RadioGraphics 2004; 24:S11–S33 ● Published online 10.1148/rg.24si045505 ● Content Codes:
1From the Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 S Kingshighway Blvd, St Louis, MO 63110. Pre-sented as an education exhibit at the 2003 RSNA scientific assembly. Received February 9, 2004; revision requested March 4 and received April 5;accepted April 14. All authors have no financial relationships to disclose. Address correspondence to S.B. (e-mail: [email protected]).
See the commentary by Katz et al following this article.
IntroductionSince its introduction by Smith et al (1) in 1995,unenhanced helical computed tomography (CT)has revolutionized the imaging evaluation of acuteflank pain. Unlike excretory urography, unen-hanced helical CT is fast (less than 5 minutes),usually does not require the intravenous adminis-tration of contrast material, and has very low in-terobserver variability (2,3). It also requires nopatient bowel preparation, making it particularlyeffective in the emergent setting.
During the past 9 years, CT has become thestandard of reference in the detection of urinarycalculi due to its high sensitivity (95%–98%),high specificity (98%–99%), and ability to helpdelineate alternative causes of flank pain (1–5).On occasion, intravenous contrast material maybe administered to further characterize noncoliccauses of flank pain or other asymptomatic find-ings.
In this article, we review causes of acute flankpain that may be identified at unenhanced helicalCT. All of the cases involved patients who pre-sented to our emergency department with acuteflank pain during the past 2 years. In all cases,patients initially underwent imaging according tothe standard urolithiasis protocol we use with un-enhanced multi–detector row CT (2.5 detectorcollimation, contiguous 3-mm image reconstruc-tion, table speed of 10–18 mm per gantry rota-tion, 120 kVp, and 200 effective mAs). In selectcases, repeat imaging with intravenous and oralcontrast material was performed. The decision torepeat CT with contrast material was based onconsensus between the radiologist and referringclinician. Repeat imaging was attempted to fur-ther characterize a finding on the unenhancedstudy or to search for alternative diagnoses whenresults of follow-up clinical examination sug-gested a diagnosis not adequately evaluated onthe unenhanced study (eg, aortic dissection).
First, we discuss urolithiasis and its secondarysigns. Next, we review and categorize, accordingto organ system, alternative entities that maymanifest as acute flank pain and may be confusedwith renal stone at clinical examination. Urinarytract calculi were observed in only one case; in allcases, the alternative diagnosis was believed to beresponsible for the patient’s emergency depart-ment presentation. Knowledge of these condi-
tions may allow the radiologist to know where tofocus his or her attention when no stone is en-countered on an unenhanced helical CT scanobtained because of flank pain, especially in anemergency department setting.
Acute Flank Pain:CT Spectrum of Disease
Symptoms associated with numerous diseases canbe indistinguishable from those of renal colic be-cause receptors of many visceral organs as well asthe body wall transmit sensation through painfibers shared with the kidneys (5). Because of thisoverlap of the autonomic nervous system, patientshave poor localization of visceral pain, and find-ings at physical examination are often nonspe-cific. Other symptoms associated with renalcolic—hematuria, nausea, and, rarely, vomiting—are also seen with other, noncolic causes of flankpain (3). This clinical overlap has made imagingindispensable for diagnosing renal colic in theemergency setting. Our experience has mirroredthat of other investigators (2,3,6,7), who havereported that 9%–29% of patients presenting withflank pain may have an alternative diagnosis atunenhanced helical CT, most commonly adnexalmasses, pyelonephritis, appendicitis, and diver-ticulitis. In fact, a renal or ureteral stone will bedetected at CT in only 33%–55% of patients withacute flank pain (2–4,7).
Figure 1. Medullary nephrocalcinosis in a 34-year-old woman with medullary sponge kidney, renal colic,and hematuria. Unenhanced helical CT scan showsseveral calcifications centered in the region of the med-ullary pyramids (arrows). No ureteral stone was found.
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CT Findings Related toUrinary Tract Stone Disease
Even though urinary calculi are seen in fewer thanone-half of patients who undergo unenhancedhelical CT, they still represent the most commoncause of flank pain in patients undergoing thisprotocol (2,3,6). Therefore, we provide a briefreview of the well-documented CT findings ofurolithiasis.
Regardless of composition, almost all renal andureteral stones are detected at helical CT becausethe attenuation of stones is inherently higher thanthat of the surrounding tissues (Fig 1) (8). Onenotable exception is the so-called indinavir stone,which may be encountered in patients with thehuman immunodeficiency virus who are undergo-ing treatment with this protease inhibitor. Thismedication can crystallize in the urine and resultin stones that may or may not be detected withCT (9). When the stones are not seen, findingswill be similar to those of a recently passed stone,including secondary findings of obstruction.Crystallized medication should be differentiatedfrom matrix stones, which refer to aggregates ofmucus that may form within the urinary tract ofboth healthy and immunosuppressed individuals(10). These matrix stones tend to have soft-tissue
attenuation at unenhanced CT unless mixed withcalcified impurities.
Attention should be focused on the most com-mon locations for obstruction by a stone. Naturalanatomic narrowing occurs in three areas of theureter: the ureteropelvic junction, the pelvic brimwhere the ureter changes caliber as it crosses theiliac vessels, and the ureterovesical junction (Fig2). Obviously, the most direct sign of a ureteralstone is a calcification within the ureteral lumen.At times, however, it can be difficult to differenti-ate a phlebolith from a stone in the ureter. Inthese cases, secondary signs of obstruction, in-cluding ureteral dilatation, asymmetric inflamma-tory change of the perinephric fat, hydronephro-sis, and nephromegaly are useful (11,12). On CTscans, phleboliths virtually never demonstrate thehypoattenuating (lucent) center that is a charac-teristic finding on plain radiographs (13). Thesoft-tissue rim sign, which refers to a soft-tissuering surrounding the calcification, is believed torepresent the edematous wall of the ureter andcan be helpful for differentiating a phlebolithfrom a ureteral stone (Fig 3) (1,2,11,13,14). At
Figure 2. Obstructing stone at the right ureterovesical junction in a 26-year-old woman with right flank pain. Un-enhanced helical CT scans show a tiny stone located at the right ureterovesical junction (arrow in b) and secondaryright hydronephrosis and perinephric stranding (arrow in a).
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times, curvilinear soft tissue can also be seen lead-ing to a pelvic calcification. This finding has beenreported in association with phleboliths and hasbeen dubbed the comet-tail sign (15). In thiscase, the soft tissue is believed to represent thedilated vein leading to the phlebolith. This lattersign has been shown to have limited value in thedifferentiation of phlebolith from distal ureteralstone (16).
An obstructing stone at the ureteral insertioncan be difficult to differentiate from a stone thathas recently passed into the bladder. In this situa-tion, it may be useful to place the patient in theprone position and obtain a repeat image of thepelvis. A stone that falls to the now-dependentanterior portion of the bladder has obviouslypassed, whereas a stone that remains at the ure-teral insertion is obstructing the distal ureter. Forstones smaller than 4 mm, prone imaging may notbe worth the added radiation, since previous workhas demonstrated that over 80% of stones 4 mmor smaller at the ureterovesical junction will passspontaneously (2,17,18).
Urinary Tract Dis-eases Unrelated to Calculi
It is important to remember that any disorder thataffects one kidney or causes hydronephrosis maymimic simple renal colic. One of the more com-mon findings simulating an obstructing ureteralstone at clinical examination, as identified at un-enhanced CT, is pyelonephritis, which may mani-fest as asymmetric perinephric stranding or mildrenal enlargement when the infection is moderateto severe (6,19). Mild disease may have no unen-hanced CT findings at all (19). When intravenous
Figure 3. Bilateral obstructing ureteral stones in a 36-year-old man who presented with flank pain and hematu-ria. (a) Unenhanced helical CT scan shows bilateral en-larged kidneys with perinephric stranding. (b, c) CT scansshow distal left ureteral stones (b) and a tiny obstructionin the right ureterovesical junction (arrow in c). Note thesoft-tissue rim sign (arrow in b).
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contrast material is given, pyelonephritis may beseen focally as wedge-shaped areas of low attenu-ation or, more generally, as striated enhancementof the kidney (Fig 4) (20). More serious compli-cations of pyelonephritis (renal or perinephricabscess) may also be depicted (Fig 5).
When unenhanced CT demonstrates unilateralperinephric stranding or nephromegaly but nostones, the use of intravenous contrast materialshould strongly be considered. Although contrast-
Figure 4. Acute pyelonephritis in a 19-year-old woman with acute left flank pain. (a) Initial unenhanced helicalCT scan shows an enlarged left kidney with perinephric stranding and urothelial thickening, but no obstructingstone. (b) Contrast-enhanced CT scan shows striated enhancement of the kidney (arrow). Results of urinalysishelped confirm the presence of urinary tract infection.
Figure 5. Renal abscess in a 26-year-old man with acquired immunodeficiency syndrome who presented with rightflank pain. (a) Initial unenhanced helical CT scan shows no obstructing stone but demonstrates a hypoattenuatingmass in the right upper pole. (b) Delayed contrast-enhanced CT scan helps confirm the presence of a cystic lesionwith adjacent renal parenchymal edema (arrows). Staphylococcus aureus was seen in cultures of the aspirated speci-men.
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enhanced CT may show findings of pyelonephritis,which is usually diagnosed at clinical examina-tion, it may occasionally reveal more serious vas-cular conditions such as renal infarction, renalvein thrombosis, or renal artery aneurysm, whichcan also manifest with acute flank pain and hema-turia (Fig 6) (19,21).
Renal and transitional cell carcinoma must beexcluded in any middle-aged to elderly patientwith flank pain and hematuria as well. On unen-hanced images, urinary tract cancers may appear
as subtle, focal contour abnormalities of the kid-ney, complex renal cysts, focal ureteral or bladderwall thickening, and soft-tissue masses in thebladder (Fig 7). If any of these signs are encoun-tered, intravenous contrast material will usuallybe useful for further characterization. Sometimes,previously occult malignancies may result inspontaneous hemorrhage and concomitant flankpain (Fig 8). When an isolated subcapsular or
Figure 6. Complicated renal arteriovenous malforma-tion in a 66-year-old man who presented with acuteright flank pain and hematuria. (a, b) Initial unen-hanced helical CT scans show a complex cystic mass ofthe right kidney with peripheral calcification (arrows ina) and blood within the bladder and right collecting sys-tem (b). No obstructing stone was found. Air within thebladder was secondary to Foley catheter placement.(c) Angiogram helps confirm the presence of a largearteriovenous malformation (arrows), as did the resultsof pathologic examination.
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perinephric hemorrhage is seen, close attentionshould be paid to exclude an underlying neo-plasm. Intravenous contrast material may enablethe detection of the cause of the hemorrhage andhelp guide management (Fig 9) (22). Intravenous
contrast material may also enable exclusion ofsoft-tissue masses that may mimic subcapsularhemorrhages on unenhanced scans (Fig 10).
Figures 7–9. (7) Transitional cell carcinoma in a 56-year-old man who presented with gross hematuria. (a) Unen-hanced helical CT scan shows a vague soft-tissue mass within the urinary bladder (arrow). (b) Delayed contrast-en-hanced CT scan enables better characterization of the mass. Results of biopsy helped confirm the presence of transi-tional cell carcinoma. (8) Hemorrhagic renal cell carcinoma in a 58-year-old man who presented with acute flankpain and hematuria. Unenhanced helical CT scan shows a large hemorrhagic mass within the left kidney (arrows).No obstructing stone was seen. Surgical findings helped confirm the presence of hemorrhagic renal cell carcinoma.(9) Spontaneous subcapsular hematoma in a patient with left renal colic who was receiving anticoagulants. Unen-hanced helical CT scan shows a subcapsular collection with high attenuation (arrows). Contrast-enhanced CT scans(not shown) helped confirm the presence of subcapsular hematoma without a distinct underlying mass.
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Other causes of flank pain that may be encoun-tered on unenhanced helical CT scans includecongenital ureteropelvic junction obstruction,ureteral obstruction from compressive lymphad-enopathy, and cystitis (Fig 11) (2,6).
Extraurinary Tract Diseases
Gynecologic ConditionsGynecologic conditions frequently manifest asabdominal and flank pain and represent one themost common nonstone findings (about 10% ofalternative diagnoses) at unenhanced CT per-formed for urolithiasis (2,6). In this group, ad-nexal masses make up most cases. Most of thesemasses tend to be ovarian cysts, usually hemor-rhagic (Fig 12), but tubo-ovarian abscesses, der-moid cysts, endometriomas, and ovarian neo-plasms may also be seen (Fig 13). In addition tohemorrhage, large adnexal masses may be painfulowing to the mass effect on the distal ureter, withresultant hydroureteronephrosis or adnexal tor-sion. Hemorrhagic masses may have high attenu-ation on unenhanced images and may be sur-rounded by free peritoneal fluid. Complex-appearing masses can be further evaluated withultrasonography (US) or magnetic resonance(MR) imaging. Although contrast-enhanced CT
may show signs of malignancy, including wall en-hancement and nodular septa, it is usually re-served for staging, not lesion characterization(22–24). Other gynecologic conditions that maybe encountered at unenhanced CT include cervi-cal cancer (which may involve the distal ureters),degenerating or twisted fibroids, and ectopicpregnancy (Fig 14) (2,6).
Figure 10. Renal lymphoma in a 75-year-old woman who presented with left renal colic. (a) Initial unenhancedhelical CT scan shows an enlarged left kidney with subcapsular soft-tissue attenuation (arrows) and an ill-definedlesion posteriorly. No obstructing stone was seen. (b) Contrast-enhanced CT scan helps confirm the presence ofboth subcapsular and parenchymal masses (arrows). Results of biopsy helped confirm the diagnosis of non-Hodgkinlymphoma.
Figure 11. Emphysematous cystitis in a 62-year-olddiabetic man who presented with groin pain and hema-turia. Unenhanced helical CT scan shows a thick-walled urinary bladder with intraluminal and intramu-ral air, a finding that is consistent with emphysematouscystitis. Escherichia coli was seen in a culture of theurine specimen.
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Gastrointestinal DiseasesAlong with gynecologic conditions, gastrointesti-nal disease represents one of the most commonclinical mimics of renal colic. Appendicitis anddiverticulitis are two of the most common condi-tions detected on stone-negative unenhanced he-lical CT scans in our emergency department andwere frequently encountered in previously pub-lished series as well, representing 10%–12% of
alternative diagnoses (2,3,6). Appendicitis shouldalways be considered in any patient presenting tothe emergency department with abdominal pain,since it is a very common cause of an acute abdo-men, especially in younger patients (Fig 15). Forthis reason, every attempt should be made toidentify the normal appendix on all CT scans ob-tained with a renal stone protocol. The normalappendix is usually less than 6 mm wide, is thin
Figure 12. Hemorrhagic cyst in a 24-year-oldwoman who presented with right-sided groin pain. Un-enhanced helical CT scan shows a right adnexal cystwith high attenuation and a hematocrit level (arrow).No obstructing stone was seen. The presence of a hem-orrhagic ovarian cyst was later confirmed with trans-vaginal US.
Figure 13. Complex ovarian mass in a 38-year-oldwoman who presented with right-sided groin pain. Un-enhanced helical CT scan shows a cystic adnexal masswith internal septa (arrow). Analysis of the surgicalspecimen confirmed the diagnosis of cystadenofibroma.
Figure 14. Ruptured ectopic pregnancy in a 42-year-old woman who presented with acute right flank pain.Unenhanced helical CT scan shows a hemorrhagicmass in the right adnexa (arrow), a finding that is asso-ciated with hemoperitoneum. No obstructing stone wasseen. Imaging was performed before results of a urinepregnancy test were known. The beta subunit of hu-man chorionic gonadotropin was later found to be posi-tive. Surgical findings helped confirm the diagnosis ofruptured ectopic pregnancy.
Figure 15. Acute appendicitis in a 30-year-oldwoman who presented with right flank pain. Unen-hanced helical CT scan shows an enlarged thick-walledappendix with periappendiceal stranding (arrow). Noobstructing stone was seen. Surgical findings helpedconfirm the diagnosis of acute appendicitis.
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walled, and may contain an appendicolith. Gaswithin the appendiceal lumen can be helpful forfinding a normal appendix. When seen in the con-text of wall thickening or stranding, however, thepresence of intraluminal gas does not exclude ap-pendicitis.
Several studies have reported that the sensitiv-ity and specificity of unenhanced helical CT aresufficiently high to exclude both ureterolithiasis
and appendicitis (25–27). The proper protocolfor evaluating appendicitis, however, remainscontroversial (28). At our institution, we prefer toadminister both oral and intravenous contrastmaterial. The use of intravenous contrast materialcan be beneficial in thin patients with only a small
Figure 16. Acute appendicitis in a 32-year-oldwoman who presented with right flank pain. Unen-hanced helical CT scan shows a dilated appendix, withperiappendiceal stranding and appendicolith (arrows).Surgical findings helped confirm appendicitis.
Figure 17. Diverticulitis in a 42-year-old man whopresented with left flank pain. Unenhanced helical CTscan shows a thick-walled colonic diverticulum associ-ated with mesocolic fluid and inflammation (arrow).No obstructing stone was seen. The diverticulitis re-solved with antibiotic therapy.
Figure 18. Cecal diverticulitis in a 40-year-oldwoman who presented with right flank pain. Unen-hanced helical CT scan shows cecal diverticula withadjacent mesocolic fluid and inflammatory changes(arrow), findings consistent with diverticulitis.
Figure 19. Closed-loop bowel obstruction in a 70-year-old man with left flank pain. Initial unenhancedhelical CT scan shows a U-shaped bowel orientation ofdilated ileal loops, a finding that represents obstruction,and associated fluid in the small bowel mesentery (ar-rows). At exploratory surgery, necrotic bowel second-ary to a closed-loop bowel obstruction was found.
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amount of intraperitoneal fat and allows bettercharacterization of complications of appendici-tis, such as perforation and abscess formation(28,29).
Because appendicitis is frequently encounteredat unenhanced helical CT performed because ofurolithiasis (about 5% of alternative diagnoses),all radiologists must be familiar with the unen-
hanced CT findings, which include dilatation ofthe appendix to more than 6 mm, inflammatorystranding of the periappendiceal and pericecal fat,and surrounding phlegmon or abscess. Althoughan appendicolith can be seen to advantage at un-enhanced CT, as an isolated finding it is not diag-nostic for appendicitis (Fig 16) (25,26,30,31).The presence of a fecalith within a fluid collectionin the right lower quadrant is very helpful formaking the diagnosis of perforated appendicitis.
Diverticulitis is also easily visualized at unen-hanced CT. Characteristic findings include in-flammation of the pericolonic fat in associationwith nearby diverticula, focal colonic wall thick-ening, thickening of adjacent fascia, thickening ofthe root of the sigmoid mesentery, and intraab-dominal abscess (Fig 17) (25,26,32). Althoughthe inflamed diverticula are usually within thesigmoid or descending colon, they may be presentwithin the transverse or ascending colon, espe-cially in younger people (Fig 18) (33). Smallbowel diverticulitis and Meckel diverticulitis maymimic nephroureterolithiasis as well, which em-phasizes the importance of careful bowel inspec-tion with unenhanced CT (34). Although lesscommon, abdominal hernias, small bowel ob-struction (Fig 19), intussusception (Fig 20), co-lon carcinomas, and inflammatory bowel diseasemay also be discovered (Fig 21) (2,6,7).
Figure 20. Enteroenteric intussusception in a 38-year-old man who presented with acute left flank pain.Unenhanced helical CT scan demonstrates an intus-susception in the left lower quadrant with telescopingof mesenteric vessels and fat (arrow). No obstructingstone was seen. Surgical findings helped confirm lym-phoma as the lead point.
Figure 21. Initial manifestation of Crohn disease in a 26-year-old woman who presented with right-sided groinpain. (a) Unenhanced helical CT scan shows several tethered small intestinal loops in the right lower quadrant, withfindings suggestive of enteroenteric fistulas (arrow). No obstructing stone was found. (b) CT scan obtained after oraland intravenous administration of contrast material enables better delineation of the enteroenteric fistulas (arrow).
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Pancreatic andHepatobiliary DisordersHepatobiliary findings at unenhanced helical CTare usually related to stones within the gallbladderor bile duct. Gallstones are commonly an inciden-tal finding in patients with true renal colic. Al-though US remains the imaging modality ofchoice for the screening for cholelithiasis and cho-ledocholithiasis, gallstones are a frequent inciden-tal finding at unenhanced CT performed becauseof renal stones and, occasionally, may help ex-plain the patient’s symptoms (2,6,35,36). UnlikeUS, which may depict more than 95% of gall-stones, unenhanced helical CT has been shown todepict only 65%–88% of them (37,38). Chole-cystitis can sometimes mimic renal colic at clini-cal examination and should be detected on CTscans obtained with a renal stone protocol (Fig22). CT, which has a reported sensitivity of 92%when intravenous contrast material is adminis-
tered, may demonstrate gallbladder wall thicken-ing, pericholecystic fluid, gallstones, gallbladderdistention, and, possibly, gas within the gallblad-der wall (39). These findings may be more diffi-cult to visualize with unenhanced CT.
Choledocholithiasis should be suspected whenbiliary ductal dilatation is present and no othersource for flank pain is found; occasionally, theintraductal stone may be seen (Fig 23). In suchinstances, further imaging with US or MR imag-ing may be warranted.
Pancreatitis may manifest as left flank pain,thus mimicking renal colic (Fig 24). Althoughintravenous contrast material is not required tomake the diagnosis of pancreatitis, it may be help-ful in the evaluation of related complications(40).
Vascular DiseasesVascular diseases represent the most difficult cat-egory of disease to diagnose at unenhanced CT,and they are potentially the most life threatening.The clinical findings of acute aortic and splanch-nic arterial conditions as well as venous condi-tions may overlap with those of renal colic (41).
Figure 22. Acute cholecystitis in a 36-year-old woman with right renal colic. Unenhanced helical CT scans ob-tained after the inadvertent administration of oral contrast material show a distended gallbladder with pericholecysticinflammation (arrows in a) and stones within the neck of the gallbladder (arrow in b). Surgical findings helped con-firm the presence of acute cholecystitis.
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Acute aortic conditions that may be detected atunenhanced helical CT include ruptured abdomi-nal aortic aneurysm and aortic dissection (Figs
25, 26). The former may manifest as a crescent-shaped area of high attenuation (higher than thatof intraluminal blood) in the wall of an abdominal
Figure 23. Choledocholithiasis in a 46-year-old man who presented with right flank pain. (a) Initial unenhancedhelical CT scan shows mild intrahepatic biliary ductal dilatation (arrow). No obstructing ureteral stone was found.(b) Unenhanced CT scan obtained slightly caudad to a shows high attenuation within the duct (arrow). Findings atendoscopic retrograde cholangiopancreatography helped confirm the presence of choledocholithiasis.
Figure 24. Acute alcoholic pancreatitis in a 46-year-old man with known renal stones who presented withleft flank pain. Unenhanced helical CT scan shows bi-lateral renal calculi as well as an edematous pancreaswith peripancreatic inflammation and fluid collections(arrowheads), findings that are consistent with acutepancreatitis.
Figure 25. Ruptured abdominal aortic aneurysm in a66-year-old man who presented with acute left flankpain. Unenhanced helical CT scan shows a ruptured8-cm abdominal aortic aneurysm with an associatedlarge retroperitoneal hematoma (arrows).
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aortic aneurysm, which is believed to represent asign of impending rupture, or as periaortic strand-ing or hemorrhage (�60 HU), which is indicativeof active bleeding (42). Although the use of intra-venous contrast material is not required to makethe diagnosis, it may be helpful if endoluminaltreatment is planned (43). Conversely, intrave-nous contrast material is almost always requiredto exclude an aortic dissection. Findings at unen-hanced CT include high attenuation in the wall ofthe aorta, which is indicative of an intramural he-matoma, or displacement of intimal calcificationinto the aortic lumen (Fig 27). Other findingsinclude unilateral perinephric stranding, which issuggestive of renal infarction from a dissectionflap into the renal artery, and actual visualizationof the flap, which can become more conspicuousif the patient is anemic (44).
Conditions affecting the mesenteric arteriesand veins can also mimic renal colic and may beeasily overlooked if clinical suspicion is not high.Occasionally, an aortic dissection may extend intothe superior mesenteric artery; rarely, an isolatedsuperior mesenteric artery dissection may bepresent. Unenhanced CT findings of arterial dis-
section include perivascular fat stranding, vesselenlargement, irregular contour, and displacementof intimal calcification. Secondary signs of vascu-lar compromise of bowel may be present, includ-ing bowel wall thickening, pneumatosis, andbowel distention (44). The sensitivity and speci-ficity of these signs have not been well studied, soa low threshold for intravenous contrast materialadministration should be maintained if mesen-teric artery dissection is suspected. Superior mes-enteric artery embolism or thrombosis and ve-nous thrombosis may also manifest as pain radiat-ing to one side. As with dissection, intravenouscontrast material is needed for their diagnosis.Findings at unenhanced CT include an enlargedvessel, perivascular stranding, and, rarely, high-attenuation material within the vessel represent-ing the clotted blood (Fig 28) (45).
Intraperitoneal and retroperitoneal hemor-rhage represent another category of vascular dis-ease that may appear on unenhanced helical CTscans. Although procedure- or trauma-relatedhemorrhages may be suspected at clinical exami-nation, spontaneous hemorrhage may not. Spon-taneous hemorrhage, which is usually related tothe use of anticoagulants, may also be seen in thesetting of bleeding diatheses, vasculitis (eg, poly-arteritis nodosa), splenic rupture, and certain
Figure 26. Ruptured common iliac artery aneurysm in a 68-year-old man with acute left flank pain. Unenhancedhelical CT scans show a ruptured left common iliac artery aneurysm with disruption of intimal calcification (arrow inb) and a large left retroperitoneal hematoma (arrow in a).
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neoplasms (Fig 29) (46). If no history of traumaor antecedent procedure is elicited, the use of in-travenous contrast material should be stronglyconsidered. Intravenous contrast material mayalso provide information about the presence andrate of active bleeding.
Musculoskeletal PainBody wall or musculoskeletal pain is commonlymistaken for renal colic in the emergency depart-ment because of its nonspecific clinical presenta-tion. Low mechanical back pain is a common ex-ample. When reading unenhanced helical CTscans, however, the radiologist should keep in
Figure 27. Acute type B aortic dissection in a 44-year-old man who presented with acute left flank pain. (a) Initialunenhanced helical CT scan demonstrates displaced intimal calcification within the abdominal aorta (arrow), a find-ing that is suggestive of aortic dissection. (b) Contrast-enhanced CT scan obtained at follow-up helps confirm thediagnosis of aortic dissection. Note the intimal flap (arrow).
Figure 28. Acute thrombosis of the left external iliacvein in a 40-year-old woman who presented with left-sided groin pain. Unenhanced helical CT scan showshigh attenuation within an enlarged left external iliacvein (arrow) and adjacent inflammatory stranding con-sistent with acute venous thrombosis.
Figure 29. Acute splenic rupture in a 40-year-oldwoman with polycythemia vera who presented with leftflank pain. Unenhanced helical CT scan shows markedsplenomegaly with hemoperitoneum, a finding that isconsistent with splenic rupture.
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mind the potentially more clinically importantmusculoskeletal causes of flank pain (47), includ-ing a missed fracture in elderly patients or inthose with osteopenia who experience complica-tions from seemingly minor injuries. In this pa-tient population, careful analysis of the thoraco-lumbar junction is warranted because of the rela-tive frequency of nontraumatic vertebral fracturesin this region (48). Metastases to the bones, mul-tiple myeloma, and psoas hematomas can also bedetected at unenhanced CT performed for flankor costovertebral angle tenderness (Fig 30) (6).
Miscellaneous ConditionsRarely, focal intraperitoneal fatty infarctions (ie,epiploic appendagitis and focal omental infarc-tions) may be confused with other causes of acuteflank pain (49). Their detection on unenhancedCT scans is dependent on careful inspection ofthe fat surrounding the colon. CT findings sug-gestive of this condition include pericolonic fatstranding without visualization of bowel wallthickening and a well-circumscribed fatty masswith a center of high attenuation (50). The differ-entiation between epiploic appendagitis and focalomental infarction is not always possible and isless important, since both tend to be treated con-servatively and are usually self-limiting (51).
ConclusionsNumerous diseases may manifest as acute flankpain and mimic urolithiasis. The ability to diag-nose these conditions with CT, in addition to thespeed and high accuracy in stone detection, hasresulted in the near-universal acceptance of unen-hanced helical CT for the initial imaging of pa-
tients suspected of having renal colic. Up to one-third of unenhanced CT scans obtained becauseof acute flank pain, however, may reveal unsus-pected or additional findings unrelated to stonedisease, which may help explain the patient’sflank pain and presentation. Most of these find-ings are related to gynecologic conditions, in par-ticular adnexal masses, and gastrointestinal dis-eases, especially appendicitis and diverticulitis.The radiologist should be aware that more seriousdiseases involving the genitourinary tract (eg,neoplasm) and abdominal vessels may have clini-cal findings similar to those of stone disease. Vas-cular causes of acute flank pain must always beconsidered, since these constitute life-threateningemergencies that may require the administrationof intravenous contrast material for their exclusion.
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Figure 30. Initial images of multiple myeloma in a 60-year-old man who presented with left flank pain. Unen-hanced helical CT scans obtained at the level of the kidneys show a destructive lytic lesion within a lumbar vertebralbody (arrow in a) and several lytic lesions within the pelvis (b), findings that are consistent with biopsy-proved mul-tiple myeloma.
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