AJR 2004; 182:1039-1041
© American Roentgen Ray Society
Normal Ureter Size on Unenhanced Helical CT
Natalie Zelenko1,
Deidre Coll2,
Arthur T. Rosenfeld3 and
Robert C. Smith4
1 Weill Medical College of Cornell University, 420 E 70th St., New York, NY
10021.
2 Department of Radiology, New York-Presbyterian Hospital, 525 E 68th St., New
York, NY 10021.
3 Department of Diagnostic Imaging, Yale University School of Medicine, 333
Cedar St., New Haven, CT 06510.
4 Fordham University School of Law, 140 W 62nd St., New York, NY 10023.
Received July 25, 2003;
accepted after revision September 25, 2003.
Presented at the 2001 annual meeting of the American Roentgen Ray Society,
Seattle, WA.
Address correspondence to N. Zelenko
(nam2001{at}med.cornell.edu).
Abstract
OBJECTIVE. Unenhanced helical CT is the imaging method of choice
when evaluating patients with acute flank pain and suspected ureterolithiasis.
In addition to directly identifying stones in the lumen of the ureter, CT
secondary signs of obstruction such as ureteral dilatation are frequently
present and can be helpful in establishing a diagnosis. The purposes of this
study were to define ureteral dilatation on unenhanced helical CT and
determine the range of normal ureter size.
MATERIALS AND METHODS. We retrospectively reviewed the unenhanced
helical CT studies of 212 consecutive patients with acute flank pain whose CT
scans showed acute ureterolithiasis. The size of the ureter was determined on
the asymptomatic side as well as on the obstructed side. Mean ureteral
diameter was determined as the largest transverse dimension along the course
of the ureter beginning 1–2 cm below the ureteropelvic junction.
RESULTS. The mean size of ureters on the asymptomatic side was 1.8
mm with a standard deviation (SD) of 0.9 mm. The mean size of ureters on the
obstructed side was 7 mm with an SD of 3.2 mm. In 96% of patients, the ureter
diameter on the asymptomatic side was 3 mm or smaller.
CONCLUSION. Three millimeters should be considered the upper limit
of normal size for nonobstructed ureters on unenhanced helical CT.
Introduction
Unenhanced CT is the imaging method of choice for evaluating patients with
acute flank pain and suspected ureteral obstruction. Elimination of the need
for IV contrast material and the speed at which a scan can be obtained have
given CT unique advantages over older imaging methods such as excretory
urography and sonography. Furthermore, CT reveals secondary signs of
obstruction such as ureteral dilatation and perinephric stranding. The
secondary signs are significant because they can confirm a diagnosis of stone
disease even when a stone has recently passed. In addition, secondary signs of
obstruction are useful when a stone is not readily visible, when indeterminate
calcific densities are present along the anatomic course of the ureter, and
when retroperitoneal fat is scarce.
To correctly diagnose ureteral dilatation, particularly in subtle or
borderline cases of suspected ureterolithiasis, having a normal reference
range for ureteral diameter is imperative. To our knowledge, no published
studies examining the size of the ureter as visualized on unenhanced CT exist.
Astonishingly, a recent review of the literature failed to identify any
definitive studies establishing a normal ureter size on older imaging methods,
including excretory urography. Recent and classic editions of uroradiology
texts quote anatomic ureter diameter, yet make no references to the ureter
diameter revealed on imaging studies
[1–3].
As an example, in Clinical Urography
[3], the description of the
ureter identifies it as a structure 2–4 mm in diameter but makes no
specific reference to any imaging method and appears almost as an anecdotal
statement. We undertook this study to determine the size of nonobstructed and
obstructed ureters and to establish a definition of ureteral dilatation on
unenhanced helical CT.
Materials and Methods
Over a 19-month period, we retrospectively reviewed the CT scans of 212
consecutive patients with acute flank pain who were diagnosed with acute
ureterolithiasis on unenhanced helical CT. Twelve patients had more than one
CT scan, and for these patients only the first CT was used. Patients who had
previous CT scans for suspected ureterolithiasis were excluded from the study.
All CT examinations were performed using a HiSpeed Advantage CT scanner
(General Electric Medical Systems). Images were obtained from the tops of the
kidneys through the bladder base using 5-mm-thick sections and a pitch of 1.
The images were examined using soft-tissue window settings on the scanner
console at a level of 40 H and a width of 400 H.
The size of the ureter was determined on the asymptomatic side and the
obstructed side using electronic calipers
(Fig. 1). All examinations were
retrospectively reviewed together by two observers. For each patient and on
each side, ureteral diameter was determined as the largest transverse
dimension along the course of the ureter beginning 1–2 cm below the
ureteropelvic junction. Single measurements were taken. We determined the
section on which the measurement was performed by visual inspection while
scrolling the images.
Results
The mean size of ureters on the asymptomatic side was 1.8 mm (range,
1–6 mm) with a standard deviation (SD) of 0.9 mm. In our study, 203
patients (96%) had ureters on the asymptomatic side that measured 3 mm or
less. The mean size of ureters on the obstructed side was 7 mm (range,
1–20 mm) with an SD of 3.2 mm. In 14 cases (6.6%) the ureteral diameter
on the symptomatic side was less than 3 mm.
Discussion
Unenhanced helical CT has a high sensitivity (97%) and a high specificity
(96%) for detecting ureteral stone disease
[4]. Most ureteral stones,
including uric acid stones (which are not visible on radiographs), are visible
on unenhanced CT images. Although prior reports indicate that only 5% of
ureteral stones will not be revealed on CT, these studies were interpreted
retrospectively by experts in the CT diagnosis of stone disease
[5,
6].
In certain small subsets of patients, stones may not be readily apparent,
even on unenhanced CT, making radiologic diagnosis of ureterolithiasis more
complex. Such cases include stones of all chemical compositions that are
smaller than 1 mm; small stones with relatively low attenuation that are
difficult to detect; stones that have recently passed; indeterminate
calcifications along the course of the ureter (e.g., phleboliths and arterial
calcifications) that may be mistaken for a ureteral stone; and stones
consisting of pure protease inhibitors, such as indinavir sulfate (Crixivan,
Merck & Co.), which may not be revealed on CT
[7–9].
Furthermore, radiologists frequently encounter cases in which a stone is not
identified on initial review of the images but is identified when the level of
suspicion increases because of the presence of secondary signs of obstruction
such as ureteral dilatation. These secondary signs prompt the observer to
examine the images more carefully to identify a stone.
Whereas ureteral size may be of no consequence when a radiologist
encounters a straightforward case in which a ureteral stone is readily
identified, in the more complex cases such as those just described, the
presence or absence of ureteral dilatation may be crucial to make or exclude
the diagnosis. When a stone is not readily visualized on unenhanced CT in a
patient with acute flank pain, the presence of both ureteral dilatation and
perinephric stranding has a positive predictive value of 99% and the absence
of both findings has a negative predictive value of 95%
[10].
Being able to properly identify ureteral dilatation is likewise important
in diagnosing conditions other than obstruction by ureterolithiasis. Chronic
vesicoureteral reflux and congenital anomalies of the urinary tract (e.g.,
posterior urethral valves, megaureter, and prune-belly syndrome) may result in
dilatation of the ureter. Similarly, infectious processes (e.g.,
Escherichia coli, Pseudomonas, and Citrobacter) can impair
ureteral peristalsis, which can cause ureteral dilatation on CT
[11,
12]. Inflammatory processes
adjacent to the ureter, such as appendicitis or diverticulitis, may also
impair ureteral peristalsis and result in ureteral dilatation
[13–15].
Compression of the ureter by a pelvic or an abdominal mass can cause
unilateral or bilateral dilatation of the ureter. Therefore, the presence of
ureteral dilatation even in the absence of perinephric stranding may be an
important clue to the diagnosis even when stone disease is absent.
This investigation was limited in that the widest diameter for measurement
was determined visually by scrolling through the images. Exact measurements
throughout the length of the ureter were not performed. In addition, a single
measurement of each ureter was taken. Consequently, no conclusions can be
reached regarding the reproducibility of finding and measuring the ureter.
Although both of these limitations are worth noting, we believe that the
results are nonetheless valid in determining the normal ureter diameter.
In view of the fact that correctly identifying ureteral dilatation may be
crucial to arrive at a correct diagnosis, the need for a definition of what
constitutes ureteral dilatation on unenhanced CT is clear. On the basis of the
results of this study, we have established 3 mm as the upper limit of normal
for ureter diameter on unenhanced CT. Although for many cases reliance on such
a measurement will be unnecessary, in the more complex cases and for more
inexperienced observers, such a measurement may be helpful.
References
- Elkin M. Radiology of the urinary system.
Boston, MA: Little Brown, 1980
- Emmett JL, Witten DM. Clinical urography: an atlas and
textbook of roentgenologic diagnosis, 3rd ed., vol.1
. Philadelphia, PA: WB Saunders, 1971:268
- Pollack HM, McClennan BL, Dyer RB, Kenney PJ, eds.
Clinical urography, 2nd ed., vol.1
. New York, NY: WB Saunders, 2000:194
- Smith RC, Vegra M, McCarthy S, Rosenfeld AT. Diagnosis of acute
flank pain: value of unenhanced helical CT. AJR1996; 166:97
–101[Abstract/Free Full Text]
- Dalrymple NC, Verga M, Anderson KR, et al. The value of unenhanced
helical computerized tomography in the management of acute flank pain.
J Urol 1998;159:735
–740[Medline]
- Smith RC, Rosenfield AT, Choe KA, et al. Acute flank pain:
comparison of non-contrast-enhanced CT and intravenous urogram.
Radiology1995; 194:789
–794[Abstract/Free Full Text]
- Blake SP, McNicholas MMJ, Raptopoulos V. Non-opaque crystal
deposition causing ureteric obstruction in patients with HIV undergoing
indinavir therapy. AJR1998; 171:717
–720[Abstract/Free Full Text]
- Schwartz BF, Schenkman N, Armenakas NA, Stoller ML. Imaging
characteristics of indinavir calculi. J Urol1999; 161:1085
–1087[Medline]
- Yanez MH, Naidich JB, Kaplan MH. Urolithiasis as a consequence of
indinavir therapy: evaluation of its frequent and radiographic appearance.
(abstr) Radiology1997; 205(P):509
–510
- Smith RC, Verga M, Dalrymple NC, et al. Acute ureteral obstruction:
value of secondary signs on helical unenhanced CT. AJR1996; 167:1109
–1113[Abstract/Free Full Text]
- Grana L, Kidd J, Idriss F, Swenson O. Effect of chronic urinary
tract infection on ureteral peristalsis. J Urol1965; 94:652
–656[Medline]
- Teague N, Boyarsky S. The effect of coliform bacilli upon ureteral
peristalsis. Invest Urol1968; 5:423
–426
- Jones WG, Barie PS. Urologic manifestations of acute appendicitis.
J Urol 1988;139:1325
–1328[Medline]
- Maio G, Aragona F, Cisternino A, et al. Urologic complications of
acute appendicitis: report of two new cases. Urol Int1992; 48:242
–244[Medline]
- Morris J, Stellato TA, Haaga JR, Lieberman J. The utility of
computed tomography in colonic diverticulitis. Ann
Surg 1987;204:128
–132
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
Top
Abstract
Introduction
