Hydronephrosis

3 things to know first

1. It describes a swollen drainage system. It does not by itself identify the cause.
2. The cause and degree matter. A temporary mild change differs from a persistent blockage.
3. Fever with urinary symptoms needs prompt care. Infection plus obstruction can be serious.

What it is

The kidney makes urine, which collects in a central space before flowing down the ureter to the bladder. Hydronephrosis means this collecting space has widened as urine backs up or drains less freely. It can affect one kidney or both. A stone, narrowing, pressure from nearby structures, or other causes may be involved.

Why it appears on your report

Ultrasound, CT, or MRI can show widening of the renal pelvis and sometimes the smaller collecting spaces. The report may call it mild, moderate, or severe; identify the side; and describe a possible stone or another cause. A finding on imaging does not always tell whether the blockage is current or how well the kidney works.

How serious is it

Mild hydronephrosis sometimes resolves, while prolonged or severe obstruction can damage kidney function. The urgency depends on symptoms, fever, kidney function, whether one or both kidneys are involved, and the suspected cause.

When to seek care urgently

Seek urgent care for fever or chills with flank pain, inability to pass urine, severe pain with vomiting, or symptoms in someone with only one functioning kidney.

What usually happens next

1. Review urine symptoms, blood and urine tests, and kidney function.
2. Identify whether there is a stone or another obstruction.
3. Discuss whether observation, repeat imaging, or prompt drainage is needed.

A simple analogy

The kidney's collecting system is like a sink basin. If the outlet is narrowed or blocked, water can collect and stretch the basin.

Further reading

• NHS — Hydronephrosis
• NIDDK — Urinary Tract Imaging