Subarachnoid hemorrhage

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Subarachnoid hemorrhage

Nervous system

Autonomic nervous system disorders

Horner syndrome

Orthostatic hypotension


Subarachnoid hemorrhage


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USMLE® Step 1 questions

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High Yield Notes

18 pages


Subarachnoid hemorrhage

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USMLE® Step 1 style questions USMLE

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A 35-year-old man is brought to the emergency department for evaluation of sudden-onset, severe headache. An hour ago, the patient was cooking dinner when he suddenly experienced a diffuse, excruciating headache. The patient has no significant medical history and takes no medications. Temperature is 37.0°C (98.6°F), pulse is 106/min, and blood pressure is 155/95 mmHg. The patient appears uncomfortable and in pain, but physical examination is otherwise within normal limits. A non-contrast CT scan is obtained and is noncontributory. A lumbar puncture is subsequently performed and yields straw-colored cerebrospinal fluid, and the patient is admitted to the neurosurgery service for management. On the 4th day of hospitalization, the patient suddenly experiences right hand weakness and difficulty speaking. Which of the following is the most likely etiology of this patient’s new onset symptoms?  

External References

First Aid








Headache p. 536

subarachnoid hemorrhage p. 532, 533, 719


subarachnoid hemorrhage p. 532, 533

Subarachnoid hemorrhage p. 532, 536

labs/findings p. 722

nimodipine for p. 325

presentation p. 719


There are two main types of stroke: a hemorrhagic stroke, which occurs when an artery ruptures and bleeds within the brain, and an ischemic stroke, which occurs when an artery gets blocked.

Hemorrhagic strokes can be further split into two types, an intracerebral hemorrhage which is when bleeding occurs within the cerebrum, and a subarachnoid hemorrhage which is when bleeding occurs between the pia mater and arachnoid mater of the meninges - the inner and middle layers that wrap around the brain.

We’ll focus on subarachnoid hemorrhage, which can quickly lead to death if they’re left untreated.

Subarachnoid hemorrhages can lead to a pool of blood under the arachnoid mater that increases the intracranial pressure and prevents more blood from flowing into the brain.

Ok - let’s start with three protective layers of the brain called meninges.

The inner layer of the meninges is the pia mater, the middle layer is the arachnoid mater, and the outer layer is the dura mater.

Between the arachnoid mater and the pia mater is the subarachnoid space, which houses cerebrospinal fluid, or CSF.

CSF is a clear, watery liquid which is pumped around the spinal cord and brain, cushioning them from impact and bathing them in nutrients.


A subarachnoid hemorrhage (SAH) is bleeding into the subarachnoid space, the area between the arachnoid membrane and the pia mater surrounding the brain. This may occur spontaneously, usually from a ruptured cerebral aneurysm, or may result from a head injury.

Symptoms of subarachnoid hemorrhage can include sudden, severe headache; nausea and vomiting, confusion, or reduced level of consciousness. Diagnosis is usually done with a CT or MRI that shows blood in the subarachnoid space and blood in a lumbar puncture. Treatment requires prompt surgery to stop the bleeding and prevent further damage. Medications may also be prescribed to reduce swelling and control seizures.


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  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "NEUROwords Dr. Thomas Willis’ Famous Eponym: The Circle of Willis" Journal of the History of the Neurosciences (2005)
  6. "Cerebral Aneurysms" New England Journal of Medicine (2006)
  7. "Subarachnoid Hemorrhage" Emergency Medicine Clinics of North America (2016)

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