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EDUCATION EXHIBIT |
Department of Radiology, Winthrop-University Hospital, Mineola, New York
Department of Radiology, School of Medicine, State University of New York at Stony Brook
*Department of Radiology, Long Island Jewish Medical Center, New Hyde Park, New York
Department of Emergency Medicine, North Shore University Hospital, Manhasset, New York
Editor’s Note.—Supplemental material available at http://radiographics.rsnajnls.org/cgi/content/full/27/3/743/DC1.
When I began practice, I was relatively safe in assuming that abdominal pain was appendicitis or green apples.—Dr Gunnar Gundersen, former President, American Medical Association, 1962
The purpose of medicine is to prevent significant disease, to decrease pain and to postpone death when it is meaningful to do so. Technology has to support these goals.
—Dr Joel Nobel, 1985
In the continuing evolution of the use of cross-sectional imaging for the assessment of patients with acute abdominal pain, MR imaging is the latest modality to be evaluated. In the past, MR imaging was not considered a routine alternative or adjunct for imaging of patients with acute right lower (or left lower) quadrant pain, for a variety of reasons, including less accessibility and availability, increased cost relative to other modalities, artifacts related to bowel motion and respiratory motion, inferior evaluation of the bowel relative to CT, increased length of the examination compared with CT, and less familiarity of radiologists with the MR imaging findings that may cause acute abdominal and pelvic pain—as well as a mind-set that MR was not a step in the algorithm for the imaging work-up of such patients.
Pedrosa et al (1) demonstrate in their well-researched and thoroughly illustrated article preceding this commentary their clinical experience over the past several years with MR for imaging patients with RLQ pain, building on a previous review of their earlier experience (2). The authors demonstrate and explain that MR currently is a viable component of the imaging work-up of patients with RLQ pain, and has overcome some of these obstacles and impediments to its use in this setting (1). In general, we agree with the situations where the authors advocate the use of MR imaging as an adjunct to initial sonography or as a replacement for CT, including patients where the exposure to ionizing radiation is less than ideal compared with alternative imaging modalities that do not use such ionizing radiation, or when the use of an intravenous contrast agent is desirable but iodinated contrast material cannot be administered.
Adult patients in the first group most importantly include pregnant women, particularly in the earlier stages of pregnancy (3), and the use of MR for imaging pregnant patients with RLQ pain will therefore be the main focus of this commentary. In a recent phantom study by Hurwitz et al (3), although the radiation dose to a fetus from multidetector CT from a single examination for suspected appendicitis was estimated to be below the level thought to be detrimental to neurologic fetal development, such exposure may theoretically double the risk of childhood malignancy. Other suitable patients for the use of MR imaging for evaluation of RLQ pain are younger men and nonpregnant women of childbearing age, especially if they have a chronic disorder such as Crohn disease requiring multiple imaging examinations over time, or a history of multiple CT or fluoroscopic studies in the past. Other patients for whom MR imaging may be appropriate include any individual who refuses CT for the evaluation of RLQ pain, or expresses substantial concerns regarding radiation exposure, and sonography does not or cannot answer the clinical question(s).
We also agree with Pedrosa and coauthors (1) that as with CT and sonography, MR imaging has the capability to demonstrate a broad spectrum of findings that may explain the etiology of a patient’s acute RLQ pain. In our clinical practices, we have recently been using MR imaging more frequently as a frontline test, or immediately following equivocal or nondiagnostic sonography, and our clinicians are increasingly ordering MR imaging, particularly in pregnant patients. We have found sonography for suspected appendicitis (4) as well as for suspected renal colic in pregnant patients, in general, to be limited, time-consuming, relatively difficult, and frustrating, with a low yield. This has particularly been the case with sonography for suspected renal colic in pregnant women, where we have found visualization of a ureteral stone to be the exception rather than the rule, and have found it difficult to distinguish secondary findings of ureteral and renal pelvic obstruction related to a stone as opposed to the frequently present dilatation of the right urinary tract related to pregnancy (5). We have also found sonography for the diagnosis of suspected pyelonephritis in pregnant women to be very difficult to interpret and of limited yield (5).
In suspected appendicitis, the situation is not much better, and even in practices where radiologists or sonographers have experience with US for suspected appendicitis in children and nonpregnant patients, the altered anatomy in pregnancy, with appendiceal displacement, often cranially, from the uterus, may make finding a normal or abnormal appendix particularly challenging (Figs 1, 2) (6,7). Patients with appendicitis in the third trimester may even present with right upper quadrant pain (6,7). Cobben et al (4) diagnosed appendicitis in three of 12 pregnant patients at MR imaging performed without oral or intravenous contrast material, found a normal appendix at MR imaging in seven patients, and could not find the appendix in the other two patients. In contrast, in the same 12 patients, the appendix could be confidently identified at sonography in only one patient. As a result, in contrast to performing MR imaging following equivocal or nondiagnostic sonography, as Pedrosa et al (1) propose, one could consider performing MR as the initial imaging examination in pregnancy, where appendicitis is the leading clinical consideration.
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We agree with Pedrosa et al (1), based on their experience reported herein as well as recently in Radiology (10), on the reports of other authors (4,7–9,11), and on our own clinical experience to date, that MR imaging is an excellent modality for the evaluation of suspected appendicitis, particularly in pregnant patients, and that a variety of alternative gastrointestinal and genitourinary tract diagnoses can also be confidently identified (Fig 3; see also Figs E7 and E8 at http://radiographics.rsnajnls.org/cgi/content/full/27/3/743/DC1). Early diagnosis of appendicitis is particularly important in pregnant patients, as perforation is more likely to occur compared with in nonpregnant women, and because fetal mortality rises significantly when perforation occurs (7,12).
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Pedrosa et al (1,10) routinely use oral contrast material, a hybrid negative agent consisting of barium and iron particles, when imaging pregnant patients with acute RLQ pain with MR, and in selective nonpregnant patients with suspected gastrointestinal tract disease. To our knowledge, they are the only such authors who advocate the use of oral contrast material for suspected appendicitis in pregnancy at MR imaging. Although their approach is rational, as with CT, oral contrast material adds an additional step and requires additional time before imaging, and any difference in accuracy of MR imaging in the same group of patients if they were to be imaged without such oral contrast material remains to be demonstrated. A low-signal-intensity appendiceal lumen, due to contrast material opacification or air, may however help add confidence in evaluating the appendix in pregnant patients, especially in lieu of intravenous contrast–enhanced imaging. Similarly, although axial images are the cornerstone of our assessment of the appendix, we do not disagree with the routine use of multiplanar imaging, and believe that the utility of coronal and sagittal images for the MR diagnosis of appendicitis in pregnancy is not proved at present, but may help in definitely identifying the appendix.
The authors also advocate the routine use of TOF sequences to help avoid confusion between the appendix and pelvic varices or a dilated right ovarian vein (1). We believe this is a scenario that would occur uncommonly, although extremely recently we had just such a patient at one of our institutions. If there is indeed uncertainty between vessel(s) and appendix, the use of white blood steady-state free precession (ie, FIESTA [with a GE Healthcare unit], true FISP [with a Siemens Medical Solutions unit], or balanced FFE [with a Philips Medical Systems unit]) images may provide a fast solution if the appendix is not fluid filled (Fig 4). The use of these sequences is mentioned by the authors only in their protocol for evaluation of suspected urolithiasis, but we believe they play an important role in the evaluation of acute abdominal pain and should be considered for inclusion in the standard imaging protocol for such patients due to their fast acquisition times, robust signal-to-noise ratio, and relative lack of degradation by respiratory motion or bowel peristalsis.
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Pedrosa et al (1) also believe that the presence of periappendiceal inflammatory changes is especially useful in early appendicitis when the appendiceal diameter is not enlarged, but this is contrary to the experience in some of the more recent CT publications on acute appendicitis, including one from their own institution (15). In a study of 228 patients with suspected appendicitis conducted by Jacobs et al (16), all patients underwent initial CT with oral contrast material only, followed immediately by repeat imaging with intravenous contrast material. The sensitivity of the most experienced radiologist retrospectively interpreting the CT images improved from 83% with oral contrast material only, to 93% with both oral and intravenous contrast material. As there is also to our knowledge to date no large imaging study on suspected appendicitis using MR in either pregnant or nonpregnant patients, these issues will need to be addressed in future investigations.
One potential problem not covered by Pedrosa et al (1) in their article, is that of MR availability on an emergent basis after hours for imaging patients with acute abdominal pain. In our own practices, CT has been available on a 24 hour, 7 days a week basis for many years, and although MR imaging has been similarly available on an on-call basis, until relatively recently only the most emergent patients (typically with suspected spinal cord compression) underwent MR imaging after hours. With the recent increasing use of MR imaging for ever-widening indications after hours, particularly for neuroradiology applications, for hospital-based practices we believe that performing MR imaging for patients with abdominal pain is less problematic than it would have been in the relatively recent past.
We again agree with Pedrosa et al (1) on the use of MR imaging in patients with known or suspected inflammatory bowel disease in pregnant patients, as well as in younger patients with inflammatory bowel disease requiring repeated imaging studies, to reduce the overall radiation dose to such patients. In particular, Crohn disease can complicate pregnancy, and pregnancy alone may simulate its symptoms in patients with known inflammatory bowel disease (12,17). MR imaging is also useful for evaluating small bowel obstruction in both pregnant and nonpregnant patients (18,19), and among other uses for imaging patients with acute RLQ pain, can reveal the diagnosis of right-sided diverticulitis (20), which often simulates appendicitis clinically (21).
MR imaging is also very useful, as pointed out by Pedrosa et al (1) as well as by other authors from their institution and elsewhere (12,22,23), for the evaluation of complex adnexal masses identified at sonography, both in pregnant and nonpregnant patients, including in sonographically equivocal cases of ovarian torsion. MR imaging also has utility for the confirmation of fibroid degeneration and for other complications of uterine fibroid disease, both in pregnant and nonpregnant patients (12,22). However, the diagnosis of ovarian dermoid rupture, which is pointed out by Pedrosa et al (1), is rarely made with cross-sectional imaging studies (24), and MR imaging, which is proposed for problem solving in selected patients with suspected ectopic pregnancy, is not usually in the imaging algorithm for this diagnosis (25).
Urinary tract stone disease complicates approximately 1 in 1500 pregnancies and is a common cause of abdominal and pelvic pain in pregnancy, especially in the second and third trimesters (26–28). Urinary tract infection occurs in upward of 10%–15% of all pregnancies (26). MR imaging of the genitourinary tract, that is, MR urography, performed without gadolinium, has been considered an alternative examination to sonography in pregnant patients (1,26,28–31). Sonography has traditionally been the first-line imaging study, but as noted earlier it has substantial limitations for the diagnosis of urinary tract stone disease in pregnancy (5,26,28,30). In our opinion, based on our clinical experiences to date, the literature has underestimated the problem of direct stone visualization at MR urography in pregnant patients.
We have found it difficult to differentiate between pyelonephritis and an obstructing stone or recently passed stone, when a filling defect consistent with a stone cannot be identified in the ureter, as both conditions may demonstrate hydroureteronephrosis and perinephric edema at MR imaging. We appreciate the comments of Pedrosa and coauthors (1) regarding what they consider to be the best MR imaging sequences for ureteral stone visualization, although we are not entirely convinced that the hydronephrosis and hydroureter of pregnancy can easily be distinguished from those due to a ureteral stone, relying on the presence (in the latter) or absence (in the former) of dilatation of the distal ureter to make the diagnosis (29). However, it is reassuring to see secondary findings consistent with either diagnosis at MR imaging or MR urography, as opposed to other explanations for a pregnant woman’s right abdominal pain; the vast majority of patients with renal colic or pyelonephritis are managed conservatively (26–28), as opposed to other diagnoses such as appendicitis that require surgical intervention.
We concur completely with Pedrosa and colleagues (1) that MR imaging is an excellent alternative cross-sectional imaging examination in a subset of patients with acute lower quadrant pain, where the use of CT and/or iodinated contrast media is not desirable, particularly in pregnancy. We believe that MR imaging will likely play a somewhat larger role in the evaluation of patients with acute abdominal and pelvic pain in general in the near future, at least in a subset of patients, for a variety of reasons, including faster and improved MR imaging sequences, improved availability after hours, and increased radiologist comfort level with MR imaging. As noted earlier, a variety of issues remain as to the optimal techniques and sequences, and regarding the use of contrast media for MR imaging in such patients, but in general we agree with the authors’ approach and anticipate future investigations by them and by others on this important topic. We commend Dr Pedrosa and colleagues on their award-winning 2005 RSNA education exhibit from which this material originated, for their current article, and for familiarizing radiologists with the MR imaging features of patients with RLQ pain.
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Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts
The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man.—George Bernard Shaw (1856–1950)
We are grateful for the opportunity to respond to the comments by Katz et al about our article. We concur with their opinion about the potential benefit of using MR imaging not only in pregnant patients but also in young adults, particularly female patients in the reproductive age and patients in whom repetitive cross-sectional imaging studies are frequently needed (eg, Crohn disease).
The routine use of a fast MR imaging protocol would reduce the number of individuals exposed to the risks of radiation and intravenous contrast material, without causing substantial delay in patient care. Should MR imaging prove to have a diagnostic accuracy at least similar (or superior) to that of CT in the evaluation of acute abdominal pain, it would be our responsibility to implement MR imaging protocols and offer the examination to patients being considered for a CT study.
Herein we offer responses to some of the specific comments by Katz et al. Some of these reflect the authors’ opinions on specific issues where there is not sufficient scientific data to support one argument or the other. We refer readers to the many cited references in the original article, in the editorial response, and in our comments to help guide their opinions on these issues.
We consider US to be a complementary test to MR imaging more than an alternative. We agree that it may be appropriate to use MR imaging as the initial imaging modality when the clinical diagnosis is highly suggestive of appendicitis. However, in our experience, it is rare that a pregnant patient presents with such a clear clinical picture (which contributes to the high false-negative laparotomy rate traditionally accepted in clinical practice) (1). Uterine, ovarian, urinary, and gastrointestinal causes (including appendicitis) may be responsible for the clinical presentation. US offers an accurate and rapid diagnosis in some of these clinical scenarios, as is the case with ectopic pregnancy and ovarian torsion. In other settings, the real-time, interactive nature of the US examination offers advantages, as in the diagnosis of fibroid degeneration when abdominal pain is reproduced by direct compression of the fibroid with the US probe.
The administration of glucagon in nonpregnant patients mitigates the bowel peristalsis that can degrade image quality in relatively long, non–breath-hold, high-resolution acquisitions. However, we agree with Katz et al in that glucagon may not be needed when ultrafast (ie, single-shot steady-state free precession) acquisitions are used.
As discussed by Katz et al, the contribution of oral contrast material to the accuracy of MR imaging in diagnosis of acute appendicitis has not been established. In our recent report of 51 consecutive patients (2), we found a trend toward a superior visualization rate of the normal appendix when the oral contrast material reaches the cecum compared to the rate in patients with poor oral preparation. However, this difference was not statistically significant. We believe oral contrast material facilitates recognition of the normal appendix and substantially increases the confidence of radiologists in identification of the normal appendix.
We also expect that, similar to the experience reported in the CT literature, oral contrast material may help reduce the number of false-positive diagnoses (3). For example, oral contrast material, by clearly marking the bowel, helps avoid confusion between fluid-filled terminal ileal loops and distended, inflamed appendices (3).
The use of multiplanar imaging has, in our opinion, several advantages. First, it helps identify the anatomic variations caused by the gravid uterus. For example, the horizontal orientation of the ascending colon and elevation of the cecum, which cause rotation of the terminal ileum and appendix, are usually better recognized on sagittal images than on axial images. Review of sagittal images facilitates the identification of the appendix by orienting the radiologist toward the area where the appendix is likely to be located, once the tip of the cecum and the terminal ileum are identified.
In the authors’ experience, use of the cross-reference tool on the picture archiving and communication system workstation helps identify the appendix and increases the radiologist’s confidence when the tubular structure is confirmed in all three orthogonal planes. Also, depending on the orientation of the appendix, it may be better visualized with coronal or sagittal images than in the axial plane. Similarly, we have recently noted improved visualization of the appendix on coronal and sagittal reformatted images from our abdominal 64–detector row CT examinations in selected patients.
Our experience differs from the comments by Katz et al regarding the presence of periovarian varices in pregnancy. We found this issue to be a very common problem and one that makes recognition of the normal appendix very challenging, particularly in the second and third trimesters. We have virtually eliminated this problem by routinely comparing the axial single-shot fast SE and TOF images, supplemented by using negative oral contrast material. The appendix and periovarian varices are frequently indistinguishable on single-shot fast SE images, while on TOF images the normal appendix stands out as a black tubular structure and the periovarian varices remain bright.
While steady-state free precession (SSFP) sequences (ie, FIESTA, true FISP, balanced FFE) facilitate the evaluation of many bowel disorders, we believe these images have disadvantages when evaluating acute appendicitis. The bright signal of both the blood pool and fluid that is inherent to this sequence family can challenge the distinction between an abnormal fluid-filled appendix and periovarian veins. Also, the prominent susceptibility effects with SSFP sequences can distort or obscure structures in the vicinity of bowel loops filled with air or iron-based contrast material, including the appendix. Furthermore, off-resonance artifacts can be problematic. Single-shot fast SE minimizes or eliminates these disadvantages. Having stated these concerns, we appreciate the few examples provided by Katz et al that demonstrate the normal and abnormal appendix with SSFP.
To the best of our knowledge, systematic studies using SSFP techniques for the diagnosis of appendicitis have not been reported. Thus, further research is needed to evaluate this sequence and its role in the MR imaging protocol as well as the suitability of this technique with the use of iron-based oral preparation.
We also agree with Katz et al that the comparative accuracy of CT and MR imaging in the diagnosis of acute appendicitis in pregnant patients has not been systematically evaluated. However, as a pertinent anecdote, we have seen a case in which the correct diagnosis of acute appendicitis was made at MR imaging after the initial nonenhanced CT images were interpreted as negative for appendicitis (Figure). Outcome studies will be useful to compare the relative value of the two modalities.
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On this basis, we agree with Katz et al that early appendicitis can be diagnosed before periappendiceal inflammation is evident. In the presence of a nonenlarged appendix, the diagnosis relies on demonstration of appendiceal wall enhancement. However, as discussed in our article, we do not administer intravenous contrast material in pregnancy; therefore, wall enhancement cannot be evaluated in this subset of patients with our MR imaging protocol.
In our experience, the diagnosis of early appendicitis on MR images is made before the appendix is dilated (<6 mm) when it is fluid-filled and the wall mildly thickened (better demonstrated on single-shot fast SE images); the degree of confidence in this diagnosis is higher when the cecum is filled with oral contrast material. Periappendiceal inflammation is absent in some of these cases. If present, periappendiceal inflammation is better appreciated on fat-saturated T2-weighted single-shot fast SE images and can help make the correct diagnosis before perforation occurs.
We acknowledge the differences that may exist among different practices regarding availability of MR imaging units. At our institution, MR imaging is available 24 hours a day, 7 days a week and the imaging units are located on the floor immediately below the emergency department. Thus, we are fortunate in that the only limitation to performing an immediate MR imaging examination is a potential delay that may result from competing use of the imaging unit. As MR imaging units proliferate in close proximity to or directly within emergency departments, our practice patterns will likely become more widely applicable.
Another factor to take into account when considering using MR imaging for RLQ pain is the radiologist’s expertise. While our current practice relies on dedicated fellowship-trained body MR radiologists to interpret these cases, we are at the early phase of an emerging practice. We fully expect a broad adoption of these techniques and applications into the mainstream of radiology practice. It is essential to educate radiologists and referring physicians regarding the use of MR imaging for RLQ pain in order to export the opportunity to the largest number of patients.
We also agree with the fact that MR imaging is not the imaging examination of choice in the evaluation of ectopic pregnancy. This is one of the reasons why we elect to perform US as the initial examination in all of our pregnant patients with RLQ pain. However, with the increased use of MR imaging, it is likely that one may eventually image a patient with an ectopic pregnancy, perhaps missed at US. An awareness of the MR imaging findings in this potentially life-threatening abdominal emergency will assist the radiologist in providing the very best care. For this reason, we included the description of the MR imaging findings of this as well as other rare clinical and surgical conditions in our article.
Our experience is similar to that of Katz et al in the differentiation between pyelonephritis and ureteral stone, when a filling defect in the ureter is not seen, or recently passed ureteral stone; distinction between these three clinical scenarios may be virtually impossible based on MR images alone. MR imaging is superior to US in determining the level of obstruction, as identification of the mid and distal ureter with transabdominal US is frequently impossible, even in the presence of dilatation, during the second and third trimester. However, we disagree with avoiding the use of US for preliminary assessment of patients with renal colic. If the obstructing stone can be seen with US, then further imaging is typically not needed.
In our experience, as well as that of others (5), hydronephrosis of pregnancy is caused by extrinsic compression of the ureter by the gravid uterus against the sacral promontory. In these circumstances, the distal ureter is typically collapsed; that collapse serves as an important negative predictor for distal stones in our routine practice. We have seen no cases where a distal ureteral stone was subsequently found in the absence of distal ureteral dilatation. However, one could argue that a small, nonobstructing stone could be found in a ureter with distal collapse. Regardless, the clinical significance of missing a nonobstructing stone requires further investigation, as it is unlikely that these patients would be managed differently.
We believe that a ureter dilated distal to the promontory should be considered abnormal. This should prompt strong consideration of a distal ureteral stone, whether or not a stone is directly visualized, or a recently passed stone. Dedicated MR sequences with increased sensitivity to the potential susceptibility effect caused by a calcified stone may help identify the filling defect (fig 21 in our article). However, even when a stone is not identified, we find that evaluation of the distal ureter with transvaginal US maximizes the chances for identification of the ureteral stone, if present. Lack of filling defects in the distal dilated ureter at both MR imaging and transvaginal US is probably an indication of a recently passed stone.
We have anecdotally experienced similar imaging findings in patients who reported passing a stone prior to the MR examination (fig 5 in reference 6). In our opinion, this clinical scenario exemplifies a situation where MR and US are complementary imaging tests, and we agree that this issue needs to be addressed in future investigations.
We share the views of Katz et al in predicting increased use of MR imaging for evaluation of abdominal pain in pregnant and nonpregnant patients and calling for expanded evaluations of currently available and newly developed MR sequences for this indication. We would like to thank Katz and collaborators for their thorough analysis and commentary and the Editor of this journal for giving us the opportunity to discuss our opinions. We are pleased to see agreement on most of the issues discussed and recognize the valuable opportunities for discussion and future research.
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