The diagnostic value of surface-stained ground sections for pathohistological evaluation of coil-embolized aneurysms

It is my privilege, being one of the pioneers using plasticembedded ground sections for the light microscopic evalua-tion of coil-embolized aneurysms, to oppose with a commenttothepaperpublished2009inActa Neurochirurgica [5]. LeoDe Ridder, Ghent University, Belgium, had criticized thattwo-dimensional (ground) sections, only stained on theirsurfaces, are not representative for microscopic evaluation ofa three-dimensional, coil-filled aneurysm.Plastic-embedded ground sections are now regarded thegold standard for hard tissue implant evaluation. Metallic,ceramic, and also polymeric implant materials can be cuttogether with undecalcified bone or teeth [6]. It was only alogical consequence to section also soft tissue implants,with the advantage of preserving, for example, the metalliccoils in situ when evaluating aneurysms. To my knowledge,first reports of using ground sections for the evaluation ofpostmortem retrieved human aneurysms [1, 7]andofexperimental aneurysms in rabbits [2]appearedin1999.Incontrast to conventional paraffin-embedded microtome sec-tions,wherethemetalliccoilsdamagetheknifeandfallout,orhave to be removed before sectioning as again advertised [4],in ground sections, the coil–tissue interfaces are preservedfor evaluating also the biocompatibility aspects of thevarious coil devices. At least for me, surface-stained groundsections can now also be regarded the gold standard forpathohistological aneurysm evaluation.Furthermore, it has to be pointed out that all conven-tional 5- to 10-µm-thick microtome sections of aneurysmsare also two-dimensional slices of a three-dimensionalstructure. Only consecutive serial microtome sections,which are technically not feasible because of artifacts andtoo elaborate, could represent the three-dimensional bodyof a coiled aneurysm. Depending on size, at least two ormore consecutive 100-µm-thick ground sections are madefrom aneurysms in my and other laboratories, eachrepresenting an initial specimen thickness of about0.5 mm. Thus, a considerable volume of the aneurysm,still containing all the loops of the coils in cross ortangential sections, is available for microscopic evaluation.Since surface stains penetrate only a few microns into thefinally 60- to 100-µm-thick ground sections of the resin-embedded tissues, solely this surface-stained layer isfocused under the light microscope, providing resolutionof cellular detail equally good to much thinner microtomesections. Our group has shown by computer-assistedmorphometry that the coil density measured in groundsections of experimental [8] and retrieved human aneur-ysms [9] corresponded well with the calculated coildensities in respective angiograms. Combined applicationof computer-assisted morphometry on angiograms andground sections allowed even for a comparison of differentcoil types in different aneurysm models from independentexperimental studies [3].Therefore, the weakness of the above cited study [5]israther the subjective estimation of angiographic aneurysmocclusion, serving as sole basis for performance ranking ofthese second-generation and bare platinum embolic devices.Apparently, only not-blinded scoring according to theRaymond scale was performed by one observer, and alsomore objective histomorphometry was not used. It is only aminor further complaint that neither the origin of thehistological specimens nor of the pathohistological evalu-ation was even acknowledged by the authors.