Diffusion-weighted MR imaging of hepatic abscesses: possibility of different apparent diffusion coefficient (ADC)-values in early and mature abscess formation

The role of "penumbra sign" and diffusion-weighted imaging in adnexal masses: do they provide a clue in differentiating tubo-ovarian abscess from ovarian malignancy?

Purpose

To evaluate the role of “penumbra sign”, diffusion-weighted imaging (DWI), and the apparent diffusion coefficient (ADC) value in differentiating tubo-ovarian abscess (TOA) from ovarian malignancy.

Material and methods

Thirty-six patients with 50 adnexal masses (tubo-ovarian abscess, n = 24; ovarian malignancy, n = 26), who underwent magnetic resonance imaging (MRI) with DWI, were retrospectively evaluated. “Penumbra sign” (hyperintense rim on T1W images), diffusion restriction, and mean apparent diffusion coefficient (ADC) values from cystic (c-ADC) and solid (s-ADC) components were evaluated for all the masses.

Results

“Penumbra sign” on T1W images was significantly more common in the TOA group (n = 21, 87.5%) than in the ovarian malignancy group (n = 2, 7.7%) (p < 0.001). Similarly, diffusion restriction in the cystic component was more frequent in the TOA group (n = 24, 100% vs. n = 2, 10.5%; p < 0.001). In contrast, diffusion restriction in the solid component was more common in the ovarian malignancy group (n = 5, 20.8% vs. n = 26, 100%; p < 0.001). The mean c-ADC value was significantly lower in TOAs (p < 0.001). A c-ADC value of 1.31 × 10^-3 mm²/s may be an optimal cut-off in distinguishing TOAs from ovarian malignancies. Conversely, the mean s-ADC value was significantly lower in the ovarian malignancy group (p < 0.001). An s-ADC value of 0.869 × 10^-3 mm²/s may be an optimal cut-off in differentiating ovarian malignancies from TOAs (p < 0.001). ROC curve analysis showed that c-ADC values had a higher diagnostic accuracy than s-ADC values.

Conclusions

“Penumbra sign” on T1W images, diffusion characteristics, and ADC values provide important clues in addition to conventional MR imaging features in differentiating TOA from ovarian malignancy.

Diffusion-weighted imaging in the evaluation of perianal fistula and abscess

Background

Perianal fistulas are a common inflammatory condition of the anal canal and perianal tissue. The introduction of MRI in the evaluation of suspected perianal inflammation has greatly improved the surgical outcome of these patients as it allowed the direct visualization of anal sphincters, levator ani muscle, and the extent of the disease in relation to these vital structures. Diffusion-weighted imaging (DWI) has been under extensive research to evaluate whether it adds any value in the setting of perianal inflammation.

The aim of our study was to evaluate the visibility of perianal inflammation on DWI and evaluate the diffusion characteristics of perianal fistulas and abscesses and how accurately can DWI classify perianal disease.

Results

Mean age of patients was 37 ± 8.9 years old. The study included 30 fistulas and 15 abscesses. Seven patients had more than 1 fistula or fistula and abscess. Perianal abscesses were well visualized equally on DWI and T2W images and correctly classified by DWI, when compared to post-contrast images. Perianal fistulas without abscesses, on the other hand, had variable visibility scores. Although the visibility of these fistulas on DWI was generally less than T2W and combined DWI and T2W, yet this did not reach a significant level and it was not significantly different between positive and negative inflammatory groups. Combined DWI and T2W evaluation had the highest performance and accurately classified 97.8 % of perianal fistulas and abscesses, and only 1 case was misclassified (2.3%).

Conclusion

DWI had a good performance in the evaluation of perianal inflammatory disease. However, combined DWI and T2W evaluation had better performance which was not significantly different from combined T2W and post-contrast images.

Multimodality Imaging of Liver Infections: Differential Diagnosis and Potential Pitfalls

Imaging plays an important role in the diagnosis, characterization, and management of infectious liver disease. In clinical practice, the main contributions of imaging are in detecting early disease, excluding other entities with a similar presentation, establishing a definitive diagnosis when classic findings are present, and guiding appropriate antimicrobial, interventional, or surgical treatment. The most common imaging features of bacterial, viral, parasitic, and fungal hepatic infections are described, and key imaging and clinical manifestations are reviewed that may be useful to narrow the differential diagnosis and avoid pitfalls in image interpretation. Ultrasonography (US), computed tomography (CT), and magnetic resonance imaging allow accurate detection of most hepatic infections and, in some circumstances, may provide specific signs to identify the underlying pathogen and exclude other entities with similar imaging features. In bacterial and parasitic infections, specific imaging features may be enough to exclude a neoplasm and, occasionally, to identify the underlying infectious agent. US and CT are important means to guide percutaneous aspiration or drainage when needed. In viral infections, imaging is critical to exclude entities that may manifest with similar clinical and laboratory findings. Disseminated fungal infections require early detection at imaging because they can be fatal if not promptly treated. Familiarity with the epidemiology, pathogenesis, clinical manifestations, imaging features, and treatment of hepatic infections can aid in radiologic diagnosis and guide appropriate patient care. (©)RSNA, 2016.

Tubo-Ovarian Abscess (with/without Pseudotumor Area) Mimicking Ovarian Malignancy: Role of Diffusion-Weighted MR Imaging with Apparent Diffusion Coefficient Values

Objective

To assess the added value of diffusion-weighted magnetic resonance imaging (DWI) with apparent diffusion coefficient (ADC) values compared to MRI, for characterizing the tubo-ovarian abscesses (TOA) mimicking ovarian malignancy.

Materials and Methods

Patients with TOA (or ovarian abscess alone; n = 34) or ovarian malignancy (n = 35) who underwent DWI and MRI were retrospectively reviewed. The signal intensity of cystic and solid component of TOAs and ovarian malignant tumors on DWI and the corresponding ADC values were evaluated, as well as clinical characteristics, morphological features, MRI findings were comparatively analyzed. Receiver operating characteristic (ROC) curve analysis based on logistic regression was applied to identify different imaging characteristics between the two patient groups and assess the predictive value of combination diagnosis with area under the curve (AUC) analysis.

Results

The mean ADC value of the cystic component in TOA was significantly lower than in malignant tumors (1.04 ± 0 .41 × 10⁻³ mm²/s vs. 2.42 ± 0.38 × 10⁻³ mm²/s; p < 0.001). The mean ADC value of the enhanced solid component in 26 TOAs was 1.43 ± 0.16×10⁻³mm²/s, and 46.2% (12 TOAs; pseudotumor areas) showed significantly higher signal intensity on DW-MRI than in ovarian malignancy (mean ADC value 1.44 ± 0.20×10⁻³ mm²/s vs.1.18 ± 0.36 × 10⁻³ mm²/s; p = 0.043). The combination diagnosis of ADC value and dilated tubal structure achieved the best AUC of 0.996. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of MRI vs. DWI with ADC values for predicting TOA were 47.1%, 91.4%, 84.2%, 64%, and 69.6% vs. 100%, 97.1%, 97.1%, 100%, and 98.6%, respectively.

Conclusions

DW-MRI is superior to MRI in the assessment of TOA mimicking ovarian malignancy, and the ADC values aid in discriminating the pseudotumor area of TOA from the solid portion of ovarian malignancy.

Liver lesion detection and characterization: role of diffusion-weighted imaging

Diffusion-weighted imaging (DWI) plays an emerging role for the assessment of focal and diffuse liver diseases. This growing interest is due to that fact that DWI is a noncontrast technique with inherent high contrast resolution, with promising results for detection and characterization of focal liver lesions. Recent advances in diffusion image quality have also added interest to this technique in the abdomen. The purpose of this review is to describe the current clinical roles of DWI for the detection and characterization of focal liver lesions, and to review pitfalls, limitations, and future directions of DWI for assessment of focal liver disease.

Differentiating hepatic abscess from malignant mimickers: value of diffusion-weighted imaging with an emphasis on the periphery of the lesion

PURPOSE

To evaluate the efficacy of diffusion-weighted imaging (DWI) in differentiating hepatic abscess from malignant mimickers with an emphasis on periphery of the lesions.

MATERIALS AND METHODS

Thirty-nine patients with hepatic abscess and 74 patients with malignant hepatic tumors were included, who underwent gadoxetic acid-enhanced MRI. For qualitative and quantitative analysis, signal intensities and apparent diffusion coefficient (ADC) values of the periphery were assessed. Two observers reviewed DWI and ADC maps rated using a 5-point scale. Diagnostic performance was evaluated using the receiver operating characteristics (ROC) curve analysis.

RESULTS

The periphery of hepatic abscesses was T1-hypointense, arterial hyperintense, and hypointense on hepatobiliary phase less frequently than that of malignant tumors (P < 0.05). No hepatic abscesses showed peripheral washout on 3-min late phase compared with malignant tumors (59.5%) (P < 0.001). Both groups showed hyperintense rims on DWI, but, 37(94.9%) abscesses revealed rims with high ADC values compared with one (1.4%) malignant tumor (P < 0.001). Mean ADC values of abscesses (1.47 × 10(-3) mm(2) /s ± 0.36 [standard deviation]) were significantly higher than those of malignancies (0.68 × 10(-3) mm(2) /s ± 0.20). Diagnostic performance (area under the ROC curve [Az]) of DWI in identifying hepatic abscess was 0.986 and 0.982 for each observer.

CONCLUSION

In addition to conventional MRI, DWI is helpful in differentiating hepatic abscess from malignant mimickers.

Differentiation between pelvic abscesses and pelvic tumors with diffusion-weighted MR imaging: a preliminary study

PURPOSE

Use diffusion-weighted magnetic resonance imaging (MRI) in differentiating pelvic abscess from pelvic cystic tumor.

MATERIALS AND METHODS

Patients with pelvic abscess (n=23) or pelvic cystic tumor (n=15) who underwent diffusion-weighted MRI were reviewed.

RESULTS

Pelvic abscesses showed hyperintensity on diffusion-weighted MRI and hypointensity on apparent diffusion coefficient (ADC) map. The mean ADC values of fluid in pelvic abscess and pelvic tumors were 0.73 ± 0.15 × 10(-3) and 2.27 ± 0.45 × 10(-3) mm(2)/s, respectively. Pelvic abscesses had significantly lower ADC values than pelvic cystic tumors (P<.001).

CONCLUSION

Diffusion-weighted MRI provides a noncontrast method for interpreting pelvic cystic lesions.

Diffusion-weighted imaging in the characterization of focal liver lesions: efficacy of visual assessment

OBJECTIVES

The objective of the study was to assess the value of visual assessment of signal intensities on b800 diffusion-weighted images and apparent diffusion coefficient (ADC) maps in differentiation of benign and malignant focal liver lesions (FLLs).

METHODS

Approval for this retrospective study was obtained from the institutional review board. One hundred forty-three FLLs in 65 patients (38 women, 27 men; mean age, 50.8 years) underwent magnetic resonance (MR) imaging and diffusion-weighted imaging (DWI) with a respiratory-triggered single-shot echo-planar imaging sequence. Focal liver lesions were evaluated visually according to the signal intensities on b800 and ADC map images, and ADC values were also calculated. The conventional MR imaging, follow-up imaging findings, and histopathologic data were regarded as gold standard. Normal distribution was assessed with Kolmogorov-Smirnov test. The accuracies of visual assessment and ADC values in differentiating benign and malignant FLLs were assessed with the Student t test, and threshold values were determined with receiver operating characteristic curve analysis.

RESULTS

By using a cutoff value of 1.21 × 10⁻³ mm²/s, ADC had a sensitivity of 100%, a specificity of 89.3%, and an accuracy of 92.3% in the discrimination of malignant FLLs. With the visual assessment of the DWIs and ADC maps, malignant lesions were differentiated from benign ones, with 100% sensitivity, 92.2% specificity, and 94.4% accuracy. Although some benign lesions were interpreted as malignant, no malignant lesion was determined as benign in visual assessment.

CONCLUSIONS

Most FLLs are benign ones such as hemangiomas and cysts, which can be readily and practically characterized only by using visual assessment of DWIs without requiring time-consuming conventional and dynamic contrast-enhanced imaging sequences. Some benign lesions that are falsely interpreted as malignant can be further characterized by using conventional and contrast-enhanced MR studies.

Diffusion-weighted MRI for evaluating perianal fistula activity: feasibility study

PURPOSE

To assess the feasibility of using diffusion-weighted magnetic resonance (MR) imaging (DWI) for evaluating perianal fistula activity.

MATERIALS AND METHODS

This study retrospectively assessed 24 patients with clinically suspected perianal fistula who underwent a total of 28 MR examinations after conservative treatment with antibiotics. DWI was performed at 1.5 T, using b-values of 0 and 1000 s/mm(2). Apparent diffusion coefficient (ADC) maps were created and ADCs of the lesions were measured. Lesions were classified into two groups based on the need for surgery and surgical findings: positive inflammation activity (PIA) and negative inflammation activity (NIA). ADCs of both groups were compared using an unpaired t-test, and Receiver Operating Characteristic (ROC) analysis was performed.

RESULTS

The ADC (in 10(-3) mm(2)/s) of the PIA group (0.908±0.171) was significantly lower (P=0.0019) than that of the NIA group (1.124±0.244). The area under the ROC curve was 0.749. An optimal cut-off ADC of 1.109 yielded a sensitivity of 95.7%, a specificity of 50%, a positive predictive value of 71%, and a negative predictive value of 90%.

CONCLUSION

DWI is a feasible method for evaluating perianal fistula activity. The diagnostic performance of this technique should be established in future, larger prospective studies.