Retroperitoneal fibrosis
Retroperitoneal fibrosis is a rare condition in which scar-like tissue grows in the space behind the abdominal lining (the retroperitoneum) and squeezes the ureters from outside.
Remember
When urine backs up slowly into both kidneys and swells their drainage systems (hydronephrosis), yet the bladder empties well and nothing is seen inside the ureters, think of tissue squeezing them from outside: retroperitoneal fibrosis is the classic example.
Memory aid
extra means outside, intra means inside, so think of a hand squeezing a hosepipe compared with a plug stuck inside it
It helps you tell a squeeze from outside the ureter from a plug blocking it from inside.
The ureters (the tubes carrying urine from the kidneys to the bladder) run through the retroperitoneum along with the kidneys. Scar-like fibrous tissue growing there wraps around the ureters, which is called encasement, and squeezes them from outside.
Urinary obstruction is classified by site and by level. By site, it is extraluminal: the lumen is the hollow channel inside the ureter, and something presses on the tube from outside. An intraluminal problem, by contrast, is inside the lumen or in the wall of the tube, as with a stone or a clot. By level, it is supra-vesical, meaning above the bladder (vesica is Latin for bladder), because the blockage lies between the kidneys and the bladder.
Urine backs up behind the narrowing and causes hydronephrosis. The tissue also pulls the ureters towards the midline, which is why imaging shows medial deviation. The typical imaging picture is medial deviation, external narrowing and hydronephrosis. The narrowing builds up slowly, which fits the gradual onset, and the ureters are often squeezed on both sides, with no stone seen. Stones typically cause sudden waves of colic (pain that comes and goes).
About two thirds of cases are idiopathic, meaning that no cause is found. Others follow malignancy (cancer), autoimmune disease, drugs or an abdominal aortic aneurysm (a swelling of the main abdominal artery), so an underlying cancer must be excluded. Treatment includes relieving the obstruction, excluding a possible underlying malignancy and using steroids or immunosuppression (lowering immunity).
Key facts
- Site
- extraluminal, so the ureters are squeezed from outside the lumen rather than blocked from inside.
- Level
- supra-vesical, above the bladder, between the kidneys and the bladder.
- Imaging
- the typical picture is medial deviation of the ureters, narrowing from outside and hydronephrosis.
- Course
- it builds up gradually, unlike the sudden waves of colic from a stone.
- Causes
- about two thirds are idiopathic, and others follow malignancy, autoimmune disease, drugs or an abdominal aortic aneurysm.
- Management
- exclude malignancy, relieve the obstruction, then use steroids or immunosuppression (treatment to cut immunity).
Exam traps
- A stone is a common cause of renal colic, but it blocks the ureter from inside and usually affects one side, so it does not fit a slow, bilateral obstruction with nothing seen inside the ureters.
- Dead tissue shed from the kidney after papillary necrosis (the tips of the kidney's drainage pyramids die) can block the ureter from inside and presents like renal colic, so it does not explain a slow squeeze from outside.
- A narrowing of the pelviureteric junction (where the kidney's collecting area meets the ureter) is usually present from birth and can cause hydronephrosis, but it is a narrowing at one junction, so it does not pull both ureters towards the midline.
Read the full notes
Tested in 13 SimpleMed+ questions
Practice it in Urinary System, with the answer and a full explanation after every question.
Practice these questions