Perimesencephalic subarachnoid hemorrhage

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Perimesencephalic subarachnoid haemorrhage (PMSAH) is a distinct pattern of subarachnoid haemorrhage (SAH), which is centred on the basal cisterns around the midbrain.

Epidemiology

PMSAH is rare with an incidence of 0.5 in 100 000 in adults ⁴. PMSAH represents 5-10% of all subarachnoid haemorrhages and ~33% of all non-aneurysmal SAH ^{3, 4}.

Clinical presentation

As per subarachnoid haemorrhage.

Pathology

Aetiology

95% of cases have a normal cerebral angiogram and the source of bleeding is not identified; the cause is thought to be a venous bleed. This is referred to as non-aneurysmal perimesencephalic SAH.

The other 5% of cases are due to a vertebrobasilar aneurysm and the prognosis is worse ^1,2. Rare causes include arteriovenous malformation, dural arteriovenous fistula, trauma and vascular tumours ⁴.

Radiographic features

CT

PMSAH has been defined as subarachnoid haemorrhage, which on CT within three days of symptom onset ⁴:

is centred anteriorly to the pons and midbrain
may extend into the basal and suprasellar cisterns and into the proximal/basal Sylvian ~~and~~ fissure and interhemispheric ~~fissures~~fissure
may settle as sediment in the occipital horns of the lateral ventricles but there is no overt intraventricular haemorrhage

Specifically, there are criteria for non-aneurysmal perimesencephalic SAH, which if fulfilled, in the presence of a negative CTA negates the need for DSA ^5:

SAH in perimesencephalic cisterns anterior to midbrain
if SAH extension into the anterior interhemispheric fissure, not extending into all of the fissure
if SAH extension into the medial Sylvian fissures, not extending into the lateral fissure
if layering interventricular extension, no frank intraventricular haemorrhage
no intraparenchymal haemorrhage

Treatment and prognosis

CTA is recommended for PMSAH to investigate for possible aneurysmal cause. Overall, PMSAH has an excellent prognosis with better outcomes compared to aneurysmal SAH ^{1, 2, 4}.

-<p><strong>Perimesencephalic subarachnoid haemorrhage (PMSAH)</strong> is a distinct pattern of <a href="/articles/subarachnoid-haemorrhage">subarachnoid haemorrhage</a> (SAH), which is centred on the <a href="/articles/basal-cisterns">basal cisterns</a> around the <a href="/articles/midbrain">midbrain</a>.</p><h4>Epidemiology</h4><p>PMSAH is rare with an incidence of 0.5 in 100 000 in adults <sup>4</sup>. PMSAH represents 5-10% of all subarachnoid haemorrhages and ~33% of all non-aneurysmal SAH <sup>3, 4</sup>. </p><h4>Clinical presentation</h4><p>As per <a href="/articles/subarachnoid-haemorrhage">subarachnoid haemorrhage</a>. </p><h4>Pathology</h4><h5>Aetiology</h5><p>95% of cases have a normal cerebral angiogram and the source of bleeding is not identified; the cause is thought to be a venous bleed. This is referred to as <strong>non-aneurysmal perimesencephalic SAH</strong>.</p><p>The other 5% of cases are due to a <a href="/articles/vertebrobasilar-aneurysm">vertebrobasilar aneurysm</a> and the prognosis is worse <sup>1,2</sup>. Rare causes include <a href="/articles/arteriovenous-malformations">arteriovenous malformation</a>, <a href="/articles/dural-arteriovenous-fistula">dural arteriovenous fistula</a>, trauma and vascular tumours <sup>4</sup>. </p><h4>Radiographic features</h4><h5>CT</h5><p>PMSAH has been defined as subarachnoid haemorrhage, which on CT within three days of symptom onset <sup>4</sup>:</p><ul>
+<p><strong>Perimesencephalic subarachnoid haemorrhage (PMSAH)</strong> is a distinct pattern of <a href="/articles/subarachnoid-haemorrhage">subarachnoid haemorrhage</a> (SAH), which is centred on the <a title="Pentagon of basal cisterns" href="/articles/suprasellar-cistern">basal cisterns</a> around the <a href="/articles/midbrain">midbrain</a>.</p><h4>Epidemiology</h4><p>PMSAH is rare with an incidence of 0.5 in 100 000 in adults <sup>4</sup>. PMSAH represents 5-10% of all subarachnoid haemorrhages and ~33% of all non-aneurysmal SAH <sup>3, 4</sup>. </p><h4>Clinical presentation</h4><p>As per <a href="/articles/subarachnoid-haemorrhage">subarachnoid haemorrhage</a>. </p><h4>Pathology</h4><h5>Aetiology</h5><p>95% of cases have a normal cerebral angiogram and the source of bleeding is not identified; the cause is thought to be a venous bleed. This is referred to as <strong>non-aneurysmal perimesencephalic SAH</strong>.</p><p>The other 5% of cases are due to a <a href="/articles/vertebrobasilar-aneurysm">vertebrobasilar aneurysm</a> and the prognosis is worse <sup>1,2</sup>. Rare causes include <a href="/articles/arteriovenous-malformations">arteriovenous malformation</a>, <a href="/articles/dural-arteriovenous-fistula">dural arteriovenous fistula</a>, trauma and vascular tumours <sup>4</sup>. </p><h4>Radiographic features</h4><h5>CT</h5><p>PMSAH has been defined as subarachnoid haemorrhage, which on CT within three days of symptom onset <sup>4</sup>:</p><ul>
~~-<li>may extend into the basal and suprasellar cisterns and into the proximal/basal Sylvian and interhemispheric fissures</li>~~
+<li>may extend into the basal and suprasellar cisterns and into the proximal/basal <a title="Sylvian fissure" href="/articles/sylvian-fissure">Sylvian fissure</a> and <a href="/articles/interhemispheric-fissure">interhemispheric fissure</a>
+</li>
~~-<li>if SAH extension into the anterior <a title="Interhemispheric fissure" href="/articles/interhemispheric-fissure">interhemispheric fissure</a>, not extending into all of the fissure</li>~~
~~-<li>if SAH extension into the medial <a title="Sylvian fissure" href="/articles/sylvian-fissure">Sylvian fissures</a>, not extending into the lateral fissure</li>~~
+<li>if SAH extension into the anterior <a href="/articles/interhemispheric-fissure">interhemispheric fissure</a>, not extending into all of the fissure</li>
+<li>if SAH extension into the medial <a href="/articles/sylvian-fissure">Sylvian fissures</a>, not extending into the lateral fissure</li>

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