Imaging description

Radiologists rely on enhancement in evaluating treatment response in glioblastoma multiforme (GBM). According to the widely used Macdonald criteria, >50% decrease in enhancing tissue indicates treatment response. Currently, anti-VGEF agents such as bevacizumab are commonly used for recurrent GBM treatment [1]. Antiangiogenic properties of this agent result in a rapid and dramatic decrease in the degree and amount of enhancement in the tumor bed with decreasing edema and mass effect and some improvement in clinical performance scores [1,2]. This translates to marked improvement in radiographic response rates and some improvement in disease-free survival rates, but no significant improvement is seen in overall survival rate in these patients (Figs. 27.1, 27.2, 27.3) [1]. While contrast-enhancing lesions decrease in size, FLAIR and DWI images may show enlargement of the tumor and are more reliable than contrast-enhanced images in evaluating treatment response [3,4].

Importance

The rapid decrease in contrast enhancement is secondary to stabilization of the blood–brain barrier rather than true tumor reduction [5]. Caution should be exercised in interpreting this as true response.

Typical clinical scenario

Bevacizumab is usually used as an alternative to the standard temozolomide and radiotherapy (TMZ+RT) or in cases of recurrent tumor, and it may generate a rapid “response,” sometimes within a few days. Enhancement and edema usually rebound with cessation of treatment enhancement and decrease with restarting of treatment.

Differential diagnosis

Response in the setting of bevacizumab treatment should be confirmed with FLAIR and DWI findings. Enlargement of infiltrative signal abnormalities on FLAIR and DWI should be interpreted as progression even when the enhancing tumor is decreasing.