The Radboud University Medical Center is a level I trauma center and approximately 400 multiple trauma patients with an Injury Severity Score (ISS) of more than 16 are admitted annually. All adult patients with a traumatic ASDH between April 2009 and April 2013 whom were offered neurosurgical treatment (evacuation hematoma) were included. The data of patients including concomitant diseases, presence of hemorrhagic diathesis and ISS, as well as the CT scans at admission were retrospectively retrieved from an electronic hospital database.
All patients were offered standard maximal intensive care treatment including ICP monitoring, hyperosmolar treatment, sedation, induced hypothermia, and decompressive surgery (evacuation of the hematoma without replacement of the bone flap except when then brain was very swollen, removal of the bone flap was considered when the intracranial pressure raised irrespective of conservative methods).
Two blinded observers (RB, FM) evaluated twice, with one month interval, head CT scans which were part of the patient’s electronic database. Measurements of MLS and the thickness of the hematoma were obtained at the level of the frontal horns using the following protocol: on the initial CT scan (viewer: Agfa Impax version 6.4, Ortsel, Belgium), MLS was measured at the level of the frontal horns using standard window widths (WW) and window levels (WL) to evaluate brain parenchyma (WW 86, WL 30). MLS was defined as the displacement of the septum pellucidum in relation to the midline in millimeters . The subdural hematoma was evaluated with adjusted WW and WL to minimize underestimation of hematoma thickness (WW 300, WL 120). The reason for choosing this method was that after preliminary review of some CT scans, the TH could reliably be established, and more importantly the midline could clearly be defined (Fig. 1). The level of the frontal horns was used for the measurement of the TH since, in our opinion, the impact on the brain will be expressed by a MLS exceeding the TH at the same level. Furthermore it will reduce inter-rater variability. The observers were blinded to the final outcome.
The difference between the MLS and the thickness of the hematoma was expressed in millimeters (mm). Then 1 mm, 2 mm and 3 mm respectively were added to the actual thickness of the hematoma, and the difference with the MLS for each new situation obtained.
So, at the end four differences were compared, the actual difference: MLS minus thickness of the hematoma, and three in which 1 mm, 2 mm and 3 mm respectively were added to the thickness of the hematoma. The difference was expressed as a nominal value (MLS more than thickness hematoma or not), and correlated with clinical outcome.
The work described has been carried out in accordance with The Code of Ethics of the World Medical Association (Declaration of Helsinki) for experiments involving humans. The study has been approved by the institutional review board CMO Arnhem - Nijmegen (IRB). The IRB waived informed consent due to the nature of the investigations.
For statistical analysis SPPS 20 (Armonk, NY, USA: IBM Corp) was used. For intra – and interobserver reliability Cohen’s kappa’s coefficient was used. The kappa’s coefficient was graded as follows: below 0.20, poor agreement; between 0.21 and 0.4, fair agreement; between 0.41 and 0.60 moderate agreement, between 0.61 and 0.80 good agreement; and > 0.80 perfect agreement . For correlation between outcome expressed as survivor or non – survivor and the difference between MLS and TH, Cramer’s V coefficient was used. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated as were the respective 95 % confidence intervals (95 % CI). For comparison of categorical data the Chi square test was used, and for independent numerical data the independent student-t test. Statistical significance was assumed for p <0.05. Data are represented as mean ± standard deviation (range) or as median (total range) depending on the distribution of the data. This study conforms to the Strengthening the Reporting of Observational studies in Epidemiology (STROBE) guidelines.