A technical description of the brain tumor window model: an in vivo model for the evaluation of intraoperative contrast agents

Abstract

The evaluation of candidate optical contrast agents for brain tumor delineation in ex vivo models may not accurately predict their activity in vivo. This study describes an in vivo model system designed to assess optical contrast agents for brain tumor delineation. The brain tumor window (BTW) model was created by performing biparietal craniectomies on 8-week-old Sprague-Dawley rats, injecting 9L glioma cells into the cortex and bonding a cover slip to the cranial defect with cyanoacrylate glue. Tumor growth was followed serially and occurred in an exponential fashion. Once tumors on the cortical surface achieved a 1mm radius, intravenous contrast agents were injected while the appearance of the cortical surface was recorded. Computerized image analysis was used to quantitatively evaluate visible differences between tumor and normal brain. Tumor margins became readily apparent following contrast administration in the BTW model. Based on red component intensity, tumor delineation improved fourfold at 50 min post-contrast administration in the BTW model (P<0.002). In summary, window placement overlying an implanted glioma is technically possible and well tolerated in the rat. The BTW model is a valid system for assessing the in vivo activity of optical contrast agents.

Fig. 1

Essential stages in the creation of a brain tumor window model: After reflecting the scalp edges laterally, a nearly full thickness craniectomy is performed, sparing the bone over the superior sagittal sinus (a). Once the remaining bone overlying the dura has been removed, a small durotomy at the base of the craniectomy is created to create a larger linear dural rent which is used to peel the dura forward, ideally in a single flap. Once the dural flap has been removed, the shiny arachnoidal surface of the brain is appreciated (b). Under microscopic guidance, a 10 μL, 26 gauge Hamilton syringe mounted to a steretactic injector is lowered through the meninges, 1 mm deep into an avasacular region of cortex (c). After injection, the surface of the brain is irrigated to remove residual tumor cells. A 10 mm glass cover slip is carefully placed on the surface of the brain and a confluent circumferential layer of cyanoacrylate glue, overlapping the edge of the coverslip and the craniectomy margin is applied (d). Glue is usually dry within 45 min at which time a plastic ring stenting the scalp open for continuous observation is applied

Fig. 2

Progression of tumor growth in the brain tumor window model. Tumor expands radially and can be tracked following implantation. A representative brain tumor window model is shown 1, 5, 9, and 13 days post-implantation

Fig. 3

Images of a brain tumor window model 12-days post-implantation before (a) and 50 min after Coomassie blue administration (b). Note the relatively subtle difference in the color of the tumor prior to contrast administration and the clear difference between the appearance of tumor and normal brain post-contrast