SPECT predicts brain surgery outcomes for epilepsy
German researchers analyzed SPECT scans of patients before they had temporal lobe epilepsy surgery to remove the area that caused their seizures. They found that patients with a “favorable ictal perfusion pattern” on SPECT can live seizure free for years, compared to months in patients who did not have the pattern before surgery.
“The expression of this model is easily calculated for the new ictal SPECT images and, therefore, could be used to support the decision for or against temporal lobe surgery in clinical patient care,” wrote a team led by the first author, Dr. Jila Taherpour of the University. Hamburg-Eppendorf Medical Center.
Medicines to prevent seizures stop working in about a third of people with temporal lobe epilepsy. In patients who subsequently undergo surgery, the seizures return in about 40%. Additionally, psychiatric disturbances, visual field abnormalities, and cognitive impairment occur in approximately 20% of patients after surgery.
An ictal perfusion SPECT is performed on patients with epilepsy during seizures to locate the area of the brain to be removed before surgery. Radiopharmaceutical absorption may reveal abnormal blood flow or specific infusion patterns during the examination.
Previous research on the predictive value of the technique was qualitative, relying on visual classification of ictal perfusion patterns, and this can vary among interpreting physicians, depending on the authors. In this prospective study, Taherpour and colleagues sought to determine whether SPECT by ictal infusion could provide unbiased quantitative evidence to predict the effectiveness of surgery.
The researchers identified 18 patients who responded to surgery for temporal lobe epilepsy after 12 months and 18 patients whose seizures had returned to some extent. They analyzed 16 models of SPECT covariance of ictal perfusion in patients who underwent CT scans (Symbia T2 or e.cam, Siemens Healthineers) before surgery.
The team found that one of 16 covariance patterns was expressed differently between responders and non-responders. This “favorable ictal perfusion pattern” resembled the typical ictal perfusion pattern in mesial temporal lobe epilepsy and provided an area under the receiver operating characteristic curve of 0.744 to predict seizure freedom 12 months after surgery, wrote the authors.
Statistical maps of hyperperfusion (red) and hypoperfusion (blue) obtained by unilateral t tests based on conventional univariate voxels corrected for injection latency, thresholded at p = 0.005 and superimposed on the parametric statistical mapping model at single subject (A). Part B shows the “favorable ictal perfusion model”. (I / C = surgery for ipsilateral / contralateral temporal lobe epilepsy). Image courtesy of Journal of Nuclear Medicine.
Kaplan-Meier analysis revealed a statistical trend towards a longer absence of seizures in patients who expressed the favorable pattern. The estimated median seizure-free time was 48 months in patients with a positive expression score versus six months in patients with a negative expression score, the researchers found.
“The expression of the ‘favorable ictal perfusion model’ identified by the analysis of covariance of the ictal cerebral perfusion SPECT provides independent information for the prediction of freedom from seizure after surgery for temporal lobe epilepsy”, have they wrote.
Classification of ictal perfusion patterns to predict surgical outcome is not common in clinical routine, the authors noted. Importantly, the calculation of the perfusion pattern in this study is fully automatic and does not require special expertise, unlike visual interpretation of ictal SPECT images, the team said.
“This simplifies widespread clinical use,” the group concluded.
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