Imaging the future of stroke: II. Hemorrhage

Abstract

Bleeding into the brain or adjacent structures is one of the most devastating neurological conditions, incurring tremendous emotional, financial, and societal costs. Imaging is essential to differentiate variants of hemorrhage, as the clinical features may be insufficient. A comprehensive approach to hemorrhage therefore relies on imaging to disclose pathophysiology, elucidate mechanisms, and thereby open further avenues to effective treatment. Hemorrhage patterns from superficial to deep locations in the brain are surveyed in this work, noting myriad potential causes and the influential pathophysiology of arterial ischemia, venous hypertension, and microvascular dysfunction. Recent progress of imaging studies and novel techniques to evaluate hemorrhage are explored. For decades, only computed tomography was available to define a hematoma without corroborating evidence of other pathology whereas multimodal computed tomography and magnetic resonance imaging, including noninvasive imaging of brain tissue, vessels, and perfusion, have now radically altered clinical practice. Imaging of the blood-brain barrier, cerebral microbleeds, coexistent ischemia, associated vascular lesions, and markers of hemorrhage expansion is possible with routine protocols akin to diagnostic strategies for ischemic stroke. Imaging applications for hemorrhagic transformation, venous thrombosis, and microvascular disorders are considered with a perspective that balances concern for hemorrhage with prevention of ischemia as these processes are often intertwined and clinical conundrums arise. Imminent imaging advances are anticipated with increased use of detailed imaging for hemorrhage and overlap with cerebral ischemia. Numerous questions abound regarding optimal management of hemorrhage and definitive treatments are lacking, yet imaging of pivotal pathophysiology offers tremendous opportunity for future progress in combating this debilitating condition.

Beyond the Lesion: Neuroimaging Foundations For Post-Stroke Recovery

“…For example, perfusion imaging provides important information about the hemodynamics in terms of affected area and degree of perfusion abnormality. Chronic carotid artery occlusion has been shown to go ahead with minor changes of the perfusion dynamics as assessed with maps of time to peak or mean transit time while the cerebral blood volume is not decreased and there are no or minor apparent diffusion coefficient changes [146,147]. Conversely, severe decreases of cerebral blood volume in acute stroke predict secondary hemorrhage after systemic thrombolysis [148].…”

Comparison of Clinical, Radiological and Outcome Characteristics of Ischemic Strokes in Different Vascular Territories

“…Many other studies also reported a low rate of mortality and major disability in patients with posterior circulation strokes [18,19]. Possible collateral circulation [20] and relative high threshold to ischemic damage [21] might explain in part the relative resistance of posterior fossa tissue to ischemia. This explains the recent data showing that time window to open occlusions in the vertebrobasilar system might be longer than that in anterior circulation [22].…”

Brain Imaging in Stroke: Insight Beyond Diagnosis

“…With imaging identification of this sign, it is important to note that several vascular and nonvascular mimics exist, which include but are not limited to central nervous system malignancy, resulting in intraparenchymal hemorrhage [18, 19]. The degree of extension of hemorrhage in itself may lie in the balance between intracranial pressure differentials, pressure differentials from adjacent tissue, and venous structures, as well as baseline condition of the surrounding white matter [20, 21]. …”

“…Using MRI imaging, Lou et al [26] demonstrateda correlation between iron content in the area of edema and the degree of perihematomal edema. MRI certainly adds to the assessment of prognosis in terms of offering additional insight into potential secondary neuronal injury resultant from initial hematoma [20]. …”

“…In some cases, hemorrhage may mask the underlying pathology on initial presentation as in the case of vascular malformations, and in other cases the hemorrhage itself directly lends clues into the existent mechanism of disease. As seen with coagulopathic conditions or in instances of venous hypertension, a blood-fluid level is usually a telling feature [20]. When taken together, this highlights the importance of multi-modal brain imaging, as well as detailed and dynamic angiographic imaging, because these modalities independently and in conjunction offer important insight into underlying pathophysiology of hemorrhage, and therefore dictate appropriate treatment.…”