DOI: 10.1148/rg.273065116
RadioGraphics 2007;27:721-743
© RSNA, 2007
MR Imaging of Acute Right Lower Quadrant Pain in Pregnant and Nonpregnant Patients1
Ivan Pedrosa, MD,
Eric A. Zeikus, MD,
Deborah Levine, MD, and
Neil M. Rofsky, MD
1 From the Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Ave, Boston, MA 02215. Recipient of a Cum Laude award for an education exhibit at the 2005 RSNA Annual Meeting. Received June 7, 2006; revision requested July 19 and received September 13; accepted September 14. N.M.R. receives research support from GE Healthcare (Waukesha, Wis), is on the advisory board of Berlex Laboratories (Wayne, NJ), and is a consultant to CAD Sciences (White Plains, NY); all other authors have no financial relationships to disclose.
Address correspondence to I.P. (e-mail: ipedrosa{at}bidmc.harvard.edu).
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Abstract
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The use of magnetic resonance (MR) imaging in the evaluation of acute abdominal pain is increasing, particularly in those circumstances where computed tomography (CT) is not desirable (eg, pregnancy, allergy to iodinated contrast material). Although ultrasonography (US) is considered the imaging study of choice for evaluation of abdominal pain in pregnant patients, MR imaging is a valuable adjunct to US in evaluation of pregnant patients with acute right lower quadrant (RLQ) pain who have inconclusive US results. MR imaging is also frequently used in patients with renal failure, in whom the use of iodinated contrast material is contraindicated, as well as in cases where CT results are inconclusive. In patients with acute RLQ pain, the breadth of abnormalities visible at MR imaging is very broad, with pathologic conditions potentially originating from multiple organ systems, but most commonly from the gastrointestinal and genitourinary systems. MR imaging is an excellent imaging modality for evaluation of RLQ pain and should be strongly considered in those patients in whom use of iodinated contrast media or radiation is not desirable.
© RSNA, 2007
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LEARNING OBJECTIVES FOR TEST 3
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After reading this article and taking the test, the reader will be able to:- Discuss MR imaging protocols for evaluation of pregnant and nonpregnant patients with acute RLQ pain.
- Describe the MR imaging appearances of the normal and abnormal appendix.
- Identify various common conditions that masquerade as acute appendicitis in both pregnant and nonpregnant patients on MR images.
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Introduction
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The broad range of conditions causing acute right lower quadrant (RLQ) pain may involve multiple organ systems, including the gastrointestinal tract, urinary tract, and female reproductive tract. Imaging examinations are frequently indicated, as the clinical presentation is commonly confusing. The diagnostic algorithm is based on the clinical history, physical examination, and laboratory analysis. Computed tomography (CT) has become the standard of care in the evaluation of patients with suspected disease of the gastrointestinal and urinary tracts. Ultrasonography (US) is preferred in patients with suspected disease affecting primarily the uterus or adnexa and in pregnant patients. However, both modalities have limitations. CT relies on use of ionizing radiation and commonly iodinated contrast material, which are less desirable in pregnancy and in patients with contrast material allergy and renal failure. US can be limited in patients with large body habitus or in the presence of extensive air or calcification, and it is very dependent on operator experience (1). Despite these limitations, US is the imaging modality of choice in pregnant patients with RLQ pain because it uses neither ionizing radiation nor intravenous contrast material (2,3).
Magnetic resonance (MR) imaging has until very recently only rarely been proposed as an alternative imaging modality for evaluation of acutely ill patients. Limited availability of MR imaging units and the complexity, length, and cost of MR imaging examinations are some of the impediments to more widespread use in the acute setting. However, its multiplanar capacity and excellent soft-tissue contrast, the lack of ionizing radiation, and the generally accepted safety of the currently available intravenous contrast agents are favorable features for MR imaging in acutely ill patients. MR imaging has recently been proposed as an adjunct to US in the evaluation of pregnant patients in whom the US results are inconclusive or nondiagnostic (4–7).
Diagnosis of acute appendicitis in pregnancy represents a clinical challenge due to the anatomic and physiologic alterations associated with pregnancy (8,9). MR imaging is an excellent modality for excluding acute appendicitis when the appendix is not visualized at US (7). Furthermore, acute appendicitis can be diagnosed with MR imaging and an alternative diagnosis can be identified in a substantial number of pregnant women with right-sided abdominal pain (7).
In this article, we present MR imaging protocols for the comprehensive evaluation of RLQ pain in both pregnant and nonpregnant patients. The MR imaging appearance of the normal anatomic structures in the RLQ is reviewed with emphasis on the normal and abnormal appendix in both pregnant and nonpregnant patients. Finally, the MR imaging findings of common and uncommon disorders arising from the gastrointestinal tract, female reproductive tract, and urinary tract that can masquerade clinically as acute appendicitis are illustrated and discussed.
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MR Imaging Protocols
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Nonpregnant Patients
The MR imaging protocol for nonpregnant patients is detailed in Table 1. A phased-array body coil is recommended whenever possible because it offers superior signal-to-noise ratio compared with that of the built-in body coil. Oral contrast material is not used routinely for patients with suspected disease of the genitourinary tract, although it may be administered in those with suspected disease of the gastrointestinal tract. Before initiation of the study, a 1-mg intramuscular dose of glucagon (Glucagen; Bedford Laboratories, Bedford, Ohio) is given to decrease artifacts arising from bowel peristalsis.
Axial T1-weighted in-phase and opposed-phase GRE images are helpful in the detection and characterization of fat-containing lesions and hemorrhagic lesions or collections with high signal intensity. Air, blood products, and calcium produce a blooming effect on MR images caused by magnetic susceptibility. Blooming effects can be easily recognized on the in-phase images (with a longer echo time) when compared with the opposed-phase images (with a shorter echo time). T2-weighted fast SE images are acquired in the axial, sagittal, and coronal planes to facilitate localization of anatomic structures and pathologic conditions. Fast SE images provide higher signal-to-noise ratios (due to multiple excitations), allow improved in-plane spatial resolution, and have less inherent blurriness for species with a short T2 than do the single-shot imaging techniques. However, motion-related artifacts in fast SE sequences may result in more blurriness than that of single-shot techniques.
We routinely administer gadopentetate dimeg-lumine (Magnevist; Berlex Laboratories, Wayne, NJ) intravenously at our institution for evaluation of abdominal and pelvic disease. MR images are obtained before and after a bolus of gadolinium contrast material at a dose of 0.1 mmol/kg and a rate of 2 mL/sec followed by a flush of 20 mL of saline given at the same rate. A bolus test of 2 mL of gadolinium contrast material at 2 mL/sec is used to time the arterial phase, as previously described by Earls et al (10). Alternatively, the arterial phase may be timed by using an automated bolus tracking device or fluoroscopic triggering technique. MR images are then acquired during the properly timed arterial phase, portal phase (20 seconds after the arterial phase), and delayed venous phase (60 seconds after the arterial phase).
Pre- and dynamic postcontrast images are obtained with a 3D fat-saturated T1-weighted spoiled GRE sequence. These 3D data sets offer superior signal-to-noise ratio and thinner sections (without an intersection gap) than do 2D acquisitions. In addition, 3D acquisitions can be used for generating multiplanar reformations or MR angiograms that allow a comprehensive evaluation of the abdomen or pelvis (11,12).
Pregnant Patients
Written informed consent regarding use of MR imaging in pregnancy is obtained before performing the examination.
MR examination is thought to be safe in pregnancy and can be used regardless of the trimester when the outcome of the examination has the potential to affect the care of the patient (13). Examinations are performed at a field strength of 1.5 T with the patient in the supine position and with a body phased-array coil. Patients receive an oral preparation consisting of 300 mL of Gastromark (Mallinckrodt Medical, St Louis, Mo) and 300 mL of Readi-cat 2 (E-Z-Em, Westbury, NY) starting 1–1.5 hours before the MR imaging examination. This solution provides negative contrast (dark signal intensity) within the bowel lumen on both T1- and T2-weighted images without causing substantial susceptibility effects that can obscure the anatomy (5,7,14). Intravenous contrast agents are not used.
The MR imaging protocol for pregnant patients is detailed in Table 2. Single-shot fast SE images are acquired in the three orthogonal planes (axial, coronal, and sagittal). Conventional SE and fast SE imaging is less desirable in the pregnant patient because fetal motion may substantially degrade image quality. Single-shot imaging provides a motion-insensitive strategy even in the presence of severe fetal motion. Furthermore, image quality in single-shot imaging is not degraded in those patients with limited breath-holding capability, a common occurrence among gravid patients. However, breath-hold acquisitions are encouraged to ensure adequate anatomic coverage and contiguous display of the anatomy.
Axial single-shot fast SE images with frequency-selective fat saturation pulses improve the detection of inflammatory changes and edema. Axial TOF GRE T2*-weighted images are used to differentiate the normal appendix from the commonly seen dilated venous tributaries of the right gonadal vein (see the "Normal Appendix" section) and to evaluate for venous thrombosis in abdominal or pelvic veins. Axial T1-weighted in-phase and opposed-phase GRE images are valuable to identify hemorrhagic and fat-containing lesions.
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Normal Appendix
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The normal appendix is a blindly ending tubular structure that averages 10 cm in length and arises in the medial aspect of the cecum, approximately 3 cm below the ileocecal valve (15). The normal appendix is either collapsed or partially filled with fluid, contrast material, or air (15). In the absence of oral contrast material, the normal appendix is seen as a cordlike structure of intermediate signal intensity, similar to that of the bowel wall (16) (Fig 1). A hyperintense center and a hypointense wall on axial T2-weighted echo train images and predominantly low signal intensity on T1-weighted images have been described as the typical appearance of the normal appendix in the pediatric population (17). The normal appendiceal wall measures less than 2 mm in thickness (15). The normal appendiceal diameter typically measures less than 6 mm on single-shot fast SE images (7). The normal appendix can be seen at MR imaging in up to 90% of nonpregnant patients (16,17) and 83%–89% of pregnant women (6,7). Definitive visualization of the normal appendix has been reported in 78% and 60% of nonpregnant patients at T1-weighted SE imaging and T2-weighted single-shot turbo SE imaging, respectively (18).
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Figure 1. Normal appendix in a 48-year-old woman with pelvic pain. Coronal T2-weighted single-shot fast SE image of the upper pelvis shows the cecum (C) and bladder (B). The normal appendix (arrows) is clearly delineated as a blind-ending tubular structure arising off the base of the cecum. In the absence of oral contrast material, the normal appendix demonstrates signal intensity similar to that of the bowel wall on single-shot fast SE images.
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The gravid uterus progressively displaces the appendix superiorly during pregnancy; therefore, the normal appendix may be seen in the right mid abdomen or right upper quadrant during the second and third trimesters (7).
Single-shot fast SE images are the cornerstone of our MR imaging protocol for pregnant women and essential to identify the appendix. In our experience, use of a cross-reference imaging tool available in our picture archiving and communication system is crucial to confirm that this structure is the appendix by identifying its typical blind-end tubular appearance in the same anatomic location in all three planes.
In our experience, the oral preparation is essential in pregnant patients, in whom intravenous administration of gadolinium contrast agents is not used (7). The iron oxide particles in the oral preparation render the bowel containing oral contrast material as dark signal with all sequences, due to T2* effect. When the appendix is filled with air or oral contrast material, it appears larger and darker on TOF T2*-weighted images than on the single-shot fast SE images, the so-called blooming effect, due to susceptibility effects. The presence of blooming effect within the appendix virtually excludes acute appendicitis (7).
Identification of the blooming effect is crucial in differentiation between the normal appendix and pelvic venous varices in pregnancy. Pregnant women, particularly during their third trimester, can develop extensive varices. These veins appear as tubular hypointense structures on T1-weighted and single-shot fast SE images, an appearance identical to that of the normal appendix. Distinction between these two structures can be very challenging. Thorough comparison of the axial single-shot fast SE and TOF images allows differentiation between the normal appendix and venous varices. Pelvic varices demonstrate high signal intensity on TOF images due to the presence of flow, whereas the normal appendix filled with air or oral contrast material remains of low signal intensity on both TOF and single-shot fast SE images and shows the characteristic blooming effect (7) (Fig 2).
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Figure 2a. Usefulness of oral contrast material and TOF imaging in evaluation of the normal appendix during pregnancy in a 31-year-old woman who was 30 weeks pregnant and had RLQ pain and nausea. (a) Axial T2-weighted single-shot fast SE image of the gravid abdomen shows the cecum (C) and terminal ileum (*). A possible normal appendix (arrow) is seen posterior to the cecum. However, other tubular hypointense structures (arrowheads) with a similar appearance are seen medial to the psoas muscle. (b) Axial TOF GRE image obtained at the same level shows the characteristic enlargement and decreased signal intensity of the appendix (arrow), the so-called blooming effect, which is caused by the susceptibility effect of air or the iron-based oral contrast medium within its lumen. Note the same effect in the cecum (C) and terminal ileum (*). This phenomenon virtually excludes appendicitis. TOF images are also essential in differentiating the common periovarian varices (arrowheads) with very high signal intensity from the hypointense appendix; this distinction cannot be made on the single-shot fast SE images alone.
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Figure 2b. Usefulness of oral contrast material and TOF imaging in evaluation of the normal appendix during pregnancy in a 31-year-old woman who was 30 weeks pregnant and had RLQ pain and nausea. (a) Axial T2-weighted single-shot fast SE image of the gravid abdomen shows the cecum (C) and terminal ileum (*). A possible normal appendix (arrow) is seen posterior to the cecum. However, other tubular hypointense structures (arrowheads) with a similar appearance are seen medial to the psoas muscle. (b) Axial TOF GRE image obtained at the same level shows the characteristic enlargement and decreased signal intensity of the appendix (arrow), the so-called blooming effect, which is caused by the susceptibility effect of air or the iron-based oral contrast medium within its lumen. Note the same effect in the cecum (C) and terminal ileum (*). This phenomenon virtually excludes appendicitis. TOF images are also essential in differentiating the common periovarian varices (arrowheads) with very high signal intensity from the hypointense appendix; this distinction cannot be made on the single-shot fast SE images alone.
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Appendiceal Disorders
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A fluid-filled appendix greater than 7 mm in diameter on single-shot fast SE images is consistent with acute appendicitis (7) (Fig 3). The presence of periappendiceal inflammation visualized as bandlike areas of high signal intensity on single-shot fast SE images supports this diagnosis. Periappendiceal inflammation is better appreciated with the use of fat saturation pulses, as high-signal-intensity fluid may be missed within the hyperintense fat on single-shot fast SE images acquired without fat saturation. The presence of periappendiceal high signal intensity (edema) is especially useful in early appendicitis when the appendiceal diameter has not enlarged (Fig 4). The thickened wall of the inflamed appendix is readily visible on single-shot fast SE images due to the contrast provided by the high-signal-intensity fluid in its lumen and by the high signal intensity of the periappendiceal fat. An appendicolith can sometimes be visible at MR imaging as a focal area of low signal intensity in the appendiceal lumen with all sequences (Fig 5). However, we believe that CT is superior to MR imaging in the demonstration of appendicoliths.
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Figure 3. Appendicitis in a 33-year-old woman who was 17 weeks pregnant and had RLQ pain and fever. Axial T2-weighted single-shot fast SE image of the lower abdomen shows the cecum (C) and terminal ileum (TI). The appendix (arrow) is identified posterior to the cecum. The appendix is enlarged (8-mm diameter) and thick walled and its lumen is filled with high-signal-intensity fluid, whereas the cecum and terminal ileum are completely filled with negative oral contrast material. The MR imaging findings were consistent with early appendicitis, which was confirmed at surgery.
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Figure 4a. Mild acute appendicitis in a 20-year-old woman who was 10 weeks pregnant and had RLQ pain. C = cecum. (a) Sagittal T2-weighted single-shot fast SE image of the right lower abdomen shows the cecum tilted superiorly. Located just beneath the cecum is the appendix (arrows). Note that the cecum is completely filled with negative contrast material, as opposed to the high-signal-intensity lumen of the appendix. The appendiceal wall is visible, but the appendix is not dilated. (b) Sagittal fat-saturated T2-weighted single-shot fast SE image obtained at the same level shows increased signal intensity in the periappendiceal fat (arrows), a finding that confirms the presence of acute inflammation. Mild acute appendicitis was found at surgery and pathologic analysis.
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Figure 4b. Mild acute appendicitis in a 20-year-old woman who was 10 weeks pregnant and had RLQ pain. C = cecum. (a) Sagittal T2-weighted single-shot fast SE image of the right lower abdomen shows the cecum tilted superiorly. Located just beneath the cecum is the appendix (arrows). Note that the cecum is completely filled with negative contrast material, as opposed to the high-signal-intensity lumen of the appendix. The appendiceal wall is visible, but the appendix is not dilated. (b) Sagittal fat-saturated T2-weighted single-shot fast SE image obtained at the same level shows increased signal intensity in the periappendiceal fat (arrows), a finding that confirms the presence of acute inflammation. Mild acute appendicitis was found at surgery and pathologic analysis.
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Figure 5. Acute appendicitis in a 25-year-old woman who was 16 weeks pregnant and had RLQ pain and leukocytosis. Axial T2-weighted single-shot fast SE image of the right midabdomen shows the appendix (black arrowhead), which is curved medially, arising from the base of the cecum (C). Note the high signal intensity within the appendiceal lumen and that the appendix is dilated. A rounded area of low signal intensity (arrow) in the proximal appendix is noted; this area represents an appendicolith. Periappendiceal fat stranding is seen as a bandlike area of high signal intensity (white arrowheads) in the adjacent fat. The MR imaging findings were consistent with acute appendicitis, which was confirmed at surgery and pathologic analysis.
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Marked appendiceal dilatation and periappendiceal edema are typically seen in more advanced cases of appendicitis. An ill-defined mass of heterogeneous moderately high signal intensity may be present, indicating a periappendiceal phlegmon (Fig 6). Patients with more subacute perforation may present with an abscess cavity in the RLQ. Abscess cavities may be seen as a fluid collection with a well-defined wall. Although non-pregnant patients with clinical suspicion of acute appendicitis are usually imaged with CT, the authors routinely use MR imaging as an initial examination after an inconclusive US study in pregnant women.
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Figure 6. Appendiceal phlegmon in a 29-year-old woman who was 27 weeks pregnant and had RLQ pain. Sagittal T2-weighted single-shot fast SE image of the right hemiabdomen shows a heterogeneous moderately hyperintense mass (arrows) in the RLQ with mass effect on the cecum (C), an appearance consistent with a phlegmon. Note that the right ovary (arrowhead) is displaced anteriorly. The patient was treated with intravenous antibiotics, and follow-up MR imaging at 32 weeks showed resolution of the phlegmon with a persistent abnormally dilated appendix. The patient underwent cesarean section and appendectomy, which confirmed the diagnosis of perforated appendicitis.
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In the authors’ experience, an appendiceal diameter of 6–7 mm without luminal air or oral contrast material is indeterminate (7). Close attention to the presence or absence of other ancillary findings (periappendiceal stranding, abscess, wall thickening, etc) can steer the radiologist to the correct diagnosis. Occasionally, contrast-enhanced CT may help in these rare, indeterminate cases to further assess subtle findings. In the absence of ancillary findings, close observation and serial abdominal examinations may facilitate the diagnosis. The use of gadolinium-based contrast agents in the evaluation of pregnant women with acute abdominal pain has been reported (19). The authors do not routinely use gadolinium, as the safety of this contrast medium in pregnancy has not been proved. However, there may be a role for gadolinium-enhanced MR imaging in the assessment of pregnant women with acute abdominal pain, particularly in those with indeterminate imaging findings. Further studies are necessary to evaluate the risks of gadolinium-based contrast agents in pregnancy.
Postsurgical inflammation at the base of the appendiceal remnant, the so-called stump appendicitis, is a rare event (20). An increased risk of this complication after laparoscopic appendectomy due to incomplete resection of the base of the appendix has been reported (21,22). The time of clinical presentation may be variable, with cases reported from 3 months to 21 years after appendectomy (23). CT findings may be similar to those present in acute appendicitis (ie, enhancing tubular structure arising from the cecum with adjacent fat stranding) if the appendiceal stump left after appendectomy is long (24). CT may also demonstrate a pericecal phlegmon or abscess, as well as thickening of the cecal wall with oral contrast material insinuating into the expected location of the appendiceal origin, the so-called arrowhead sign (25). Phlegmon, abscess formation, and wall thickening in the cecum are also visible at MR imaging (5).
An appendiceal mucocele is a rare entity that accounts for 0.25% of appendectomies (26,27). The clinical presentation and imaging findings can mimic acute appendicitis. Appendiceal mucoceles may be caused by different underlying conditions, and the result is a dilated, fluid- or mucus-filled appendix. Four histologic subtypes, ranging from benign to malignant processes, have been described: postobstructive mucous retention cyst, mucosal hyperplasia (resembling a hyperplastic polyp), mucinous cystadenoma (resembling an adenomatous polyp), and invasive mucinous cystadenocarcinoma (26,28–30). Most appendiceal mucoceles are found incidentally or due to chronic RLQ abdominal pain. Acute RLQ pain may occur secondary to perforation of the appendix. Appendiceal mucoceles may rupture, causing spillage of the mucinous contents into the peritoneal cavity or pseudomyxoma peritonei, which can be focal or diffuse (28,29).
The mucinous contents within the mucocele have high signal intensity on T2-weighted images. Although a fluid-filled appendix may be seen in both acute appendicitis and appendiceal mucoceles, the former typically has associated wall thickening and periappendiceal inflammation. In general, the degree of distention of the appendix in patients with mucoceles is disproportionate to the amount of appendiceal wall thickening and periappendiceal inflammation, with the exception of those in whom the mucocele is ruptured (Fig 7). Enlargement of the appendix beyond 15 mm in diameter should be viewed with suspicion, and careful attention should be paid to other findings that may indicate the presence of a neoplasm (31). In the presence of an appendiceal cystadenoma or cystadenocarcinoma, a focal mass may be seen at cross-sectional imaging.
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Figure 7a. Ruptured appendiceal mucocele in a 72-year-old man with right-sided pelvic pain and abnormal appearance of the appendix at prior CT performed at another institution. (a) Coronal T2-weighted single-shot fast SE image shows the cecum (C), normal terminal ileum (black arrowheads), and bladder (B). A thick-walled appendix (arrow) is present, surrounded by an irregularly shaped fluid collection (white arrowheads). (b) Axial T2-weighted fast SE image shows cystic dilatation of the appendiceal tip (*) and periappendiceal free fluid (arrowheads), findings suggestive of a ruptured appendiceal mucocele. A ruptured mucocele secondary to an appendiceal cystadenoma was found at surgery and pathologic analysis.
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Figure 7b. Ruptured appendiceal mucocele in a 72-year-old man with right-sided pelvic pain and abnormal appearance of the appendix at prior CT performed at another institution. (a) Coronal T2-weighted single-shot fast SE image shows the cecum (C), normal terminal ileum (black arrowheads), and bladder (B). A thick-walled appendix (arrow) is present, surrounded by an irregularly shaped fluid collection (white arrowheads). (b) Axial T2-weighted fast SE image shows cystic dilatation of the appendiceal tip (*) and periappendiceal free fluid (arrowheads), findings suggestive of a ruptured appendiceal mucocele. A ruptured mucocele secondary to an appendiceal cystadenoma was found at surgery and pathologic analysis.
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Other Disorders Arising from the Gastrointestinal Tract
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Pathologic processes involving the small and large bowel as well as the mesentery and omentum can give rise to RLQ pain. Terminal ileitis, mesenteric adenitis, diverticulitis (cecal, ascending colonic, Meckel, or ileal), typhlitis, primary epiploic appendagitis, and omental infarction are among the processes involving the gastrointestinal tract and mesentery or omentum that may result in RLQ pain.
MR imaging allows exquisite visualization of the small and large bowel. Patients with inflammatory bowel disease (eg, Crohn disease and ulcerative colitis) presenting with acute RLQ pain can be adequately evaluated with MR imaging. Bowel wall edema is readily appreciated on T2-weighted single-shot fast SE images as a band of increased signal intensity within the wall thickness. Superior sensitivity of MR imaging compared with that of CT has been reported for detection of early and mild forms of inflammatory bowel disease (32). The degree of wall enhancement on gadolinium-enhanced images and the degree of high signal intensity on fat-saturated T2-weighted images correlate with disease activity (33,34).
Pelvic and perineal complications of Crohn disease including enteroenteric and enterovesical fistulas or abscesses can be accurately seen at MR imaging (35). MR imaging findings in patients with RLQ pain secondary to an acute flare of Crohn disease are variable depending on the stage of the disease. Mild acute inflammation usually manifests as mild thickening of the small bowel (particularly the terminal ileum) or colon. Prominence, dilatation, and tortuosity of the vasa recta coursing through proliferative mesenteric fat, the so-called comb sign, can be readily appreciated at MR imaging (Fig 8). However, similar findings can be seen in patients with other forms of ileitis (eg, infectious). An inflammatory phlegmon can be seen as a soft-tissue mass of intermediate signal intensity on T1-weighted images and mild increased signal intensity on T2-weighted images (better appreciated with fat saturation techniques). Frank increased signal intensity on T2-weighted images typically represents liquefaction within an abscess (Fig 9).
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Figure 8a. Crohn disease in a 26-year-old woman with RLQ pain and fever. (a) Axial T2-weighted fast SE image of the lower abdomen shows marked mural thickening in the distal ileum (arrows) with a layer of increased signal intensity suggestive of submucosal edema. There is prominence, dilatation, and tortuosity of the vasa recta coursing through proliferative mesenteric fat, the comb sign (arrowheads). (b) Axial gadolinium-enhanced 3D fat-saturated T1-weighted GRE image obtained at the same level shows marked mural enhancement (arrows) in the abnormal loop of distal ileum. Linear areas of low signal intensity in the wall correspond to the edema in the bowel wall. The comb sign is better appreciated with gadolinium contrast material (arrowheads). These findings are consistent with an acute flare of Crohn disease.
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Figure 8b. Crohn disease in a 26-year-old woman with RLQ pain and fever. (a) Axial T2-weighted fast SE image of the lower abdomen shows marked mural thickening in the distal ileum (arrows) with a layer of increased signal intensity suggestive of submucosal edema. There is prominence, dilatation, and tortuosity of the vasa recta coursing through proliferative mesenteric fat, the comb sign (arrowheads). (b) Axial gadolinium-enhanced 3D fat-saturated T1-weighted GRE image obtained at the same level shows marked mural enhancement (arrows) in the abnormal loop of distal ileum. Linear areas of low signal intensity in the wall correspond to the edema in the bowel wall. The comb sign is better appreciated with gadolinium contrast material (arrowheads). These findings are consistent with an acute flare of Crohn disease.
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Figure 9a. Abscess in a 59-year-old man with a history of Crohn disease who presented with fever, chills, and lower abdominal pain. (a) Axial T2-weighted fast SE image shows a thick-walled fluid collection (arrows) in the left hemipelvis, adjacent to the sigmoid colon (arrowheads). (b) Axial gadolinium-enhanced 3D fat-saturated T1-weighted GRE image obtained during the delayed venous phase shows peripheral rim and septal enhancement of the fluid collection (arrows). The sigmoid colon is again visualized (arrowheads). The diagnosis of an abscess related to Crohn disease was confirmed with percutaneous drainage of the fluid collection.
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Figure 9b. Abscess in a 59-year-old man with a history of Crohn disease who presented with fever, chills, and lower abdominal pain. (a) Axial T2-weighted fast SE image shows a thick-walled fluid collection (arrows) in the left hemipelvis, adjacent to the sigmoid colon (arrowheads). (b) Axial gadolinium-enhanced 3D fat-saturated T1-weighted GRE image obtained during the delayed venous phase shows peripheral rim and septal enhancement of the fluid collection (arrows). The sigmoid colon is again visualized (arrowheads). The diagnosis of an abscess related to Crohn disease was confirmed with percutaneous drainage of the fluid collection.
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The multiplanar capability and inherent excellent soft-tissue contrast of MR imaging are useful in the evaluation of patients with small bowel obstruction. T2-weighted half-Fourier single-shot fast SE images can accurately demonstrate the degree and level of small bowel obstruction without the need for intravenous or oral contrast material (36). The cause of the obstruction may be recognized on these images in one-half of patients with small bowel obstruction (36) (Fig 10).
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Figure 10a. Small bowel obstruction in a 34-year-old woman with a history of ulcerative colitis and prior total colectomy who was 19 weeks pregnant and presented with nausea, vomiting, and abdominal pain. (a) Coronal T2-weighted single-shot fast SE image of the abdomen and pelvis shows the gravid uterus with the placenta (P). There is diffuse dilatation of fluid-filled loops of small bowel. Well-circumscribed areas of high signal intensity surround the bowel (arrows) and conform to the borders of the abdominal wall, a finding indicative of free fluid. (b) Sagittal T2-weighted single-shot fast SE image of the RLQ shows the dilated, fluid-filled small bowel loops. The patient’s ostomy (large arrowhead) is collapsed, and the end ileal loop (arrow) tapers abruptly to the ostomy; these findings indicate the transition point of the small bowel obstruction caused by stenosis at the level of the os-tomy. The free fluid is seen beneath the small bowel loops (small arrowhead). The small bowel obstruction was relieved after placement of a catheter and dilation of the ostomy.
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Figure 10b. Small bowel obstruction in a 34-year-old woman with a history of ulcerative colitis and prior total colectomy who was 19 weeks pregnant and presented with nausea, vomiting, and abdominal pain. (a) Coronal T2-weighted single-shot fast SE image of the abdomen and pelvis shows the gravid uterus with the placenta (P). There is diffuse dilatation of fluid-filled loops of small bowel. Well-circumscribed areas of high signal intensity surround the bowel (arrows) and conform to the borders of the abdominal wall, a finding indicative of free fluid. (b) Sagittal T2-weighted single-shot fast SE image of the RLQ shows the dilated, fluid-filled small bowel loops. The patient’s ostomy (large arrowhead) is collapsed, and the end ileal loop (arrow) tapers abruptly to the ostomy; these findings indicate the transition point of the small bowel obstruction caused by stenosis at the level of the ostomy. The free fluid is seen beneath the small bowel loops (small arrowhead). The small bowel obstruction was relieved after placement of a catheter and dilation of the ostomy.
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Detection of bowel wall pneumatosis may be very challenging at MR imaging, as air is devoid of signal with all MR pulse sequences. In-phase and opposed-phase GRE images may help demonstrate this finding because a characteristic blooming effect occurs on the in-phase images (acquired with a longer echo time) compared to the opposed-phase images in the presence of air due to susceptibility effects. Single-shot fast SE images can help confirm this finding by demonstrating an area of very low signal intensity within the wall and showing the mucosa separating this area from the bowel lumen (Fig 11). Ancillary findings including bowel wall thickening, mesenteric fat stranding, or air in the portomesenteric venous system provide further evidence that supports the diagnosis of pneumatosis. However, CT should be considered to confirm or exclude this finding when MR imaging features are equivocal.
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Figure 11a. Cecal pneumatosis in a 47-year-old diabetic woman with fever and abdominal pain 2 months after pancreatic transplantation. She had undergone renal transplantation 5 years before this admission. (a) Axial T2-weighted single-shot fast SE image of the lower abdomen shows an air-fluid level in the lumen of the cecum (black arrowhead). A curvilinear area of low signal intensity that conforms to the wall of the cecum (arrows) represents pneumatosis. Part of the cecal wall appears as a thin line of intermediate signal intensity (white arrowhead) that separates the luminal air from the pneumatosis. (b) Axial gadolinium-enhanced 3D fat-saturated T1-weighted GRE image of the upper abdomen, obtained during the portal venous phase, shows lack of signal within the left portal vein (arrow) due to air in the portal vein. (c) Unenhanced CT scan shows the cecal pneumatosis (arrows) and cecal wall thickening (arrowhead); CT also showed the air in the left portal vein. At surgery, a perforated diverticulum was found in the cecum.
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Figure 11b. Cecal pneumatosis in a 47-year-old diabetic woman with fever and abdominal pain 2 months after pancreatic transplantation. She had undergone renal transplantation 5 years before this admission. (a) Axial T2-weighted single-shot fast SE image of the lower abdomen shows an air-fluid level in the lumen of the cecum (black arrowhead). A curvilinear area of low signal intensity that conforms to the wall of the cecum (arrows) represents pneumatosis. Part of the cecal wall appears as a thin line of intermediate signal intensity (white arrowhead) that separates the luminal air from the pneumatosis. (b) Axial gadolinium-enhanced 3D fat-saturated T1-weighted GRE image of the upper abdomen, obtained during the portal venous phase, shows lack of signal within the left portal vein (arrow) due to air in the portal vein. (c) Unenhanced CT scan shows the cecal pneumatosis (arrows) and cecal wall thickening (arrowhead); CT also showed the air in the left portal vein. At surgery, a perforated diverticulum was found in the cecum.
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Figure 11c. Cecal pneumatosis in a 47-year-old diabetic woman with fever and abdominal pain 2 months after pancreatic transplantation. She had undergone renal transplantation 5 years before this admission. (a) Axial T2-weighted single-shot fast SE image of the lower abdomen shows an air-fluid level in the lumen of the cecum (black arrowhead). A curvilinear area of low signal intensity that conforms to the wall of the cecum (arrows) represents pneumatosis. Part of the cecal wall appears as a thin line of intermediate signal intensity (white arrowhead) that separates the luminal air from the pneumatosis. (b) Axial gadolinium-enhanced 3D fat-saturated T1-weighted GRE image of the upper abdomen, obtained during the portal venous phase, shows lack of signal within the left portal vein (arrow) due to air in the portal vein. (c) Unenhanced CT scan shows the cecal pneumatosis (arrows) and cecal wall thickening (arrowhead); CT also showed the air in the left portal vein. At surgery, a perforated diverticulum was found in the cecum.
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Occasionally, RLQ pain may be secondary to herniation of a bowel loop through a defect in the anterior abdominal wall. MR imaging provides exquisite visualization of the fascia and muscles in the anterior abdominal wall, allowing clear depiction of bowel herniating through an existing defect.
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Obstetric and Gynecologic Disorders
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The female reproductive tract gives rise to a multitude of pathologic conditions that can manifest as acute RLQ pain. Most important, some of these entities may require surgical intervention, including ectopic pregnancy and ovarian torsion.
Ovarian Disorders
Hemorrhagic cysts are a very common cause of RLQ pain, frequently resulting from rupture into the peritoneal cavity. Hemorrhage may be seen in both functional and corpus luteum cysts. The signal intensity of the cyst varies depending on the age of the hemorrhage. Subacute hemorrhage (deoxyhemoglobin) is of intermediate signal intensity on T1-weighted images and low signal intensity on T2-weighted images. Later, the presence of intracellular methemoglobin causes increased signal intensity on T1-weighted images and decreased signal intensity on T2-weighted images. Layering blood products within the dependent portion of the cyst, the so-called hematocrit effect, can be seen on both T1- and T2-weighted images.
Pelvic endometriosis is another cause of RLQ pain. Endometriosis is defined as the presence of endometrial tissue outside the uterus. The most common location of ectopic endometrial tissue is the ovaries (37). Hormonal stimulation of the endometrial tissue causes enlargement and hemorrhage with subsequent formation of endometrial cysts (endometriomas) (37). MR imaging findings that suggest the diagnosis of endometrial cysts include homogeneous high signal intensity (equal to or greater than that of fat) on T1-weighted images; areas of decreased signal intensity or "shading" effect on T2-weighted images (usually mixed with areas of high signal intensity) in cysts that exhibit high signal intensity on T1-weighted images; and multiplicity (more than two cysts with increased signal intensity at T1-weighted imaging that adhere to each other) (37) (Fig 12). The shading effect is likely caused by the presence of high-viscosity contents, high protein concentration, and/or high iron concentration within the fluid (37,38).
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Figure 12a. Endometriosis in a 37-year-old woman with RLQ pain and a right adnexal mass at US. (a) Axial T1-weighted GRE image shows two lesions (arrows) with homogeneous high signal intensity in the pelvis. (b) Sagittal T2-weighted fast SE image shows heterogeneous decreased or low signal intensity (shading) in the two lesions (arrows), which are located immediately superior to the uterus (U). Gadolinium-enhanced MR imaging showed no enhancement within the lesions. Endometriomas were confirmed at surgery and pathologic analysis.
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Figure 12b. Endometriosis in a 37-year-old woman with RLQ pain and a right adnexal mass at US. (a) Axial T1-weighted GRE image shows two lesions (arrows) with homogeneous high signal intensity in the pelvis. (b) Sagittal T2-weighted fast SE image shows heterogeneous decreased or low signal intensity (shading) in the two lesions (arrows), which are located immediately superior to the uterus (U). Gadolinium-enhanced MR imaging showed no enhancement within the lesions. Endometriomas were confirmed at surgery and pathologic analysis.
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Ancillary findings that suggest endometriosis include a low-signal-intensity rim in the cysts, peritoneal implants, bowel tethering and angulation, and adhesions (39,40). Obliteration of the posterior cul-de-sac in the pelvis may also be seen in patients with endometriosis (41). However, these findings are considered insensitive for the diagnosis of endometriosis (39,42). Differentiation between endometriomas and hemorrhagic cysts is not always possible with a single imaging study. Comparison with study results at other points in time can be helpful.
Ovarian torsion occurs as a result of twisting of the ovary around its vascular pedicle, leading to ischemia. An ovarian lesion serves as the leading point in the majority of cases. Ovarian or paraovarian cysts are the most common lesions encountered in these patients. The ovarian cysts can be physiologic or neoplastic, with the most common neoplasm leading to torsion being a dermoid (43). Other conditions that may lead to ovarian torsion include ovarian hyperstimulation syndrome, abscesses, and malignant neoplasms (44). Ovarian torsion is occasionally seen in pregnancy.
MR imaging findings in ovarian torsion vary depending on the stage of the disease. Initially, there is ovarian enlargement caused by stromal edema, which is appreciated as diffuse high signal intensity on T2-weighted images (45). Fat saturation techniques improve the detection of ovarian edema on T2-weighted images (Fig 13). In the presence of a mass, detection of edema in the ovarian stroma may be challenging (45). Increased signal intensity of the ovarian stroma is an early sign, and a viable ovary is frequently found at surgery in these patients (45). As torsion progresses, the signal intensity in the ovary is variable due to the presence of hemorrhage and necrosis. Decreased signal intensity on T1- and T2-weighted images indicates hemorrhagic infarction (46).
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Figure 13a. Ovarian torsion in a 31-year-old woman who was 30 weeks pregnant and had RLQ pain and nausea. US showed a mildly enlarged right ovary with normal arterial and venous flow. (a) Axial T2-weighted single-shot fast SE image of the right pelvis shows a mildly enlarged right ovary with areas of increased signal intensity in its stroma (arrow), findings consistent with edema. (b) On an axial fat-saturated T2-weighted single-shot fast SE image obtained at the same level, the high signal intensity within the ovarian stroma (*) caused by edema is seen more clearly. Note the peripherally located follicles, which appear prominent due to the stromal edema. A small amount of fluid is also present surrounding the ovary (arrowheads); this fluid was not appreciated without fat saturation. These MR imaging findings are characteristic of ovarian torsion, and the diagnosis was confirmed at surgery.
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Figure 13b. Ovarian torsion in a 31-year-old woman who was 30 weeks pregnant and had RLQ pain and nausea. US showed a mildly enlarged right ovary with normal arterial and venous flow. (a) Axial T2-weighted single-shot fast SE image of the right pelvis shows a mildly enlarged right ovary with areas of increased signal intensity in its stroma (arrow), findings consistent with edema. (b) On an axial fat-saturated T2-weighted single-shot fast SE image obtained at the same level, the high signal intensity within the ovarian stroma (*) caused by edema is seen more clearly. Note the peripherally located follicles, which appear prominent due to the stromal edema. A small amount of fluid is also present surrounding the ovary (arrowheads); this fluid was not appreciated without fat saturation. These MR imaging findings are characteristic of ovarian torsion, and the diagnosis was confirmed at surgery.
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Other findings that aid in recognition of ovarian torsion include tubal thickening, increased signal intensity (edema) within the tube on T2-weighted images (45), deviation of the uterus to the side of the torsion, and a twisted vascular pedicle (47) (Fig 14). A hemorrhagic tube, hemorrhage within the twisted adnexal mass, and hemoperitoneum can be seen, although these are typically present only in torsion with hemorrhagic infarction (43). Fat-saturated T1-weighted images help identify high signal intensity associated with blood products (43).
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Figure 14a. Ovarian torsion in a 29-year-old woman who was 9 weeks pregnant. (a) Coronal fat-saturated T2-weighted single-shot fast SE image shows enlargement and increased signal intensity of the right fallopian tube (large arrow) due to edema. The right ovary is enlarged (arrowhead), and its stroma is hyperintense relative to that of the left ovary (small arrow). Note the multiple fibroids (*) in the gravid uterus. (b) Axial fat-saturated T2-weighted single-shot fast SE image shows enlargement and increased signal intensity of the right fallopian tube (arrowheads). A twisted configuration of the right ovarian vascular pedicle (arrow) is appreciated within the edematous tube. * = fibroid. Ovarian torsion was confirmed at surgery.
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Figure 14b. Ovarian torsion in a 29-year-old woman who was 9 weeks pregnant. (a) Coronal fat-saturated T2-weighted single-shot fast SE image shows enlargement and increased signal intensity of the right fallopian tube (large arrow) due to edema. The right ovary is enlarged (arrowhead), and its stroma is hyperintense relative to that of the left ovary (small arrow). Note the multiple fibroids (*) in the gravid uterus. (b) Axial fat-saturated T2-weighted single-shot fast SE image shows enlargement and increased signal intensity of the right fallopian tube (arrowheads). A twisted configuration of the right ovarian vascular pedicle (arrow) is appreciated within the edematous tube. * = fibroid. Ovarian torsion was confirmed at surgery.
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Similar to Doppler US findings in incomplete or partial torsion, the presence of flow seen on TOF and contrast-enhanced MR images in the affected ovary does not exclude torsion. In our experience, lack of enhancement is best appreciated on subtraction images and is typically seen in chronic stages.
Ovarian hyperstimulation syndrome occurs as a result of ovulation induction. Although up to 65% of patients undergoing ovulation induction have a mild form of this condition, the rare severe presentations require hospitalization. Patients present with pelvic pain, ascites, and bilateral ovarian enlargement with multiple cysts (48). Cysts with increased signal intensity are commonly seen secondary to hemorrhage (48). The prevalence of ovarian torsion is increased in patients with ovarian hyperstimulation syndrome (49). The clinical assessment of hyperstimulated patients with pelvic pain can be difficult. MR imaging can be helpful by showing the increased signal intensity of the ovarian stroma secondary to edema on T2-weighted images (Fig 15).
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Figure 15. Ovarian torsion in ovarian hyperstimulation syndrome after ovulation induction in a 31-year-old woman who was 11 weeks pregnant and presented with acute RLQ pain. Axial fat-saturated T2-weighted fast SE image of the lower pelvis shows the cervix (white arrowhead) and rectum (R). Both ovaries are visible anteriorly and are enlarged with multiple follicles (black arrowheads). These findings are consistent with ovarian hyperstimulation syndrome, which was known to be present clinically. Note the asymmetrical enlargement of the right ovary, which also demonstrates a subtle increase in signal intensity of the stroma (*). A small amount of fluid is seen between the two ovaries (arrow). Although the right ovary had arterial and venous flow at Doppler US, the MR imaging find-ings were consistent with right ovarian torsion, which was confirmed at laparotomy.
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Ovarian masses, either benign or malignant, can also cause acute RLQ pain. Dermoid cysts (mature cystic teratomas) can cause pain when they rupture with ensuing chemical peritonitis or when they serve as a lead point in torsion (50). The fat-containing elements of the dermoid are well visualized with T1-weighted, in-phase, and opposed-phase sequences (Fig 16) and confirmed by using fat saturation techniques. Rupture can be confirmed by seeing fluid or calcifications outside the confines of the cyst or by the associated peritonitis. Thickened peritoneal margins can be visible on single-shot fast SE or T2-weighted fast SE images or as enhancement on postgadolinium T1-weighted images (51).
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Figure 16a. Ruptured ovarian dermoid cyst in a 59-year-old woman with pelvic pain. (a) Axial T2-weighted fast SE image shows an enlarged uterus (U) and a right adnexal mass (*). A moderate amount of free intraperitoneal fluid (black arrowheads) is seen as high signal intensity tracking posteriorly from the adnexal mass. There is thickening of the posterior peritoneum (white arrowhead). An exophytic nodule (arrow) is seen arising from the adnexal mass. Note the chemical shift artifact (black and white lines at the anterior and posterior margins of the nodule, respectively) between the nodule and the surrounding free fluid, a finding that suggests the presence of fat. (b, c) Axial in-phase (b) and opposed-phase (c) T1-weighted GRE images obtained at the same level show the intermediate-signal-intensity mass in the right adnexa (* in b). The exophytic nodule is seen as an ovoid area of high signal intensity (arrow). A thin hypointense rim (India ink artifact) is seen around the nodule on the opposed-phase image (arrow in c); this artifact is characteristically seen on opposed-phased images at the interface of bulk fat and water. The presence of bulk fat within an adnexal mass is virtually pathognomonic of an ovarian dermoid cyst. A ruptured ovarian dermoid cyst causing chemical peritonitis was found intraoperatively and at histologic analysis. U in b = uterus.
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Figure 16b. Ruptured ovarian dermoid cyst in a 59-year-old woman with pelvic pain. (a) Axial T2-weighted fast SE image shows an enlarged uterus (U) and a right adnexal mass (*). A moderate amount of free intraperitoneal fluid (black arrowheads) is seen as high signal intensity tracking posteriorly from the adnexal mass. There is thickening of the posterior peritoneum (white arrowhead). An exophytic nodule (arrow) is seen arising from the adnexal mass. Note the chemical shift artifact (black and white lines at the anterior and posterior margins of the nodule, respectively) between the nodule and the surrounding free fluid, a finding that suggests the presence of fat. (b, c) Axial in-phase (b) and opposed-phase (c) T1-weighted GRE images obtained at | |
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Abstract
LEARNING OBJECTIVES FOR TEST...
