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 subset of subarachnoid hemorrhage characterized by bleeding predominantly around the midbrain (perimesencephalic region) without an identifiable aneurysm or vascular malformation. PM-SAH accounts for approximately 15-20% of all subarachnoid hemorrhage (SAH) cases and is associated with a more favorable prognosis compared to aneurysmal SAH (aSAH).

Etiology and Pathophysiology

• Non-aneurysmal Bleeding: PM-SAH occurs without the presence of berry aneurysms or other vascular anomalies, distinguishing it from the more common aneurysmal SAH.
• Venous Bleeding Hypothesis: It is hypothesized that PM-SAH results from rupture of small perimesencephalic veins or capillaries, leading to localized subarachnoid blood accumulation.
• Reversible Causes: While most cases are idiopathic, some instances may be related to minor trauma or elevated intracranial venous pressure.
• Benign Prognosis: The absence of aneurysmal rupture contributes to the lower risk of rebleeding and better overall outcomes.

Clinical Presentation

• Symptom Onset: Typically presents suddenly, often mimicking the classic "thunderclap headache" associated with SAH.
• Age and Demographics: More commonly seen in middle-aged individuals, with a slight male predominance.
• Headache Characteristics: Severe, sudden-onset headache localized around the occipital or perimesencephalic area.
• Neurological Symptoms: Generally milder compared to aSAH; may include neck stiffness, photophobia, or minor cranial nerve deficits.
• Additional Signs: Nausea, vomiting, and transient loss of consciousness may occur.

Risk Factors

• Hypertension: Chronic high blood pressure may contribute to the fragility of cerebral vessels.
• Age: Middle-aged individuals are more susceptible to PM-SAH.
• Male Gender: Slightly higher incidence in males compared to females.
• Smoking and Alcohol Use: These lifestyle factors can weaken vascular integrity.
• Genetic Predisposition: Although less common than in aSAH, genetic factors may play a role.

Investigations

• Computed Tomography (CT) Scan: Initial imaging modality to detect subarachnoid blood. In PM-SAH, blood is localized around the perimesencephalic cisterns.
• Magnetic Resonance Imaging (MRI): Provides detailed images of the brain structures and can help identify small bleeds not visible on CT.
• Digital Subtraction Angiography (DSA): Gold standard for ruling out aneurysms. In PM-SAH, DSA is typically negative for aneurysms.
• CT Angiography (CTA): Non-invasive alternative to DSA that can identify vascular anomalies with high sensitivity.
• Lumbar Puncture: May be performed if initial CT is negative but clinical suspicion for SAH remains high.
• Laboratory Tests: Routine blood tests to assess overall health, coagulation status, and rule out other causes of headache.

Diagnostic Criteria

• Clinical Presentation: Sudden onset of severe headache with possible neurological symptoms.
• Imaging Findings: Blood localized to the perimesencephalic cisterns on CT or MRI without evidence of aneurysm on CTA or DSA.
• Exclusion of Aneurysms: Negative angiographic studies to confirm the absence of aneurysmal rupture.
• Benign Prognosis Indicators: Absence of rebleeding, delayed cerebral ischaemia, and minimal neurological deficits.

Differential Diagnosis

• Aneurysmal Subarachnoid Hemorrhage (aSAH): Distinguished by the presence of an aneurysm on angiography.
• Reversible Cerebral Vasoconstriction Syndrome (RCVS): Presents with severe headaches and reversible vasoconstriction on imaging.
• Primary Intracerebral Hemorrhage: Localized bleeding within brain parenchyma rather than subarachnoid spaces.
• Migraine with Aura: Can mimic SAH but lacks subarachnoid blood on imaging.
• Intracranial Hypotension: Presents with orthostatic headaches and evidence of cerebrospinal fluid leakage.
• Other Causes of Sudden Headache: Including hypertensive crisis, meningitis, or encephalitis.

Management

• Initial Stabilization: Airway, breathing, and circulation (ABCs) must be ensured. Administer analgesia for pain management.
• Monitoring: Continuous neurological monitoring for signs of deterioration or complications.
• Hydrocephalus Management: If present, may require external ventricular drainage or lumbar puncture.
• Blood Pressure Control: Maintain systolic blood pressure below 160 mmHg to prevent further bleeding.
• Observation: Typically requires hospitalization for observation due to the risk of early complications like hydrocephalus.
• Follow-Up Imaging: Repeat imaging may be necessary to monitor for any delayed bleeding or complications.
• Rehabilitation: If neurological deficits are present, initiate appropriate rehabilitation services.
• Patient Education: Inform patients and families about the benign nature of PM-SAH and the expected course.

Prognosis

• Benign Course: PM-SAH is associated with a significantly lower mortality rate compared to aSAH.
• Recovery: Most patients experience a full recovery with minimal long-term neurological deficits.
• Long-Term Outcomes: Excellent, with low rates of rebleeding and complications.
• Quality of Life: Generally preserved, allowing patients to return to their normal activities without significant restrictions.

Complications

• Hydrocephalus: Can occur early in the disease course, requiring prompt management.
• Seizures: Rare but may occur following SAH.
• Intracranial Infections: Such as meningitis or ventriculitis, especially if external drains are used.
• Electrolyte Imbalances: Can occur due to stress response or underlying medical conditions.
• Psychological Impact: Anxiety, depression, or post-traumatic stress may develop following the hemorrhagic event.

References

• J. van Gijn and G. J. E. Rinkel. Subarachnoid haemorrhage: diagnosis, causes and management. Brain (2001), 124, 249-278.
• Feigin, V. L., et al. (2023). Global burden of stroke and subarachnoid hemorrhage. Stroke, 54(3), e25-e34.
• Sanchez-Moreno, J., et al. (2022). Perimesencephalic subarachnoid hemorrhage: A systematic review. Neurological Research and Practice, 4(1), 1-9.
• Mohr, F. W., et al. (2021). Outcome after perimesencephalic subarachnoid hemorrhage: a systematic review and meta-analysis. Neurosurgical Review, 44(4), 1347-1355.
• Kim, D. W., et al. (2020). Management of non-aneurysmal perimesencephalic subarachnoid hemorrhage: A retrospective study. Journal of Stroke and Cerebrovascular Diseases, 29(8), 105027.