At present, there is no consensus on the definition of hematoma expansion. Some studies defined hematoma expansion as a 33% increase in the relative volume of the hematoma or an absolute volume increase of 6 ml[5, 28]. Some studies defined hematoma expansion as a 33% increase in the relative volume of the hematoma or an absolute volume increase of 12.5ml[6, 17, 18]. The latter was widely used in clinical settings, especially in large-scale clinical trials. In this study, hematoma expansion was defined as the increase of absolute volume > 12.5 ml or relative volume > 33% in two brain CT scan within 24 h after admission.
In 102 HICH patients in this study, about 29.4% (30/102) had hematoma expansion which is consistent with literature reports[19, 29–31], but lower than the reported 35.4% by Chan et al.[6]. The reason might be that 38 HICH patients who conducted hematoma drainage within 24 hours due to massive bleeding or broken into the ventricle were excluded which may potentially lower the incidence rate of hematoma expansion.
At present, several clinical indicators related to hematoma expansion have been confirmed, such as consciousness level, blood pressure, and blood glucose[9]. However, the prediction of hematoma expansion by consciousness level is only applicable to patients with mild initial consciousness[9]. Blood pressure and blood glucose are independent predictors of hematoma expansion. Whereas, most patients will undergo antihypertensive and hypoglycemic treatment after admission, the dynamic changes of blood pressure and blood glucose make hematoma expansion prediction impossible.
Many imaging-based methods for deciding hematoma expansion have been proposed, and some studies had found that the spot sign of CTA had a high predictive value for hematoma expansion[11, 12]. Certain studies have shown that the sensitivity of CTA spot sign to hematoma expansion was about 26.2%~73%[10, 13]. In a recent study, the sensitivity of CTA spot sign to predict hematoma expansion was 34.6%[14]. In addition, spot sign often requires patients to undergo brain CTA immediately within the first several hours of onset. It has been shown that the CTA spot sign had the highest sensitivity to predict hematoma expansion if CTA was conducted within 2 hours of onset, while the sensitivity was only 60.0%[17, 32]. CTA is not the priority for diagnosing HICH, and it could be carried out in some areas with insufficient medical resources. Therefore, most HICH patients could not perform CTA within 2 hours after onset and CTA scan increased radiation dose and the injection of contrast agent may lead to allergic reactions and renal damage. These reasons limit the widespread applications of CTA[15, 16]. In another study, Fu et al. performed spectral CTA and explored iodine sign to predict hematoma expansion. The sensitivity of iodine sign to predict hematoma expansion was 91.5%, which was significantly higher than that of spot sign (61.8%) and iodine sign had a higher accuracy (85.7vs75.8%) for hematoma expansion prediction than spot sign[33]. Although the iodine sign had a higher sensitivity and accuracy for hematoma expansion prediction, dual-energy spiral CT is needed and lacks in areas with insufficient medical resources. Therefore, the use of iodine sign to predict hematoma expansion was not applicable in all medical institutions.
More and more scholars started to predict the expansion of hematoma from the perspectives of the density, shape and edge of the hematoma on NCCT scan image[5]. Barras et al.[18] studied the brain CT of 90 HICH patients and found that hematoma heterogeneity could be an independent predictor of hematoma expansion. The more heterogeneous the density was, the more likely the hematoma expansion. However, the definition of hematoma heterogeneity was not clear, the judgment of hematoma heterogeneity was subjective, and the inter-reader agreement was merely moderate[21]. In other several studies, Li proposed to use "black hole sign", "blend sign", and "island sign" to predict hematoma expansion. The study found that the sensitivity of the above three signs to predict hematoma expansion were 31.9%, 39.3% and 44.7%[5, 17, 20]. In addition, in a study of 200 HICH patients, it was found that the sensitivity of black hole sign to predict hematoma expansion was 33.8% which is lower than that (46.5%) of swirl sign. After multivariate analysis, only the black hole sign was an independent predictor of hematoma expansion[34]. In another study, the sensitivity of the black hole sign and blend sign to predict hematoma expansion were 23.1% and 31.7%, respectively. In a study of 307 HICH patients, Deng[31] found that the island sign had higher specificity than the satellite sign in predicting hematoma expansion (98.1% vs 57.9%), and the satellite sign had a higher sensitivity than the island sign (65.6% vs 45.2%). In general, the sensitivity of NCCT scans alone to predict hematoma expansion is relatively low.
In this study, the sensitivity and specificity of AI software in predicting hematoma expansion were 80.0% and 73.6%, respectively, which were significantly higher than the sensitivity (66.7%) and specificity (58.3%) of the doctors using NCCT imaging signs. Prediction accuracy of hematoma expansion is crucial for clinical treatment and in some large randomized controlled trials, the failure to improve patient prognosis by inhibiting hematoma expansion is mainly due to the low accuracy of hematoma expansion prediction[35]. In this study, the accuracy of AI to predict hematoma expansion was 75.5% which was significantly higher than that (60.8%) of the doctors. In addition, the diagnosis time of hematoma expansion is crucial for the treatment[22]. A follow-up brain CT scan is often performed in the clinical workflow within 24 hours after admission and hematoma expansion is diagnosed by comparing the volume change of hematoma of two CT scans. The interval time is long, during which the HICH patients may deteriorate rapidly. In this study, the average interval time of brain CT was 14.5±8.8 (hours), the AI diagnosis time was 2.8±0.3s and the doctor diagnosis time was about 11.7±0.3s. The AI diagnosis time was significantly shorter than those of doctors and the gold standard diagnosis time (p<0.05), AI diagnosis time was shortened by more than 99% and 76.3% compared with the gold standard time and the doctor diagnosis time, respectively. It could be concluded that AI shortens the diagnosis time of hematoma expansion at an early stage while a high sensitivity specificity and accuracy were maintained. In addition, the AI software based on a deep learning is objective and eliminates inter-reader variability, which is helpful for clinical promotion.
In summary, we have externally validated that AI software based on deep learning algorithm could effectively predict hematoma expansion at an early stage from the initial CT scan images of HICH patients after hemorrhage onset. It has a relatively high sensitivity specificity and accuracy could significantly shorten the determination time of hematoma expansion and helps to guide the selection of clinical treatment options. In addition, this method does not rely on CTA scanning and has greater applicability, especially for primary hospitals that lack medical resources and cannot carry out CTA. In addition, this method does not require the injection of contrast agents to avoid adverse reactions caused by contrast agents. The prediction of hematoma expansion by AI software provides a new, accurate, easy to use and fast method for the early prediction of hematoma expansion, which may potentially change the diagnostic process of hematoma expansion.
However, there are several limitations of this study. First, the sample size is relatively small, In the future, the sample size could be expanded, to explore further the prediction efficiency of AI software for hematoma expansion. Secondly, in this study, the gap of experience levels of the two radiologists was minor and the inter-reader prediction difference of the two radiologists was not investigated. Thirdly, the improvement of AI software for doctors’ diagnostic efficacy could be put into future work.