Subarachnoid hemorrhage
Three distinct patterns of subarachnoid hemorrhage have been described, each with its own etiology and treatment/prognostic implications.:
suprasellar cistern with diffuse peripheral extension
perimesencephalic and basal cisterns
isolated cerebral convexity
Suprasellar cistern with diffuse peripheral extension
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The suprasellar cistern is located above the sella turcica, under the hypothalamus and between the uncus of the temporal lobes. It has roughly the shape of a pentagon at the level of the optic chiasma, and of a six-point star at the level of cerebral peduncles.
Unenhanced axial computed tomography (CT) shows diffuse SAH within the basal cisterns and extension into both Sylvian fissures. An oval less dense region (arrow) is present in the suprasellar cistern, suggesting thepresence of an aneurysm.
Perimesencephalic
Perimesencephalic cisterns:
interpeduncular cistern (unpaired): between the cerebral crura
crural cisterns (paired): between the cerebral crus and uncus of the temporal lobe
ambient cisterns (paired): posterolateral to the midbrain
quadrigeminal cistern (unpaired): between colliculi, splenium of the corpus callosum, and superior surface of the cerebellum
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The interpeduncular cistern is an unpaired CSF-filled subarachnoid cistern located between the cerebral peduncles.
The quadrigeminal cistern is located between the colliculi, the splenium of the corpus callosum and the superior surface of the cerebellum and extends from the third ventricle to the great cerebral vein.
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The quadrigeminal cistern is located between the colliculi, the splenium of the corpus callosum and the superior surface of the cerebellum and extends from the third ventricle to the great cerebral vein.
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Quadrigeminal cistern
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The ambient cistern is a thin, sheet-like extension of the quadrigeminal cistern that extends laterally around the midbrain and posterior to the thalami. It acts as the connection between the quadrigeminal cistern and the interpeduncular cistern.
Image at level of the pons shows SAH confined to the right prepontine cistern (arrow). Note the absence of hemorrhage in the remainder of the visualized subarachnoid spaces,
Image at level of the midbrain show SAH confined to the interpeduncular cistern (arrow). The image is notable for the absence of hemorrhage in other portions of the subarachnoid spaces.
The term perimesencephalic hemorrhage refers to SAH in which hemorrhage is predominantly distributed around the midbrain in a pattern unlike that seen with aneurysmal SAH
A number of clinical features suggest that the cause of this type of hemorrhage is venous in origin (unlike aneurysmal hemorrhage).
Emerg Radiol (2009) 16:441–451
Isolated cerebral convexity
Thin right-sided acute subdural hematoma with subarachnoid component. Note moderate midline shift and compression of the anterior horn on the right. Right frontal contusion bleedings. Contra-coup subarachnoid bleeding in the right frontal region.
Cases from Radiopaedia
Case 1: Subarachnoid haemorrhage - left PCOM aneurysm. Fischer scale group 3.
Case 2: Perimesencephalic subarachnoid haemorrhage
Case 3: CT image shows diffuse subarachnoid haemorrhage in all basal cisterns, bilateral sylvian fissures and inter-hemispheric fissure with a component of left subdural hematoma.
Case 4: Prepontine and right ambient cisternal subarachnoid haemorrhage.
Case 5: Hyperdense subarachnoid haemorrhage in the basal cisterns and surrounding to the corpus callosum.
Case 6: CT image shows diffuse subarachnoid haemorrhage in all basal cisterns, bilateral sylvian fissures and inter-hemispheric fissure
Case 7: Extensive subarachnoid blood is demonstrated not only around the circle of Willis but also extending up into both Sylvian fissures, inter-hemispheric fissure anteriorly and over the convexities. In addition, blood has filled the pre-pontine and cerebellopontine cisterns and refluxed into the ventricular system, with some blood pooling in the occipital horns of the lateral ventricles. Hydrocephalus is present.
Location:
Large amount of blood within the interhemispheric fissure and the suprasellar cistern commonly indicate a ruptured anterior communicating artery aneurysm,
Blood mostly confined to one Sylvian fissure is associated with a middle cerebral artery bifurcation aneurysm
Patterns of blood distribution along the basal cisterns may point characteristically to basilar terminus and posterior inferior cerebellar artery (PICA) aneurysms. PICA aneurysms cause isolated posterior fossa hemorrhage in only about one third of cases, and intraventricular hemorrhage is present in 95% of cases.
Emerg Radiol (2009) 16:441–451
Normal sagittal midline demonstrating the central venous vasculature and cisterns.
1. Great cerebral vein of Galen
2. Internal cerebral vein
3. Thalamostriate vein
A. Cistern of the laminae terminalis
B. Chiasmatic cistern
C. Interpeduncular cistern
D. Ambient cistern
E. Quadrigeminal cistern
F. Cerebellopontine cistern
G. Prepontine cistern
H. Lateral cerebellomedullary cistern
I. Cisterna magna
Normal sagittal midline demonstrating the continuity of the CSF flow channels.
1. Intraventricular foramen of Monroe
2. Posterior floor of the third ventricle formed by the convex superior border of the midbrain
3. Cerebral aqueduct of Sylvius
4. Median aperture of Magendie
Subarachnoid hemorrhage is present in both the right and the left Sylvian fissures. The predominance of hemorrhage in the right Sylvian fissure and the finding of a central lucency (arrow) within that hemorrhage are features suggesting that a right middle cerebral artery bifurcation aneurysm is the responsible lesion.