Role of diffusion-weighted echo-planar MRI in distinguishing between brain abscess and tumour: a preliminary report

Abstract

Our purpose was to evaluate diffusion-weighted (DW) echo-planar MRI in differentiating between brain abscess and tumour. We examined two patients with surgically confirmed pyogenic brain abscess and 18 with metastatic brain tumours or high-grade glioma, using a 1.5 T system. The apparent diffusion coefficient (ADC) of each necrotic or solid contrast-enhancing lesion was measured with two different b values (20 and 1200 s/mm2). All capsule-stage brain abscesses (4 lesions) and zones of cerebritis (2 lesions) were identified on high-b-value DWI as markedly high-signal areas of decreased ADC (range, 0.58-0.70 [(10-3 mm2/s; mean, 0.63)]). All cystic or necrotic portions of brain tumours (14 lesions) were identified on high-b-value DWI as low-signal areas of increased ADC (range, 2.20-3.20 [(10-3 mm2/s; mean, 2.70)]). Solid, contrast-enhancing portions of brain tumours (19 lesions) were identified on high-b-value DWI as high-signal areas of sightly decreased or increased ADC (range, 0.77-1.29 [(10-3 mm2/s; mean, 0.94)]). Our preliminary results indicate that DW echo-planar MRI be used for distinguishing between brain abscess and tumour.

Biological correlates of diffusivity in brain abscess

“…In patients with brain abscess, viscosity has been considered to be an important factor in causing restricted diffusion (3,13,14). We did not observe any correlation between the viscosity and the mean wholecavity ADC of the brain abscesses.…”

“…There was a significant decrease in the ADC of the pellet after centrifugation as compared to the whole-pus ADC (P Ͻ 0.001). The restricted cell density (cell density over the pellet portion) of the pus after centrifugation was 1.3 Ϯ 0.7 ϫ 10 5 cells/mm 3 , whereas the whole-pus cell density was 0.9 Ϯ 0.4 ϫ 10 5 cells/mm 3 . The viscosity of these pus samples was 52 Ϯ 13 centipoise, and the extracellularprotein concentration was 62 Ϯ 3 mg/ml.…”

“…The viscosity, cell density, and concentration of extracellular protein were measured. Cell counts were done in a hemocytometer (Burker-Turk, Japan), after the pus was diluted 100-to 1000-fold in white blood cell (WBC) diluting solution, and expressed as cells/mm 3 . We identified nonviable cells by trypan blue (0.5%) staining, and the percent viability and restricted cell density were calculated as described in the previous paragraph.…”

“…Diffusion-weighted imaging (DWI) is widely used in the detection and characterization of a large number of brain pathologies, such as stroke, abscess, encephalitis, and tumors involving the central nervous system (1)(2)(3)(4)(5)(6). The movement of water molecules is altered in a wide range of pathological conditions, resulting in high sensitivity and low specificity of DWI.…”

Magnetic resonance spectroscopy in the diagnosis and etiological definition of brain bacterial abscesses

“…Pus is a viscous fl uid content of infl ammatory cells, mucoid protein, bacteria and necrotic tissue. Microscopic diffusion movement of water molecules are expected to be decreased in the cavity containing pus, whereas in necrotic tumor or cystic metastases, the cystic contents are less viscous, containing less infl ammatory cells and more serous fl uid 7,8 . So, bacterial abscess produce high signal on DWI and low ADC values, ranged from 0.45 to 0.8 9 .…”