<s>[INST] context: The most important clinical aspect of retroperitoneal fibrosis is that the fibrotic process frequently entraps and constricts the ureters thereby causing obstructive uropathy.
Retroperitoneal fibrosis -

It is a nonspecific, nonsuppurative inflammation of fibro-adipose tissue of unknown cause that produces symptoms by the gradual compression of tubular structures in retroperitoneal space.

Aetiology of retroperitoneal fibrosis - 

About 2/3rd cases are primary idiopathic, are also known as Ormond's disease

Secondary Retroperitoneal fibrosis

a variety of inflammatory conditions - chronic pancreatitis, histoplasmosis, tuberculosis, or actinomycosis.
drugs
methysergide (most imp.)
β blockers
hydralazine
α methyldopa
Etacapone (used in the t/t of Parkinson's ds.) -
malignancies (prostate, non-Hodgkin's lymphoma, sarcoma, characinoid & gastric cancer).
antoimmune disorders (ankylosing spondylitis, SLE PAN etc.)

Symptoms of retroperitoneal fibrosis  -

It is more common in men between 40-60 yrs of age
Early symptoms are nonspecific and vague. These are
Pain → Dull noncolicky and insidious in onset.
Anorexia, nausea
General malaise, diarrhea

Later on, symptoms result from compression of tubular retroperitoneal structures. The major structure involved are-

Ureter - Most commonly involved
Aorta
Inferior venacava


Symptoms due to the involvement of ureter (usually b/1 involvement)
Dysuria
Frequency of urination
Chills and fever occur with secondary infection of a hydronephrotic kidney.
Hematuria can occur.

Diagnosis 

The diagnosis of retroperitoneal fibrosis usually can be made accurately by intravenous pyelography if uremia is not present.
The characteristic finding on pyelogram are


Hydronephrosis with a dilated tortuous upper ureter.
Medial deviation of the ureter
Extrinsic ureteral compression

Note: In a retroperitoneal tumor, ureter is laterally deviated while in retroperitoneal fibrosis ureter medially deviates.

Currently, the imaging procedure of choice is the CT scan.
But if renal function is compromised contrast agents are not given and then MRI is the procedure of choice.

T/T of Retroperitoneal fibrosis 
Corticosteroids, with or without surgery, are the mainstay of medical therapy.
Surgical treatment is required in patients who present with moderate or massive hydronephrosis. It consists primarily of ureterolysis (freeing the ureter from adhesions and surrounding tissue) or ureteral stenting..
Also, know

Partial or complete ureteral obstruction occurs in 75 to 85% of patients.
Most common site of urethral obstruction is lower third of the ureter. [/INST] question: Most common organ involved in retroperitoneal fibrosis is - | options: A: Aorta B: Ureter C: Inferior vena cava D: Sympathetic nerve plexus | answer: B </s>