Hydronephrosis
Hydronephrosis is the name for a swelling of the collecting spaces inside the kidney — the renal pelvis and the calyces — which happens when urine struggles…
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Hydronephrosis is the name for a swelling of the collecting spaces inside the kidney — the renal pelvis and the calyces — which happens when urine struggles to make its way down into the bladder. It is not a disease in its own right but the trace of one: somewhere along the route between kidney and exit an obstacle has appeared, and fluid backs up above it. Hence two jobs in sequence: first take the pressure off the kidney, then find and deal with whatever was blocking the flow. The less time a kidney spends under pressure, the more fully it recovers.
What happens inside the kidney
The kidney works without pause: it filters blood and delivers finished urine into the renal pelvis, and from there it runs down the ureter into the bladder. The flow goes one way only and rests on a very small difference in pressure. Block the tube and urine keeps arriving with nowhere to go: pressure in the pelvis rises and is passed backwards into the very tissue where filtering takes place.
At first the kidney copes: it widens, it stretches, it works more slowly. If the obstacle clears within a few days, everything returns to how it was. If the pressure stays for weeks and months, the filtering layer thins out and is replaced by scar tissue, and that share of the work is lost for good. Meanwhile the other kidney shoulders the load and the person notices nothing for a long time, which is why one-sided hydronephrosis is so often picked up by chance, on a scan ordered for something else entirely.
What it feels like
The picture depends on how quickly the outflow closed. When a ureter is blocked suddenly — most often by a stone — the pain arrives abruptly: it begins in the loin, to one side, travels down into the groin and thigh, comes in waves and does not ease with a change of position. There is no posture that helps, and that is what sets it apart from muscular pain. Nausea and vomiting often come with it.
When the narrowing builds up slowly there may be no pain at all. What remains is a dull heaviness in the flank that grows after drinking a lot, or a vague sense of being unwell. Sometimes the only clue is in the blood and urine tests: a rising creatinine, traces of blood.
On top of this come the signs of whatever is doing the blocking. A stone often shows itself as blood in the urine. An enlarged prostate weakens the stream, makes passing urine slow to start, brings trips to the toilet at night and leaves the feeling that the bladder has not emptied. An infection turns the urine cloudy and brings stinging and frequent urges.
When to call an ambulance
A swollen kidney on its own puts up with a great deal. It becomes dangerous in two situations: when infection joins the stagnant urine, and when both sides are blocked.
- pain in the loin or flank together with a temperature above 38 °C, chills or shivering;
- confusion, sudden weakness, cold clammy skin, a racing heart;
- barely any urine, or none at all, for several hours;
- pain so severe that vision swims and ordinary painkillers do nothing;
- relentless vomiting that makes drinking or taking medicines impossible.
Blocked drainage plus a fever is dealt with within the hour. Urine trapped in a closed kidney is a culture medium: infection multiplies inside it and within hours spills into the bloodstream. Antibiotics do poorly while the urine has no way out, so the kidney is drained first and the infection treated afterwards. Delay here is counted in hours, not days.
Passing no urine at all means both kidneys are blocked, or the only working one is. That is an emergency too. The emergency number in Spain, Italy, Portugal, Poland and Ukraine is 112.
What blocks the flow
The cause is hunted along the whole length of the route, from the renal pelvis to the way out.
- stones, the commonest reason for a ureter to close suddenly;
- an enlarged prostate: the bladder never empties fully, pressure climbs and in time reaches both kidneys;
- pregnancy, where the growing womb presses on the ureters, more often the right one; mild widening in the second half of pregnancy is taken as normal;
- a scarred narrowing of the ureter after surgery, injury, radiotherapy or a catheter left in place for a long time;
- a narrowing present from birth where the renal pelvis joins the ureter, which can give no sign of itself for years;
- tumours of the pelvic organs — bladder, prostate, cervix, rectum — pressing on the ureter from outside;
- a blood clot inside the ureter after bleeding from the kidney;
- a bladder that fails to empty because of nervous system disease or spinal injury, with nothing mechanical in the way at all.
There is also an uncommon cause worth knowing about: retroperitoneal fibrosis. The tissue behind the abdominal lining thickens, wraps around the ureters like a sleeve and gradually squeezes them shut. It advances quietly, gives vague back pain and tiredness, and is mistaken for other things for a long while — yet it begins as widening of both kidneys with no stone anywhere in sight. When imaging shows an obstruction but none of the usual culprits, this is the kind of possibility being looked for.
A swollen kidney before birth
Mild widening of the renal pelvis in an unborn baby is a fairly common finding on the mid-pregnancy scan. Most of the time it is a passing feature of a urinary system that is still growing: it settles by itself before delivery or during the first months of life. The mother feels nothing from it and the pregnancy takes its usual course.
After birth the scan is repeated, though not in the first hours: a newborn passes little urine at that stage and the picture looks misleadingly calm, so it waits a few days. The result decides whether watching is enough or a deeper look is needed. Some babies are given a low dose of antibiotic to keep infection away while the urinary tract matures; surgery is needed by a minority, those in whom the swelling grows or the kidney starts to lose function.
Parents of such a child should take away one point: a temperature without an obvious cold during the first year calls for a urine test. In babies a urinary infection often looks like nothing more than fever, floppiness and refusing feeds.
How it is confirmed
An ultrasound scan comes first. It is painless, involves no radiation and shows straight away whether the spaces inside the kidney are widened and by how much. That settles the question of whether urine is backing up, but not why.
- a urine test for blood, inflammation and bacteria, with a culture if infection is suspected;
- a blood test for creatinine, which shows how far the filtering has suffered;
- a CT scan, the best way to see a stone and the exact point of narrowing, and with contrast the wall of the ureter as well;
- examination of the prostate in men and measurement of how much urine is left in the bladder after passing water;
- an isotope study, which answers what a picture cannot: whether the narrowing is genuinely getting in the way, and how much working kidney is left behind it;
- cystoscopy, a look inside the bladder, when a tumour is suspected or the opening of the ureter is covered over.
In pregnancy and in children the work starts and often ends with ultrasound; if more detail is needed, magnetic resonance imaging gives it without radiation.
How the flow is restored
Treatment moves in two steps, and the order of them matters more than the choice of tools.
First the urine is let out. If the obstacle sits low down, at the bladder outlet, a catheter is enough and relief comes almost at once. If the ureter is the problem, a stent is placed: a fine tube passed up from inside that holds the channel open. When a stent cannot be placed, or the person is too unwell for the procedure, a nephrostomy is done instead — a drain brought out from the kidney itself through the skin of the back, guided by ultrasound. It is neither a verdict nor a permanent arrangement: the drain comes out once the cause has been dealt with.
Then the cause itself is tackled. A stone is broken up or removed, a narrowed stretch of ureter is widened or cut out and rejoined, an enlarged prostate is treated with medicines or operated on, and where there is a tumour the plan is drawn up by a cancer specialist. Infection is treated with the antibiotic the culture points to.
Once drainage is restored the person is watched for the first few days: a kidney that has spent a long time under pressure sometimes starts producing very large amounts of urine. The body then loses water and salts faster than it can replace them, so in hospital the output is measured and fluids are given into a vein if needed. This is expected rather than a complication, but it is not something to leave unsupervised.
What happens if it drags on
With help in good time the kidney usually returns to work and leaves no trace behind. Trouble comes where the pressure was allowed to sit for months.
Long-standing back-up ends in a shrunken kidney: it grows smaller, filters less and less, and that cannot be undone. When both sides have suffered, the road leads to chronic kidney disease; when the blockage is complete, to kidney failure within days. There is a separate line of trouble as well, that of infection: stagnant urine becomes infected readily, episodes repeat, and each one takes away a little more working tissue. Stones follow too, since they form more easily in a widened renal pelvis.
So even a quiet, painless hydronephrosis found by accident is not left unexplained. The widening is a message about an obstacle, and it is the obstacle that has to be sorted out.
Online consultation
In an online appointment a doctor can go through the nature of the pain and where it travels, ask about passing urine, fever and past operations, and look through any imaging and test results that already exist. That is enough to judge whether a trip to hospital is needed straight away or a scan can be arranged calmly, and which investigation should come first so that time is not wasted going in circles. The doctor will also spell out which signs mean calling an ambulance rather than waiting for the next appointment.
This material is for information only and does not replace medical advice.
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