====== Perimesencephalic subarachnoid hemorrhage ======

//[[J.Sales-Llopis]]//

//Neurosurgery Department, [[General University Hospital Alicante]], [[Spain]]//
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===== Latest PubMed Articles =====


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Perimesencephalic [[subarachnoid hemorrhage]] (PMSAH) is a distinct pattern of [[subarachnoid hemorrhage]] (SAH), which is centered on the [[basal cistern]]s around the [[midbrain]].




===== Epidemiology =====

[[Perimesencephalic Subarachnoid Hemorrhage Epidemiology]].

===== Classification =====

There are two main categories based on the distribution of blood on the initial CT:

==== 1. Classic (Pure) Perimesencephalic SAH ====

Blood is confined to the cisterns around the midbrain and pons, especially:

Interpeduncular cistern

Prepontine cistern

Ambient cistern

Minimal or no extension into lateral sylvian fissures or interhemispheric fissure

No intraventricular or intraparenchymal hemorrhage

No aneurysm on CTA/DSA

==== 2. Non-Classic (Non-Pure) or Atypical Perimesencephalic SAH ====

Blood starts in the perimesencephalic region but extends into:

Sylvian fissures

Interhemispheric fissure

Other cortical cisterns

May raise suspicion for aneurysm → usually leads to repeat angiography to exclude a missed aneurysm

Still, if angiography remains negative, often behaves like classic PNSAH
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see [[Non-aneurysmal perimesencephalic subarachnoid hemorrhage]].

===== Etiology =====

see [[Perimesencephalic Subarachnoid Hemorrhage Etiology]].



===== Clinical features =====

see [[Subarachnoid hemorrhage clinical features]]. 

===== Diagnosis =====

[[Perimesencephalic subarachnoid hemorrhage diagnosis]].

===== Treatment =====

[[Perimesencephalic subarachnoid hemorrhage treatment]].


===== Outcome =====

[[Perimesencephalic subarachnoid hemorrhage outcome]]

===== Retrospective observational studies =====

van Gijn et al. studied 28 patients with subarachnoid hemorrhage and normal angiograms. On early CT (within 5 days) in 13 cases, blood was seen mainly or only in the cisterns around the midbrain. This pattern of hemorrhage was found in only 1 of 92 patients with a ruptured aneurysm. None of the unexplained perimesencephalic hemorrhages was associated with intracerebral hematoma or intraventricular hemorrhage. The clinical features also differed from those of aneurysmal hemorrhage; loss of consciousness was rare, and after 3 months, all 13 patients had returned to normal life. The cause of this benign disorder remains elusive, but a venous or capillary source seems likely
((van Gijn J, van Dongen KJ, Vermeulen M, Hijdra A. Perimesencephalic hemorrhage: a nonaneurysmal and benign form of subarachnoid hemorrhage. Neurology. 1985 Apr;35(4):493-7. doi: 10.1212/wnl.35.4.493. PMID: 3982634.))

===== Case reports =====

[[Perimesencephalic subarachnoid hemorrhage case reports]]