Abdominal CT findings in Urolithiasis Method: Step 1 – evaluate for signs of obstruction
1. asymmetric stranding of perinephric fat
a. Perninephric fat stranding represents fluid accumulation in bridging septa
of the perinephric fat as a result of increased lymphatic pressure.
b. usually obviousc. may appear as loss of interface between kidney and perinephric fatd. may be fine linear strandinge. may be slight difference in perinephric fat density at poles of kidneyf. fluid collection around kidney suggests obstruction and forniceal rupture
2. dilation of intrarenal collecting system – less variation in size of intrarenal
a. analyze the renal sinus in the upper and lower poles of the kidneyb. analyze for obliteration of renal sinus fat due to compression of a dilated
c. Unilateral loss of white pyramids suggest urinary tract obstruction
3. hydroureter -- Abnormal enlargement of the ureter caused by any blockage that
prevents urine from draining into the bladder.
a. Usually apparent if presentb. Follow from kidney to bladder
Step 2 – Evaluation of the ureters for calcifications
1. Follow the ureters from the renal pelvis to the base of the bladder
a. Easiest with PACS system (picture archiving and communications system)b. Areas of difficulty
i. Level of the mid-pelvis – bifurcation of the iliac vessels widens
makes it difficult to follow the ureters – many vessels, lymphchannels and collapsed unopacified bowel loops
ii. Phleboliths versus distal ureteral calculi
1. Uteral stone versus pelvic phlebolith is difficult to
diffrentiate for inexperienced readers.
2. A rim of edematous ureteral tissue or localization of the
stone at the UVJ often helps make this distinction.
3. phlebolithis are usually below the ischial spine4. ureters usually enter the bladder above the level of the
iii. Recently passed stone and stone at UVJ
1. both demonstrate rim sign2. both demonstrate signs of obstruction3. if uncertain – rescan patient in the prone position as a
1. excreted drug is often in the form of crystals that are not
c. More difficult to follow if they are normal or patient has minimal body fatd. UVJ identification
i. High-attenuation area in the posterior wall of the bladder
ii. Ureters enter the bladder wall lateral to the UVJ
2. Stone locations (in descending order of frequency)
a. UVJ*b. Pelvic Brimc. Transition between the renal pelvis and ureter (UPJ)*d. *Ureter changes calibur at the UVJ and UPJ
3. Rim sign – halo of soft-tissue attenuation seen around the circumference of an
intraureteral calculus on unenhanced axial CT-has been described as useful indifferentiating ureteral calculi from extraurinary abdominal or pelviccalcifications
a. Helps to distinguish between ureterolithiasis and ileac artery calcifications
b. Helps to distinguish between ureterolithiasis and phleboliths
1. Primary - demonstration of a high attenuation stone within a well-identified ureter
or at the ureter-vesicular junction (UVJ).
2. Secondary signs of ureteral obstruction
a. Unilateral dilation of the involved ureterb. Dilation of the intrarenal collecting systemc. Stranding of the perinephric fat
Definitions: Hydronephrosis is defined as a dilation of the renal pelvis and calyces. Hydroureter - Abnormal enlargement of the ureter caused by any blockage that prevents urine from draining into the bladder.
Multidetector unenhanced CT scan versus intravenous pyelogram (IVP)
• Faster• No contrast• More radiation• Identifies alternative source of symptoms• Not a physiologic study• Non therapeutic
Unenhanced helical CT scan will replace IVP as the “gold standard” for the diagnosis ofureteral stone.
CT scan can detect 95 to 98% of obstructing stones. Secondary signs are seen in 90 to 95% of patients.
Secondary signs of obstruction but no stone is present:
1. recently passed stone2. pyelonephritis3. urinary tract obstruction unrelated to stone disease4. protease inhibitor deposition diseases
1. Vaswani KK, El-dieb A, Vitellas KM, Bennett WF, Bova JG. Ureterolithiasis:
classical and atypical findings on unenhanced helical computed tomography. Emergency Radiology (2002) 9:60-66.
2. Anatomy, A regional atlas of the human body, 3rd Ed. Clemente, CD. Urban &
3. Emergency Radiology. Schwartz DT, Reisdorff EJ. McGraw-Hill, New York
4. Dalrymple NC, Casford B, Raiken DP, Elsass KD, Pagan RA. Pearls and pitfalls
in the diagnosis of ureterolithiasis with unenhanced helical CT. RadioGraphics
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