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Genitourinary Imaging |
1 From the Department of Radiology, University of Texas Health Science Center at Houston, Tex. From the 1997 RSNA scientific assembly. Received January 28, 1998; revision requested April 7; revision received October 12; accepted November 9. Address reprint requests to I.C.B., Mallinckrodt Institute of Radiology, Washington University Medical Center, 9th Fl, Box 8131, 510 S Kingshighway Blvd, St Louis, MO 63110.
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Abstract |
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MATERIALS AND METHODS: The nonenhanced helical CT scans in 82 patients with a confirmed diagnosis of pelvic ureterolithiasis were retrospectively reviewed. Each calcification along the ureter was classified as a phlebolith or a ureteral calculus on the basis of clinical and imaging findings and was analyzed for the presence of a tail sign.
RESULTS: Eighty-two patients each had a single ureteral calculus. None of these calculi were associated with a positive tail sign. Sixty-nine phleboliths were present in 35 patients. Forty-five phleboliths (65%) were associated with a positive tail sign. Of the remaining 24 phleboliths, 17 (25%) were associated with a negative tail sign and seven (10%) were indeterminate. The tail sign has a sensitivity of 65% (45 of 69; 95% CI: 53%, 75%) and a specificity of 100% (82 of 82; 95% CI: 96%, 100%) in differentiating phleboliths from ureteral calculi.
CONCLUSION: The tail sign is an important indicator that a suspicious calcification represents a phlebolith. Absence of the tail sign indicates that the calcification remains indeterminate.
Index terms: Kidney, CT, 81.12111, 81.12115 • Ureter, calculi, 82.811 • Ureter, CT, 82.12111, 82.12115
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Introduction |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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MATERIALS AND METHODS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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All the CT scans were retrospectively reviewed jointly by two radiologists (I.C.B., P.N.). A consensus was reached for each finding. We chose to include in the study only those patients in whom a definitive ureteral calculus had been identified so that it could be certain that all other suspicious calcifications represented phleboliths. One hundred two patients had a ureteral stone as the cause of their acute flank pain. The diagnosis of ureterolithiasis was made at nonenhanced helical CT when a calculus was identified in the lumen of the ureter.
The diagnosis was substantiated at CT by the presence of a positive tissue rim sign and of the secondary signs of ureteral obstruction, including dilatation of the ureter and collecting system above the calculus, stranding of the perinephric and periureteral fat, and nephromegaly. The diagnosis of ureteral stone disease was also corroborated with the findings at excretory urography and retrograde pyelography, when available, and with the clinical findings of flank pain and of subsequent stone passage. We decided to exclude 20 patients in whom the calculus was located in the proximal or midureter above the iliac crests, because phleboliths are rare in the abdomen and their differentiation from ureteral calculi is usually not a diagnostic problem in that location. Therefore, 82 patients (48 male patients, 34 female patients; age range, 16–69 years; mean age, 33 years) with a confirmed diagnosis of pelvic ureterolithiasis were selected to form the study population.
The CT scans of these 82 patients were evaluated for all calcifications along the course of the ureters from the iliac crests to the bladder base. Arterial and myometrial calcifications were excluded because their characteristic location and appearance allow easy differentiation from ureteral calculi. One hundred fifty-one calcifications met the inclusion criteria and constitute the study group. Each calcification was categorized as either a ureteral calculus or a phlebolith on the basis of clinical manifestation (flank pain in 82 patients, history of stone passage in 42 patients) and imaging findings (nonenhanced helical CT in 82 patients, excretory urography in 39 patients, and retrograde pyelography in three patients).
Each calcification was also analyzed for the presence of a tail sign. The tail sign was considered positive when a linear or curvilinear area of soft-tissue attenuation of varying length and thickness extended to and came in contact with the calcification (Fig 1). The tail sign was also considered positive when the calcification was located within the crescentic area of soft-tissue attenuation produced by the rectovesical or uterovaginal venous plexus (Fig 2). The tail sign was considered negative when the calcification was surrounded by fat but no soft-tissue tail was present (Fig 3). When there was no clear fat plane around the calcification, the tail sign was considered indeterminate.
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RESULTS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Therefore, the sensitivity and specificity of the tail sign in differentiating a phlebolith from a ureteral calculus are 65% (45 of 69; 95% CI: 53%, 75%) and 100% (82 of 82; 95% CI: 96%, 100%), respectively.
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DISCUSSION |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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In some cases, it may be difficult to confidently differentiate ureteral calculi from other calcifications along the course of the ureters. The most common periureteral calcification to be confused with a ureteral calculus is a pelvic phlebolith. In the presence of a suspicious calcification, the most reliable signs of ureterolithiasis are those that indicate ureteral obstruction, including nephromegaly, ureteral dilatation, and perinephric edema (stranding of the perinephric fat, perinephric fluid collections, and thickening of the renal fascia) (5). However, the presence of these secondary CT signs does not always imply that the suspicious calcification represents a ureteral calculus rather than a phlebolith. These signs may be absent in patients with nonobstructing calculi, or they may still be present in patients with recently passed calculi.
The tissue rim sign has been useful in differentiating ureteral calculi from pelvic phleboliths. The tissue rim sign is described as a halo of soft-tissue attenuation around a suspicious calcification and is very specific for ureteral calculi rather than for phleboliths. This sign has a reported sensitivity of 50%–77% and specificity of 92%–100% (6,7). The rim of soft tissue is thought to represent the edematous wall of the ureter around the calculus.
Our study findings suggest that the tail sign may also be helpful in distinguishing phleboliths from ureteral calculi (sensitivity of 65%, specificity of 100%). The tail of soft tissue is thought to represent the vein, venule, or venous plexus in which the phlebolith is located. However, a curvilinear segment of nondilated ureter leading to a calculus may have a similar appearance to that of the venous structure in which a phlebolith is located, a situation that can be termed the "pseudotail sign." This may be more likely in the pelvis near the ureterovesical junction, where the ureter assumes a more axial orientation. Although not encountered in our study population, this situation represents a potential limitation of the tail sign. This potential pitfall may be avoided by carefully assessing the relationship of the tail to the ureter, by analyzing the attenuation of the center of the tail, and by evaluating the orientation of the tail with respect to the suspicious calcification.
A pseudotail sign is present if the ureter above communicates with the tail below and if fluid-attenuation urine, even if minimal, is noted in the center of the tail. A true tail sign is present if the ureter and the tail are separate in space on contiguous images and if the tail is of uniform soft-tissue attenuation. In addition, a tail cannot represent a nondilated ureter above a calculus if it does not follow the expected medial and anterior course of the distal ureter near the ureterovesical junction.
When interpreting a nonenhanced helical CT scan in a patient suspected of having ureterolithiasis, one may use the following algorithm. When a calcification is identified within the lumen of the ureter or at the ureterovesical junction, the diagnosis of ureteral stone disease can be made with confidence. In the presence of a suspicious calcification along the course of the ureter on the symptomatic side, the presence of secondary signs of ureteral obstruction and of the tissue rim sign around the calcification are evidence of ureterolithiasis. The tail sign should be used as an ancillary sign in equivocal cases. When a suspicious calcification is associated with a positive tail sign, the odds are strong that it represents a phlebolith rather than a ureteral calculus. In its absence, the calcification remains indeterminate. In patients in whom confident differentiation cannot be achieved, contrast material administration may be required. In such cases, one of the major advantages of nonenhanced helical CT is precluded.
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Footnotes |
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References |
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