Letter to Editor. Giant intracranial aneurysms of the posterior circulation

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  • All India Institute of Medical Sciences (AIIMS), New Delhi, India
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TO THE EDITOR: We read with great interest the article by Lenga et al.1 (Lenga P, Hohaus C, Hong B, et al: Giant intracranial aneurysms of the posterior circulation and their relation to the brainstem: analysis of risk factors for neurological deficits. J Neurosurg 131:403–409, August 2019). In their study, the authors examined the risk factors for cranial nerve deficits, motor deficits, and disability in patients with giant intracranial aneurysms of the posterior circulation (GPCirAs). They found that higher degrees (incidence and magnitude) of neurological deficits and disability were significantly associated with aneurysm volume but not with brainstem displacement.

Although it appears logical that the extent of brainstem displacement will be correlated with the volume (diameter) of the aneurysm sac, the results in this study differ from this logic. We think that the method of measuring the brainstem displacement is inappropriate. In the article by Lenga et al., the basis of measuring brainstem displacement is analogous to that for measuring basilar invagination (BI).1 Brainstem displacement (ΔMT) is measured as the distance between the highest tip of the GPCirA and the McRae line, as is done in cases of BI. Applying this method of measurement to aneurysms is not justified. Aneurysms arising from posterior circulation will displace the brainstem away from the clivus, predominantly posteriorly, and the ideal method for measuring brainstem displacement may be the perpendicular distance from the Wackenheim clivus canal line.2 Vertebral artery (VA)–posterior inferior cerebellar artery aneurysms arising posterolaterally may displace the brainstem anteriorly or medially, and in these particular cases, axial T2-weighted MRI may be more accurate for assessing brainstem displacement in the respective directions.

An essential point to note here is that since the vertebrobasilar arterial system is ventral to the brainstem, it is expected to displace the brainstem away from the clivus (and not away from the foramen magnum, as assumed in the present article). Being a caudal structure, the odontoid tip is expected to displace the brainstem predominantly superiorly, with additional posterior displacement when associated with atlantoaxial dislocation. Thus, this methodology for measuring BI is inappropriate for measuring brainstem displacement, and it might have affected the results. Also, with the authors’ method a distal aneurysm will cause greater brainstem displacement; for example, an aneurysm of the basilar artery (BA)–superior cerebellar artery junction will produce greater brainstem displacement than a VA-BA junction aneurysm of same volume because the distance is measured with reference to the McRae line.

We think that, because of this inappropriate method of measurement, the authors could not find a correlation between GPCirA volume and the extent of brainstem displacement. And because of this fallacy, the authors reported that “the actual craniodorsal [italics added] displacement of the brainstem by the GPCirA and GPCirA volume seem to be 2 separate risk factors.” A modified and more logical method to measure brainstem displacement away from the clivus may find a correlation between aneurysm volume and brainstem displacement and also between brainstem displacement and neurological deficits/disability.

Disclosures

The authors report no conflicts of interest.

References

  • 1

    Lenga P, Hohaus C, Hong B, Kursumovic A, Maldaner N, Burkhardt JK, : Giant intracranial aneurysms of the posterior circulation and their relation to the brainstem: analysis of risk factors for neurological deficits. J Neurosurg 131:403409, 2019

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  • 2

    Wackenheim A: Roentgen Diagnosis of the Cranio-Vertebral Region. New York: Springer-Verlag, 1977

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  • 1 Brandenburg Medical School Theodor Fontane, Bad Saarow, Germany
  • 2 Helios Clinic, Bad Saarow, Germany
  • 3 Charité–Universitaetsmedizin Berlin, Germany

Response

We thank Drs. Verma and Singh for their interest in our article and for their comments. Drs. Verma and Singh object to the measurement technique used in our study to quantify brainstem displacement and propose that the perpendicular distance from the Wackenheim clivus line is a more useful alternative.

The main idea of the letter to the editor by Drs. Verma and Singh is in line with numerous interactions that members of the Giant Intracranial Aneurysm Study Group have encountered in recent years within the scientific community, be it during review processes or in discussions at conferences. The most frequent misunderstanding arises when giant aneurysms are viewed through the same lens as nongiant aneurysms. This has likely happened in their letter as well, since Drs. Verma and Singh exclusively refer to “aneurysms” throughout their critique of our article. The word “giant” does not appear at all in that context. We are happy to concede that had we examined “regular” nongiant aneurysms, then, yes, one might suspect that brainstem displacement was potentially better quantified using a different method. But since, in our multicenter interdisciplinary experience, GPCirAs tend to exert upward mass effect on the brainstem, quite comparable to the mass effect exerted by a deformed odontoid process in BI, we think it is quite justified to transfer some of the ideas valid in the context of BI, such as using the McRae line as reference for measuring brainstem displacement, to the interface between the brainstem and a giant aneurysm.

Our article presents data from the Giant Intracranial Aneurysm Registry, which was established in 2008 as an international prospective and retrospectice interdisciplinary network of 32 centers that exclusively deals with giant intracranial aneurysms. Previous publications from this network highlight the radiological and clinical uniqueness of these rare lesions, especially when compared to nongiant aneurysms.1,5 A recurring theme in our findings is that the sheer volume and mass effect caused by giant aneurysms affect the brain in ways that are not observed in cases of nongiant aneurysms. As a side note, since Drs. Verma and Singh equate volume and diameter in their comments, we would like to mention that our previous findings suggest that those two modes of quantification are actually not interchangeable in giant aneurysms, mainly due to the wide range of giant aneurysm shapes.2 So while in nongiant aneurysms measuring the diameter may still be the gold standard of quantification,4 in giant aneurysms measuring volumes may be a more attractive mode of quantification in the future.

The 1-year clinical results of the Giant Intracranial Aneurysm Registry have recently been published in the Journal of Neurosurgery,3 and we hope to be able to provide 3-year results in the not too distant future.

References

  • 1

    Dengler J, Maldaner N, Bijlenga P, Burkhardt JK, Graewe A, Guhl S, : Perianeurysmal edema in giant intracranial aneurysms in relation to aneurysm location, size, and partial thrombosis. J Neurosurg 123:446452, 2015

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  • 2

    Dengler J, Maldaner N, Bijlenga P, Burkhardt JK, Graewe A, Guhl S, : Quantifying unruptured giant intracranial aneurysms by measuring diameter and volume—a comparative analysis of 69 cases. Acta Neurochir (Wien) 157:361368, 2015

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  • 3

    Dengler J, Rüfenacht D, Meyer B, Rohde V, Endres M, Lenga P, : Giant intracranial aneurysms: natural history and 1-year case fatality after endovascular or surgical treatment. J Neurosurg [epub ahead of print December 6, 2019. DOI: 10.3171/2019.8.JNS183078]

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  • 4

    Hackenberg KAM, Hänggi D, Etminan N: Unruptured intracranial aneurysms. Stroke 49:22682275, 2018

  • 5

    Maldaner N, Guhl S, Mielke D, Musahl C, Schmidt NO, Wostrack M, : Changes in volume of giant intracranial aneurysms treated by surgical strategies other than direct clipping. Acta Neurochir (Wien) 157:11171123, 2015

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Contributor Notes

Correspondence Satish Kumar Verma: drsatishsx@gmail.com.

INCLUDE WHEN CITING Published online December 20, 2019; DOI: 10.3171/2019.9.JNS192427.

Disclosures The authors report no conflicts of interest.

  • 1

    Lenga P, Hohaus C, Hong B, Kursumovic A, Maldaner N, Burkhardt JK, : Giant intracranial aneurysms of the posterior circulation and their relation to the brainstem: analysis of risk factors for neurological deficits. J Neurosurg 131:403409, 2019

    • Search Google Scholar
    • Export Citation
  • 2

    Wackenheim A: Roentgen Diagnosis of the Cranio-Vertebral Region. New York: Springer-Verlag, 1977

  • 1

    Dengler J, Maldaner N, Bijlenga P, Burkhardt JK, Graewe A, Guhl S, : Perianeurysmal edema in giant intracranial aneurysms in relation to aneurysm location, size, and partial thrombosis. J Neurosurg 123:446452, 2015

    • Search Google Scholar
    • Export Citation
  • 2

    Dengler J, Maldaner N, Bijlenga P, Burkhardt JK, Graewe A, Guhl S, : Quantifying unruptured giant intracranial aneurysms by measuring diameter and volume—a comparative analysis of 69 cases. Acta Neurochir (Wien) 157:361368, 2015

    • Search Google Scholar
    • Export Citation
  • 3

    Dengler J, Rüfenacht D, Meyer B, Rohde V, Endres M, Lenga P, : Giant intracranial aneurysms: natural history and 1-year case fatality after endovascular or surgical treatment. J Neurosurg [epub ahead of print December 6, 2019. DOI: 10.3171/2019.8.JNS183078]

    • Search Google Scholar
    • Export Citation
  • 4

    Hackenberg KAM, Hänggi D, Etminan N: Unruptured intracranial aneurysms. Stroke 49:22682275, 2018

  • 5

    Maldaner N, Guhl S, Mielke D, Musahl C, Schmidt NO, Wostrack M, : Changes in volume of giant intracranial aneurysms treated by surgical strategies other than direct clipping. Acta Neurochir (Wien) 157:11171123, 2015

    • Search Google Scholar
    • Export Citation

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