Fandino, Javier

Marbacher, Serge

Sherif, Camillo

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LETTER TO THE EDITORComputerized angiographic evaluation of coil densityand occlusion rate in embolized cerebral aneurysmsCamillo Sherif & Serge Marbacher & Javier FandinoReceived: 8 October 2010 /Accepted: 30 October 2010 /Published online: 16 November 2010# Springer-Verlag 2010The recently published article by Kang et al. [3] is a timelyand important contribution to our understanding of themechanisms of rebleeding in cerebral aneurysms. Wenonetheless wish to add the following comments:To determine the success of embolization, Kang et al.calculate angiographic “coil density” (CD) as according tomethods earlier described by Tamatani et al., and which weand others have previously employed [5, 7, 8]. Simplisti-cally, the aneurysm's total volume is first calculatedassuming an ellipsoid aneurysm shape; coil volume iscalculated as a summation of cylindrical coil shapes(calculated angiographic coil density thus expressed as apercentage of all coil volumes within the estimatedaneurysm volume). While recognizing several limitationsand drawbacks of this mathematical approximation, Kanget al. nevertheless concluded that calculated CD was the onlyavailable objective measurement to estimate acceptable coilembolization at the time of their data registration. We stronglydisagree in that point:As in our study which the authors cite, we proved theinvalidity of this parameter [5]. We compared angiographiccalculated CD with direct measurements of CD incorresponding histologic ground sections. These histomet-ric evaluations allow for calculation of intraaneurysmalmorphology using the highest currently available resolution[1, 4]. We found a statistically significant differencebetween angiographic CD and histometric CD with differ-ences of more than 10% in four out of 14 aneurysms. In 12out of 14 aneurysms angiographic values were higher thanthe corresponding “real” histometric CD values. Our dataclearly suggests that angiographically calculated CD is notonly inaccurate, but could potentially result in patient harmif this (often over-) estimation of aneurysm size were usedto guide clinical decision making.When hypothesizing as to possible reasons for earlyaneurysm rebleeding, Kang et al. cite uneven coil distribu-tion and inter-coil-loop thrombolysis. We would like to addtwo additional possibilities: a major cause for rebleeding of“successfully” embolized aneurysms (Roy Class 1 and 2)may be the tendency of subjective overestimation ofocclusion rates. This has been shown in the above-citedpaper which compared subjective occlusion rate estimationswith a new method of computerized occlusion rating (COR)[5]. In ten of 14 aneurysms, computerized measurements ofCOR were 5–15% lower than subjective estimations. Thisis potentially dangerous especially in cases of COR RoyClass 3 aneurysms (residual filling of the aneurysm neckand dome) whereby subjective overestimation may lead tomisclassification as Roy Class 2 (residual filling within theaneurysm neck only). The major reasons for superiority ofCOR over subjective estimations were (1) the betterdefinition of the aneurysm border using computerizedC. SherifDepartment of Neurosurgery, Hospital Rudolfstiftung,Juchgasse 25,A-1030, Vienna, AustriaC. Sherif (*) : S. Marbacher : J. FandinoCerebrovascular Research Group, Department of Intenisve CareMedicine, University of Berne,Berne, Switzerlande-mail: camillo.sherif@meduniwien.ac.atS. Marbachere-mail: serge.marbacher@ksa.chJ. Fandinoe-mail: javier.fandino@ksa.chC. Sherif : S. Marbacher : J. FandinoDepartment of Neurosurgery, Cantonal Hospital of Aarau,Tellstrasse,CH-5001, Aarau, SwitzerlandActa Neurochir (2011) 153:343–344DOI 10.1007/s00701-010-0867-3image superimposition of pre- and post-embolizationimages and (2) the higher resolution power of the intra-aneurysmal contrast medium gray values. Subjectiveocclusion rate estimation is not that precise in intraaneur-ysmal contrast medium gray value recognition. This resultsin subjective underestimation of smaller contrast medium-filled intraaneurysmal areas, leading to falsely high subjec-tive occlusion rates. As initial occlusion rate is a powerfulpredictor of aneurysm recanalization and rebleeding [2], wewant to emphasize the clinical importance of minimizingthis subjective bias, ideally by objective three-dimensionalCOR in prospective series or at a minimum with two-dimensional COR for retrospective evaluations.Finally, in an experimental autopsy study using a rabbitaneurysm model, we compared angiographic andcorresponding histologic findings using COR [6]. In theanimal sacrificed at 1 h post-embolization, we found 80%angiographic COR compared with only 32.6% histometricCOR. This wide discrepancy between the two methods isthought to be due to DSA's insensitivity to blood stasis,instead displaying the contrast medium flow only. Inclinical practice, there is usually no blood flow inside theaneurysm after embolization because the coil constructcompletely obstructs the contrast medium inflow, as seenon the respective DSA. This is initially interpreted ascomplete or near-complete aneurysm occlusion and theclinical aim appears to be realized. But extremely low“real” histometric occlusion at this early time point isrevealed by the histological ground section in our speci-men. Consequently, we cannot expect stable thrombusformation and thus safe aneurysm occlusion in the firsthours after embolization. Any factor leading to changes ofintraaneurysmal blood flow (e.g., elevated blood pressure,or changing shear stress patterns, particularly in the regionof the aneurysm neck) may theoretically lead to earlyrebleeding. It is our hope that future studies will betterelucidate the role of these underlying hemodynamic issueson post coil-occlusion aneurysmal rebleeding rate.Conflicts of interest None.References1. Cruise G, Shum J, Plenk H (2007) Hydrogel-coated and platinumcoils for intracranial aneurysm embolization compared in threeexperimental models using computerized angiographic and histo-logic morphometry. J Mater Chem 17:3965–39732. Johnston S, Dowd C, Higashida R, Lawton M, Duckwiler for theCarat Investigators (2008) Predictors of rehemorrhage aftertreatment of ruptured intracranial aneurysms: the Cerebral Aneu-rysm Rerupture After Treatment (CARAT) Study. Stroke 39:120–1253. Kang D, Kim Y, Baik S, Park S, Park J, Hamm I (2010) Acuteserious rebleeding after angiographically successful coil emboliza-tion of ruptured cerebral anerysms. Acta Neurochir 152:771–7814. Plenk H (1986) The microscopic evaluation of hard tissue implants.In: Williams D (ed) Techniques of biocompatibility testing. CRC-Press Inc., Boca Raton Florida, pp 35–815. Sherif C, Bavinzski G, Dorfer C, Kanz F, Schuster E, Plenk H(2009) Computerized assessment of angiographic occlusion rateand coil density in embolized human cerebral aneurysms. Am JNeuroradiol 30:1046–10536. Sherif C, Plenk H Jr, Grossschmidt K, Kanz F, Bavinzski G (2006)Computer-assisted quantification of occlusion and coil densities onangiographic and histological images of experimental aneurysms.Neurosurg 58:559–5667. Tamatani S, Ito Y, Abe H, Koike T, Takeuchi S, Tanaka R(2002) Evaluation of the stability of aneurysms after emboliza-tion using detachable coils: correlation between stability ofaneurysms and embolized volume of aneurysms. Am J Neuro-radiol 23:762–7678. Yoshino Y, Niimi Y, Song J, Silane M, Berenstein A (2004)Endovascular treatment of intracranial aneurysms: comparativeevaluation in a terminal bifurcation aneurysm model in dogs. JNeurosurg 101:996–1003344 Acta Neurochir (2011) 153:343–344

Computerized angiographic evaluation of coil density and occlusion rate in embolized cerebral aneurysms

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Computerized angiographic evaluation of coil density and occlusion rate in embolized cerebral aneurysms

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