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DOI: 10.1148/radiol.2441060920
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(Radiology 2007;244:174-183.)
© RSNA, 2007

Gastrointestinal Imaging

Acute Cholecystitis: MR Findings and Differentiation from Chronic Cholecystitis1

Ersan Altun, MD, Richard C. Semelka, MD, Jorge Elias, Jr, MD, PhD, Larissa Braga, MD, PhD, MPH, Vasilis Voultsinos, MD, Jignesh Patel, MD, N. Cem Balci, MD, and John T. Woosley, MD

1 From the Departments of Radiology (E.A., R.C.S., V.V., J.P.) and Pathology (J.T.W.), and School of Public Health (L.B.), University of North Carolina at Chapel Hill, Campus Box 7510, 2000 Old Clinic Bldg, Chapel Hill, NC 27599-7510; Department of Radiology, School of Medicine of Ribeirao Preto, University of Sao Paulo, Ribeirao Preto, Brazil (J.E.); and Department of Radiology, Saint Louis University, St Louis, Mo (N.C.B.). Received May 25, 2006; revision requested July 27; revision received September 1; accepted October 5; final version accepted December 12. J.E. supported by CNPq (The National Council of Scientific and Technological Development of Brazil). Address correspondence to R.C.S. (e-mail: richsem{at}med.unc.edu).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCE IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
 References
 
Purpose: To retrospectively determine the sensitivity and specificity of magnetic resonance (MR) imaging for differentiation between acute and chronic cholecystitis, with histopathologic analysis as the reference standard.

Materials and Methods: Institutional review board approval with waived informed consent was obtained for this HIPAA-compliant study. Four reviewers blinded to the cholecystitis type but aware that cholecystitis was present retrospectively evaluated MR images for predetermined findings in 32 patients (15 male, 17 female; mean age ± standard deviation, 55 years ± 20) with histopathologically proved acute or chronic cholecystitis. The final MR diagnoses and MR findings in both groups were compared with each other and with the histopathologic diagnoses to determine the sensitivity and specificity of MR imaging. {chi}2 tests were used to detect differences in MR findings between the acute and chronic cholecystitis groups.

Results: MR imaging sensitivity and specificity for detection of acute cholecystitis were 95% (18 of 19 patients) and 69% (nine of 13 patients), respectively. The sensitivities of increased gallbladder wall enhancement and increased transient pericholecystic hepatic enhancement were 74% (14 of 19 patients) and 62% (10 of 16 patients), respectively. Both findings had 92% (12 of 13 patients) specificity. Sensitivities of increased wall thickness, pericholecystic fluid, and adjacent fat signal intensity changes were 100% (19 of 19 patients), 95% (18 of 19 patients), and 95% (18 of 19 patients), respectively; specificities were 54% (seven of 13 patients), 38% (five of 13 patients), and 54% (seven of 13 patients), respectively. Pericholecystic abscess, intraluminal membranes, and wall irregularity or defect each had 100% (13 of 13 patients) specificity; sensitivities were 11% (two of 19 patients), 26% (five of 19 patients), and 21% (four of 19 patients), respectively. Increased gallbladder wall enhancement (P < .001) and increased transient pericholecystic hepatic enhancement (P = .003) were the most significantly different between acute and chronic cholecystitis.

Conclusion: Increased gallbladder wall enhancement and increased transient pericholecystic hepatic enhancement had the highest combination of sensitivity and specificity for the diagnosis and differentiation of acute and chronic cholecystitis.

© RSNA, 2007


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCE IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
 References
 
Ultrasonography (US) and cholescintigraphy are the imaging modalities most commonly used to diagnose acute cholecystitis (1–18). Owing to their varying sensitivity (40%–90%) and specificity (40%–95%), however, the results of these tests can be inconclusive in some patients (2,7,8). Computed tomography (CT) has been reported to have high sensitivity and specificity (95% for both) for the diagnosis of acute cholecystitis but important limitations, including limited soft-tissue contrast resolution, radiation exposure, and potential nephrotoxic effects from iodinated contrast media (2,7,8,16). Accordingly, magnetic resonance (MR) imaging may have a role in the diagnosis of acute cholecystitis given its inherent superior soft-tissue contrast resolution without risks of radiation exposure or nephrotoxicity.

Few reports describe the use of MR imaging in the diagnosis of acute cholecystitis (19–27). To our knowledge, there is no MR imaging report in which all of the findings of acute and chronic cholecystitis are compared. Thus, the purpose of our study was to retrospectively determine the sensitivity and specificity of MR imaging in the differentiation between acute and chronic cholecystitis, with histopathologic analysis as the reference standard.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 ADVANCE IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
 References
 
Patient Selection
Institutional review board approval with waived informed patient consent was obtained for our Health Insurance Portability and Accountability Act–compliant study. Pathology and radiology department databases were searched for all patients with histopathologically proved cholecystitis who had undergone upper abdominal MR examinations within 1 month before surgery between January 2004 and February 2006. All MR examinations were performed for abdominal pain and problem solving. Patients who presented with predominantly findings of pancreatitis were excluded from the study. The final study group consisted of 32 patients: 19 with acute cholecystitis and 13 with chronic cholecystitis (Table 1).


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  		Table 1. Characteristics of Study Population

 
MR Imaging Technique
MR imaging of the upper abdomen was performed with 1.5-T MR systems (Vision, Sonata, or Avanto; Siemens Medical Systems, Malvern, Pa) by using a phased-array torso coil. MR examinations were performed by using a breathing-dependent or breathing-independent patient protocol, depending on the patient's ability to suspend respiration (Table 2). The breathing-dependent protocol sequences required suspended respiration, whereas the breathing-independent protocol sequences were performed during respiration. In all patients, gadodiamide (Omniscan; GE Healthcare, Oakville, Ontario, Canada) was administered intravenously in a power-injected (Medrad, Pittsburgh, Pa) bolus of 0.1 mmol per kilogram of body weight at 2 mL/sec.


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  		Table 2. MR Imaging Sequences and Parameters

 
MR Image Interpretation
The upper-abdomen MR images obtained in all patients were independently and retrospectively evaluated by two radiologists (E.A., J.E.) who were blinded to the clinical information and the type of cholecystitis but aware that cholecystitis was present. These reviewers assessed all image studies on the basis of predetermined findings, and the final diagnoses made by the reviewers were recorded. The findings were as follows: gallstones, increased wall thickness (>3 mm [28]), mural striation (layered pattern of gallbladder wall with different alternating signal intensities [22]), increased gallbladder dimension (>40 mm in transverse plane [29]), increased contrast enhancement of the gallbladder wall, increased transient contrast enhancement of the liver parenchyma adjacent to the gallbladder, pericholecystic fluid, signal intensity changes in the fat planes surrounding the gallbladder (increased or decreased signal intensity in the pericholecystic fat on T2- and T1-weighted images, respectively [28]), pericholecystic abscess (encapsulated fluid collection adjacent to the gallbladder [28]), intraluminal membranes (irregular, intraluminal linear soft-tissue signal intensity [28]), wall irregularity or defect (irregularity or focal absence of the gallbladder wall [28]), and gas in the wall or lumen (signal void gas bubbles in the gallbladder wall or lumen and air-fluid level in the lumen on T1- or T2-weighted images [30]).

In the 28 patients with normal renal function, increased contrast enhancement of the gallbladder wall was evaluated on postcontrast delayed interstitial-phase images by means of comparison with the renal parenchymal enhancement (31). Increased gallbladder wall enhancement was accepted as positive for acute cholecystitis when it was equal to or greater than the renal parenchymal enhancement qualitatively. In the four patients with chronic renal failure, gallbladder wall enhancement was evaluated solely on the basis of the reviewers' experiences. Focally increased liver parenchymal enhancement adjacent to the gallbladder was assessed on immediate-postcontrast hepatic arterial-dominant phase images (32). On the basis of these findings, the reviewers were asked to evaluate the presence of acute or chronic cholecystitis.

Two additional observers (R.C.S., L.B.) blinded to the diagnoses determined the frequencies and proportions of the findings (qualitative analysis), as well as the gallbladder wall thickness, gallbladder dimension, and signal intensities of the gallbladder wall and renal parenchyma (quantitative analysis). In all patients, gallbladder wall thickness and dimension were measured on the viewing station monitor from the sections showing the thickest part of the wall and the largest transverse gallbladder dimension. Measurements of the renal medulla parenchyma were performed. The signal intensities of the gallbladder wall and renal parenchyma on gadolinium-enhanced interstitial-phase images were determined by using standardized region-of-interest measurements in 26 (of the 32) patients (15 of 19 patients with acute and 11 of 13 with chronic cholecystitis) who were examined in a breathing-dependent protocol and had normal renal function. Region-of-interest sizes were similar for all measurements and patients and varied between 0.03 and 0.06 cm2. These measurements were not performed in the patients who were examined in a breathing-independent protocol because the signal-to-noise ratio with the magnetization-prepared rapid acquisition gradient-echo sequence was lower than that with the two- and three-dimensional gradient-echo sequences (33), and, thus, including these measurements would have affected the statistical analysis adversely. Discordances between these observers were resolved by consensus.

Statistical Analyses
The qualitative and quantitative MR findings in the acute and chronic cholecystitis patient groups determined by two observers (R.C.S., L.B.) in consensus and the final MR diagnoses made by the two reviewers (E.A., J.E.) were compared with each other and with the histopathologic diagnoses. Analyses were performed by using the "Proc Freq" procedure in the Statistical Analysis System (SAS, version 8.02; SAS Institute, Cary, NC). The Mann-Whitney U test was used to evaluate differences in gallbladder wall thicknesses, transverse gallbladder dimensions, gallbladder wall and renal parenchyma signal intensities, and MR imaging–surgery time intervals between the acute and chronic cholecystitis groups. {chi}2 tests were used to detect differences in MR findings between the two groups. The consensus data of the two observers (R.C.S., L.B.) were used to perform the Mann-Whitney U and {chi}2 tests. Kappa statistics were used to assess the interrater reliability of the final MR diagnoses between the two reviewers (E.A., J.E.). Associations were considered significant at two-tailed P < .05. The accuracy of MR imaging and of each MR finding in the diagnosis and differentiation between acute and chronic cholecystitis was calculated on the basis of the histopathologic diagnosis (reference standard).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 ADVANCE IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
 References
 
The average time intervals between MR imaging and surgery for acute or chronic cholecystitis were significant (P = .005) (Table 1).

MR Findings of Acute Cholecystitis in Both Groups
Acute cholecystitis group.—Acute cholecystitis was correctly identified at MR imaging in 18 of 19 patients (Fig 1). One patient, who had only two findings—increased gallbladder wall thickness and gallstones—represented a case of missed diagnosis. The other 18 patients had a combination of at least three findings (Figs 2, 3; Table 3) not including gallstones.


Figure 1
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  		Figure 1: Flow diagram of the study group.

 

Figure 2A
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  		Figure 2a: Transverse MR images in patient with acute calculous cholecystitis. (a) Half-Fourier rapid acquisition with relaxation enhancement image ({infty}/90, 180° flip angle) shows gallstones (arrow), pericholecystic fluid, and fat signal intensity changes surrounding the gallbladder. (b) Fat-suppressed three-dimensional gradient-echo image (4.3/1.7, 3.5° flip angle) shows thickened hyperintense gallbladder wall (arrow), indicating hemorrhage. (c) Contrast-enhanced hepatic arterial-dominant phase fat-suppressed three-dimensional gradient-echo image (4.3/1.7, 3.5°) shows patchy increased transient pericholecystic hepatic parenchymal enhancement (arrows). (d) Two-minutes-postcontrast interstitial-phase fat-suppressed spoiled gradient-echo image (140/4.4, 80° flip angle) shows the hepatic parenchyma that was enhancing in c is now isointense to the remaining liver parenchyma.

 

Figure 2B
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  		Figure 2b: Transverse MR images in patient with acute calculous cholecystitis. (a) Half-Fourier rapid acquisition with relaxation enhancement image ({infty}/90, 180° flip angle) shows gallstones (arrow), pericholecystic fluid, and fat signal intensity changes surrounding the gallbladder. (b) Fat-suppressed three-dimensional gradient-echo image (4.3/1.7, 3.5° flip angle) shows thickened hyperintense gallbladder wall (arrow), indicating hemorrhage. (c) Contrast-enhanced hepatic arterial-dominant phase fat-suppressed three-dimensional gradient-echo image (4.3/1.7, 3.5°) shows patchy increased transient pericholecystic hepatic parenchymal enhancement (arrows). (d) Two-minutes-postcontrast interstitial-phase fat-suppressed spoiled gradient-echo image (140/4.4, 80° flip angle) shows the hepatic parenchyma that was enhancing in c is now isointense to the remaining liver parenchyma.

 

Figure 2C
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  		Figure 2c: Transverse MR images in patient with acute calculous cholecystitis. (a) Half-Fourier rapid acquisition with relaxation enhancement image ({infty}/90, 180° flip angle) shows gallstones (arrow), pericholecystic fluid, and fat signal intensity changes surrounding the gallbladder. (b) Fat-suppressed three-dimensional gradient-echo image (4.3/1.7, 3.5° flip angle) shows thickened hyperintense gallbladder wall (arrow), indicating hemorrhage. (c) Contrast-enhanced hepatic arterial-dominant phase fat-suppressed three-dimensional gradient-echo image (4.3/1.7, 3.5°) shows patchy increased transient pericholecystic hepatic parenchymal enhancement (arrows). (d) Two-minutes-postcontrast interstitial-phase fat-suppressed spoiled gradient-echo image (140/4.4, 80° flip angle) shows the hepatic parenchyma that was enhancing in c is now isointense to the remaining liver parenchyma.

 

Figure 2D
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  		Figure 2d: Transverse MR images in patient with acute calculous cholecystitis. (a) Half-Fourier rapid acquisition with relaxation enhancement image ({infty}/90, 180° flip angle) shows gallstones (arrow), pericholecystic fluid, and fat signal intensity changes surrounding the gallbladder. (b) Fat-suppressed three-dimensional gradient-echo image (4.3/1.7, 3.5° flip angle) shows thickened hyperintense gallbladder wall (arrow), indicating hemorrhage. (c) Contrast-enhanced hepatic arterial-dominant phase fat-suppressed three-dimensional gradient-echo image (4.3/1.7, 3.5°) shows patchy increased transient pericholecystic hepatic parenchymal enhancement (arrows). (d) Two-minutes-postcontrast interstitial-phase fat-suppressed spoiled gradient-echo image (140/4.4, 80° flip angle) shows the hepatic parenchyma that was enhancing in c is now isointense to the remaining liver parenchyma.

 

Figure 3A
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  		Figure 3a: Transverse MR images in patient with acute acalculous cholecystitis (AAC). (a) Fat-suppressed half-Fourier rapid acquisition with relaxation enhancement image ({infty}/90, 180° flip angle) shows pericholecystic fluid (arrows). (b) Contrast-enhanced hepatic arterial-dominant phase spoiled gradient-echo image (140/4.4, 80° flip angle) shows patchy increased transient pericholecystic hepatic parenchymal enhancement (arrows). (c) Two-minutes-postcontrast interstitial-phase fat-suppressed spoiled gradient-echo image (140/4.4, 80° flip angle) shows the hepatic parenchyma that had increased enhancement in b is now isointense to the remaining liver parenchyma. Increased gallbladder wall thickness and enhancement are also noted.

 

Figure 3B
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  		Figure 3b: Transverse MR images in patient with acute acalculous cholecystitis (AAC). (a) Fat-suppressed half-Fourier rapid acquisition with relaxation enhancement image ({infty}/90, 180° flip angle) shows pericholecystic fluid (arrows). (b) Contrast-enhanced hepatic arterial-dominant phase spoiled gradient-echo image (140/4.4, 80° flip angle) shows patchy increased transient pericholecystic hepatic parenchymal enhancement (arrows). (c) Two-minutes-postcontrast interstitial-phase fat-suppressed spoiled gradient-echo image (140/4.4, 80° flip angle) shows the hepatic parenchyma that had increased enhancement in b is now isointense to the remaining liver parenchyma. Increased gallbladder wall thickness and enhancement are also noted.

 

Figure 3C
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  		Figure 3c: Transverse MR images in patient with acute acalculous cholecystitis (AAC). (a) Fat-suppressed half-Fourier rapid acquisition with relaxation enhancement image ({infty}/90, 180° flip angle) shows pericholecystic fluid (arrows). (b) Contrast-enhanced hepatic arterial-dominant phase spoiled gradient-echo image (140/4.4, 80° flip angle) shows patchy increased transient pericholecystic hepatic parenchymal enhancement (arrows). (c) Two-minutes-postcontrast interstitial-phase fat-suppressed spoiled gradient-echo image (140/4.4, 80° flip angle) shows the hepatic parenchyma that had increased enhancement in b is now isointense to the remaining liver parenchyma. Increased gallbladder wall thickness and enhancement are also noted.

 

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  		Table 3. Frequencies of MR Findings of Acute and Chronic Cholecystitis

 
Focal transient liver enhancement adjacent to the gallbladder was not assessed in three of 19 patients, and two of these three patients were examined with a breathing-independent protocol. Immediate-postcontrast images were obtained in these three patients but not during the hepatic arterial-dominant phase. In 16 of the 19 patients with acute cholecystitis, hepatic arterial-dominant phase images were obtained. In the patients in whom the hepatic parenchyma showed increased enhancement during the hepatic arterial-dominant phase, the enhancement became isointense to the remaining liver tissue during the portal and interstitial phases of enhancement.

In the two patients with abscess at MR imaging, pericholecystic abscesses were not detected at surgery or histopathologic analysis. Of the five patients who had intraluminal membranes, four had gangrenous or necrotic gallbladder at surgery and histopathologic analysis. Of the four patients with wall irregularity or defect (Fig 4), three had histopathologically detected gangrenous or necrotic gallbladder, but perforation was not observed in any of these patients at surgery or histopathologic analysis.


Figure 4A
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  		Figure 4a: Coronal MR images in patient with necrotizing acute calculous cholecystitis. (a) Half-Fourier rapid acquisition with relaxation enhancement ({infty}/90, 180° flip angle) and (b) fat-suppressed magnetization-prepared rapid acquisition gradient-echo (2000/1.7, 15° flip angle) images show focal absence and irregularity at the superior aspect of the gallbladder wall (arrow).

 

Figure 4B
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  		Figure 4b: Coronal MR images in patient with necrotizing acute calculous cholecystitis. (a) Half-Fourier rapid acquisition with relaxation enhancement ({infty}/90, 180° flip angle) and (b) fat-suppressed magnetization-prepared rapid acquisition gradient-echo (2000/1.7, 15° flip angle) images show focal absence and irregularity at the superior aspect of the gallbladder wall (arrow).

 
Quantitatively, increased enhancement of the gallbladder wall was detected in 11 of 15 patients. In the remaining four patients, the gallbladder wall enhancement was less intense than the renal parenchymal enhancement. Increased gallbladder wall enhancement was detected qualitatively but not quantitatively in one patient with necrotic gallbladder wall. This discordance arose from the small quantitative signal intensity difference between the gallbladder wall and the renal parenchyma, which was not appreciated qualitatively. The mean signal intensities of the gallbladder wall and the renal parenchyma were not significantly different (P = .20) in the patients who had increased gallbladder wall enhancement quantitatively (Table 4).


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  		Table 4. Quantitative Analyses of Patient Findings in the Two Cholecystitis Groups

 
Chronic cholecystitis group.—Thirteen patients had chronic cholecystitis at histopathologic analysis. At MR imaging, four of these patients were considered to have acute cholecystitis on the basis of the combination of at least five findings not including gallstones (Table 3). The remaining nine patients had a combination of at most three MR findings of gallbladder disease not including gallstones. At clinical examination, three of the four patients who received an incorrect diagnosis of acute cholecystitis at MR imaging were considered to have acute cholecystitis; the fourth patient had received an initial clinical diagnosis of symptomatic cholelithiasis, in keeping with the other patients in the chronic cholecystitis group.

Both the mean wall thickness (P = .001) and the mean gallbladder dimension (P = .014) for the chronic cholecystitis group were significantly lower than those for the acute cholecystitis group (Table 4). Increased gallbladder wall enhancement was not detected qualitatively in 12 of the 13 patients. In one patient, increased gallbladder wall enhancement and increased transient focal pericholecystic hepatic parenchymal enhancement were detected on the interstitial-phase and hepatic arterial-dominant phase images both qualitatively and quantitatively (Fig 5).


Figure 5A
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  		Figure 5a: Transverse fat-suppressed MR images in patient with chronic cholecystitis. (a) Hepatic arterial-dominant spoiled gradient-echo image (140/4.4, 80° flip angle) shows patchy transient pericholecystic hepatic parenchymal enhancement (arrows). (b) On 2-minutes-postcontrast interstitial-phase spoiled gradient-echo image (140/4.4, 80° flip angle), the hepatic parenchyma seen in a is now isointense to the remaining liver parenchyma. Increased gallbladder wall enhancement is also seen.

 

Figure 5B
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  		Figure 5b: Transverse fat-suppressed MR images in patient with chronic cholecystitis. (a) Hepatic arterial-dominant spoiled gradient-echo image (140/4.4, 80° flip angle) shows patchy transient pericholecystic hepatic parenchymal enhancement (arrows). (b) On 2-minutes-postcontrast interstitial-phase spoiled gradient-echo image (140/4.4, 80° flip angle), the hepatic parenchyma seen in a is now isointense to the remaining liver parenchyma. Increased gallbladder wall enhancement is also seen.

 
There was no discordance between the qualitative and quantitative analysis findings in any chronic cholecystitis group patients. There was no significant difference in mean signal intensity between the gallbladder wall and the renal parenchyma in those patients who did not have increased wall enhancement (P = .28). The mean signal intensity of the gallbladder wall for the acute cholecystitis group was higher than that for the chronic cholecystitis group but not significantly different (P = .27) (Table 4).

Accuracy of MR Imaging and MR Findings for Diagnosis and Differentiation of Acute Cholecystitis
The sensitivity, specificity, and positive and negative predictive values of MR imaging for the diagnosis and differentiation of acute and chronic cholecystitis in the entire study population were 95% (18 of 19 patients), 69% (nine of 13 patients), 81% (18 of 22 patients), and 90% (nine of 10 patients), respectively (Table 5). MR imaging sensitivities for the diagnosis of acute calculous cholecystitis and AAC were 93% (13 of 14 patients) and 100% (five of five patients), respectively. Excellent interrater reliability (0.92) was demonstrated at {kappa} analysis.


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  		Table 5. Distribution of Patients according to MR Results and Histopathologic Diagnoses of Acute Cholecystitis

 
Increased wall thickness (100%), pericholecystic fluid (95%), and adjacent fat signal intensity changes (95%) had the highest sensitivities for the detection of acute cholecystitis (Table 6). However, the individual specificities of these three findings were low. Gallstones and increased gallbladder dimension had moderate sensitivity, and gallstones had the lowest specificity (23%) of all the findings. Mural striation had moderate sensitivity (74%) and specificity (69%). Increased gallbladder wall enhancement (74%) and increased transient pericholecystic hepatic parenchymal enhancement (62%) also had moderate sensitivity but high specificity (92% for both). Pericholecystic abscess, intraluminal membranes, and wall irregularity or defect each had 100% specificity; however, their sensitivities were very low because these findings were rarely present and were observed only in association with complicated forms of acute cholecystitis. Intraluminal membranes and wall irregularity or defect enabled an accurate prediction of gangrenous or necrotic gallbladder in 80% (four of five) and 75% (three of four) of patients, respectively. Gas was not detected in the wall or lumen of the gallbladder in any patient; therefore, sensitivity and specificity values for this finding could not be determined. {chi}2 Analysis revealed the most significant differences in increased gallbladder wall enhancement (P < .001) and increased transient pericholecystic hepatic enhancement (P = .003) between the acute and chronic cholecystitis groups.


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  		Table 6. Sensitivity and Specificity of MR Findings for Diagnosis and Differentiation of Acute Cholecystitis in Entire Study Population

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
ADVANCE IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
 References
 
In our study, the sensitivity of MR imaging for the diagnosis and differentiation of acute cholecystitis was 95%, concurrent with similar findings in the literature (19,23–28,34). Acute calculous cholecystitis was missed in one patient, who had only two findings—increased wall thickness and gallstones; however, these two findings were not exclusive indicators of acute cholecystitis because of their low specificity.

The specificity of MR imaging for the diagnosis and differentiation of acute and chronic cholecystitis was 69%. This relatively low specificity was due to the four patients with discordant findings: They had chronic cholecystitis at histopathologic analysis but were considered to have acute cholecystitis at MR imaging. Three of these patients also presented with clinical findings of acute cholecystitis. In their cases, an explanation for the relatively low specificity may be that the histopathologic features and clinical findings clearly demonstrated a disease spectrum between acute and chronic cholecystitis (3,4,22). At times, the findings of acute and chronic cholecystitis may overlap radiologically, clinically, and even histopathologically (3,4,22). In the three patients with clinical acute findings, the acute inflammation seen at the time of the initial clinical diagnosis and MR imaging may have subsided by the time of histopathologic analysis owing to antibiotic therapy and/or the time interval between initial presentation and surgery. In the fourth patient, the reason for the discordance may have been simply overlapping clinical and radiologic findings between acute and chronic cholecystitis. If a healthy patient group had been compared with the acute cholecystitis group in our study, the specificity probably would have been much higher (19).

Highly specific and relatively frequent findings were increased gallbladder wall enhancement and increased transient pericholecystic hepatic enhancement; these were also the most discriminative and useful findings for the diagnosis of acute cholecystitis and the differentiation between acute and chronic cholecystitis—an observation that to our knowledge had not been previously reported. Statistical analysis results also supported these findings. The specificities of these two findings for the differentiation of acute cholecystitis would have been even higher if comparisons had been made with normal gallbladders (32,35). An important aspect in the detection of these two findings is the need for optimal timing of the postcontrast sequences (32,35). Ideally, pericholecystic transient hepatic enhancement should be evaluated during the hepatic arterial-dominant phase. During the portal venous and interstitial phases, the inflamed liver parenchyma adjacent to the gallbladder tends to rapidly become isointense to the remaining liver parenchyma (32,35). Therefore, if the immediate data acquisition is too early or too late, excluding the hepatic arterial-dominant phase, then pericholecystic transient hepatic parenchymal enhancement will not be appreciated. The gallbladder wall should be evaluated during the interstitial phase because it enhances maximally during this phase (28,34,35). In the setting of acute inflammation, gallbladder wall enhancement should be comparable to renal parenchymal enhancement (32). Increased enhancement is usually seen, at least in some part of the gallbladder wall, even in the setting of acute cholecystitis with necrosis (28), although it is a typical finding of acute cholecystitis without necrosis.

The use of pericholecystic abscess, intraluminal membranes, and wall irregularity or defect for the diagnosis and differentiation of acute cholecystitis was limited because of their very low sensitivities (28,34). Pericholecystic abscesses were not detected at histopathologic analysis or surgery. We believe that because the abscesses were small, they had probably ruptured and drained unnoticeably at surgery owing to intense generalized acute inflammation. Intraluminal membranes and wall irregularity or defect enabled successful predictions of gangrenous or necrotic gallbladder. These findings concur with previous reports (28).

The use of increased wall thickness, pericholecystic fluid, and pericholecystic fat signal intensity changes for the diagnosis and differentiation of acute cholecystitis was limited owing to their low specificities. In our study, the sensitivities of these three findings were slightly higher and the specificities were slightly lower compared with values in previously reported studies (28,34). These findings probably had relatively low specificity because they were compared with findings in the chronic cholecystitis group. They may have had relatively high sensitivity because of the reviewers' experiences and because the complex cases were referred for MR imaging.

Gallstones and increased transverse gallbladder dimension are frequent findings in both healthy individuals and patients with chronic cholecystitis (28,34). Mural striation, which may be seen with both acute and chronic cholecystitis, is difficult to detect without using thin sections and MR cholangiopancreatographic images (22,28,34). Thus, these findings had limited usefulness in the diagnosis of acute cholecystitis.

MR imaging has many advantages in the diagnosis of acute cholecystitis. In young patients, who are most susceptible to the harmful effects of radiation and have a relatively higher incidence of AAC, MR imaging should be considered the first imaging choice more often than radiation-generating modalities (9,10). Moreover, because AAC frequently develops in critically ill patients, who often have borderline renal function, the use of gadolinium chelates, as opposed to the iodinated contrast media used in CT, is advantageous for preserving renal function (8). In addition, MR imaging better reveals some of the complications and associated conditions of acute cholecystitis, such as choledocholithiasis (19,20).

There are a few disadvantages to using MR imaging to diagnose acute cholecystitis. AAC commonly develops in critically ill patients who are too unstable to be transported and/or are unable to be placed in or stay in the MR unit owing to their poor medical condition, metallic implants, or medical devices (7,8). However, many new MR examinations are fast and result in consistent image quality such that they can be tolerated by many severely ill patients. Despite the inability to elicit focal pain overlying the gallbladder with MR imaging, as can be done with US, our study results showed that acute cholecystitis can still be diagnosed successfully with MR imaging. In addition, because many critically ill patients are sedated, US may not demonstrate pain overlying the gallbladder for the diagnosis of AAC (7,8).

One limitation of our study was the small size of the patient population, which prevented us from obtaining significant quantitative signal intensity analysis results. Another limitation was the retrospective design of the study, which necessitated the use of three 1.5-T MR systems with potentially different magnetic field homogeneities. However, the magnetic field homogeneities of these systems were maximal and in the range of acceptable high-quality diagnostic standards. Therefore, we believe that the effect of magnetic field inhomogeneities on signal intensity measurements was negligible. The other limitation was the referral of patients with inconclusive findings for MR imaging, which probably skewed the population toward patients with more complex disease. We believe this may have contributed to the diminished specificity—rather than increased the accuracy—of MR imaging.

In conclusion, the results of our study show that MR imaging is accurate for the diagnosis of acute cholecystitis. Increased gallbladder wall enhancement and increased transient pericholecystic hepatic parenchymal enhancement are specific and frequent MR findings of acute cholecystitis. The clinical findings of acute cholecystitis and chronic cholecystitis may overlap, and MR imaging may be used for differentiation. MR imaging may be the most beneficial in the diagnosis of AAC, which is particularly difficult to detect with US. Our results showed MR imaging to have high sensitivity for this diagnosis.


   ADVANCE IN KNOWLEDGE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCE IN KNOWLEDGE
IMPLICATIONS FOR PATIENT CARE
 References
 


   IMPLICATIONS FOR PATIENT CARE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCE IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
References
 


   FOOTNOTES
 

Abbreviations: AAC = acute acalculous cholecystitis

Authors stated no financial relationship to disclose.

Author contributions: Guarantors of integrity of entire study, E.A., R.C.S., J.E.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, E.A., J.E., V.V.; clinical studies, E.A., R.C.S., J.E., V.V., N.C.B., J.T.W.; statistical analysis, L.B.; and manuscript editing, E.A., R.C.S., L.B., V.V., J.P.


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCE IN KNOWLEDGE
 IMPLICATIONS FOR PATIENT CARE
 References
 

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