Conventional endoscopy, an invasive procedure for most surgeons, remains the gold standard for the identification and characterization of airway lesions of any size . Endoscopy, however, may fail to provide sufficient information when the lesion is completely obstructing trachea, thus making it impossible to assess distal segments. Also, conventional endoscopy in some patients is impossible to perform or to finish, because of the presence of severe bleeding following a biopsy attempt, or because of some concomitant conditions (advanced age, tracheomalacia, etc.) . In addition, it is an uncomfortable, poorly tolerated procedure that requires local sedation [7, 8, 12, 13] and is associated with a 0.8% morbidity [7, 15, 18].
The present study demonstrated the high diagnostic accuracy, sensitivity, and specificity of virtual endoscopy. Finkelstein et al.  found that VE had a sensitivity of 100% for the detection of obstructive lesions. Shitrit et al.  found the evaluation of bronchial stenosis by VE to be highly correlated not only with FT, as reported previously, but also with pulmonary function test. Hoppe et al.  demonstrated that virtual endoscopy images, axial CT images alone, and multiplanar reformatted images were found to be highly accurate (VE images, 98%; axial CT slices and reformatted coronal images, 96%; reformatted sagittal images, 96.5%) in the depiction of tracheobronchial stenosis. Taha et al.  evaluated the usefulness and accuracy of spiral CT in detection and assessment of post-intubation tracheal stenosis. The sensitivity and specificity of both CT and tracheobronchoscopy in the detection of subglottic stenosis was 100%.
Virtual endoscopy is not operator dependent , and reports have demonstrated a 63–100% sensitivity and a 61–99% specificity for this method for the identification of central stenosis [4, 7, 11, 12]. Nevertheless, virtual examinations to date are unable to replace conventional imaging because of several intrinsic limitations. These include the inability to perform biopsies for histological assessment [5, 7, 12] and to provide distinction in color or texture between normal mucosa and pathological tissue [4, 14, 18].
A major advantage of VE when compared with FT is its noninvasiveness; the method can be used in patients who are not able to undergo or whose parents refuse conventional endoscopy. Furthermore, VE can depict passage through high-grade stenoses, which enables evaluation of the poststenotic airway segments . Finally, VE can be complementary to FT in the interventional setting, including stent implantation or tracheotomy. Disadvantages of VE include the inability to perform biopsies and therapeutic maneuvers and that color representation of mucosal surface in VT is artificial.
In the present study, negative predictive value (NPV) was low there were five false-negative findings with MPR reconstruction and only two with VE (patients with tracheobronchomalacia and normal findings at multidetector CT with VT). Similar results were reported by Heyer et al. . Heyer et al.  reported that NPV was low; there were five false-negative findings with multidetector CT with VE (patients with tracheobronchomalacia and normal findings at multidetector CT with VE). This can be explained by the fact that tracheomalacia and bronchomalacia do not account for fixed narrowing and therefore can be reliably diagnosed only with functional studies. On the other hand Sun et al.  had 11.1% false results and 92% stenosis detection rate.
The present study demonstrated that VE which when integrated with MPR images, provided data for the detailed information of tracheal stenosis like grading, stenosis length, length from vocal cord and length of planned resection segment of the trachea before treatment. Thus information can be helpful for the planned treatment. Taha et al.  evaluated the usefulness and accuracy of spiral CT in detection and assessment of post-intubation tracheal stenosis. The results were compared with the intra-operative findings. They reported that detection rate for tracheal stenotic lesions was 94% by CT and 88% by rigid bronchoscopy. The preoperative assessment of the length of stenosis was accurate in 87% of the stenotic segments detected by CT and in 73% of the segments detected by bronchoscopy. The length of stenosis as assessed intra-operatively significantly correlated with the data obtained from CT examination (r = 0.98, p < 0.001) and rigid tracheobronchoscopy (r = 0.94, p < 0.001). The grade of stenosis was correctly assessed by bronchoscopy in 86% of patients.
The problem is when the stenosis can lead to progressive, often debilitating airflow obstruction that may be difficult to clinically differentiate from other causes of airflow limitation . The correct diagnosis is important because, in most cases, the stenosis can be successfully treated with laser or by dilation and stent placement . FT is the current standard for diagnosis of anastomotic complications, including stenosis . However, it is invasive and may not be well tolerated. FT also provides only limited information on the length of the stenosis or the patency of the distal airways, which are important factors in planning treatment . Nevertheless, VE may provide important diagnostic and potentially therapeutic information before FT is undertaken. It can also be used to evaluate patients with known tracheobronchial stenosis after treatment and may thereby reduce the frequency of repeated invasive FT performed for that purpose.
The 3D reconstruction software allows the user to navigate through the tracheobronchial tree  with same endoluminal perspective as conventional endoscopy [19, 24]. The virtual endoscopy images are displayed on the monitor alongside the multiplanar CT axial, sagittal and coronal oblique reference sections, on which the position and direction of the “virtual” bronchoscope is marked with a cursor. This makes it possible to explore the tracheobronchial tree from the inside by moving the cursor on the reference CT sections or by “navigating” the airway with a kind of “virtual airplane”, with which direction and speed are controlled manually . Some authors claimed that the information provided by spiral CT scan with MPR and VE may be considered as a substitute to direct endoscopic examination [1, 16].
This policy can minimize patient morbidity and spare them an extra anesthetic for evaluation. VE in multiview mode may also substitute conventional bronchoscopy in the follow-up of patients after endobronchial procedures in cases where the monitoring of changes in stenosis degree is important and successive bronchoscopy are unpleasant for the patient [1, 11]. In the view of these findings, MPR and VE can be proposed as preliminary investigation to accurately characterize stenotic lesions, shorten conventional endoscopy time, and plan the most appropriate therapy.
In conclusion, the results of our study indicate that VE is an excellent, consistent and objective technique. VE with MPR is very useful in diagnostic evaluation and treatment planning in patients with tracheal stenosis.