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Clinical Observations |
1 Department of Radiology, University of Pittsburgh Medical Center (Presbyterian
Campus), 200 Lothrop St., Rm. 3950 CHP MT, Pittsburgh, PA 15213.
2 Present address: Institute of Radiology, University of Udine, Udine,
Italy.
3 Department of Emergency Medicine, University of Pittsburgh Medical Center,
Pittsburgh, PA.
4 Department of Urology, University of Pittsburgh Medical Center, Pittsburgh,
PA.
Received July 23, 2007;
accepted after revision September 10, 2007.
Address correspondence to M. P. Federle
(federlemp{at}upmc.edu).
Abstract
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CONCLUSION. Nonobstructing renal stones on unenhanced CT are a frequent finding in patients evaluated in the emergency department for suspected renal colic. These stones are usually not recognized as the cause of pain by physicians and may be responsible for multiple clinical and radiologic evaluations. In the absence of other clinical or CT evidence of a separate cause, these stones are likely to be the cause of a patient's acute pain.
Keywords: flank pain • kidney calculi • spiral CT
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Many emergency department patients imaged for suspected renal colic have an abdominal CT scan that is judged unremarkable except for the presence of small renal calculi without evidence of obstruction, commonly referred to as nonobstructive renal stones. When these patients complain of flank discomfort, most physicians do not consider the stone to be the source of the pain, and patients are discharged with a diagnosis of "pain of undetermined origin." We have noted that many such patients return to the emergency department or other care sites repeatedly with pain ipsilateral to the side of the small stones without ever having an alternative cause established by CT or clinical criteria.
The purpose of our study was to determine the incidence of nonobstructing renal stones on unenhanced CT in patients presenting to the emergency department with renal colic and to assess the potential relationship to each patient's symptoms.
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CT was performed with a 4-MDCT scanner (LightSpeed QXi, GE Healthcare) with contiguous 5-mm-thick axial images from the dome of the diaphragm to the ischial tuberosities. Our department CT protocol for evaluation of a patient with suspected renal colic calls for sections through the abdomen and pelvis without the use of an oral or IV contrast medium.
In addition to the original interpretation, the senior author, an abdominal radiologist with 30 years of experience, reviewed all CT studies for the presence and size of ureteral or renal calculi, signs of obstruction such as hydronephrosis and asymmetric perinephric fat stranding [4], and the presence of other intraabdominal or pelvic abnormalities. All CT studies were reviewed on a PACS workstation (Stentor, Philips Medical Systems) as axial images; coronal reformations were not used. The reviewer was aware of the indications for the study but unaware of the clinical history, laboratory data, results of previous imaging studies, reports of emergency department visits, and final discharge diagnosis. The medical records were reviewed by a certified research coordinator who registered the clinical data and gathered the CT scans for review. For each patient, all the reports of emergency department visits were reviewed for symptoms, presence of hematuria, clinical or radiologic evidence of other sources of pain, and the final discharge diagnosis.
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Four (2%) patients were discharged from the emergency department with the diagnosis of a recent passage of a stone. In these cases, CT showed no evidence of a ureteral stone but did show residual minimal hydronephrosis and minimal perinephric fat stranding on the symptomatic side. In addition, each patient's clinical history was considered positive for passage of a stone.
In 31 (18%) cases the cause of the patient's pain was judged to be of abdominopelvic origin but not ureterolithiasis: in eight patients, musculoskeletal pain; in five, sigmoid diverticulitis; in five, pyelonephritis; in five, urinary tract infection; and in one each, appendicitis, ovarian torsion, retroperitoneal hemorrhage, bladder mass obstructing the ureter, ruptured ovarian cyst, splenic infarct, congenital obstruction of the ureteropelvic junction, and ureteral stricture. The CT findings in these cases were essentially the same on the initial and retrospective interpretations and directly supported the discharge diagnosis in most cases. The CT findings were inconclusive in the patients with urinary tract infection, ureteral stricture, and musculoskeletal pain. CT findings for four of these patients showed evidence of small nonobstructing renal stones on the same side as the pain; however, this was not considered the cause of the patient's symptoms, and the final discharge diagnosis was urinary tract infection in two cases and diverticulitis in two cases.
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CT findings for six of these patients had been interpreted as having equivocal signs of obstruction on the original interpretation, but this was not confirmed after review by the senior author. In four cases, CT showed small renal calculi and no sign of ureteral obstruction, but the patients reported a clinical history compatible with the passage of a stone. Data regarding the presence of hematuria were available in 27 patients with nonobstructing renal stones. Among them, 20 (74%) were positive for hematuria and seven were negative.
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We focused our attention on the incidence and clinical relevance of small renal stones without any sign of obstruction on abdominal CT of patients presenting to the emergency department for suspected renal colic. When these nonobstructing renal stones are identified in patients with flank pain, they are commonly not regarded as a possible cause of the symptoms by clinicians or radiologists even if no other explanation for the pain is evident after clinical and radiologic evaluation.
Our results show that small renal stones not associated with any CT sign of obstruction are a frequent finding (18%) in patients presenting to the emergency department with renal colic. Fourteen of these patients were evaluated multiple times in our emergency department for flank pain, and each time CT showed the presence of nonobstructing renal stones on the side ipsilateral to the flank pain without ureteral stone or any other sign of acute extraurinary disease. Twenty-seven of the 31 patients in this group were evaluated for hematuria, which was present in 20 (74%). Despite these findings, all these patients were discharged from the emergency department with a diagnosis of abdominal pain of unknown cause.
The presence of nonobstructing renal stones on the symptomatic side without any other radiologic or clinical signs explaining the patient's symptoms and the repeated emergency department evaluations for the same symptoms and with the same CT findings strongly suggest that these stones are, in some way, causing the patient's pain and hematuria. It is generally agreed that stones in the urinary tract cause colicky pain by obstructing the flow of urine and thus increasing the pressure in the collecting system and the wall tension of the ureter and renal pelvis [7].
Small, nonobstructing renal stones are commonly not considered to be a potential source of the pain because they do not interfere with the flow of urine. We think, in concordance with other investigators [8, 9], that a small renal stone may intermittently obstruct at the ureteropelvic junction or at the infundibulum–caliceal level, potentially causing pain and uroepithelial damage with hematuria. Because an obstruction may only be intermittent or intrarenal, the expected CT signs of obstruction (hydronephrosis and perirenal stranding) may be minimal or absent.
Unknown to us at the initiation of this study, other investigators have reported substantial series of patients with recurrent flank pain who had relief of symptoms after surgical removal of "small, nonobstructing renal stones" [8–12]. These investigators described the same clinical pattern that we observed, with patients having repeated visits to hospitals and doctors' offices with complaints of flank pain, usually not as acutely severe as that associated with an obstructing ureteral calculus. The authors of one report stated, "These patients have not uncommonly plagued the offices of multiple physicians in search of narcotic pain medications" [8], and that the patients had repeatedly been assured that their renal calculi were not the source of their symptoms. Nevertheless, 34 (95%) of 36 patients in that study reported complete resolution of their pain once the nonobstructing calculus was removed (by nephrostolithotomy) [8].
It must be noted that the previous reports of symptomatic, nonobstructing renal calculi were published in the era before CT when the diagnosis of renal calculi was by radiography and excretory urography. The calculi in those reports generally were between 5 and 15 mm in diameter (mean size not reported). It is likely that the stones identified by urography are larger than many of those detected by CT, and subtle signs of obstruction would be more difficult to detect on urography.
As with any retrospective study, ours has some limitations. Because the patients in our series did not have the calculi removed (by surgery or lithotripsy), our data can only suggest the probability that the calculi caused the pain. Only a controlled trial to eliminate the stone and look for pain relief would confirm the association between small renal stones and flank pain.
We conclude that renal calculi that are regarded as nonobstructing on unenhanced CT are a frequent finding in patients evaluated in the emergency department for suspected renal colic. These stones are usually not recognized as the cause of pain by the physicians and may be responsible for multiple clinical and radiologic evaluations. In the absence of other clinical or CT evidence of a separate cause, these stones are likely to be the cause of a patient's acute pain.
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