Diffusion-weighted magnetic resonance imaging for detection of postoperative intracranial pyogenic abscesses in neurosurgery.

BACKGROUND

Diffusion-weighted magnetic resonance imaging (MRI-DWI) is the modality of choice for detecting intracranial abscesses; however, it is unclear whether prior brain surgery has an influence on its diagnostic value. Thus, we assessed the robustness of MRI-DWI and determination of an ADC cutoff value for detecting intracranial abscesses in patients who underwent brain surgery.

METHODS

We retrospectively evaluated 19 patients prior to surgery for postoperative supratentorial parenchymal abscesses by means of MRI-DWI. Forty randomly selected patients with routine postoperative MRI-DWI were used for comparative analyses. Clinical and serum biomarkers (C-reactive protein, interleukin-6, white blood cell count) as well as from results of early postoperative imaging findings (computed tomography and/or MRI scan) were recorded. Additionally, ADC values, T1±gadolinium, and T2/fluid-attenuated inversion recovery sequences were investigated.

RESULTS

After initial surgery, early postoperative control imaging showed evidence of hemorrhage and/or hemostatic agents within the resection cavity in 10/19 patients of the abscess group and in 16/40 patients of the control group. No postoperative ischemia was detected. Neither hemostatic agents nor blood affected the mean ADC values in both the reference group (blood 2.96 ± 0.22 × 10-3 mm2/s vs. no blood 2.95 ± 0.26 × 10-3 mm2/s, p = 0.076) and in the abscess group (blood 0.87 ± 0.07 × 10-3 mm2/s vs. no blood 0.76 ± 0.06 × 10-3 mm2/s, p = 0.128). The mean ADC value within the resection cavity was significantly lower in the abscess group (1.5 T 0.88 ± 0.41 vs. 2.88 ± 0.20 × 10-3 mm2/s, p < .01; 3.0 T 0.75 ± 0.24 vs. 3.02 ± 0.26 × 10-3 mm2/s, p < 0.01). The optimal ADC cut-off for the differentiation of an abscess from normal postoperative findings was found at 1.87 × 10-3 mm2/s (area-under-the-curve 1.0, sensitivity = 100%, specificity = 100%). Moreover, no differences between the abscess patients and the control group were seen with respect to the analyzed serum biomarkers.

CONCLUSION

MRI-DWI provides a robust tool to discriminate postoperative abscess formation from normal postoperative changes.