Diffusion imaging and inflammation

MR Images of 70-Year-Old Man with History of Recent Vertigo and Disequilibrium

Figures 1, 2. Axial (1) T2-weighted fast spin-echo image (5,300/128) obtained with two signals averaged, 6-mm section thickness, echo train of 23, and 230 × 512 matrix, and (2) T1-weighted contrast-enhanced spin-echo image (580/14) obtained with two signals averaged, 6-mm section thickness, and 192 × 256 matrix.




Figures 3, 4. (3) Axial diffusion-weighted (x sensitizing direction) multishot echo-planar image (800/123) obtained with one signal acquisition and 6-mm section thickness, and (4) corresponding ADC map.The preoperative diagnosis following conventional MR imaging was glioblastoma or metastasis. However, the very low ADC value of 0.3 found on the diffusion-weighted image (*) suggests the diagnosis of abscess or subchronic hemorrhage. A brain abscess with Streptococcus anginosus was found at surgery.

MR Images of 57-Year-Old Woman with Cerebral Metastasis







Figures 5, 6. Axial (5) T2-weighted fast spin-echo image (6,000/128) obtained with two signals averaged, 5-mm section thickness, echo train of 23, and 230 × 512 matrix, and (6) T1-weighted contrast-enhanced spin-echo image (600/14) obtained with two signals averaged, 6-mm section thickness, and 128 × 256 matrix. On T2-weighted fast spin-echo and contrast-enhanced T1-weighted spin-echo images the differential diagnosis between metastasis and abscess is impossible.

Figures 7, 8. (7) Axial diffusion-weighted (z sensitizing direction) multishot echo-planar image (800/123) obtained with one signal acquisition and 6-mm section thickness, and (8) corresponding ADC map. Central hypointensity is seen on the diffusion-weighted image and hyperintensity on the ADC map, consistent with the diagnosis of tumor.


Inflammation
The differential diagnosis between intracerebral necrotic tumors and cerebral abscesses is frequently impossible on conventional MR images. In our experience, the abscesses are hyperintense on diffusion-weighted images (1) with a very low ADC value of 0.3-0.4. Therefore, the diffusion-weighted imaging and ADC findings may be useful in the differential diagnosis of "ring-enhancing" cerebral masses. The presence of a central area of hyperintensity on diffusion-weighted images and very low ADC values strongly suggest the presence of pus and abscess. These characteristics are also present in acute infarction. However, ring enhancement in acute ischemic stroke is unusual, and ADC values are higher after 8 hours. The ring-enhancing mass with central hypointensity on diffusion-weighted images and increased ADC values suggest cerebral glioma or metastasis (2). We may only hypothesize about the low ADC values of pus (related to fibrinogen accumulation?), but this reduced diffusion may explain the reduced activity of antibiotics in the presence of suppuration.
References

1. Lövblad KO, Laubach HJ, Baird AE, et al. Clinical experience with diffusion-weighted MR in patients with acute stroke. AJNR 1998;19:1061-1066.

2. Tien RD, Felsberg GJ, Friedman H, Brown M, MacFall J. MR imaging of high-grade cerebral gliomas: value of diffusion-weighted echoplanar pulse sequences. AJR 1994;162:671-677.