Table 2. HRCT- and MRI-based staging system of otogenic skull base osteomyelitis.

Stage	Disease extent (cortical bone destruction on HRCT or low signal intensity of bone marrow on T1WI MRI)		Diagnosis
	Petrous portion of temporal bone	Clivus
1	+	–	Mild SBO
2	+	Less than half	Moderate SBO
3	+	Exceeding the midline	Severe SBO
4	+	Whole	Very severe SBO

Abbreviations: HRCT, high resolution computed tomography; MRI, magnetic resonance imaging; SBO, skull base osteomyelitis; T1WI, T1-weighted image.

Note: Central SBO lacks a temporal bone lesion, but this staging system can also be clinically applied to the central SBO by disease extent in the clivus.