Nontraumatic convexal subarachnoid hemorrhage (cSAH)

Created 06/04/2021, last revision 07/12/2022

Definition

non-traumatic spontaneous subarachnoid hemorrhage at the convexity (non-traumatic convexal SAH – cSAH) is defined as a collection of blood in 1 or more adjacent sulci in the absence of SAH in another localization
it is relatively rare, but the etiological DDx is quite broad
- in patients ≤ 60 years of age, the most common cause is RCVS [Kumar, 2010]
- in patients > 60 years of age, the most common cause is CAA

severe headache typical for classic SAH is usually not present [Beitzke, 2011]
- headaches are generally present in cerebral venous thrombosis, RCVS, and PRES
transient focal symptoms (paresthesias, paresis) are frequent, which leads to suspicion of stroke/TIA (cSAH belongs to stroke mimics)
- etiopathogenesis of transient symptoms is unclear; a cortical spreading depression triggered by blood in the SA space is considered [Beitzke, 2011]

the primary diagnostic method
a finding of sulcal hyperdensity leads to the indication of CTA (both arterial and venous phase)
- CT sensitivity is approx. 90% in the acute phase but decreases quickly with time (the lesion becomes isodense)
because of the wide DDx, it is advisable to add MRI

perform the following sequences:
- FLAIR
- GRE or SWI
- DWI+ADC
- 3D TOF MRA + MR venography
- T1 and T1 C+
FLAIR is highly sensitive to lesions in the subarachnoid space; cSAH appears as a hyperintense band
in DDx of cSAH exclude:
- meningitis
- leptomeningeal metastases (LMM) and leptomeningeal melanosis
- post status epilepticus lesions
- previous contrast examination with gadolinium
- artifact
FLAIR further reveals other typical structural changes in the parenchyma (e.g., PRES, etc.)
GRE/SWI – confirms the hemorrhagic nature of sulcal hyperintensities and may also help in the detection of older hemorrhages or venous thrombosis

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traumatic SAH
- history of trauma
- usually, a more significant extent of SAH on the imaging methods
- concurrent contusions (sometimes only seen on a follow-up CT scan)
- a skull bone trauma visible in the bone window
cortical laminar necrosis
- associated hyperintense lesions on MR DWI
leptomeningeal metastases