Chronic subdural hematoma (CSDH) is one of the most common neurosurgical disorders [1]. CSDH incidence is increasing due to the aging global population [2]. A single burr hole craniostomy, intraoperative irrigation, and subsequent subdural drain placement are used as consecutive surgical treatments for CSDH [1], [3], [4]. However, reaccumulating CSDH or reoperation after initial surgery occurs in approximately 1.3–13.8 % of patients following proper treatment [1], [3], [4], [5], [6], [7], [8], [9].

Computed tomography (CT) is the mainstay diagnostic method for CSDH [1], and the CT scan characteristics of CSDH continue to attract much attention from researchers for predicting CSDH recurrence after surgery. In recent years, there has been an increase in interest in developing various clinical scoring systems for predicting recurrence following the evacuation of CSDH [10], [11], [12], [13], [14], [15], [16]. Interestingly, most of these reports revealed that preoperative and/or postoperative hematoma/cavity volumes were significant predictive variables for CSDH recurrence. Furthermore, several cohort studies suggested an association between hematoma volumetric analysis and CSDH recurrence rate [13], [17], [18], [19], [20]. Thus, hematoma volumetric analysis plays a pivotal role in predicting CSDH recurrence.

However, of particular concern is the methodology of hematoma volumetric analysis. For instance, Stanišić et al. [17] reported that both preoperative hematoma volume (pre-HV) and postoperative cavity volume were significant predictive factors for recurrence using the software tool BrainVoyager QX 2.0 (Brain Innovation). In contrast, Ridwan et al. [19] showed that postoperative HV was the strongest predictor of recurrence using the computer software iplanNet (Brainlab AG). However, it is unclear how the difference in measuring the hematoma/cavity volumes can impact the predictive function for CSDH recurrence. Moreover, volumetric measurements are vexatious, and the development of a simpler predictive method is needed.

Measuring hematoma thickness (HT) and midline shift (MLS) are fascinating alternative length variables for predicting CSDH recurrence. These can be easily measured without using any specific software. In their meta-analysis, Miah et al. [21] reported that HT and MLS were associated with CSDH recurrence. The two clinical scoring systems described above also showed that preoperative HT (pre-HT) and MLS (pre-MLS) were significant predictors for recurrence [12], [16]. However, most studies related to developing predictive systems have focused on creating more accurate predictive models that combine various variables. Currently, there has been little discussion on the possibility of constructing a prediction system without hematoma volumetric analysis. A previous study has shown a correlation between intra-hematoma pressure and MLS [22], but no previous study has investigated the possibility of creating a predictive model using alternative length variables, such as pre-HT, pre-MLS, postoperative cavity thickness, and postoperative MLS, particularly in unilateral CSDH. This study aimed to develop and validate a new predictive model for unilateral CSDH recurrence based on the previous model developed by Stanišic et al. [10].