Subarachnoid hemorrhage differential diagnosis

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Syed Ahsan Hussain, M.D.[2] Sara Mehrsefat, M.D. [3]


Differential diagnosis

It is clinically difficult to distinguish subarchnoid hemorrhage from an ischemic stroke. However, the symptoms like headache, nausea, vomiting, and depressed level of consciousness should raise the suspicion for a hemorrhagic event compared to ischemic stroke.[1][2]

Disease Findings
Ischemic stroke
  • Occurs when a clot or a mass clogs a blood vessel and cutting off the blood flow to the brain
  • Present as a
    • Thrombotic stroke (thrombus develops at the clogged part of the vessel)
    • Embolic strokes (blood clot that forms at another locations usually the heart and large arteries of the upper chest and neck, and travels to the brain)
  • Urgent evaluation with brain / neurovascular imaging (such as MRI, CT, CTA, MRA), cardiac, and metabolic evaluation is often necessary
transient ischemic attack (TIA)
  • Caused by a temporary clot which often called a “mini stroke”
  • Occurs rapidly and presents as a sudden onset of a focal neurologic symptom/sign lasting less than 24 hours
  • Urgent evaluation with brain / neurovascular imaging (such as MRI, CT, CTA, MRA), cardiac, and metabolic evaluation is often necessary
Acute hypertensive crisis/Malignant hypertension
  • Presents as significantly elevated blood pressure (systolic pressure ≥180 and/or diastolic pressure ≥120 mmHg) with or wihout acute end-organ injury
  • Urgent evaluation with MRI and CT of the brain, serum creatinine, urinalysis, cardiac (EKG, chest x ray, and cardiac enzymes) and metabolic evaluation is often necessary
Sentinel headache[3]
  • Caused by small aneurysmal leaks into the subarachnoid space
  • Presents as a episode of headache similar to that accompanying subarachnoid hemorrhage (days to weeks prior to aneurysm rupture) and focal neurologic symptoms and signs are usually absent
  • Presents with acute and subacute headaches and facial pain
Pituitary apoplexy[4]
  • Caused by pituitary gland infarct or hemorrhage secondary to pitutiery adenoma
  • Presents with acute headache, change in mental status, ophthalmoplegia, and decreased visual acuity
    • Brain CT and MRI are the preferred imaging techniques
Cerebral venous thrombosis[5][6]
  • Presents with isolated gradual onset headache or in combination with papilledema, seizures, bilateral focal deficits, and change in mental status
  • Brain MRI with venography should be considered
Colloid cyst of the third ventricle[7]
  • Caused by an acute obstructive hydrocephalus secondary to sudden obstruction in cerebrospinal fluid flow by the cyst
  • Presents with an acute onset fronto-parietal or fronto-occipital headache which relieved by taking the supine position and may be associated with nausea, vomiting, mental status changes, seizures, coma
  • Head CT or MRI of the brain are usually diagnostic
Cervical artery dissection[8][9]
  • It usulay occurs spontaneously or after head and neck injury
  • Presents with gradual onset head and neck pain with a local manifestations (such as Horner syndrome, pulsatile tinnitus, bruit, or cranial neuropathies)
  • Neuroimagings are usually preferred (brain MRI with MRA and cranial CT with CTA)
Reversible cerebral vasoconstriction syndrome
  • Occurs spontaneously and trigerred by sexual activity, exertion, emotion, and constriction of the cerebral arteries
  • Presents with acute severe headache with or without focal deficits or seizures that resolves spontaneously within 12 weeks
Spontaneous intracranial hypotension[10][11]
  • Presents with orthostatic headaches, nausea, vomiting, dizziness, diplopia, interscapular pain
  • Caused by cerebrospinal fluid (CSF) leakage from spinal meningeal defects or dural tears
  • Brain MRI is the preferred imaging techniques
Diseases Diagnostic tests Physical Examination Symptoms Past medical history Other Findings
Na+, K+, Ca2+ CT /MRI CSF Findings Gold standard test Neck stiffness Motor or Sensory deficit Papilledema Bulging fontanelle Cranial nerves Headache Fever Altered mental status
Brain tumour[12][13] Cancer cells[14] MRI Cachexia, gradual progression of symptoms
Delirium tremens Clinical diagnosis Alcohol intake, sudden witdrawl or reduction in consumption Tachycardia, diaphoresis, hypertension, tremors, mydriasis, positional nystagmus,
Subarachnoid hemorrhage[15] Xanthochromia[16] CT scan without contrast[17][18] Trauma/fall Confusion, dizziness, nausea, vomiting
Stroke Normal CT scan without contrast TIAs, hypertension, diabetes mellitus Speech difficulty, gait abnormality
Neurosyphilis[19][20] Leukocytes and protein CSF VDRL-specifc

CSF FTA-Ab -sensitive[21]

Unprotected sexual intercourse, STIs Blindness, confusion, depression,

Abnormal gait

Viral encephalitis Increased RBCS or xanthochromia, mononuclear lymphocytosis, high protein content, normal glucose Clinical assesment Tick bite/mosquito bite/ viral prodome for several days Extreme lethargy, rash hepatosplenomegaly, lymphadenopathy, behavioural changes
Herpes simplex encephalitis Clinical assesment History of hypertension Delirium, cortical blindness, cerebral edema, seizure
Wernicke’s encephalopathy Normal History of alcohal abuse Ophthalmoplegia, confusion
CNS abscess leukocytes >100,000/ul, glucose and protien, red blood cells, lactic acid >500mg Contrast enhanced MRI is more sensitive and specific,

Histopathological examination of brain tissue

History of drug abuse, endocarditis, immune status High grade fever, fatigue,nausea, vomiting
Drug toxicity Lithium, Sedatives, phenytoin, carbamazepine
Conversion disorder Diagnosis of exclusion Tremors, blindness, difficulty swallowing
Electrolyte disturbance or Depends on the cause Confusion, seizures
Febrile convulsion Not performed in first simple febrile seizures Clinical diagnosis and EEG Family history of febrile seizures, viral illness or gastroenteritis Age > 1 month,
Subdural empyema Clinical assesment and MRI History of relapses and remissions Blurry vision, urinary incontinence, fatigue
Hypoglycemia ↓ or Serum blood glucose


History of diabetes Palpitations, sweating, dizziness, low serum, glucose

Subarachnoid hemorrhage should be differentiated from other diseases causing severe headache for example: [22][23][24][25][26][27][28][29][30][31]

Disease Symptoms Diagnosis
CT/MRI Other Investigation Findings
Subarachnoid hemorrhage
  • CT scan of the head may be performed before LP to determine the risk of herniation.
  • Diagnosis is based on clinical presentation in combination with CSF analysis.
  • CSF analysis is the investigation of choice.
  • For more information on CSF analysis in meningitis please click here.
Intracranial mass
  • CT or MRI is the initial test to detect intracranial lesions.
  • These imaging tests determine the location of intracranial mass lesion(s) and help in guiding therapy.
  • Biopsy of the lesion is needed to identify the nature of the lesion such as:
  • X- ray of the skull is a non specific test, but useful if any of the lesions are calcified.
Cerebral hemorrhage
  • Progression of focal neurological deficits over periods of hours
  • CT scan without contrast is the initial test performed to diagnose ischemic stroke and rule out hemorrhagic stroke.
  • CT is very sensitive for identifying acute hemorrhage which appears as hyperattenuating clot.
  • Gradient echo and T2 susceptibility-weighted MRI are as sensitive as CT for detection of acute hemorrhage and are more sensitive for identification of prior hemorrhage.
Cerebral Infarction The symptoms of an ischemic stroke vary widely depending on the site and blood supply of the area involved. For more information on symptoms of ischemic stroke based on area involved please click here.
Intracranial venous thrombosis
  • The classic finding of sinus thrombosis on unenhanced CT images is a hyperattenuating thrombus in the occluded sinus.
  • Cerebral angiography may demonstrate smaller clots, and obstructed veins may give the "corkscrew appearance".
  • CT and MRI may be needed to rule out other suspected possible causes of headache.
Migraine is a clinical diagnosis that does not require any laboratory tests. Laboratory tests can be ordered to rule out any suspected coexistent metabolic problems or to determine the baseline status of the patient before initiation of migraine therapy.
Head injury
  • CT scan is the first test performed and identifies cerebral hemorrhage (appears as hyperattenuating clot) following head injury. CT scan is also less time consuming.
  • MRI is more sensitive, takes more time and is done in patients with symptoms unexplained by CT scan.
Lymphocytic hypophysitis Lymphocytic hypophysitis is most often seen in late pregnancy or the postpartum period with the following symptoms:
  • CT & MRI typically reveal features of a pituitary mass.
Radiation injury

CT & MRI will show:

PET scan


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