Objective To summarize the clinical features, neuroimaging findings and pathological characteristics of 45 patients with tumefactive demyelinating lesion (TDL) confirmed by histopathalogy for better diagnosis and differential diagnosis.Methods The clinical features, neuroimaging findings and pathological characteristics of 45 patients (male 24,female 21) with histologically proved TDL (43-case brain-type and 2-case spinal cord-type) were retrospectively reviewed.Results The mean onset age was 34.6±12.7 (6~69) years.40 cases had good prognosis with with the median followed-up duration of 38 months.2 patients were respectively died of post-operative complication and pulmonary infection and the remianing 3 patients were lost to followed up.The TDL patients almost showed monophasic clinical setting.Headache, indifference accompanied with hypomnesis were the most common initial symptoms.The positive or abnormolity rate of cerebrospinal fluid oligoclonal bands (OCB) and myelin basic protein (MBP) in TDL patients were high.34 patients with CT unenhanced scanning showed hypodense lesions.Long TlWI and long T2WI intensity were showed on MRI and most cases apeared round-like lesion in shape.Acccording to the shape of enhancement of the 41 patients performed with contrast agents, 27 cases were shown with open-ring enhancement, 5 cases (including 3 cases accompanied with open-ring enhancement) with complete rim enhancement, 3 cases with asymmetrical dotted enhancement, 3 cases with diffused even enhancement, and no enhancement was seen in the other 6 cases.Furthermore, 29 cases with DWI and 22 with FLAIR all appeared hyperdensity.The typical pathological changes were demyelinating, perivascular inflammatory cells infiltration and reactive gliosis, occationally, the Creutzfeuldt cells were also found in brain tissue of some patients.Conclusions TDL was a distinct demyelinating disease entity.In spite of being apt to be confused with the neoplasm in brain and spinal cord.TDL had self-features, for example, OCB was freqently positive in patients with TDL and the level of MBP may be significantly increased.Furthermore, the involvements of bilateral and multi-lesions were most common in TDL, and most cases showed open-ring enhancement or complete rim enhancement on MRI.In addition, all cases showed with hypodense lesions on unenhanced CT and patients with hyperdense seemed not to allow for TDL.