Considering hounsfield units in native CT- scans for diagnosing spondylodiscitis

The significance of native Computer tomography (CT) Scans as an alternative diagnostic tool beside Magnetic Resonance Imaging (MRI) for spondylodiscitis is poor according to the current data. CT Scans are currently reserved to analyze the bony destruction and for settings in which performing an MRI is contraindicated. Therefore, the aim of this study was to investigate, whether spondylodiscitis leads to a significant pattern of the density distribution from the affected vertebral bodies and discs measured by Hounsfield Units (HU) in native CT Scans. Such a parameter would be a useful tool to aid in the early diagnosis of spondylodiscitis using CT.

In a retrospective study we analyzed data from 136 patients, who were treated for spondylodiscitis. Patients who provided MRI- and CT- scans of the spine were included. In axial CT planes HU from the affected intervertebral disc as well as from the affected vertebral bodies and from the unaffected adjacent intervertebral discs and vertebral bodies from the level above and below as reference were measured.

The average measured HU of the affected disc were 26.0% less than in the not affected adjacent discs (p < 0.001). The average measured HU of the affected vertebral bodies were 33.77% higher than in the not affected adjacent vertebral body's (p < 0.001)). These findings are independent from the affected part of the spine (e.g. cervical, thoracic or lumbar) and from the degree of bony destruction according to Eysel-Peters classification.

A reduction in the HU of the affected intervertebral disc by approximately 25% and/or an increase in the HU of the affected vertebral bodies by approximately 30% compared to the adjacent intervertebral discs or vertebrae indicates spondylodiscitis even in the early stages without destruction and regardless of the location.