EDUCATION EXHIBIT 1419 MR Imaging of the Acute Abdomen … … · EDUCATION EXHIBIT 1419 MR Imaging of the Acute Abdomen and Pelvis: Acute Appendi-citis and Beyond1 Ajay Singh, MD

EDUCATION EXHIBIT 1419

MR Imaging of theAcute Abdomen andPelvis: Acute Appendi-citis and Beyond1

Ajay Singh, MD ● Raman Danrad, MD ● Peter F. Hahn, MD, PhDMichael A. Blake, MRCPI, FFR(RCSI), FRCR ● Peter R. Mueller, MDRobert A. Novelline, MD

Acute abdominal and pelvic processes account for more than half of allsurgical procedures performed in the emergency setting. Rapid andaccurate diagnosis in the emergency department is essential for the ap-propriate management of these acute conditions. Magnetic resonance(MR) imaging is an attractive modality for diagnostic imaging in pa-tients for whom the risks of radiation or the potential nephrotoxicity ofiodinated contrast agents is a major concern, such as pregnant and pe-diatric patients. MR imaging is most useful for evaluating pregnantpatients with acute lower abdominal pain believed to have an extra-uterine cause, such as appendicitis or ovarian torsion. Other patientswith other conditions commonly seen in the emergency setting may bebetter evaluated with another cross-sectional imaging modality. Imag-ing protocols should be adapted to the constraints of acute illness, withemphasis placed on minimizing the duration of image acquisition, andshould include strategies to decrease motion-related artifacts. A pru-dent approach is to select the imaging modalities that can best depict aparticular subset of clinical conditions to help narrow the differentialdiagnosis. Disadvantages of MR imaging include its high cost, the lim-ited availability of MR imaging systems and trained radiologists, andthe incompatibility of MR imaging systems and the equipment used forintensive care and monitoring of patient status.©RSNA, 2007

Abbreviations: ACR � American College of Radiology, SE � spin echo, STIR � short inversion time inversion recovery

RadioGraphics 2007; 27:1419–1431 ● Published online 10.1148/rg.275065021 ● Content Codes:

1From the Department of Radiology, University of Massachusetts Memorial Medical Center, Worcester, Mass (A.S., R.D.); and Department of Radi-ology, Massachusetts General Hospital, Boston, Mass (A.S., P.F.H., M.A.B., P.R.M., R.A.N.). Presented as an education exhibit at the 2005 RSNAAnnual Meeting. Received March 10, 2006; revision requested May 10 and received January 24, 2007; accepted April 4. P.R.M. is a consultant withCook Group, Bloomington, Ind; all remaining authors have no financial relationships to disclose. Address correspondence to A.S., 10 MuseumWay, Suite 524, Boston, MA 02141 (e-mail: [email protected]).

©RSNA, 2007

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IntroductionRapid and accurate diagnosis is essential for theappropriate management of acute abdominal andpelvic conditions in the emergency department.Emergent abdominal surgical procedures accountfor approximately 53% of all nontrauma-relatedsurgical interventions performed in the acute caresetting (1). Four-quadrant screening ultrasonog-raphy (US) and computed tomography (CT) tra-ditionally have been the dominant cross-sectionalimaging modalities for evaluating acute abdomi-nal and pelvic conditions. The relatively high costof magnetic resonance (MR) imaging, in additionto its limited availability and generally lengthyexamination times, has been a major deterrent toits use in the emergency setting. However, MRimaging also offers a number of advantages, and itis the imaging modality of choice for abdomino-pelvic evaluations in selected patients with spe-cific conditions (eg, pregnant women with symp-toms of acute appendicitis or adnexal torsion).

The article provides an overview of the advan-tages and disadvantages of MR imaging in com-parison with CT, US, and other modalities for thediagnosis of acute abdominopelvic conditions inthe emergency department. The optimization ofMR imaging protocols for use in the emergencysetting is discussed in detail. MR imaging featuresof various common acute conditions (acute ap-pendicitis, adnexal torsion, pelvic inflammatorydisease, fibroid degeneration, endometriosis, he-matometra, acute epiploic appendagitis, andCrohn disease) are described and, where appro-priate, compared with CT and US findings.

Advantages andDisadvantages of MR Imaging

According to Saini et al, the technical cost of anexamination with US, CT, and MR imaging attheir tertiary-care center was $50, $112, and$267, respectively (2). The greater cost of MRimaging compared with that of US or CT is a ma-jor hindrance to the use of MR imaging in theacute care setting.

However, the lack of ionizing radiation and theexcellent safety profile of the gadolinium-basedcontrast agents used in MR imaging are two ma-jor advantages. MR imaging also provides supe-rior contrast resolution and excellent character-ization of pathologic tissue. Its capability for di-rect multiplanar imaging without the need to

reposition the patient also is useful for determin-ing the origin of lesions in the abdomen and pel-vis, although multiplanar reformatting of multide-tector CT image data makes modern CT com-petitive with MR imaging in this respect.

One of the limitations of MR imaging is a con-traindication to the use of gadolinium in earlypregnancy because of its classification as a class Cdrug. The safety of MR imaging for the fetus alsohas not been proved according to Food and DrugAdministration guidelines. Thus, it is prudent toperform MR imaging of pregnant patients onlywhen US findings do not suffice to establish thediagnosis and when CT cannot be used becauseof concerns regarding the risk of radiation to thefetus. However, gadolinium-enhanced MR imag-ing may be performed if nonviability of the fetushas been confirmed by other test results (3).Other limitations of MR imaging include poorerspatial resolution compared with that of CT, in-creased sensitivity to motion-related artifacts, andlimited compatibility with equipment used in in-tensive care and monitoring of patients (4). CT ismany times faster than MR imaging, even whenthe latter is performed with fast gradient-echosequences, and therefore CT is more suitable fordiagnostic imaging of an acutely ill patient whomay be unable to cooperate and lie still for theduration of MR image acquisition. Finally, mostradiologists are more familiar with the appearanceof acute abdominal and pelvic conditions on CTscans than they are with the MR imaging features,and their lack of familiarity with the latter is a hin-drance to the use of MR imaging in an emergencysetting.

MR Imaging ProtocolsMR imaging protocols should be tailored to thepatient’s clinical condition, and image acquisitiontime should be minimized. The use of oral con-trast material is optional. The combination offerumoxsil (Gastromark; Mallinckrodt Medical,St. Louis, Missouri) and dilute barium sulfate(Readi-Cat 2; E-Z-Em Canada, Westbury, NewYork) has provided excellent depiction on bothT1-weighted and T2-weighted images withoutcausing magnetic susceptibility artifacts (5). Gad-olinium-based contrast agents such as gadopente-tate dimeglumine (Magnevist; Berlex Laborato-ries, Wayne, New Jersey) are routinely used intra-venously except in pregnant patients and patientswith marked renal impairment. T1-weighted im-ages with fat saturation are obtained before andafter the administration of an intravenous con-trast agent.

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MR imaging protocols used in an emergencysetting can be broadly classified into two groups:free-breathing protocols and breath-hold proto-cols. The use of a free-breathing protocol is pref-erable for patients who are unable to hold theirbreath for longer than 20 seconds (6). With theuse of free breathing, the most reproducible posi-tion is at end expiration. Magnetization-preparedT1-weighted sequences and single-excitationhalf-Fourier T2-weighted sequences are themainstay of free-breathing protocols. With bothsequence types, image data are acquired on a sec-tion-by-section basis at the rate of approximatelyone section per second.

T1-weighted breath-hold sequences includedual-echo sequences that produce both in-phaseand out-of-phase images. In patients with acuteabdominal conditions, these sequences can beused to define hemorrhagic collections, whichhave high signal intensity on T1-weighted images.Artifacts due to air, metallic objects, or hemosid-erin and calcium deposits are more visible on T1-weighted images obtained with longer echo times.T2-weighted images obtained with a half-Fouriersingle-shot spin echo (SE) or a half-Fourier rapidacquisition with relaxation enhancement provideexcellent depiction of the pancreaticobiliary tree,ascites, pleural effusion, hydronephrosis, andfluid-filled bowel. Contrast-enhanced T1-weighted imaging with a fat-saturated three-di-mensional volumetric isotropic acquisition (pro-prietary sequence acronyms include VIBE,THRIVE, FAME, and LAVA) allows coverage ofthe liver in 20–30 seconds with an interpolatedsection thickness of 3–4 mm. The upper abdo-men is imaged in three contrast enhancementphases: arterial, portal venous, and delayed ve-nous (7). The use of coherently balanced steady-state sequences (TrueFISP, FIESTA), which aresensitive to the T2/T1 ratio rather than to T1 orT2 separately, also has been advocated. Such se-quences play an increasing role in abdominal im-aging, especially for visualization of the anatomybefore organ transplantation or for evaluation ofvessels for thrombosis or dissection (8). The ad-vantage these sequences provide over single-shotfast SE sequences for the evaluation of blood ves-sels is that the signal in a thrombus appears hy-pointense in comparison with the higher signalintensity of flowing blood. Coherently balancedsteady-state sequences also are useful for evaluat-ing fluid-filled bowel loops (9). Thus, a typicalMR imaging protocol for emergency evaluation ofthe abdomen includes axial and coronal single-shot fast SE, axial short inversion time inversion

recovery (STIR), axial T1-weighted in-phase andout-of-phase, axial and coronal steady-state pre-cession, and unenhanced and contrast-enhancedthree-phase volumetric acquisitions.

Clinical ApplicationsMR imaging is an excellent modality for assessingpelvic abnormalities, particularly in pregnant andpediatric patients, because it does not involve ex-posure to ionizing radiation. Depending on thepatient’s condition, the duration of the MR imag-ing examination can be shortened, and the proto-col can be tailored on the basis of clinical mani-festations to answer a specific diagnostic question.

Acute AppendicitisAcute appendicitis is the most common nonob-stetric surgical condition during pregnancy andthe most common surgical emergency in children.The symptoms of acute appendicitis in pregnantpatients often are nonspecific because the appen-dix and omentum are displaced by the graviduterus. Moreover, leukocytosis, which in non-pregnant patients may be predictive of appendici-tis, may occur as a normal physiologic conditionduring pregnancy.

Currently, CT and US are widely used for thepreoperative diagnosis of acute appendicitis inadults. Although US is the first-line investigationfor suspected appendicitis in a pregnant patient,MR imaging is better than CT as the second-lineimaging modality when US results are nondiag-nostic or equivocal. According to the AmericanCollege of Radiology (ACR) appropriateness cri-teria, MR imaging is more appropriate than CTfor use in pregnant patients with right lowerquadrant pain, fever, and leukocytosis. MR imag-ing also is an attractive alternative after US for theevaluation of pregnant and pediatric patients, forwhom exposure to ionizing radiation is a majorconcern (10). MR imaging can be helpful for di-agnosing a wide variety of conditions, includingappendicitis, abscesses, colitis, ovarian disease,pyelonephritis, fibroid degeneration, hemorrhage,and intussusception (11).

Although the safety of MR imaging to the fetushas not been proved, no proved human terato-genic or carcinogenic effects of MR imaging havebeen described in the literature. According to anACR white paper about MR imaging safety, preg-nant patients may undergo MR imaging at any

RG f Volume 27 ● Number 5 Singh et al 1421

TeachingPoint

TeachingPoint

Teaching Point Although US is the first-line investigation for suspected appendicitis in a pregnant patient, MR imaging is better than CT as the second-line imaging modality when US results are nondiagnostic or equivocal.

Teaching Point Although the safety of MR imaging to the fetus has not been proved, no proved human teratogenic or carcinogenic effects of MR imaging have been described in the literature.

Figure 1. Normal appendix during the second trimester of pregnancy. Coronal (a) and axial (b) T2-weighted fast SE MR images demonstrate an intermediate-signal-intensity tubular structure (arrow) thatarises from the inferomedial aspect of the feces-laden cecum. The appendix has a diameter of 6 mm, con-tains no intraluminal fluid, and is located posterior to the gravid uterus.

Figure 2. Acute appendicitis in a 20-year-old pregnantpatient. (a, b) Axial MR images obtained with a T2-weighted fat-suppressed fast SE sequence (a) and a STIRsequence (b) show a dilated appendix with a diameter of12 mm, wall edema, and appendicoliths (arrowheads) inthe right lower quadrant. The periappendiceal rim of highsignal intensity in b is indicative of inflammation. (c) Axialunenhanced CT image shows two appendicoliths (arrow-heads) in the prominent appendix, with a periappendicealrim of high attenuation due to inflammation.


stage of pregnancy if the radiologist determinesthat it is warranted by the risk-benefit ratio. Aftera discussion with the ordering physician, the radi-ologist should document that the following threecriteria have been satisfied: first, the informationcould not be obtained with US; second, the infor-mation to be obtained with MR imaging likelywill affect the care of the patient, the fetus, orboth; and third, it is not prudent to postpone im-aging until the patient is no longer pregnant (3).

At our institution, when appendicitis is sus-pected, we initially perform MR imaging in threeplanes with a single-shot fast SE sequence, fol-lowed by a STIR sequence and a T2-weightedfat-suppressed fast SE sequence in the plane inwhich the appendix is best depicted. If the patientis not pregnant, these sequences are followed byT1-weighted imaging before and after the admin-istration of contrast material. The imaging time isreduced by adjusting the examination protocolafter localization of the appendix. The typical MRimaging room time is less than 30 minutes perexamination. Although the use of intravenouscontrast material with T1-weighted fat-sup-pressed sequences provides excellent results forthe diagnosis of acute appendicitis, its use is con-traindicated during pregnancy, especially in thefirst trimester. The MR imaging protocol used for

other pelvic indications is similar. We do not useoral contrast material. However, Pedrosa et alreported the use of a combination of 300 mL offerumoxsil (Gastromark) and 300 mL of dilutebarium sulfate (Readi-Cat 2) in a study of 51 con-secutive patients; and others have reported similaruses of oral contrast material (12–20).

The normal appendix is a blind tubular struc-ture with a diameter of less than 7 mm and a wallthickness of less than 2 mm (Fig 1). It is seen atMR imaging in an estimated 65% of patients, atminimum, and it is best depicted on T2-weightedimages (11–14). STIR sequences are sensitive toan edematous and inflamed appendix but areleast likely to depict the normal appendix. Theinflamed appendix has a caliber of 7 mm or moreand a thickened wall that appears hypointense onT1-weighted images and hyperintense on T2-weighted images (Figs 2–6). The lumen may ormay not have a signal intensity similar to that offluid. Periappendiceal fat inflammation has a hy-perintense signal on T2-weighted images, a find-ing that is consistent with edema. MR imaginghas reported sensitivity of 97%–100%, specificityof 92%–93.6%, and accuracy of 92%–94% forthe diagnosis of acute appendicitis (15–17).

Figure 3. Acute appendicitis in a 21-year-old pregnant patient. (a) Coronal T2-weighted MR image shows a di-lated appendix (arrow) with a diameter of 12 mm and periappendiceal fluid at the base of the cecum in the rightlower quadrant. (b) Axial unenhanced CT image shows the prominent appendix (arrow) with a location medial tothe cecum.


Figure 4. Acute appendicitis in a nonpregnant patient. Axial (a) and coronal (b) contrast-enhanced T1-weightedMR images show the enlarged appendix (arrow) with a diameter of 8 mm and an enhancing wall.

Figures 5, 6. (5) Perforating appendicitis in a 16-year-old girl. (a, b) Contrast-enhanced T1-weighted MR images(a at a level higher than b) show extensive peritoneal enhancement in the right lower pelvis surrounding the perfo-rated appendix, which appears as an enhancing tubular structure in a (arrows) and has a thickened and enhancingwall in b (arrow). (c) Contrast-enhanced CT image obtained with rectally administered contrast material shows soft-tissue infiltration (arrow) at the base of the cecum, with thickening of the adjacent small-bowel wall. The lack of vis-ibility of the appendix at CT prompted MR imaging. (6) Gangrenous appendicitis in a pregnant patient. Axial T2-weighted MR image shows a dilated, fluid-filled appendix (arrow) to the right of the uterus, with appendiceal wallthickening to 5 mm.


Oto et al demonstrated progressive cranial dis-placement of the appendix and cecum duringpregnancy. The location of the appendix is usu-ally caudal to the level of the iliac crest during thefirst trimester and cranial to it during the thirdtrimester (13).

Adnexal TorsionAdnexal torsion most commonly occurs in thefirst 3 decades of life. It most frequently involvesan ovary and the corresponding fallopian tube.Torsion of the fallopian tube leads to vascularcompromise, which, if unrelieved, can cause irre-versible hemorrhagic infarction of the tube andthe ovary. Early diagnosis is critical to save theovary.

According to the ACR appropriateness criteria,US is the imaging modality of choice for evalua-tion of an adnexal mass or adnexal torsion in pre-menopausal as well as postmenopausal women.Although US is the modality most commonlyused for the diagnosis of adnexal torsion, its effec-tiveness is particularly limited in patients with alarge body habitus and those in whom the ovariesare not visible because of intervening structures.Moreover, an ovary that is affected by torsion

may still demonstrate flow at Doppler US be-cause of a secondary blood supply via the uterineartery branches.

The suitability of MR imaging is equal to thatof CT in patients in whom an adnexal lesion isbelieved to be present, according to the ACR cri-teria; however, in postmenopausal women with acomplex or solid adnexal mass depicted at US,MR imaging is considered superior to CT. MRimaging and CT are used mainly when the pres-ence of acute torsion with a pelvic mass is sus-pected or when the signs and symptoms are sug-gestive of a subacute or chronic condition.

The MR imaging features of ovarian torsion,which have been well described, include ovarianenlargement with stromal edema (Fig 7) (18–20).The common CT and MR imaging features ofadnexal torsion include thickening of the twistedfallopian tube, smooth thickening of the wall ofthe cystic ovarian mass, ascites, and uterine devia-tion to the side of torsion. Less common findingsinclude hemorrhage in the thickened tube, hem-orrhage within the adnexal mass, and hemoperi-toneum. An associated benign ovarian cyst or

Figure 7. Adnexal torsion. (a) Axial T2-weighted MR image shows an enlarged left ovary (arrows)with stromal edema indicated by widely scattered follicles. The left fallopian tube is thickened and has awhorled appearance. (b) Contrast-enhanced T1-weighted MR image demonstrates the thickened leftfallopian tube, an absence of central ovarian parenchymal enhancement, and an enhancing ovarian rim(arrows).


TeachingPoint

Teaching Point The common CT and MR imaging features of adnexal torsion include thickening of the twisted fallopian tube, smooth thickening of the wall of the cystic ovarian mass, ascites, and uterine deviation to the side of torsion.

benign neoplasm is seen in most cases. Cysticteratoma is the most common benign neoplasmassociated with ovarian torsion. If there is an as-sociated mass, the wall of the mass may show ec-centric thickening. The findings of a hemorrhagicfallopian tube, hemorrhagic ovarian mass, andhemoperitoneum are indicative of hemorrhagicinfarction due to torsion. To detect hemorrhage,it is important to apply a T1-weighted sequencewith fat suppression. A lack of enhancement ofmural nodules or septa within the tumor is indica-tive of vascular compromise.

Pelvic Inflammatory DiseasePelvic inflammatory disease most commonlyoriginates in infection that ascends from the fallo-pian tubes. It is seen in sexually active patientsand manifests with nonspecific low abdominopel-vic pain. Immediate antibiotic treatment is thetherapy of choice. Possible sequelae of pelvic in-flammatory disease include tubo-ovarian abscess,ectopic pregnancy, and infertility.

MR imaging, given the lack of a radiation-asso-ciated risk and the relative safety of gadolinium-based contrast agents, is an attractive alternativeto CT for the evaluation of pelvic inflammatorydisease. US only poorly depicts the changes char-acteristic of pelvic inflammatory disease, otherthan an abscess or hydrosalpinx. Compared withUS, MR imaging provides superior depiction ofadnexal edema. T2-weighted fat-saturated imagesshow parametrial signal hyperintensity due toedema. A tubo-ovarian abscess appears with mildsignal hyperintensity on T1-weighted images andhigh signal intensity on T2-weighted images be-cause of internal debris. At contrast-enhancedMR imaging, an abscess has a thick enhancingwall. Occasionally, an adjacent fluid-filled tubularstructure, which represents an inflamed fallopiantube, is seen: Hydrosalpinx, which may manifestwith acute lower abdominal pain, is well depictedat MR imaging (Fig 8).

Fibroid DegenerationFibroid degeneration may cause localized pain,tenderness, fever, and leukocytosis that last a fewdays. When fibroids increase in size, they mayoutgrow their blood supply; degeneration (mostcommonly hyaline, myxoid, cystic, or red degen-eration) often follows. During pregnancy, en-largement of the uterus may interfere with theblood supply to fibroids and cause either cysticdegeneration or infarction of the fibroids.

In pregnant patients with acute pelvic pain,fibroid degeneration may be diagnosed on thebasis of US findings. MR imaging may be helpfulin complicated cases but should not be used in-discriminately. T1-weighted MR images mayshow diffuse or peripheral high signal intensityfrom hemorrhage (20). A hyperintense rimaround a fibroid may be due to obstructed veinsat the periphery of the mass. Edema, which mayprecede degeneration, may cause a diffuse in-crease in the signal intensity of uterine fibroids onT2-weighted images. Degenerated fibroids have

Figure 8. Pelvic inflammatory disease and hydrosal-pinx. Axial T2-weighted MR image shows bilateral tor-tuous tubular structures (arrows) that represent dilatedfallopian tubes.


higher signal intensity and greater heterogeneityon T2-weighted images (Fig 9) and show lessmarked contrast enhancement than do cellularfibroids (21).

Other Pelvic AbnormalitiesEndometriosis represents extrauterine implanta-tion of endometrial mucosa. This ectopic mucosaresponds to cyclic hormonal changes and eventu-

ally bleeds, forming hemorrhagic cysts or hemor-rhagic ascites in the cul-de-sac. The commonlyinvolved structures are the ovaries, cul-de-sac,posterior uterine wall, uterosacral ligaments, an-terior uterine wall, and bladder dome (22). Al-though US and CT are capable of depicting thehemorrhagic cysts known as endometriomas andCT may show hyperattenuation indicative ofblood products, the presence of blood is moreconclusively established on the basis of the MRimaging appearance (specificity of �90%). OnT1-weighted images, endometriomas appear asareas of “lightbulb” signal hyperintensity, unlikecysts and abscesses, which have low signal inten-sity on T1-weighted images (23). The signal

Figure 9. Fibroid degeneration. (a) Axial T2-weighted MR image, obtained in a pregnant womanwith right lower quadrant pain at 28 gestational weeks,shows an 8-cm-diameter necrotic fibroid (arrows) witha central area of high signal intensity. (b) Axial STIRMR image demonstrates two large fibroids (arrows)with necrotic centers. (c) Pelvic US image obtained 3weeks earlier shows a single fibroid without any centralcystic areas.


hyperintensity of endometriomas is even morepronounced on images acquired with fat suppres-sion. This T1-weighted signal hyperintensity isdue to the presence of intracellular as well as ex-tracellular methemoglobin. On T2-weighted im-ages, endometriomas may demonstrate signal hy-pointensity due to the presence of old blood prod-ucts (presumably the result of periodic bleeding),unlike cysts or abscesses, which appear hyperin-tense on T2-weighted images (Fig 10). An ap-pearance of shading (signal hypointensity on T2-weighted images) may be produced by T2 short-ening in an adnexal cyst that has hyperintensesignal on T1-weighted images. The area of shad-ing most often either completely occupies the cystor is seen as a dependent layer (fluid level). Endo-metriotic cysts contain high concentrations ofprotein and iron from recurrent hemorrhage, andthese contents are believed to produce the effectof shading. Hemorrhagic functional ovarian cystsare most often solitary, are brighter than endo-metriomas on T2-weighted images, and do notgenerally exhibit shading. The T2-weighted sig-

nal intensity of endometriomas also may decreasein response to medical treatment with buserelinacetate (24).

Hematometra is due to an imperforate hymen,which originates from a congenital anomaly of themullerian duct. The result is an accumulation ofmenstrual fluid in the endometrial cavity and thesuperior two-thirds of the vagina. MR imagingconclusively demonstrates the presence of bloodproducts and helps differentiate hematometrafrom other cystic lesions that may arise at the in-troitus in adolescent girls. MR images show a dis-tended endometrial cavity that contains bloodproducts, with distention also of the upper part ofthe vagina. The fluid has a hyperintense signal onT1-weighted images and appears less hyperin-tense than the bladder on T2-weighted images(25) (Figs 11, 12).

Acute epiploic appendagitis is characterized byan oval fatty lesion, which most commonly is lo-cated adjacent to the sigmoid colon and associ-ated with stranding of the periappendicular fatand thickening of the parietal peritoneum (Fig13). The diagnosis most often is established withCT, and early recognition allows conservativemanagement (26,27).

Figure 10. Endometriosis. (a) Axial T1-weighted fat-saturated MR image shows high-signal-intensity endometri-otic cysts (arrows) in the right rectus abdominis muscle and the left adnexa. The smaller of the two cysts contains adependent layer of lower-signal-intensity blood products. (b) T2-weighted MR image obtained without fat saturationshows the same cysts, both with dependent fluid levels (arrowheads). Shading also is seen in the smaller cyst.


TeachingPoint

Teaching Point An appearance of shading (signal hypointensity on T2-weighted images) may be produced by T2 shortening in an adnexal cyst that has hyperintense signal on T1-weighted images. The area of shading most often either completely occupies the cyst or is seen as a dependent layer (fluid level).

Figures 11, 12. Hematometra. (11) Sagittal T2-weighted MR image shows dilatation of the vagina(straight arrows) and resultant cranial displacement of the uterus (curved arrow). (12) Sagittal T2-weighted MR image in a patient with a double uterus shows a dilated vagina that contains subacute bloodand dependent debris (arrowheads).

Figure 13. Acute epiploic appendagitis. (a) Axial STIR MR image shows an oval fatty lesion (arrow) with a high-signal-intensity rim and inflammation in the surrounding fat. (b) Axial contrast-enhanced CT image demonstratesthe same lesion (arrow) with a ring sign and surrounding inflammation.


Crohn disease is a subacute or chronic enteritisthat usually occurs in the terminal ileum but alsomay involve other segments of the gastrointestinaltract. CT enterography, small-bowel follow-through study, and CT with oral and intravenouscontrast material have higher appropriateness rat-ings for diagnosing and monitoring Crohn diseasethan does MR imaging with or without contrastmaterial. However, MR imaging has the advan-tages of excellent contrast resolution, depiction ofany extraluminal disease, and lack of ionizing ra-diation (28–31). MR imaging features of Crohndisease may include mural thickening, mural en-hancement, hypervascularity, abscess, fistula, andstricture (Fig 14). MR enterography and MR en-teroclysis have been advocated by some authorsas potential imaging modalities of choice forevaluating Crohn disease. Godefroy et al found asensitivity of 100% and a specificity of 83% forMR enterography in the assessment of Crohn dis-ease in pediatric patients (28).

ConclusionsWhen US findings are nondiagnostic or equivo-cal, MR imaging is the most appropriate modalityfor the evaluation of acute appendicitis in preg-nant women. It also may be useful for the diagno-sis of other pelvic and lower abdominal abnor-malities. MR imaging provides an alternative toCT enterography and the small-bowel follow-through study for evaluation of Crohn disease inpatients for whom radiation exposure is an impor-tant clinical consideration. Although the high costand restricted availability of MR imaging limit itsutility in the emergency setting, the absence ofionizing radiation and the improved contrast reso-lution make MR imaging an appropriate modalityfor use in selected patients. Attention to properMR imaging technique and tailored protocols areessential for optimizing the effectiveness of theexamination and maximizing diagnostic accuracy.

The recently increased awareness of and concernabout radiation-related health risks warrant theadoption of a flexible approach to imaging in theemergency setting, particularly in pregnant andpediatric patients.

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TeachingPoint

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RG Volume 27 • Volume 5 • September-October 2007 Singh et al

MR Imaging of the Acute Abdomen and Pelvis: Acute Appendicitis and Beyond Ajay Singh, MD et al

Page 1421 Although US is the first-line investigation for suspected appendicitis in a pregnant patient, MR imaging is better than CT as the second-line imaging modality when US results are nondiagnostic or equivocal. Page 1421 Although the safety of MR imaging to the fetus has not been proved, no proved human teratogenic or carcinogenic effects of MR imaging have been described in the literature. Page 1425 The common CT and MR imaging features of adnexal torsion include thickening of the twisted fallopian tube, smooth thickening of the wall of the cystic ovarian mass, ascites, and uterine deviation to the side of torsion. Page 1428 An appearance of shading (signal hypointensity on T2-weighted images) may be produced by T2 shortening in an adnexal cyst that has hyperintense signal on T1-weighted images. The area of shading most often either completely occupies the cyst or is seen as a dependent layer (fluid level). Page 1430 Although the high cost and restricted availability of MR imaging limit its utility in the emergency setting, the absence of ionizing radiation and the improved contrast resolution make MR imaging an appropriate modality for use in selected patients.

RadioGraphics 2007; 27:1419–1431 ● Published online 10.1148/rg.275065021 ● Content Codes:

EDUCATION EXHIBIT 1419 MR Imaging of the Acute Abdomen … … · EDUCATION EXHIBIT 1419 MR Imaging of the Acute Abdomen and Pelvis: Acute Appendi-citis and Beyond1 Ajay Singh, MD

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