What causes the ivy sign on FLAIR MRI of the brain?
Let me know in the comments.
Click to reveal the answer
Answer:
The ivy sign is diffuse linear hyperintensity along the cortical sulci and over the brain surface on FLAIR images, corresponding to leptomeningeal enhancement on post-contrast T1-weighted imaging. In moyamoya disease it represents slow, retrograde flow in engorged pial and leptomeningeal collateral vessels recruited to supply cortex distal to the steno-occlusive internal carotid disease. Its importance is that it is a marker of haemodynamic compromise: the extent of the ivy sign correlates with reduced cerebrovascular reserve and with the perfusion deficit on arterial spin labelling or SPECT, and it typically regresses after successful direct or indirect revascularisation, so it is used as a non-invasive follow-up measure. Comparative studies show good but not perfect agreement between the FLAIR sign and contrast-enhanced imaging, so contrast is not always required to demonstrate it. The differential for FLAIR sulcal hyperintensity is important and includes subarachnoid haemorrhage, meningitis, leptomeningeal carcinomatosis, supplemental oxygen administration during anaesthesia, propofol sedation, gadolinium leakage in renal failure and artefact from cerebrospinal fluid pulsation. In acute ischaemic stroke the same appearance is called the FLAIR vascular hyperintensity sign and indicates slow collateral flow distal to a large-vessel occlusion.
Why is it called so?
The fine linear hyperintensities creeping along the sulci resemble ivy creeping over a stone wall.
Pathophysiology
As the terminal internal carotid arteries progressively occlude in moyamoya, perfusion pressure in the distal cortical territories falls. Leptomeningeal anastomoses between the anterior, middle and posterior cerebral arteries dilate and carry flow retrogradely across the cortical surface, and transdural collaterals from the external carotid circulation contribute. Flow in these vessels is slow, so spins remain within the imaging slice long enough to escape the flow void that fast arterial flow produces, and instead appear hyperintense on FLAIR. Slow flow with an increased intravascular blood volume and a degree of blood-brain barrier permeability also accounts for the corresponding leptomeningeal enhancement after contrast.
Alternative names: Leptomeningeal ivy sign; FLAIR vascular hyperintensity
Other associated named signs: Puff of smoke sign on angiography and the brush sign of prominent deep medullary veins on susceptibility-weighted imaging
References
Access all radiology signs posted so far: https://radiogyan.com/radiology-signs/
Improve Content And Help Your Colleagues!
Found an error in the post? Please let us know using our contact page and we will update it with due credits!
If you wish to contribute radiological images for this case (or any other article on the website), you can submit them here and you will be duly credited: Submit radiology case