Perimesencephalic Subarachnoid Hemorrhage

PM NASAH

CAUSES OF PERIMESENCEPHALIC SAH

in 2-9% – cause is a ruptured sacular aneurysm, from posterior circulation (basilar tip, vertebrobasilar junction, PICA, SCA or PCA)

In majority, etiology is not defined = PM-NASAH (Perimesencephalic Non-aneurysmal SAH).

Theories for origin of these cases include:

  1. rupture of a perforating artery
  2. venous bleed
  3. basilar artery wall hematoma

RUPTURE OF PERFORATING ARTERY

  • HTN is a risk factor for perforating artery disease, as well as for PM-NASAH
  • location consistent with bleeding from perforating artery arising from posterior circulation

VENOUS ORIGIN

  • suggested by limited extension of blood and low rate of rebleeds – source of bleed is low pressure
  • also, PM-NASAH often occurs in setting of physical exertion – increases intrathoracic pressure – impairs jugular venous return – elevates ICP – leakage of venous blood
  • higher incidence of primitive venous drainage on venography – basal vein of Rosenthal and/or perimesencephalic veins drain directly into dural sinus rather than vein of Galen – more susceptible to venous congestion

BASILAR ARTERY WALL HEMATOMA

  • abnormal contour of basilar artery observed – small bulge or luminal narrowing – ?intramural hematoma as source of bleed?
  • rupture of vasa vasorum is source of limited bleeding

Other Potential Causes of PM-NASAH

  • rupture of cryptic vascular malformation
  • high cervical spinal dural AVF
  • cavernous angioma
  • capillary telangiectasia
  • occult aneurysm

References

Uptodate.com,. ‘Perimesencephalic Nonaneurysmal Subarachnoid Hemorrhage’. N.p., 2015. Web. 16 Oct. 2015.

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