Reactive gliosis mimicking tumor recurrence - a case series documenting MRI abnormalities and neuropathological correlates

Abstract

The aim of this study is to identify, in our center, all cases of foreign-body reactions to hemostatic agents or other prostheses resulting in a radiological suspicion of tumor recurrence. We interrogated our internal database to identify all such cases and systematically evaluated the MRI brain scans of patients: (i) at the time of initial tumor diagnosis, (ii) postoperatively, (iii) and at the time of suspected tumor recurrence. In addition, we reviewed each patient's operative notes and reviewed the histology of all cases following a second surgical intervention. In total, we identified 8 patients, 7 of whom had a WHO grade II glioma at initial surgery. We did not identify any distinguishing radiological abnormalities from the initial diagnostic brain scan to the suspected recurrence, and histologically all cases were characterized by extensive gliosis; with both macrophages and reactive astrocytes present throughout. The cause of gliosis was identified as being relating to hemostatic agents in 4 cases; in the other 4 cases, the foreign-body reaction was presumed to be caused be materials used in a craniotomy or cranioplasty. This study highlights the difficulty in radiologically diagnosing a foreign-body reaction and also identifies that such a gliotic reaction may occur as a consequence of exogenous materials used in a craniotomy or cranioplasty. .

Figure 1.. An example of MRI scans in a case with suspected tumor recurrence (case 2). Diagnostic scans (A, B, C) demonstrate a lesion in the right frontal lobe, as indicated by the yellow arrow. Postoperative images (D, E, F) were obtained within 24 hours of surgical resection of a WHO grade II oligodendroglioma (displayed in Figure 2), and display high-signal abnormality around the resection cavity on T2-weighted imaging (D and E) and hemorrhage within the cavity as a T1-weighted hyperintensity (F). Scans suggesting radiological evidence of tumor recurrence are shown (G, H), obtained 23 months from initial resection, the increase in the margin of T2-weighted abnormality surrounding the resection site, as seen in G and H, raised the suspicion of tumor recurrence. No evidence of gadolinium enhancement is seen at this time point (I). A, D, G: T2-weighted image. B, E, H: fluid attenuated inversion recovery (FLAIR) image. C, F, I: T1-weighted image post administration of gadolinium.

Figure 2.. Histology of lesion identified on MRI scan in Figure 1 (A, B, C), demonstrating an oligodendroglioma WHO grade II. A: H & E × 40. B: IDH mutant × 40 – demonstrated using IDH1 R132H immunohistochemical stain.

Figure 3.. Histology of lesion identified in Figure 1 (G, H, I) suspected to be recurrence of tumor. A: Amorphous material and chronic inflammation H & E × 40. B: Macrophage accumulation × 40. C: CD68 confirms macrophage accumulation × 40.