Midline Levels Analysis (Grayson)
The Midline Levels analysis follows the multiplane cephalometric method described by Dr. Barry H. Grayson and colleagues in the early 1980s. Its premise is that a face does not have one midline but many: at each depth and each level of the craniofacial skeleton, the local midline can be reconstructed from the paired structures at that level, and in an asymmetric patient those local midlines do not stack up into a single straight vertical plane.
Instead of a flat midsagittal plane, the stacked midpoints describe what Grayson called a warped midsagittal "plane" — a surface that bends toward the affected side wherever the asymmetry is located. This makes the method a localization tool rather than a scoring tool: it does not just say how asymmetric a face is, it says at which level of the skeleton the midline first departs from centre. It was developed for the assessment of severe congenital and acquired asymmetries such as hemifacial microsomia (underdevelopment of one side of the face) and unilateral condylar hyperplasia (overgrowth of one jaw joint), and remains useful for any case where the origin of an asymmetry is not obvious.
What It Evaluates
The analysis is entirely self-referential — the norm at every level is that the local midpoint lies on the reference midline, i.e. an offset of zero. No population data, age, or sex adjustment is involved.
A single vertical reference is established from the orbital region: a horizontal line between the left and right latero-orbitale points (the outer border of each eye socket), with the mid-sagittal reference erected perpendicular to it through its midpoint. Then, at each of several levels down the face, the left and right members of a paired landmark are bisected and the resulting midpoint is measured against that reference. Reading the offsets from top to bottom shows the profile of the warp.
Learn more: Analysis of Craniofacial Asymmetry by Multiplane Cephalometry — PubMed
Key Measurements
Each level contributes one value: the signed distance from the bisected midpoint of that level's paired landmarks to the mid-sagittal reference. The norm at every level is 0 mm, and the sign indicates the side toward which that level of the skeleton is displaced.
- Zygomaticofrontal level — midpoint of the left and right zygomaticofrontal sutures, where the cheekbone meets the frontal bone. The most superior and most growth-stable level; an offset here points to an asymmetry originating in the cranial base or upper midface.
- Zygomatic arch level — midpoint of the left and right zygion points (the widest point of each cheekbone), describing the midface.
- Maxillary level — midpoint of the left and right jugale points, where each side of the upper jaw meets the cheekbone. Describes the skeletal midline of the maxilla.
- Mandibular body level — midpoint of the left and right antegonial notches, describing the midline of the body of the lower jaw.
- Mandibular ramus level — midpoint of the left and right gonion points (the jaw corners), describing the midline at the level of the ascending branches of the mandible.
The orbital level itself is not reported as a variable, since its midpoint defines the reference and therefore lies on it by construction.
Learn more: Basilar Multiplane Cephalometric Analysis — PubMed
Clinical Interpretation
The values are read as a vertical profile, top to bottom, and two patterns matter most. In the first, the offsets are near zero at the upper levels and grow progressively larger toward the mandible: the asymmetry is acquired lower down, in the maxilla or mandible, and the upper face provides a symmetric foundation to correct against. This is the more favourable pattern, and the level at which the offset first becomes significant marks the upper boundary of the region needing treatment. In the second pattern, the offsets are already substantial at the zygomaticofrontal or zygomatic level: the asymmetry is inherited from above, the lower jaw is following an asymmetric base, and correcting only the mandible would leave the face unbalanced — a finding that reframes both the surgical plan and the conversation about realistic outcomes.
A third and more informative case is a genuine warp: midpoints falling on opposite sides of the reference at different depths. This indicates a rotational component rather than a simple lateral shift, meaning the face is twisted around a vertical axis rather than displaced along a horizontal one, and it typically signals compensatory growth — one region drifting to counteract a deficiency elsewhere. This is exactly what the method was designed to surface, and it is not detectable from a single midline measurement at chin level.
One limitation is worth stating. Grayson's complete method combines the frontal cephalogram with a basilar (submentovertex) radiograph, which adds the front-to-back dimension and allows the true three-dimensional warped plane to be reconstructed. On a frontal film alone, the analysis maps the midline across vertical levels but not across anterior-posterior depth, so the vertical profile of the warp is available while its depth component is not. As with all frontal cephalometry, reproducible head positioning at exposure is a precondition for trusting the values, since head rotation shifts paired landmarks unequally.
Learn more: Hemifacial Microsomia — StatPearls, NCBI Bookshelf