Collateral leptomeningeal arteries: where are the anastomosis?

Key point:

  • To provide a review of existing (and often conflicting) knowledge concerning human leptomeningeal arteries (LMA) from an anatomical and physiological standpoints.

Vascular architecture of leptomeningeal arteries

More than 300 years ago, Willis T. characterized the arterial ring at the base of the brain and began debate concerning whether the circle functions primarily as a flow equalizer or as an anastomosis. Heubner O., in 1874, was the first to produce a well-documented study demonstrating the existence of LMA; he was trying to establish the ACA, MCA, and PCA territories by injecting 1 of these arteries and, unexpectedly, the whole cerebral arterial system was filled. Despite this evidence, other contemporary anatomists, like Duret, Charcot and Testut, were not convinced of the importance of LMA. Vander Eecken H.M. and Adams R.D., in 1953, were the first to provide a comprehensive anatomic description of LMA; they showed their microscopic anatomy, defined their number and diameter, studied inter- and intra-individual variability, between the two hemispheres of same brain, in LMA size, number, and localization.

Anatomic Evidence of LMA

Really, what distinguished anatomists (Testut, Duret, etc.) questioned from the beginning of these investigations was the compensatory capacity of LMA. De Seze S., in 1931, gave the first evidence of this capacity in Pression artérielle et ramollisement cerebral: Recherches cliniques physiopathologiques et therapeutiques; he radiographically observed, in cadaveric study, that injected fluid in ACA or PCA retrogradely filled the MCA branches. However, due to an extreme variability in patients outcomes associated with an almost constant presence of LMA on arteriography, it was not reached a common opinion. A different perspective on the hemodynamic functionality of LMA came from Viñuela et al. (1986), who observed refilling of arteriovenous malformations in conditions of complete occlusion of feeding vessels as a result of LMA and other vessels. Studies about stroke gave great importance to LMA compensatory capacity; in 1992 Ringelstein et al. hypothesized that LMA could influence penumbra extension and therapeutic window in MCA occlusion, observing that wider distal end-to-end anastomoses appear to correlate with more tissue protection. Nowadays, mechanisms controlling luminal size of the distal anastomoses are unknown.

Factors Influencing the Compensatory Capacity of LMA

 In conclusion,with the introduction of the concept of penumbra there was great interest to understand physiological behavior of LMA. It is known that there is great interindividual variability in distribution, size and number of LMA, but no study shows the range of this variability and associates variability to compensatory capacity.

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