valves) (Debus 2012).

Blood test:

• Erythropoietin level often elevated due to local O2 - deficiency (Herold 2021).
• Erythrocytosis (as a result of increased secretion of erythropoietin (Kasper 2015).

Suspicious for urinary tract obstruction is the triad of:

• Azotemia (due to impaired excretory function of the kidneys).
• Hyperkalemia
• metabolic acidosis (Kasper 2015).

Urinalysis:

• Urine sediment often unremarkable

If not, may be present:

• Hematuria
• Pyuria
• Bacteriuria (Kasper 2015)

• multicystic kidney
• polymegacalicosis
• retrocaval ureter
• obstruction of the ureteral valves (Hegele 2015)

If the dilatation of the urinary tract is not treated immediately, non-regressive hydroureters or megaureters may develop. In the kidney, hydronephrosis leads to internal pressure in the renal pelvis:

• flattening and indentation of the medullary papillae
• Pressure atrophy of the
  • collecting tubes
  • Tubules
  • Nephrons
• Reduction of blood flow
• Narrowing of the renal parenchyma

(Häring 2011)

The primary therapeutic goal of hydronephrosis is to relieve the urinary tract.

Temporary relief can be achieved with:

• Double J catheters
• Pigtail catheter
• percutaneous drainage of the renal pelvis (so-called nephrostoma).

The causal therapy should follow immediately. Depending on the etiology, this may consist of interventional or surgical measures. The indication for antibiotic administration should be generous (Keller 2010).

In congenital hydronephrosis, surgical treatment (in the form of renal pelvicoplasty [Hegele 2015]) is required in the majority of cases (60%) (Entezami 2002).

The indication for nephrectomy may be given in:

• Hydronephrosis with non-functioning kidney (Manski 2019).
• hydronephrosis with symptoms that cannot be controlled by other means (Geiger 2003)

• Congenital hydronephrosis:

In the congenital form, of the hydronephroses diagnosed prenatally, up to 40% disappear spontaneously postnatally. Children treated surgically have a good prognosis with regard to further renal performance (Entezami 2002).

• Acquired hydronephrosis:

If sufficient healthy parenchymal margin remains, renal function may recover over a period of weeks. Excessive diuresis with sodium loss occurring during this time is not uncommon and requires appropriate drug treatment.

(Keller 2010)

Complete obstructive nephropathy can lead to irreversible renal damage after only 1 week. Among dialysis patients, 1% have causative obstructive nephropathy (Kuhlmann 2015).

The end state of untreated or late treated hydronephrosis is hydronephrotic aqueous sac kidney (Häring 2011).

Hydronephrosis triggered by obstruction of the urinary tract in the course of pyelonephritis can lead to pyelonephritic shrunken kidney (Herold 2021).

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