Histopathologic evaluation of aneurysms treated with Guglielmi detachable coils or matrix detachable microcoils

Abstract

Background and purpose: The purpose of this study was to evaluate the degree of organization and fibrocellular tissue development in aneurysms treated with bare platinum or biologically active microcoils.

Methods: Twelve aneurysms were removed at autopsy between 1-18 days and another 2 between 2-3 months posttreatment. Four aneurysms were surgically removed between 6 months and 3 years following treatment. One aneurysm removed at 8 days and another at 6 months were treated with bioactive (Matrix) coils; the other 16 with bare platinum (Guglielmi detachable coils; GDCs). All specimens were embedded in plastic, stained with hematoxilin-eosin and elastin and examined by light microscopy.

Results: All specimens removed within 3 weeks demonstrated intra-aneurysmal thrombus, without signs of organization or fibrotic tissue formation over the neck regardless of the type of coils used. In the GDC-treated aneurysms, evidence of early thrombus organization was observed within 2-3 months, and completed yet imperfect fibrocellular reaction together with residual thrombus at 2-3 years. In the Matrix-treated specimens, the aneurysm cavity was completely filled with granulation tissue corresponding to still ongoing fibrocellular reaction at 6 months, including newly formed blood vessels, smooth muscle cells, and collagen deposition without signs of residual thrombus.

Conclusions: Our results indicate that in aneurysms treated with bare platinum coils thrombus organization does not occur until late after treatment and may remain imperfect for years. In one aneurysm studied 8 days following treatment with Matrix coils, no difference was noted compared to aneurysms treated with bare platinum coils. In another aneurysm examined 6 months following packing with Matrix coils, the histologic changes support the hypothesis that the biologically active polymer may accelerate aneurysm healing.

Fig 1.

Ruptured aneurysm of the PComA removed 2 months after treatment with GDCs (case 10, Tables 1 and 2). A, Digital subtraction angiography (DSA) before treatment demonstrates PComA aneurysm. B, DSA immediately following treatment demonstrates minimal neck remnant. C, Gross pathology, demonstrating free coils covered by an incomplete fibrin layer (arrow). D, Microscopic section (H&E stain, low-power magnification, 2×) demonstrates unorganized thrombus in the aneurysm sac (arrow) and exposed coils within the neck (open arrow).

Fig 2.

Ruptured aneurysm of the MCA removed surgically 3 years after treatment with GDCs (case 9, Tables 1 and 2). A, DSA before treatment. B, DSA immediately following treatment with standard GDCs, demonstrating neck remnant (broken arrow). C, DSA 3 years after treatment demonstrates aneurysm recanalization (broken arrow). D, Gross pathology demonstrating partially exposed coils within the neck (arrow) and coils protruding through the thin wall of the aneurysm dome. E, Histologic section (H&E stain, low-power magnification, 2×) of the same specimen. Most of the aneurysm sac is filled with organized thrombus, but a large empty space is also seen (arrow). F, Higher power magnification (20×) demonstrates attenuated fibrocellular tissue (arrow), an empty space (open arrow), and residual unorganized thrombus (broken arrow) within the same aneurysm.

Fig 3.

Ruptured aneurysm of the AComA, treated with Matrix coils and removed during surgery 6 months later (case 18, Tables 1 and 2). A, DSA before treatment demonstrates ruptured AComA aneurysm (arrow) and a small incidental aneurysm at the pericallosal artery (open arrow). B, DSA immediately after treatment demonstrating a small neck remnant (arrow). C, DSA, 6 months later, demonstrates growing neck remnant (arrow). Two incidental aneurysms (one on the left MCA and the other on the left pericallosal artery) were clipped, and the AComA aneurysm was clipped and removed during surgery. D, Gross pathology of the surgical specimen. The coils within the neck (arrow) are covered by a thick tissue layer. The wall of the aneurysm is very thin. E, Microscopic section of the specimen (H&E stain, low magnification, 2×). The aneurysm cavity is filled with fibrocellular tissue without any residual blood clot or empty spaces. F, Higher magnification (10×) H&E stain demonstrates coils embedded in fibrocellular granulation tissue with multiple neocapillaries (arrowheads). G, Higher power view (20×) demonstrates collagen deposition (arrow), smooth muscle cells (broken arrow), and small blood vessels (arrowheads). H, Leukocyte invasion (arrow) represents granulation tissue (20×, H&E stain).