PURPOSE: To determine the value of bilobate anterior epidrual extension(AEE) on MRI in differential diagnosis of tuberculous spondylitis, pyogenic spondylitis and malignant tumor. MATERIALS AND METHODS: SE TI-,T2- and Gd-DTPA enhanced Tl-weighted, sagittal and axial MR images of 39 patients(40 vertebral lesions), including 16 tuberculous spondylitis, 7 pyogenic spondylitis(8 lesions, consisting of 2 separate lesion of 1 patient), and 16 malignant vertebral tumors(15 metastases,1 lymphoma) with an AEE were reviewed. The frequency of bilobate AEE shown as double-convexity in the anterior epidural space on axial scans was evaluated in the above vertebral diseases. RESULTS: The bilobate AEE on the axial scans was seen in 12 out of the 16 tuberculous spondytitis(75%) and 1 out of 8 pyogenic spondylitis(13%), and 10 out of the 16 malignant tumor including 15 metastasis and 1 lymphoma(63%). CONCLUSION: The bilobate' ^EE of vertebral lesions is suggestive of tuberculous spondylitis or malignant tumor rather than pyogenic spondylitis. This pattern seems to be related with the preservation of the structures, including midline septurn, F~LL(Posterior longitudinal ligament), lateral membrane and fibrous membrane, limiting and surrounding the extension of the tuberculous spondylitis and malignant tumor, and with the early penetration or disruption of PLL, midline septurn, lateral & fibrous membranes in the pyogenic spondylitis.