| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Sapir Medical Center 44281 Kfar Saba, Israel Sackler Faculty of Medicine Tel-Aviv University 69978 Tel-Aviv, Israel
I read with interest the case report by Dr. Amilineni et al. [1] about the contrast-enhanced CT diagnosis of a renal infarction. I would like to make a significant commentary about the diagnostic imaging workup and the invasive procedures that were used in the evaluation of the reported patient. As was mentioned in the case presentation, an unenhanced abdominal CT scan showed an ectopic right kidney with no evidence of a calculus or hydronephrosis. On a subsequent excretory urogram, faint opacification of the right kidney was found. Taking into consideration that a normal-sized kidney was actually present, seen on both unenhanced CT and sonography [2] (imaging methods that give anatomic information only), the patient should have undergone CT immediately after excretory urography. In this instance, the contrast material that had been injected for excretory urography could have been used for the correct diagnosis and an invasive procedure, retrograde pyelography with right ureteric stent placement, would have been avoided.
Typical nephrographic abnormalities, as well as characteristic pathologic features, on the delayed parenchymal phase images have been reported on CT in various clinical conditions that cause poor opacification or nonopacification of a normal- or increased-sized kidney [2]. Awareness of these findings explains why performing CT after excretory urography could be diagnostic.
Regarding the ideal diagnostic test for the evaluation of patients with an acute nontraumatic abdomen, several CT techniques are currently being used [3]. Each imaging center chooses which technique seems to be the optimal diagnostic approach based on local scanner availability, patient demograhics, level of radiologic expertise, and economic considerations [3]. At our institution, we routinely use the best known technique, administration of oral contrast material followed by IV injection of contrast material, unless contraindicated. This approach takes into consideration that contrast-enhanced CT gives functional data in addition to anatomic data. Using IV contrast material, we have diagnosed unsuspected acute pyelonephritis when the patient presented with acute right abdominal pain, justifying emergent abdominal CT for the clinical diagnosis of an acute appendicitis. In the absence of perirenal changes, the correct diagnosis could not have been established without the use of contrast injection Fig. 1).
|
In summary, whenever excretory urography is performed for any clinical indication and the nephrographic phase of a kidney that is known to be present is not shown, the radiologist should recommend immediate CT. This approach not only expands and usually terminates the imaging evaluation but also may prevent a delay in the diagnosis and treatment and unnecessary additional diagnostic procedures.
References
St. Francis Medical Center Pittsburgh, PA 15201
We thank Dr. Zissin for his interest in our article [1]. First, acute ureteral obstruction from an impacted stone is perhaps the single most common cause of acute flank pain. Several studies have indicated that unenhanced helical CT may be the ideal diagnostic test for the evaluation of acute flank pain [2, 3]. As with all new solutions to old problems, unenhanced helical CT has not been universally accepted for this purpose. However, unenhanced helical CT has become the first imaging study for patients with acute flank pain in most teaching institutions in the United States. In the largest series published to date, performed by Smith et al. [4], unenhanced helical CT had a positive predictive value of 98% and a negative predictive value of 97% for determining the presence or absence of ureterolithiasis in patients with acute flank pain. When ureterolithiasis is absent, CT enables diagnosis of a wide range of extraurinary causes of acute flank pain that are unrelated to stone disease.
Smith et al. [4] examined 417 patients with flank pain using unenhanced CT. Of the 236 patients with CT studies negative for stone disease, 65 patients (28%) had CT findings positive for other diagnoses. Of the 65 patients, 43 had abnormalities unrelated to the urinary tract and 22 patients had abnormalities of the urinary tract unrelated to stone disease.
Second, after unenhanced helical CT revealed negative findings, CT should have been repeated with IV contrast material. That was a missed opportunity. The primary goal of our article [1] is to convince our imaging colleagues not to hesitate to repeat the study with IV contrast material in the event of negative or equivocal findings. With the current popularity of unenhanced helical CT, there is a reluctance to use contrast material for diagnosis of flank pain. This reluctance may be related to the ability of unenhanced helical CT to show most, if not all, abdominal and pelvic pathologic processes; the experience of the radiologist interpreting scans comfortably even in the absence of IV contrast material; cost considerations; or the need for a physician to be present during contrast administration. However, we do not recommend IV contrast material for every patient who presents to the emergency department with acute flank pain. The following groups of patients will benefit from IV contrast administration: patients who continue to have acute flank pain despite normal findings on unenhanced helical CT and other imaging studies; patients for whom unenhanced helical CT shows secondary signs—such as perinephric fat stranding, perinephric fluid collection, thickening of renal fascia, renomegaly, and focal renal bulging—in the absence of renal or ureteric calculi; patients who are at risk for thromboembolic occlusion of renal artery, including those with atrial fibrillation, valvular heart disease, and prosthetic valves; and patients with an elevated level of serum lactate dehydrogenase, which is a serum marker that is consistently elevated in cases of renal infarction.
Third, the patient in our case report voided a 3-mm calculus during the delayed phase of the excretory urogram. Despite the passage of a stone, the patient continued to be symptomatic, leading to urologic consultation, retrograde pyelography, and stent placement. The voiding of a stone after excretory urography and the normal findings on a subsequent retrograde pyelogram misled the interpreters to diagnose a calculus-related obstruction rather than occlusion of the renal artery.
Finally, we neither recommend nor practice routine use of oral and IV contrast material for every patient with acute flank pain. Because an impacted ureteral stone is the most common cause of acute flank pain, unenhanced helical CT is the first imaging study of choice at our institution. Our CT protocols are targeted to confirm or exclude a certain diagnosis on the basis of clinical presentation rather than to rule out disease based on a generalized protocol.
References
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
