Makindo Medical Notes

Related Subjects: |Subarachnoid Haemorrhage |Perimesencephalic Subarachnoid haemorrhage |Haemorrhagic stroke |Cerebellar Haemorrhage |Putaminal Haemorrhage |Thalamic Haemorrhage |ICH Classification and Severity Scores

🧠 Perimesencephalic Subarachnoid Haemorrhage (PM-SAH) is a subtype of subarachnoid haemorrhage where bleeding is localised around the midbrain without aneurysm or vascular malformation. It represents 15–20% of all SAH cases and carries a much better prognosis than aneurysmal SAH (aSAH).

📌 Etiology & Pathophysiology

• Non-aneurysmal bleeding: Distinguishes PM-SAH from aSAH.
• Venous bleeding hypothesis: Rupture of small perimesencephalic veins → localised blood accumulation.
• Possible triggers: Minor trauma or raised intracranial venous pressure.
• Benign prognosis: No risk of aneurysmal rebleeding → favourable long-term outcomes.

🩺 Clinical Presentation

• Onset: Sudden, thunderclap headache.
• Typical patient: Middle-aged, slight male predominance.
• Headache: Severe, occipital or retro-orbital.
• Neuro features: Usually mild – meningism, photophobia, occasional cranial nerve deficits.
• Other: Nausea, vomiting, transient LOC.

⚠️ Risk Factors

• Hypertension
• Age (middle-aged)
• Male sex
• Smoking & alcohol
• Rarely genetic predisposition

🔬 Investigations

• CT head: Blood around perimesencephalic cisterns.
• MRI brain: More sensitive for small bleeds.
• CTA / DSA: Angiography shows no aneurysm (exclusion diagnosis).
• LP: Used if CT is negative but suspicion remains.
• Bloods: FBC, U&E, clotting.

🧾 Diagnostic Criteria

• Sudden severe headache ± neuro features.
• Blood confined to perimesencephalic cisterns.
• No aneurysm on angiography (CTA/DSA).
• Absence of poor prognostic markers (e.g. rebleeding).

🔍 Differential Diagnosis

• Aneurysmal SAH (aSAH)
• Reversible cerebral vasoconstriction syndrome (RCVS)
• Intracerebral haemorrhage
• Migraine with aura
• Intracranial hypotension
• Meningitis or encephalitis

💊 Management

• Initial: ABCs, analgesia, admission for observation.
• Monitor: Neuro obs, BP (keep SBP <160 mmHg).
• Hydrocephalus: If present → ventricular drain or LP.
• Hospitalisation: Short-term observation due to early complication risk.
• Follow-up imaging: To exclude delayed vascular findings.
• Rehabilitation: For residual deficits.
• Patient education: Reassure about benign course compared to aneurysmal SAH.

📈 Prognosis

• Benign course: Mortality far lower than aSAH.
• Most achieve full recovery with minimal long-term deficits.
• Rebleeding and vasospasm are rare.
• Excellent quality of life in survivors.

⚠️ Complications

• Hydrocephalus (early)
• Rare seizures
• Infections (if drains used)
• Electrolyte disturbance (stress-related)
• Psychological sequelae – anxiety, PTSD

📚 References

• van Gijn & Rinkel. Subarachnoid haemorrhage: diagnosis & management. Brain 2001.
• Feigin VL et al. (2023). Global burden of stroke & SAH. Stroke, 54(3).
• Sanchez-Moreno J et al. (2022). PM-SAH: a systematic review. Neurol Res Pract, 4(1).
• Mohr FW et al. (2021). Outcome after PM-SAH: meta-analysis. Neurosurg Rev, 44(4).
• Kim DW et al. (2020). Management of non-aneurysmal PM-SAH. J Stroke Cerebrovasc Dis, 29(8).