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:
- rupture of a perforating artery
- venous bleed
- 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
- 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
Uptodate.com,. ‘Perimesencephalic Nonaneurysmal Subarachnoid Hemorrhage’. N.p., 2015. Web. 16 Oct. 2015.