Ivy Sign

In normal subjects, intracranial structures including venous sinuses, cortical veins, and choroids plexus are commonly but not always enhanced on gadolinium-enhanced MR images, but there is no apparent leptomeningeal enhancement. Leptomeningeal enhancement on postcontrast MR images has been described in association with meningoencephalitis, meningeal carcinomatosis, and vasculitis.     

Demaerel et al observed marked meningeal enhancement in a girl with moyamoya disease. The ivy sign was described by Ohta et al, referring to the diffuse leptomeningeal enhancement that resembles creeping ivy on stones in patients with moyamoya disease.

Creeping Ivy on Stones.

The ivy sign can be found on FLAIR images, as well as on contrast-enhanced MR images. Characteristic enhancement is caused by an engorged pial network via leptomeningeal anastomosis. Surgical findings of engorged pial vessels with thickened arachnoid membranes and edema are described in some cases, which may explain the leptomeningeal enhancement on contrast-enhanced MR images. Dilated pial vessels were pre-existing rather than newly formed. The source of leptomeningeal high signal intensity on FLAIR images may be complex and is not clear. As for the leptomeningeal enhancement on post-contrast T1-weighted images, it seems largely due to slow-flowing vessels of the engorged pial network.

Transverse postcontrast T1-weighted MR image shows diffuse enhancement along leptomeningeal surfaces (arrowheads), predominantly in right hemisphere.

Transverse unenhanced FLAIR MR image shows bilateral areas of high signal intensity (arrowheads) along leptomeninges.

Thickening with congestion of the leptomeninges can take part in the mechanism causing high signal intensity. Thus, the mechanism of the leptomeningeal ivy sign can be explained mainly by an engorged pial network and possibly by congested leptomeninges.                              

Moyamoya Disease

Moyamoya disease (MMD) is a progressive occlusive disease of the cerebral vasculature with particular involvement of the circle of Willis and the arteries that feed it. The image below contains a schematic representation of the circle of Willis, arteries of the brain, and brain stem.

Schematic representation of the circle of Willis, arteries of the brain, and brain stem.

Moyamoya i.e. Japanese word for "puff of smoke" characterizes the appearance on angiography of abnormal vascular collateral networks that develop adjacent to the stenotic vessels. The steno-occlusive areas are usually bilateral, but unilateral involvement does not exclude the diagnosis.

The diagnosis is initially suggested by CT, MRI, or angiogram. Contrast-enhanced T1-weighted images are better than FLAIR images for depicting the leptomeningeal ivy sign in moyamoya disease. MRI and MRA should be performed for the diagnosis and follow-up of moyamoya disease. Diffusion-weighted imaging can also be used for following the clinical course of children with moyamoya disease, in whom new focal deficits are highly suspicious of new infarcts.

Often nuclear medicine studies such as SPECT (single photon emission computerized tomography) are used to demonstrate the decreased blood and oxygen supply to areas of the brain involved with moyamoya disease. Conventional angiography provided the conclusive diagnosis of moyamoya disease in most cases and should be performed before any surgical considerations.