Diagnosis:
CT or MRI: blood in CSF space around the midbrain i.e. peri-mesencephalic. Usually in prepontine cistern or quadrageminal cistern.
+Catheter Angiography: that excludes any cause of SAH. Especially posterior circulation aneurysm.
+absence of trauma
DDx.
- Aneurysmal subarachnoid hemorrhage due to ruptured posterior inferior cerebellar artery (PICA) aneurysms
- 7% of Posterior circulation aneurysms may present this way
Related articles:
References:
- van Gijn J, van Dongen KJ, Vermeulen M, et al. Perimesencephalic hemorrhage: a nonaneurysmal and benign form of subarachnoid hemorrhage. Neurology 1985;35:493–97
- Kallmes DF, Clark HP, Dix JE, et al. Ruptured vertebrobasilar aneurysms: frequency of the nonaneurysmal perimesencephalic pattern of hemorrhage on CT scans. Radiology 1996;201:657–60
- Brinjikji W, Kallmes DF, White JB, Lanzino G, Morris JM, Cloft HJ. Inter- and intraobserver agreement in CT characterization of non-aneurysmal perimesencephalic subarachnoid hemorrhage. AJNR Am J Neuroradiol. 2010;31:1103–1105