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I./3.3.: Hydronephrosis in a radiologist point of view
The radiologist will be informed if it is only a case of a „simple” hydronephrosis or the renal function is also impaired besides the dilatation of the urine collecting system (obstructive nephropathy).
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Dilatation of the urine collecting system depends on the duration of the obstruction and if „supplying” urine excretion is still present and of which extent. In addition, if the spontaneously developed decompression (e.g. pyelon rupture) could decrease the existing strain.
The radiologist (using the above mentioned imaging methods: US, CT, MRI, probably angiography) collects data on the grade of the residual renal cortex which has an important prognostic value.
Acute hydronephrosis. Most frequent cause is obstruction by a stone. The following locations are predilectious for stone obstruction (so it is expedient to seek a stone in these places) according to the downwards movement of the stone: ureteropelvic junction, crossing of the iliac vessels, ureterovesical junction. Stones should be looked for in these places both by US and CT. In case of a stone sticked in the ureterovesical stenosis, to state by traditional radiography that the stone is located really in the ureter is sometimes a difficult task.
To distinguish a stone from the very closely located phleboliths is sometimes impossible. Acute hydronephrosis might develop due to a blood clot as well (e.g. bleeding pyelon tumor, bleeding from an AV malformation, consequence of anticoagulant therapy, in trauma). Following a catheter guided intervention, injured ureteral mucosa might cause edema. Ureter strangulation might occur postsurgically. Ureter compression might occur in pregnancy. In addition, therapeutically applied sulphonamide can be crystallized and aggregated in sour urine. Acute ureter obstruction is characterized by strong pain, nausea and vomiting. Accompanying infection is common.
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In this case, imaging methods show a kidney of normal shape and size, parenchyma thickness is normal. Using excretion methods (X-ray, CT), the density of the kidney is increased on the nephrography (obstructional nephrography). The excretion or the filling up of the urine collecting system is drawn out on the radiograph which refers to the decline in glomerular filtration. The end point of the contrast enhanced, X-ray absorbing urine column indicates the obstruction site. Jet sign, which is a normal finding on US imaging, cannot be seen in this case. Stag-horn stone might be misleading if the entire urine collecting system is filled completely.
No pathognomic signs can be observed neither in hyperacute case if the urine collecting system is not dilated. If the patient is dehydrated (elderly/newborn) or the obstruction is partial, findings might be negative. False positivity can be caused by drawn out excretion due to full bladder, hyperhydration, diabetes insipidus and excessive diuretics use. False positivity might be also caused by acute pyelonephritis, sudden ease of obstructive situation (e.g. surgically) and vesicoureteral reflux.
Dilatation of the pyelon and the ureter, infiltration of the perinephric/periureteral adipose tissue (higher density) can be already observed on unenhanced CT imaging. Calcified stone can be seen on CT, even if it is barely calcified. In addition, ureteral ring sign can be detected in nearly two-third of the cases which indicates the edema around the sticked stone in the wall of the ureter.
Congenital hydronephrosis can be often already detected in the first year of life, however, diagnosis can be drawn out even till the 5th year of life. Congenital hydronephrosis is frequent in Down syndrome and often bilateral. Its most common cause is the ureteropelvic obstruction, followed by the posterior urethral valve and the ectopic ureterokele, etc. Most frequently it is recognised as a palpable abdominal mass, however it can be already detected in utero based on its intrauterine US findings (kidney size/control of pyelon diameters according to the kidney sizes referred to gestational age). In a suspicious case, ultrasound control is necessary in several days after birth.
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