Objective:To evaluate the diagnosis value of CT scan for skull base chordoma.Methods:422 patients with suspected skull base chordomas were enrolled in this study.They all received CT examination.Double-blind rule was used for film-reading.Diagnosis gold standard was set as pathologic findings or long-term follow-up results.We use specificity

sensitivity

rate of misdiagnosis and missed diagnosis rate positive predictive value and negative predictive value to evaluate the diagnostic value.Results:There were 39 chordoma patients

diagnosed by gold standard

in 422 enrolled patients(9.2%).Sensitivity was 0.795(31/39)

95% CI was [0.635-0.907];the specificity was 0.992(380/383)

95% CI was [0.977-0.998];misdiagnosis rate was 0.008(3/383);misdiagnosis rate of 0.205(8/39);positive predictive value was 0.912(31/34);negative predictive value was 0.979(380/388);diagnostic accuracy rate was 0.974(411/422).CT scans for chordoma were divided into four types:saddle type

slope type

middle cranial fossa type and nasopharyngeal type.Saddle-type was the most common one

accounting for 51.6%

Tumors were oval and irregular fractal.Tumors were high-low density mixed

both calcification.The most common cause of misdiagnosis and missed diagnosis were skull base meningiomas and neurogenic tumors.Conclusion:① There were nearly 10% of patients with chordoma in patients who had clinical manifestations of "decreased visual acuity

headache

dysphagia".② CT diagnosis of the skull base chordoma has a high specific

medium sensitivity;the reduced sensitivity mainly caused by is low incidence of skull base chordomas

and not taken into account while reading the CT.③ The most common cause of misdiagnosis and missed diagnosis for CT diagnosis of skull base chordomas were skull base meningiomas and neurogenic tumors.