CT permeability can help emergency physicians assess the risk to an acute ischemic stroke patient of developing hemorrhagic transformation after receiving thrombolytic treatment. Perfusion-derived permeability surface area product maps (PS) can predict the occurrence of subsequent intracranial bleeding with relatively high sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV), according to an article published in the World Journal of Radiology.
Thrombolytic therapy used to restore blood flow and reperfuse ischemic brain tissue at risk is considered to be the most promising and currently used treatment for ischemic stroke patients. However, a portion of patients subsequently develop hemorrhagic transformation. Diagnostic imaging information that could help predict this risk has a twofold benefit. First, emergency physicians would have better information in hand to determine if thrombolytic treatment is appropriate for the patient. Second, patients with large volume tissue involvement considered inappropriate for this treatment based on American Stroke Association guidelines could be individually reassessed.
Co-author Jai Jai Shiva Shankar, MD, associate professor of medicine in the Department of Diagnostic Radiology at Queen Elizabeth II Health Sciences Centre in Halifax, Nova Scotia , and colleagues conducted a study to assess whether PS maps are predictive diagnostic tools, and if so, whether the severity of the hemorrhagic event can be anticipated. They retrospectively reviewed the medical records of all patients who presented with symptoms of acute ischemic stroke at the hospital over a five month time period.
The researchers identified 42 patients who had a CT scan at time of admission and a subsequent CT scan after initial treatment. The patients were predominantly older, but included an age range of 45 to 93 years. Over 90%, or 32 patients, received intravenous thrombolytic therapy and five patients also received mechanical thrombus extraction. Four patients did not receive either treatment. The patient cohort was equally divided with respect to left- and right-sided symptoms. The patients were grouped into those who had intracranical hemorrhage (15 patients) and those who did not (27 patients).
The authors calculated PS for the side of the ischemia and/or infarction and for the contralateral unaffected side at the same level, and used the cerebral blood flow map to delineate the ischemic territory. They subsequently drew a region of interest at the center of the territory on the PS parametric map, and created a mirror region of interest on the contralateral side at the same level.
The rPS derived using the normal side as the internal control was significantly higher in cases of hemorrhagic transformation compared to patients who did not. Values above the threshold of the overall mean rPS of 1.3 as a cutoff showed an increasingly likelihood of subsequent hemorrhagic transformation. The authors reported a score accuracy of 76.2, a sensitivity of 71.4, specificity of 78.5, PPV of 62.5, and NPV of 84.6. The authors advised that the odds ratio for patients with a value of 1.3 or greater had an odds ratio of 9.2 with respect to having a hemorrhagic transformation. However, severity of intracranial bleeding could not be predicted.
The authors recommend that additional research be undertaken to better identify patients who will develop serious symptomatic complications using CT images.They note that although MRI is a superior imaging technology compared to CT for hemorrhage detection, it may not be feasible to get access to and perform a MRI exam within the treatment time window. “Development of an extended CT stroke protocol may be more practical in the acute setting because it is the modality of choice for the initial investigation,” they concluded.
CT permeability can help predict hemorrhagic transformation after ischemic stroke. Appl Radiol.