Variability of morphology and signal intensity of alar ligaments in healthy volunteers using MR imaging

Abstract

Background and purpose: Evaluation of alar traumatic injuries by using MR imaging is frequently performed. This study investigates the variability of morphology and signal intensity of alar ligaments in healthy volunteers so that pathology can be more accurately defined.

Materials and methods: Fifty healthy volunteers were examined on a 1.5T MR imaging scanner with 2-mm PD-weighted sequences in 3 planes. Delineation of the alar ligaments in 3 planes and signal-intensity characteristics on sagittal planes were analyzed by using a 4-point grading scale. Variability of courses and morphologic characteristics were described.

Results: Delineation of alar ligaments was best viewed in the coronal plane, followed by the sagittal and axial planes. In the sagittal view, 6.5% of alar ligaments appeared homogeneously dark. Hyperintense signal intensity in up to one-third of the cross-sectional area was present in 33% of cases; in up to two-thirds of the cross-sectional area, in 45% of cases; and in more than two-thirds of the cross-sectional area, in 15% of cases. Of alar ligaments, 58.5% ascended laterally, 40.5% ran horizontally, and 1% descended laterally. The cross-sectional area was round in 41.5%, oval in 51.5%, and winglike in 6.5%.

Conclusions: On 1.5T MR imaging, the alar ligaments can be delineated best in the coronal and sagittal planes. Our data indicate a remarkable variability of morphology and course as well as signal intensity. This finding is contradictory to former publications assigning such alterations exclusively to patients with trauma.

Fig 1.

Proton attenuation−weighted MR images of alar ligaments (arrows) in the coronal plane demonstrate the variations in the course of the ligaments. Laterally ascending (A), lateral (B), and laterally descending (C) orientations of the alar ligament are shown.

Fig 2.

PD−weighted MR images of alar ligaments (black arrows) demonstrate their different orientations in the axial plane. Straight lateral (A) and posterolateral (B) orientations of the alar ligament are shown.

Fig 3.

PD−weighted MR images of 3 alar ligaments (arrows) in the sagittal plane demonstrate the 3 different shapes in cross-section. A, Round ligament. B, Ovoid ligament. C, Winglike ligament.

Fig 4.

Three examples of grades of delineation and signal intensity of alar ligaments. A and B, PD−weighted MR images of 3 alar ligaments in the sagittal (A) and coronal (B) planes. The dashed lines in B1–3 indicate the orientation of the respective sagittal sections in A1–3. In A1, the alar ligament shows a good delineation (grade 3) and low signal intensity (grade 0). A2 is classified as grade 2 for signal intensity (high signal intensity in one-third to two-thirds of the cross-section) and delineation (moderate). In A3, the alar ligament is hardly definable (grade 1), with high signal intensity throughout the cross-section (grade 3).