Moderate and severe traumatic brain injury: A descriptive report of how the Abbreviated Injury Scale dictionary assesses traumatic axonal injury in relation to early clinical MRI findings

Background: This is a large prospective study of patients with moderate-severe traumatic brain injury (TBI) examined with early MRI. The primary aim was to assess how traumatic axonal injury (TAI) is coded in practice with Abbreviated Injury Scale (AIS), and examine the association between AIS head severity scores and TAI grade diagnosed with clinical MRI. As a secondary aim, we wanted to assess the number of patients eligible to receive a TAI code in AIS with respect to the original criteria in the AIS 2005 Dictionary. Materials and method: 274 patients with moderate (n = 136) or severe (n = 138) TBI (aged 8 – 69 years) admitted to St. Olav’s Hospital (Trondheim University Hospital) and with clinical MRI within six weeks (median 9 days) were included in this study. Main MRI sequences for assessing TAI were FLAIR, DWI and T2*GRE/SWI. TAI codes in AIS were reported using a modified AIS TAI coding practice. MRI findings and TAI grade were given by consultants in radiology. Eligibility for TAI codes with respect to original AIS criteria were analysed retrospectively. Results: 116 (42 %) patients received a TAI code with the use of modified AIS TAI coding, while 223 (81%) patients had TAI lesions on clinical MRI. Ultimately, AIS scoring left 108 (39%) patients without a TAI code, despite TAI lesions on clinical MRI. 51 (19%) patients were not assigned a TAI code despite having TAI grade 2 or 3 on clinical MRI. When analysing the data material retrospectively, only four (1%) patients met the original AIS criteria to be eligible for a TAI code. Conclusion: There is a large inconsistency between the current AIS coding practices for traumatic axonal injury and actual findings observed on MRI. An updated AIS coding practice for traumatic axonal injury reliant on imaging findings, in particular findings on MRI, seem warranted.