Differential diagnosis of skull base osteomyelitis from malignancies focusing on the radiological features on HRCT

OBJECTIVE: Skull base osteomyelitis (SBO) is a rare but life-threatening inflammatory disease often misdiagnosed as a malignancy, such as nasopharyngeal carcinoma (NPC) and external auditory canal cancer (EACC), due to extensive bone destruction. This study aimed to identify the radiological features of SBO using high-resolution CT, which could help in the differential diagnosis of malignancies. METHODS: High-resolution CT findings of 14 patients with SBO, 25 with NPC, and 19 with EACC were retrospectively reviewed. Abnormal findings at seven sites: 1) external auditory canal, 2) mastoid portion, 3) petrous portion of the temporal bone, 4) clivus, 5) jugular foramen, 6) nasopharyngeal soft tissue thickness, and 7) torus tubarius shape were compared among the patient groups on axial slice of HRCT. RESULTS: When comparing SBO and NPC, there were significant differences in sites 1) (p = 0.0001), 3) (p = 0.0064), 5), and 7) (p < 0.0001); among them, the most specific finding was the site 7). When comparing SBO and EACC, there were significant differences in sites 1) (p = 0.0084), 3) (p < 0.0001), 4) (p = 0.0013), 5) (p = 0.0015), and 6) (p < 0.0001); among them, the most specific finding was cortical bone destruction in site 3). CONCLUSION: Our findings indicated that the bilateral preservation of "μ-shape sign" in the torus tubarius and bone destruction in the petrous portion on HRCT were the most specific signs differentiating SBO from NPC and EACC, respectively. Knowledge of these features can contribute to prompt diagnosis and treatment of SBO.