Table 1.
Exclusion criteria for our patient selection.
Fig 1.
CT scan neck sagittal section (a) showing how glottic anatomy was studied in two axial planes, non-parallel, NPVC ①and parallel to vocal cord PVC ②. Scout CT (c) is showing predefined non-parallel CT scan lines and reformatted CT scan (b) showing PVC reformation lines in sagittal. Qualitative and quantitative parameters of glottis noted in both ① and ②. Dotted oval = cricoarytenoid joint (a,1,2), o = angulation between two planes (a), TVC = true vocal cord, red lumen trace = Cross-sectional area, dotted white lines = anteroposterior and transverse dimensions, double arrow line = anterior commisure, yellow dots = region of vocal cord width measurement.
Fig 2.
CT neck sagittal section (a) and its 3D volumetric reconstruction (b) showing how anterior neck length was measured (double arrow line).
Fig 3.
Flowchart summarising patient selection in this study.
CECT = contrast enhanced CT scan.
Fig 4.
Sagittal post-contrast CT scan neck (a-c) showing two axial CT scan plane lines, non-parallel① and parallel to vocal cord ② intersecting at level of cricoarytenoid joint (dotted circle). Altered glottic parameters in plane① (1a-1c) are shown i.e., change in glottic lumen shape from tear (t) to mushroom (m), oval (o) and round (r), open and close thyroid laminae (yellow and blue arrowheads), inclusion of submental triangle (SMT, horizontal double head arrows) and adipose tissue (red arrows). Crossing of two axial planes (①,②) through cervical vertebrae (4,5,6) are also shown. Parallel plane② CT scans are also displayed for comparison (2a-2c).
Fig 5.
Axial (a) and sagittal (b) post-contrast CT neck showing glottis in non-parallel plane①. Split appearance of thyroid laminae (TL) shown by cross linking (+) this gap in a, b and 3D CT volumetric neck reconstruction. It is in actual a thyroid notch (c). Adipose tissue (red arrow), cricoarytenoid joint (dotted oval) and oblique crossing of plane① through vertebrae (5, 6) are also shown.
Table 2.
Comparison of glottic appearance on CT scan in plane, non-parallel and parallel to vocal cord (n = 95).
Table 3.
Area under curve (AUC) values of qualitative parameters of glottis.
Fig 6.
Bar chart illustrating percentages of cases in non-parallel plane① CT scan having higher values of glottic measurements.
ACom = anterior commissure, VCw = vocal cord width, Tr = transverse width, AP = anteroposterior, dimen. = dimension, () = no.of patients.
Table 4.
Comparison of glottic dimensions in plane non-parallel and parallel to vocal cord.
Table 5.
Ranges of vocal cord and glottic dimensions with minimum (min) and maximum (max) differences among these parameters.
Fig 7.
Scatter plot (a, b) showing negative correlation of anterior neck length (aNL) with Body mass index (BMI) and angle (°) between two CT planes (or cord angle).
Fig 8.
Diagrammatic representation of a larynx showing position of vocal cord (VC) in relation to cervical vertebrae (CV).
Details about specific location of VC at each vertebral level is also tabulated.
Fig 9.
Post-contrast CT neck showing mushroom (m) shape of glottic lumen in non-parallel vocal cord (NPVC) plane① due to crossing of plane① (a) through laryngeal ventricle (+, a, b) rather than a true vocal cord. Left laryngeal ventricle is marked by + sign.
Table 6.
Tabulated representation to show influence of angle between PVC and NPVC planes (deviation angle from true plane) on 5 parameters of glottic anatomy.
Fig 10.
3D CT volumetric neck reconstruction of short versus long neck (a, b) along with comparison of their necks on sagittal and axial CT scans.
Obliquity of non-parallel vocal cord (NPVC) plane (o) and variation of plane crossing vertebrae are shown in sagittal sections indicating more in short neck. Visualisation of structures which are not part of glottis are seen more in short neck (1a) than long neck (1b). Different shapes (round, r/oval, 0) affect quantitative parameters as well.
Table 7.
Checklist of qualitative features (at glottic level), which if present identifies pseudoglottic level due to non-parallel vocal cord plane.
Table 8.
Possible pitfalls which can be encountered when interpreting images of larynx in non-parallel CT larynx plane.
Table 9.
Points need to be remembered by radiologist and laryngeal surgeons while interpreting laryngeal CT.