Usage of Hounsffeld unit to differentiate idiopathic condylar resorption: a preliminary study

The Hounsfield unit (HU) is a quantitative scale used to describe radiodensity in computed tomography (CT) scans. Since idiopathic condylar resorption (ICR) and temporomandibular joint osteoarthritis (TMJOA) involve destruction of bone and cartilage in the mandibular condyle, we hypothesized that HU values might be used to differentiate between the two conditions. This study aimed to evaluate the usefulness of HU values in the differential diagnosis of ICR and TMJOA.

Twelve TMJOA and 9 ICR patients, and 11 healthy subjects were recruited as the TMJOA, ICR, and control groups, respectively. CT scans were performed, and HU values were measured in the region of interest (ROI) with 5 mm thickness along the Z-axis from superior condylar surfaces. HU distributions were then analyzed for each ROI.

Control and TMJOA patients were significantly older than those in the ICR group. Median HU values of the mandibular condyle did not differ significantly among the three groups. All groups showed a unimodal HU distribution peaking at 250-450 HU, while ICR condyles exhibited a tendency to have an additional peak at 1350-1500 HU. Compared to the control group, the HU distribution of the TMJOA and ICR condyles was significantly lower at 250-450 HU. After age adjustment, significant intergroup differences in the voxel ratio were noted at each HU level at 250-300, 300-350, 400-450, 1400-1450, and 1800-1850 HU. However, no significant differences in HU values were observed between the ICR and TMJOA groups.

HU values and distributions of the mandibular condyle may be used to differentiate between the control group and the ICR and TMJOA groups. Further studies with a sufficient sample size are needed to confirm whether HU values and distribution could become important indicators for distinguishing between the TMJOA and ICR condyles.