Perilymphatic fistula (PLF) is a breach in a labyrinthine window. The opening might decrease the radiological density of the window. To evaluate the radiological density of the labyrinthine windows by virtual endoscopy on CT scan. This prospective study included 47 adult patients with PLF and 98 control patients. Diagnosis of PLF was based on a composite radio clinical score and/or intra operative visualization of the fistula and/or resolution of the symptoms after surgery. On routine CT-scan, labyrinthine windows were examined by virtual endoscopy. The reconstruction threshold was gradually increased until a virtual opening appeared (opening threshold [OT]) and compared to the contralateral window (OT difference). The OT difference was higher in patients than in controls (60.2 ± 10.36 (SEM),  = 47 28.0 ± 2.29 Hounsfield units (HUs),  = 98,  < .01 unpaired -test). A ROC analysis showed that at an OT difference of 31.5 UH had a sensitivity of 75% and a specificity of 75% for the PLF diagnosis. CT-scan virtual endoscopy and threshold variation provided high specificity and sensitivity in the PLF diagnosis. This post processing of radiological data appears to enhance the diagnostic value of CT scan.