Perfusion Imaging in Multiple Sclerosis

Because it has long been noted that vascular inflammation in the brain is the critical event in the pathogenesis of MS, there has been an increasing interest in studying the microvascular abnormalities in MS by using advanced MR imaging. The assessment of brain hemodynamics, including cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) is now possible by applying dynamic susceptibility contrast MR imaging (DSC-MR imaging), a technique that is being used more widely in clinical practice for measuring blood perfusion. Studies by using DSC-MR imaging demonstrate a significantly decreased CBF and prolonged MTT in periventricular regions of NAWM(normal appearing white matter) in patients with MS compared with controls. The diminished perfusion in NAWM is supported by the histopathologic evidence and may indicate that MS has a primary vascular pathogenesis. The frequent edematous onion-skin changes on the vein wall and vascular occlusion have been documented in the early pathologic studies. Recent work based on modern histopathologic techniques also demonstrates the hypoxia-like tissue injury or thrombosis of small veins.

Studies of MS lesions by using perfusion MR imaging have also shown evidence of hemodynamic abnormalities including the increased CBV in acute lesions, which suggests that microcirculation may be modulated by inflammation or acute hypoxia. In a study by Wuerfel et al, the altered local perfusion changes can be detected before the disruption of the BBB and new lesion formation. By detecting various lesion types, Ge et al1found not only enhancing lesions, but also some chronic nonenhancing lesions showing increased perfusion, which may indicate lesion reactivity or renewed inflammatory changes, which are also before BBB breakdown and not visible on conventional MR imaging. These findings are important in that hemodynamic abnormality is a significant component in the pathophysiology of MS lesions. Perfusion imaging may have a predictive role of lesion reactivity and/or new lesion formation and, therefore, has the potential to predict disease activity, and monitor disease progression or the effects of therapy.

In conclusion imaging characteristics in multiple sclerosis in Perfusion imaging:

• Decreased CBF and CBV in general
• Locally increased CBV in enhancing lesions
• Locally increased CBV in some chronic lesions