Protein and synthetic polymer injection for induction of obstructive hydrocephalus in rats

Abstract

Background: The objective of this study was to develop a simple and inexpensive animal model of induced obstructive hydrocephalus with minimal tissue inflammation, as an alternative to kaolin injection.

Materials: Two-hundred and two male Sprague-Dawley rats aged 3 weeks received intracisternal injections of kaolin (25% suspension), Matrigel, type 1 collagen from rat tail, fibrin glue (Tisseel), n-butyl-cyanoacrylate (NBCA), or ethylene vinyl alcohol copolymer (Onyx-18 and Onyx-34). Magnetic resonance imaging was used to assess ventricle size. Animals were euthanized at 2, 5, 10 and 14 days post-injection for histological analysis.

Results: Kaolin was associated with 10% mortality and successful induction of hydrocephalus in 97% of survivors (ventricle area proportion 0.168 +/- 0.018). Rapidly hardening agents (fibrin glue, NBCA, vinyl polymer) had high mortality rates and low success rates in survivors. Only Matrigel had relatively low mortality (17%) and moderate success rate (20%). An inflammatory response with macrophages and some lymphocytes was associated with kaolin. There was negligible inflammation associated with Matrigel. A severe inflammatory response with giant cell formation was associated with ethylene vinyl alcohol copolymer.

Conclusion: Kaolin predictably produces moderate to severe hydrocephalus with a mild chronic inflammatory reaction and fibrosis of the leptomeninges. Other synthetic polymers and biopolymers tested are unreliable and cause different types of inflammation.

Figure 1

T2-weighted magnetic resonance images showing coronal slices through 5-week-old rat brain at the level of the anterior third ventricle. Cerebrospinal fluid (CSF) is bright. In normal rats (and induction failures) the ventricles are barely visible (upper panel; arrow). Kaolin injected at age 3 weeks is associated with marked enlargement of the lateral and third ventricles (middle panel; in this example the ventricle size index is 0.15). Other agents were less reliable. Matrigel caused moderate enlargement (lower panel; in this example the ventricle size index is 0.06). White matter edema is also apparent (arrow); it is usually associated with active enlargement.

Figure 2

Photomicrographs showing effects of kaolin injection. The subarachnoid space ventral to the medulla is expanded (arrow in A; H&E stain) by aggregates of inflammatory cells and kaolin (dark granules) (B; H&E stain). Fourteen days post-injection (C; H&E stain), the kaolin has been engulfed by macrophages in the subarachnoid space (arrow); there is no abnormality apparent in the adjacent medulla. There is also arachnoid fibrosis (D; Masson's Trichrome stain) with green stained collagen (arrow) in the midst of the macrophages. Scale Bar (shown in frame D) is 50 μm for B and D, 100 μm for C, and 1600 μm for A.

Figure 3

Photomicrographs showing effects of Matrigel injection. Two days post-injection (A; H&E stain) the ventral subarachnoid space is filled with Matrigel, which appears as an amorphous protein gel with scattered blood cells. Five to 14d post-injection (B; H&E stain), the Matrigel spreads around the cerebellum and into sulci (arrow) forming an acellular mass that does not elicit an inflammatory response but traps some of the blood cells. Scale Bar (shown in frame A) is 25 μm for A and 100 μm for B.

Figure 4

Photomicrographs showing effects of ethylene vinyl alcohol copolymer (Onyx) injection. At low magnification (A; H&E stain), the black tantalum granules in the polymer matrix are obvious in the fourth ventricle (arrow). By 2d (B; H&E stain) multinucleate (foreign body reaction) giant cells are apparent (arrow) adjacent to the Onyx. By 14d (C; H&E stain) the giant cell and fibroblastic reaction is more advanced, surrounding the Onyx clusters. There is associated collagen (green material, arrow) deposition as early as 5d (D; Masson's trichrome stain). Scale Bar (shown in frame D) is 50 μm for B and D, 100 μm for C, and 1600 μm for A.