Temporal changes in magnetic resonance imaging characteristics of Gliadel wafers and of the adjacent brain parenchyma

Abstract

Carmustine is used in the treatment of glioblastomas as locally applied chemotherapy in the form of biodegradable wafers, which are lined on the walls of the resection cavity at the end of the resection, to increase local concentrations and decrease systemic toxicity. A total of 44 patients with glioblastoma with gross macroscopic tumor removal were included. MRIs were performed at various times postoperatively (within 24 hours, 1 week, 1 month, 2 months, 3 months, 6 months, 9 months, and 1 year). MR protocols included a T2-, diffusion-weighted, and T1-weighted sequences with and without intravenous administration of gadolinium. On T1, the wafers change from their initial hypointense to an isointense appearance after a period during which they appear to be hypointense, with a hyperintense rim most prominent less than 1 month postoperatively. On T2 they change from a hypointense to an isointense appearance. Restricted diffusivity reshaping the silhouette of the wafer's surface at the rim of the resection cavity can be found as early as day 1 postoperatively; however, 1 month after implantation, they all show areas of restricted diffusion, which may remain up to 1 year. Contrast enhancement at the rim of the resection cavity can already be found at day 1 postoperatively, with a peak shortly after 1 month after surgery. These changes can easily be mistaken for an abscess and hamper the early differentiation between residual tumor tissue and normal postoperative changes. However, early changes in either appearance do not predict overall survival or the progression free interval.

Fig. 1.

Distribution of the appearance of the Gliadel wafers in T1-weighted imaging (T1WI). These wafers change from a hypointense-dominated appearance into an isointense appearance after a period during which they appear to be hypointense with a hyperintense rim most prominent less than 1 month after implantation. None of these changes was a predictor for other changes depicted with MRI or long-term survival.

Fig. 2.

Distribution of the appearance of the Gliadel wafers in T2-weighted imaging (T2WI). These wafers change from a hypointense appearance to an isointense appearance over time. None of these changes was a predictor for other changes depicted with MRI or long-term survival.

Fig. 3.

Temporal course of the restricted diffusivity in the resection cavity and the adjacent brain parenchyma underneath the wafers and contrast enhancement of the rim of the resection cavity. Restricted diffusivity reshaping the silhouette of the wafer's surface at the rim of the resection cavity can be found as early as postoperative day 1. One month after implantation, they all showed this area of restricted diffusion, which may remain up to 1 year after surgery. Contrast enhancement at the rim of the resection cavity appeared to be delayed, compared with changes of restricted diffusivity; however, we sometimes observed it on postoperative day 1, and we also noticed a peak a little over 1 month after surgery. Especially 1 month after surgery, the resection cavity showed the peak of restricted diffusivity, which usually disappeared 6 months after surgery. Together with the contrast enhancement of the rim of the resection cavity, it could easily be mistaken as an abscess. Changes in diffusivity in the resection cavity or the parenchyma adjacent to the wafers occurred during the period in which we think BCNU is delivered from the wafer into the tumor bed (over a period of up to 3 weeks),^– whereas the appearance of contrast enhancement at the rim of the resection cavity showed a peak shortly after these changes.

Fig. 4.

Postoperative MR images of a patient after the resection of a left parietal glioblastoma multiforme: postoperative day 1 (A), 1 month after surgery (B), approximately 2 months after surgery (C), approximately 3 months after surgery (D), approximately 6 months after surgery (E), approximately 9 months after surgery (F); diffusion weighted images (left column), T1WI with intravenous administration of gadolinium (middle), and T2WI (right column). The wafers in T1WI and T2WI on postoperative day 1 appeared to be hypointense, best appreciated in T2WI. Note the susceptibility artefacts resulting from residual air and changes caused by blood products in the resection cavity. In the adjacent brain parenchyma underneath the medial, dorsal, and lateral wafer, restricted diffusivity reshaping the silhouette of the wafer's surface can be found. One month after the resection (B), the wafer appeared to be hypointense in T1WI, with a hyperintense rim. There was enhancement of the wall of the resection cavity. In T2, the wafers can still best be appreciated as hypointense discs (B) with a tendency to a more isointense appearance compared to the immediately performed postoperative MRI (A). The restricted diffusivity underneath the wafer was no longer present in this case; however, the resection cavity developed restricted diffusivity, which together with the contrast enhancement of the rim of the resection cavity, can easily be mistaken as the typical MR appearance of an abscess. Over time (C–E), restricted diffusivity of the resection cavity initially remains stable and finally disappears in the later follow-up (F). In T1WI (middle column), the wafers appear to be hypointense with a hyperintense rim (C and D) and, finally, were almost indistinguishable within the resection cavity (E and F). There is enhancement of the wall of the resection cavity, which remained until the last follow-up MRI. There was no nodular enhancement over time and no recurrent disease. In T2WI (right column), the wafers became more isointense over time (C–E) and were finally almost indistinguishable from the resection cavity (F). Note the marked edema that finally disappears together with changes of the resection cavity (F).

Fig. 5.

Kaplan-Meier 39 survival curve in days from the date of operation until death.