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Gastrointestinal Imaging |
1 From the Departments of Radiology (A.O., R.D.E., R.S., M.K., G.C.) and Obstetrics and Gynecology (A.F.G., N.Z., G.S.), University of Texas Medical Branch at Galveston, 301 University Blvd, Galveston, TX 77555-0709. Received December 9, 2003; revision requested February 17, 2004; final revision received April 4; accepted May 12. Address correspondence to A.O. (e-mail: ayoto@utmb.edu).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODS RESULTSDISCUSSIONREFERENCES |
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MATERIALS AND METHODS: Informed consent and institutional review board approval were obtained. Images obtained with a 1.5-T MR imager and medical records of 23 pregnant women (age range, 19–34 years; mean age, 24.7 years) who presented with acute right-lower-quadrant pain were retrospectively reviewed. MR protocol included use of transverse, coronal, and sagittal noncontiguous T2-weighted single-shot fast spin-echo (SE) sequences; transverse fat-suppressed T2-weighted fast SE sequences; transverse T1-weighted gradient-recalled-echo sequences; and transverse and coronal short inversion time inversion-recovery sequences performed through the lower abdomen and pelvis. MR findings were evaluated by two radiologists and compared with surgical and pathologic findings and clinical follow-up data.
RESULTS: Appendix was detected in 20 (86.9%) of 23 patients. Seven patients underwent surgery; four had acute appendicitis, and three had ovarian torsion. Two patients with pelvic abscesses not related to appendicitis underwent percutaneous drainage. Fourteen patients were treated medically. Dilated thick-walled appendix and periappendiceal inflammation were detected in three (75%) of four patients with acute appendicitis. In one patient with appendicitis, the appendix could not be visualized, but inflammation was present in the right lower quadrant. In three patients with ovarian torsion, MR imaging demonstrated right adnexal mass or inflammation. MR imaging was used to correctly identify pelvic abscesses and healthy appendix in two patients. A healthy appendix was depicted in 17 (89.5%) of 19 patients without acute appendicitis.
CONCLUSION: MR imaging shows promise for evaluation of pregnant women in whom acute appendicitis is suspected by enabling diagnosis of other possible causes of right-lower-quadrant pain, including ovarian torsion or pelvic abscesses, and demonstrating a healthy or unhealthy appendix.
© RSNA, 2004
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTSDISCUSSIONREFERENCES |
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With recent developments in fast sequences and coil technology, magnetic resonance (MR) imaging is often used in the obstetric setting for imaging of both maternal and fetal diseases. Excellent soft-tissue contrast resolution and multiplanar imaging capability, in combination with lack of ionizing radiation, make MR imaging a promising modality for use in pregnant women. There is no clinical or experimental evidence of teratogenic or other adverse effects of MR imaging during pregnancy (4,5). MR imaging allows characterization of pelvic masses discovered during pregnancy and diagnosis of postpartum complications and various acute conditions in pregnant women (4–10). To our knowledge, no data exist in the literature about the use of MR imaging in the diagnosis of acute appendicitis in pregnant women. Thus, the purpose of our study was to determine if there is a role for MR imaging in the evaluation of pregnant women with acute right-lower-quadrant pain and in whom acute appendicitis is suspected.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTSDISCUSSIONREFERENCES |
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MR Imaging
MR imaging was performed with a 1.5-T superconducting system (Signa; GE Medical Systems, Milwaukee, Wis), with a phased-array coil placed over the pelvis. The MR protocol included transverse, coronal, and sagittal T2-weighted single-shot fast spin-echo (SE) imaging (repetition time msec/echo time msec, 
/80; matrix, 256 x 256; bandwidth, 31.25 kHz; section thickness, 6 mm; section gap, 2 mm); transverse fat-suppressed fast SE T2-weighted imaging (2500, 3200/90; two signals acquired; echo train length, 17; matrix, 192 x 256; bandwidth, 20.83 kHz; section thickness, 7 mm; section gap, 1 mm); transverse short inversion time inversion-recovery imaging (repetition time msec/echo time msec/inversion time msec, 7750/34/150; two signals acquired; echo train length, 17; matrix, 160 x 256; bandwidth, 15.63 kHz; section thickness, 7 mm; section gap, 1 mm); and transverse T1-weighted fast SE imaging (700/minimum; three signals acquired; echo train length, two; matrix, 192 x 256; bandwidth, 20.83 kHz; section thickness, 6 mm; section gap, 1 mm). Single-shot fast SE sequences were performed during sustained respiration at the end of expiration. All other sequences were performed during quiet respiration. The region of interest extended from the level of the kidneys to the symphysis pubis. The field of view varied from 25 to 40 cm.
MR examination times recorded in the MR log books were reviewed. The mean total examination time was 29 minutes (range, 23–37 minutes).
Image Interpretation
Two radiologists (A.O., R.D.E.) who were blinded not only to the findings of surgical and pathologic examinations but also to the information in the patient chart reviewed the MR images together in consensus. These radiologists had subspecialty training in abdominal imaging, and each had more than 5 years of experience in abdominal MR imaging. The images were evaluated with a monochrome 1024-pixel picture archiving and communications system. Analysis of imaging findings included evaluation of the appendix (detection, size, wall thickening, and periappendiceal collection were evaluated), ovaries (detection and adnexal masses were evaluated), right-lower-quadrant inflammation, presence of pelvic abscesses, and any other abnormal finding.
The appendix was considered normal if its maximum outer diameter measured less than 7 mm, its wall measured less than 2 mm, and there was no sign of periappendiceal fluid collection. An enlarged appendix (>7 mm in maximum outer diameter) with a thick wall (>2 mm) and periappendiceal inflammation or fluid collection was considered to indicate acute appendicitis. Diameter of the appendix was measured on magnified MR images with electronic calipers.
Ovary location was assessed in all patients. If an adnexal mass was detected, its organ of origin (eg, ovarian or uterine) was determined. If an ovarian mass was detected, it was further characterized according to the imaging characteristics (eg, solid or cystic and presence of hemorrhage or fat). Signs of ovarian torsion, such as a thickened fallopian tube, presence of hemorrhage within the ovary, wall thickening of a pelvic mass, or ascites, were specifically sought (11).
Right-lower-quadrant inflammation was considered to be present if localized increased intensity was detected on T2-weighted MR images, especially on images obtained with fat-suppressed T2-weighted fast SE and short inversion time inversion-recovery sequences around the cecum.
Hyperintense lesions with hypointense walls on T2-weighted images, separate from the ovaries and bowel, were accepted as fluid collections that were suspected of being abscesses. Presence of air, which appeared as hypointense foci on T1- and T2-weighted images, within these lesions enabled definitive diagnosis of an abscess.
Clinical Information
Medical records of all 23 patients were reviewed (R.S., G.S., N.Z., A.F.G. together) for clinical progress of patients from admission for acute right-lower-quadrant pain until discharge, type of treatment (eg, medical, surgical, or interventional), diagnosis at discharge, possible readmission to the hospital within 1 month of discharge with recurrent symptoms, and surgical and pathologic findings (if applicable). MR findings were compared (A.O., R.D.E., G.C. together) with information obtained from clinical records of patients.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTSDISCUSSIONREFERENCES |
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Of 23 patients, 14 (60.9%) were treated with medical and/or expectant treatment. In four of these patients, gastroenteritis (n = 1), respiratory tract infection (n = 1), chorioamnionitis (n = 1), or urinary tract infection (n = 1) were clinically diagnosed, and patients were treated accordingly. No source of infection or other acute clinical cause could be determined in the other 10 (43.5%). When their symptoms improved, these patients were discharged from the hospital; neither acute appendicitis nor any other abdominal disease was diagnosed. None of these patients were readmitted to the hospital with the same symptoms within 1 month of discharge.
MR Findings
The appendix could be visualized in 20 (86.9%) patients. It appeared normal in 17 (89.5%) of the 19 patients without acute appendicitis (Fig 1). Both ovaries could be seen in 19 (82.6%) of 23 patients, whereas only a single ovary could be detected in the other four (17.4%).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTSDISCUSSIONREFERENCES |
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Traditionally, ultrasonography (US) has been the initial imaging modality of choice in the evaluation of obstetric patients because it is safe and inexpensive and can be performed easily at the bedside. In pregnant women, graded-compression US has been shown to be accurate in the first and second trimesters but technically difficult in the third trimester (13,14). In addition, US is highly operator dependent, and factors such as intervening bowel gas, the gravid uterus, and obesity may interfere with the quality and adequacy of images. Moreover, even experienced sonographers may have difficulty detecting a retrocecal appendix. These commonly encountered disadvantages of US have limited its use in the evaluation of appendicitis in adults and made abdominal computed tomography the preferred modality in the diagnosis of acute appendicitis (15).
Recently, helical CT has been investigated in a small series of patients for diagnosis of acute appendicitis in pregnant women (16). Helical CT is a well-established technique for diagnosis of acute appendicitis in patients who are not pregnant, and the results in pregnant women were also promising (16). CT is of limited use in obstetric patients, however, because of concerns about radiation-induced teratogenesis (17).
MR imaging findings in various gynecologic emergencies, including ovarian hemorrhage, ectopic pregnancy, tumor rupture, torsion, hemorrhage, infarction, and pelvic inflammatory diseases, were recently described (6). The main advantage of MR imaging is its ability to depict the organ from which abdominal pain originates when this organ is not clearly revealed by other imaging modalities (6). MR imaging was also found to be accurate and superior to US in revealing suspected appendicitis in adults (18). Incesu et al (18) reported that an inflamed appendix demonstrates marked wall enhancement with slight distention. They concluded that the fat-suppressed contrast material–enhanced T1-weighted MR sequence was the most useful for diagnosis. On the other hand, in another series of pediatric patients (19), accurate diagnosis of acute appendicitis could be made even without administration of intravenous contrast material. In the report by Hormann et al (19), T2-weighted SE MR imaging was the most sensitive sequence.
Our MR protocol was composed predominantly of T2-weighted sequences. Imaging of the bowel was shown to be superior with single-shot fast SE MR imaging because the short imaging time minimized artifacts due to peristalsis and the long T2 relaxation time of the luminal contents created high-resolution images of the mucosal surfaces (20,21). T2-weighted single-shot fast SE sequences obtained in all three orthogonal planes formed the backbone of our protocol, and we identified a normal-appearing appendix in 20 (86.9%) of 23 pregnant women. We used gaps between single-shot fast SE sections in our protocol; however, considering the negligible effect of crosstalk in single-shot fast SE sequences, performing the same sequences contiguously may actually further improve detectability of the appendix. In our series, the number of patients with appendicitis was small, which limited the value of statistical analysis. MR imaging was used to make a specific diagnosis in three (75%) of four patients, however, and showed local inflammation in the right lower quadrant in all four patients with acute appendicitis.
Detection of local inflammation is important in the evaluation of patients with acute abdomen. In our protocol, we used images obtained with T2-weighted fast SE and short inversion time inversion-recovery sequences to detect inflammation. With these sequences, even subtle inflammation appears bright on a dark background; however, the sequences were not obtained with breath holding, and acquisition times can range from 3 to 5 minutes. It is possible that single-shot fast SE sequences with addition of fat suppression or with longer echo times may also be sensitive in the detection of inflammation and may replace the non–breath-hold T2-weighted and short inversion time inversion-recovery sequences in the acute abdomen MR imaging protocol. This strategy may help to further reduce the total imaging time.
The safety of intravenous administration of gadolinium-based contrast agents in pregnant women has not been widely tested and established (4,22). We did not use gadolinium in our study protocol. In three patients with acute appendicitis, the dilated appendix with hyperintense lumen and hypointense thickened wall could be easily seen on images obtained with T2-weighted single-shot fast SE sequences. This appearance was similar to the findings of Hormann et al (19).
MR imaging of the pelvis allows evaluation of both medically emergent and nonemergent causes of right-lower-quadrant pain other than acute appendicitis. Several investigators found that MR imaging provided specific useful information about various gynecologic diseases (4,6,7,11,23). In our study, MR imaging also helped us accurately diagnose ovarian torsion, pelvic abscess unrelated to appendicitis, hemorrhagic cyst, and exophytic fibroid.
Ovarian torsion accounts for approximately 3% of gynecologic emergencies, and 10%–20% of ovarian torsions are found in pregnant women. Findings of ovarian torsion on unenhanced MR images include a thick edematous pedicle, signal intensities indicative of hemorrhage within the ovary or fallopian tube, and smooth wall thickening of the twisted ovarian cystic mass (11,24). Ovarian torsion was present in three patients in our series. MR findings could suggest a diagnosis of adnexal torsion because of a thickened fallopian tube in one patient and hemorrhage in the ovary in the other.
In one patient with ovarian torsion, we could not see the right ovary or the appendix, and the only MR finding that was positive was localized inflammation in the right lower quadrant. MR findings were similar in one patient with acute appendicitis. Again, the ovary and appendix could not be visualized, and localized inflammation and fluid in the right lower quadrant were the only positive findings. We found the presence of local inflammation in the right lower quadrant to be a dependable indicator of an acute process in the abdomen that required surgical and/or interventional therapy. This finding is especially helpful if the inflamed organ cannot be clearly visualized. Focal right-lower-quadrant inflammation was not present in any of the patients treated with medical or expectant therapy.
The multiplanar imaging capability of MR imaging helps to distinguish an abscess from bowel loops or pyosalpinx (25). In the two patients with pelvic abscesses in our series, MR imaging was used not only to accurately locate the abscesses but also to demonstrate a normal appendix and ovaries. MR images also facilitated decisions involving the choice of appropriate routes of intervention in these two patients.
The diagnosis of appendicitis is confirmed in only 36%–50% of pregnant women who undergo appendectomy (26,27). This percentage reflects the lack of sensitivity of the preoperative clinical evaluation. Accuracy of diagnosis drops as the pregnancy advances, and more than 40% of patients who undergo appendectomy in the second or third trimester have a healthy appendix (3). Patients who undergo appendectomy are not free from risk, and preterm contractions are common in as many as 83% of patients who undergo appendectomy during pregnancy (28). In our series, MR imaging demonstrated a healthy appendix in 17 (89.5%) of 19 patients without acute appendicitis. Demonstration of a normal appendix is important in the care of pregnant women in whom acute appendicitis is suspected, and it can potentially decrease the false-positive appendectomy rates.
The lack of information about the presence or absence of US examinations before patients underwent MR imaging is a limitation of our study and is related to its retrospective design. Some of the pelvic US examinations were performed by our clinical colleagues. Additionally, we were unsure if a graded-compression technique that was described in the literature was used. With these limitations, we thought that it would not be fair and accurate to compare the results of MR imaging and US in our study. US is probably the imaging modality of choice in pregnant women with acute abdominal pain, especially in the first trimester, when it is least limited by pregnancy-related alterations in the body. During the first trimester, MR imaging is not recommended, unless it is absolutely clinically necessary.
Another limitation of our study is related to 14 patients with MR studies that were negative; these patients were discharged and spontaneously recovered. In our retrospective study, we did not have follow-up data for these patients after discharge; thus, we cannot entirely exclude the possibility of acute appendicitis after discharge. Again, in these patients, we cannot exclude the possibility of resolution of acute appendicitis after medical therapy without surgery. The relatively small size of our study population in comparison with that of other imaging series is another limitation.
The results of our study suggest that MR imaging shows promise in the evaluation of pregnant women with acute right-lower-quadrant pain and suspected acute appendicitis. MR imaging provides a broad evaluation of the pelvic organs and enables diagnosis of other causes of right-lower-quadrant pain, including ovarian torsion, adnexal masses, and pelvic abscesses. By depicting abnormalities in the organs or demonstrating local inflammation in the right lower quadrant, MR imaging may help in the triage of pregnant women. Visualization of the normal appendix in patients without acute appendicitis is another important advantage that may save patients from undergoing unnecessary appendectomy.
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FOOTNOTES |
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Authors stated no financial relationship to disclose.
Author contributions: Guarantor of integrity of entire study, A.O.; study concepts, N.Z., G.C., R.S., M.K., A.O., R.D.E., G.S.; study design, A.F.G., A.O., R.D.E., R.S., G.S.; literature research, A.O., M.K., A.F.G.; clinical studies, A.O., R.D.E., G.S., R.S.; data acquisition, all authors; data analysis/interpretation, A.O., R.S., R.D.E., G.S.; manuscript preparation and definition of intellectual content, A.O., M.K., R.D.E., G.S.; manuscript editing, R.D.E., M.K., G.S.; manuscript revision/review and final version approval, all authors
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTSDISCUSSIONREFERENCES |
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