Abstract
Objectives
The aim of this study was to create an evidence-based three-dimensional cephalometric analysis of orbits in order to perform time-efficient measurements of postoperative orbital morphology changes.
Materials and Methods
The authors used 23 (11 bilateral and 1 unilateral) anatomical landmarks. Based on these, 6 planes, 12 angular and 16 linear measurements were determined. A three dimensional analysis was performed twice by two observers on pre and post-operative computed tomography scans of six patients who had undergone midface advancement. The mean, minimal and maximal difference, as well as standard deviation (SD) and intraclass correlation coefficient (ICC) for the inter- and intra-observer landmark selection reliability were calculated. Additionally, the mean, minimal, maximal difference and standard deviation between pre- and post-operative angular and linear measurements were calculated to examine a connection between the established measurements and any morphological change.
Results
The inter and intra-examiner accuracy of all landmarks for three axes was >0.9 ICC. Despite excellent inter and intra-examiner agreement (<2.49 mm ± 2.05 mm SD) for the landmark selection, linear and angular measurements showed a mismatch, the mean SD for angular measurements was found to be 8.2° and the linear 3.04 mm.
Discussion
The possible causes of linear and angular measurement discrepancies are discussed and the future direction for the development of three-dimensional cephalometric analysis of orbits proposed.
Keywords: Skull, Morphology, Dimensional measurement accuracy, Imaging, Reproducibility of results, Cephalometry
Introduction
Midface hypoplasia is a morphological anomaly characterized by a withdrawn upper lip and seemingly forward protruding chin rather than when compared to a retruded midface. Shorter maxillary bones result in a reduction of orbital depth, which can cause exophthalmos. In addition, morphology of the sphenoid bone is deranged, sphenoid angel of divergence measured between the greater wings is more obtuse and pterygoid plates are posteriorly rotated. The sagittal dimension of anterior cranial fossa are also shorter, though despite these morphological changes, there is no volumetric deficiency [1].
Midface hypoplasia can occur self-reliant or as a component of complex syndromic defects such as: Apert, Cruzon or Pferiffer syndrome. A severe form of midface hypoplasia is associated with ocular and respiratory complications [2, 3]. It is caused by reduced nasopharyngeal, velopharyngeal and orbital volume [4].
The current gold standard is surgical treatment in the form of LeFort III monoblock advancement or distraction osteogenesis after a LeFort III osteotomy [2, 3, 5]. Forward displacement of the bony block after the LeFort III osteotomy results in an enlargement of orbital and airway volume [4, 6]. However, there is no specified minimum range of midface advancement which can prevent the occurrence of further complications. This may arise from difficulties in the collection of a sufficiently large study group or the fact that the calculation of orbital or pharyngeal volume change is rarely performed due to the time consuming nature of procedures. In this study we wish to propose a more practical approach based on three-dimensional cephalometry. Our aim was to create an evidence-based three-dimensional cephalometric analysis of the orbits in order to perform no time-consuming orbital morphology change measurements.
Materials and Methods
The study was based on 6 male patients (mean age 10.8 ± 4) suffering from severe midface hypoplasia associated with one of the syndromes: Cruzon, Apert, Binder, Tyabi-Rubinstein, Pfeiffer and Marshall-Stickler. All patients underwent midface advancement following a Le Fort III osteotomy by the same surgeon using rigid external distractors (RED, KLS Martin, Tuttlingen, Germany). After consent from the local ethics committee (no 27/2013/V) was obtained, pre and post-operative computed tomography (CT) scans were collected. All CT scans were carried out using a BrightSpeed Elite scanner (GE Healthcare, Little Chalfont, United Kingdom) with the following scan parameters: slice thickness, 0.625 mm; tube voltage, 120 kVp; tube current, 100–140 mA; 25 × 25 cm field of view; 512 × 512 matrix. Acquired DICOM files were loaded into Maxilim software (Medicim, Leuwen, Belgium) and reconstructed in three-dimensional (3D) space using a threshold filter with a value of >700 HU. On 3D reconstruction 23 anatomical landmarks (11 bilateral and one unilateral) (Table 1; Fig. 1), were selected twice by two observers (TS, MJ—residents). These landmarks were adopted and modified from a study measuring the influence of intentional cranial deformations on orbital morphology [7]. Based on the selected landmarks, 6 planes, 12 angular and 16 linear measurements were determined (Tables 2, 3). The mean, minimal and maximal difference, as well as standard deviation (SD) and intraclass correlation coefficient (ICC) for inter- and intra-observer landmark reliability were calculated. In addition, the mean, minimal, maximal difference and standard deviation between linear and angular measurements for pre- and post-operative scans were calculated to assess a possible connection between established measurements and morphological change.
Table 1.
Definitions of the landmarks
| Landmark | Definition | Type |
|---|---|---|
| Anterior nasal spine | Tip of anterior nasal spine | Unilateral |
| Posterior choanae | Lower lateral corner of the posterior choanae, at the junction between the palatine bone and the pterygoid process | Bilateral |
| Clival anterior | Inferior and-lateral aspect of the anterior clinoid process, on the lesser wing of the sphenoid bone, lateral to the optic canal (approach to the landmark should be performed from the orbit) | Bilateral |
| Inferior orbital fissure | Most anterior point of the inferior orbital fissure at the level of the orbital floor | Bilateral |
| Superior orbital fissure (posterior and inferior) | Lower medial tip of the superior orbital fissure, at the top of foramen rotundum | Bilateral |
| Superior orbital fissure (anterior and superior) | Upper tip of the superior orbital fissure, at the junction between the lesser and the greater wings of the sphenoid bone | Bilateral |
| Frontomaxillary suture | Midpoint on the frontomaxillary suture which is build up from frontal process of maxillary bone and frontal bone | Bilateral |
| Frontozygomatic suture | Anterior midpoint at the frontozygomatic suture (between frontal process of zygomatic bone and frontal bone, on lateral wall of the orbit) | Bilateral |
| Lacrimal canal | Antero-lateral border of the orbital opening of the naso-lacrimal duct, at the junction between the lacrimal bone and the maxillary bone | Bilateral |
| Paraforamen caecum (right and left) | Lateral wall of foramen caecum which is situated in midline in front of the crista galli process | Bilateral |
| Planum sphenoidale | Upper surface of the lesser wing of the sphenoid bone, on the highest concavity of upper border of the optic canal | Bilateral |
| Small wing of the sphenoid | Lateral border of the small wing of the sphenoid bone, at the junction with the orbital plate of the frontal bone | Bilateral |
Fig. 1.
Landmark positions: (1) Anterior nasal spine; (2) Posterior choanae left and right; (3)Lacrimal canal right; (4) Inferior orbital fissure, Superior orbital fissure (posterior and inferior), Superior orbital fissure (anterior and superior); (5) Clival anterior left and right; (6) Frontozygomatic suture right; (7) Frontomaxillary suture left; (8) Paraforamen caecum left and right; (9) Planum sphenoidale right; (10) Small wing of the sphenoid right
Table 2.
Planes definitions
| Landmark | Definition | Type |
|---|---|---|
| Horizontal maxillary plane | Anterior nasal spine, right posterior choanae, left posterior choanae | Plane defined by 3 points |
| Orbital floor | Lacrimal canal, superior orbital fissure (posterior–inferior end), medial inferior orbital fissure | Plane defined by 3 points |
| Lateral orbital wall | Superior orbital fissure (anterior–superior end), superior orbital fissure (posterior–inferior end), medial inferior orbital fissure | Plane defined by 3 points |
| Orbital roof | Foramen caecum, planum sphenoidale, small wing of the sphenoid | Plane defined by 3 points |
| Medial orbital wall | Superior orbital fissure (anterior–superior end), anterior clinoid process, fronto–maxillary suture | Plane defined by 3 points |
| Anterior orbital wall | Fronto–maxillary suture, fronto–zygomatic suture, perpendicular to the horizontal maxillary plane | Plane defined by 2 points and perpendicular to another plane |
Table 3.
Angles and distances definitions
| Landmark | Definition | Type |
|---|---|---|
| Medio-lateral orbital angle (left and right) | Median orbital wall, lateral orbital wall | Angle between 2 planes |
| Anterior orbital angle | Left anterior orbital plane, right anterior orbital plane | Angle between 2 planes |
| Median orbital angle | Left medial orbital wall, right medial orbital wall | Angle between 2 planes |
| Vertical orbital angle (left and right) | Orbital roof, orbital floor | Angle between 2 planes |
| Relative lateral orbital angle (left and right) | Lateral orbital wall, orbital floor | Angle between 2 planes |
| Relative medial orbital angle (left and right) | Medial orbital wall, orbital floor | Angle between 2 planes |
| Lateral orbital angle (left and right) | Lateral orbital wall, maxillary horizontal plane | Angle between 2 planes |
| Anterior orbital width | Fronto–zygomatic suture, fronto–nasal suture | Distance between 2 points |
| Lateral orbital depth | Fronto–zygomatic suture, superior orbital fissure (posterior–inferior end) | Distance between 2 points |
| Median orbital depth | Fronto–maxillary suture, superior orbital fissure (posterior–inferior end) | Distance between 2 points |
| Deep orbital height | Superior orbital fissure (posterior–inferior end), orbital roof | Distance between a point and a plane |
| Sphenoidal orbital height | Medial inferior orbital fissure, orbital roof | Distance between a point and a plane |
| Anterior orbital height | Lacrimal canal, orbital roof | Distance between a point and a plane |
| Posterior orbital width | Superior orbital fissure (anterior–superior end), lateral orbital wall | Distance between a point and a plane |
| Central orbital depth | Superior orbital fissure (posterior–inferior end), anterior orbital wall | Distance between a point and a plane |
Results
The inter and intra-examiner accuracy of all landmarks for three axes was >0.9 ICC (Tables 4, 5). Despite excellent inter and intra examiner agreement (<2.49 ± 2.05 mm SD), linear and angular measurements displayed an inaccuracy: the mean SD for angular measurements was 8.20 and for linear 3.04 mm (Table 6).
Table 4.
Intraobserver reproducibility
| Landmarks | X axis | Y axis | Z axis | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Mean (mm) | SD (mm) | Min (mm) | Max (mm) | ICC | Mean (mm) | SD (mm) | Min (mm) | Max (mm) | ICC | Mean (mm) | SD (mm) | Min (mm) | Max (mm) | ICC | |
| Anterior nasal spine | 0.18 | 1.15 | 0.03 | 0.44 | 0.979 | 0.22 | 0.11 | 0.07 | 0.42 | 0.997 | 0.34 | 0.29 | 0.02 | 0.89 | 0.992 |
| Posterior choanae left | 1.11 | 0.82 | 0.04 | 2.38 | 0.9987 | 0.78 | 1.09 | 0.03 | 2.99 | 0.971 | 0.54 | 0.54 | 0.01 | 1.49 | 0.967 |
| Posterior choanae right | 0.41 | 0.52 | 0.02 | 1.34 | 0.988 | 0.32 | 0.34 | 0.00 | 1.12 | 0.979 | 0.85 | 0.70 | 0.02 | 2.28 | 0.920 |
| Clival anterior left | 0.37 | 1.19 | 0.12 | 1.10 | 0.967 | 0.21 | 0.11 | 0.01 | 0.39 | 0.996 | 0.32 | 0.25 | 0.03 | 0.85 | 0.992 |
| Clival anterior right | 0.58 | 1.12 | 0.04 | 1.33 | 0.955 | 0.29 | 0.19 | 0.04 | 0.59 | 0.991 | 0.37 | 0.26 | 0.06 | 0.90 | 0.991 |
| Inferior orbital fissure left | 0.76 | 0.74 | 0.01 | 1.90 | 0.992 | 0.91 | 0.89 | 0.10 | 3.29 | 0.912 | 0.53 | 0.70 | 0.03 | 2.56 | 0.952 |
| Inferior orbital fissure right | 0.52 | 0.65 | 0.10 | 1.91 | 0.988 | 0.45 | 0.47 | 0.01 | 1.38 | 0.974 | 0.31 | 0.33 | 0.00 | 1.03 | 0.990 |
| Superior orbital fissure (anterior–superior) left | 0.23 | 0.47 | 0.01 | 0.69 | 0.994 | 0.82 | 1.59 | 0.04 | 5.77 | 0.942 | 0.33 | 0.21 | 0.04 | 0.67 | 0.991 |
| Superior orbital fissure (anterior–superior) right | 0.24 | 0.57 | 0.00 | 0.96 | 0.989 | 0.26 | 0.25 | 0.02 | 0.78 | 0.985 | 0.26 | 0.09 | 0.15 | 0.46 | 0.996 |
| Superior orbital fissure (posterior-inferior) left | 0.52 | 0.96 | 0.00 | 1.01 | 0.970 | 0.55 | 0.73 | 0.01 | 2.61 | 0.953 | 0.49 | 0.27 | 0.05 | 0.96 | 0.980 |
| Superior orbital fissure (posterior-inferior) right | 0.63 | 1.15 | 0.09 | 1.57 | 0.947 | 0.56 | 0.48 | 0.08 | 1.36 | 0.963 | 0.46 | 0.45 | 0.05 | 1.56 | 0.987 |
| Frontomaxillary suture left | 0.51 | 0.90 | 0.03 | 1.71 | 0.985 | 1.10 | 0.69 | 0.20 | 2.46 | 0.947 | 0.94 | 1.22 | 0.08 | 4.49 | 0.948 |
| Frontomaxillary suture right | 0.64 | 0.95 | 0.13 | 1.62 | 0.957 | 1.06 | 0.72 | 0.03 | 2.26 | 0.945 | 0.81 | 0.60 | 0.13 | 1.75 | 0.979 |
| Frontozygomatic suture left | 0.76 | 1.04 | 0.08 | 1.88 | 0.972 | 0.66 | 0.73 | 0.01 | 2.11 | 0.969 | 0.47 | 0.52 | 0.03 | 1.79 | 0.973 |
| Frontozygomatic suture right | 0.40 | 0.58 | 0.02 | 1.18 | 0.975 | 0.78 | 0.86 | 0.05 | 2.53 | 0.964 | 1.11 | 1.51 | 0.05 | 5.32 | 0.984 |
| Lacrimal canal left | 0.67 | 2.05 | 0.04 | 2.06 | 0.923 | 0.63 | 0.74 | 0.02 | 2.35 | 0.960 | 0.38 | 0.33 | 0.00 | 1.11 | 0.989 |
| Lacrimal canal right | 0.30 | 1.34 | 0.05 | 0.71 | 0.959 | 0.43 | 0.57 | 0.01 | 2.08 | 0.981 | 0.22 | 0.23 | 0.03 | 0.72 | 0.997 |
| Paraforamen caecum left | 0.29 | 0.52 | 0.01 | 0.97 | 0.994 | 0.32 | 0.33 | 0.05 | 1.22 | 0.990 | 0.44 | 0.32 | 0.02 | 0.84 | 0.993 |
| Paraforamen caecum right | 0.26 | 0.54 | 0.02 | 0.84 | 0.991 | 0.47 | 0.61 | 0.01 | 2.21 | 0.980 | 1.17 | 1.83 | 0.01 | 6.21 | 0.981 |
| Planum sphenoidale left | 0.39 | 1.07 | 0.00 | 1.07 | 0.972 | 0.78 | 1.11 | 0.02 | 3.91 | 0.943 | 0.44 | 0.40 | 0.04 | 1.19 | 0.983 |
| Planum sphenoidale right | 0.47 | 0.80 | 0.02 | 1.30 | 0.976 | 0.52 | 0.68 | 0.03 | 2.34 | 0.976 | 0.36 | 0.33 | 0.02 | 1.24 | 0.990 |
| Small wing left | 0.82 | 1.42 | 0.03 | 2.66 | 0.971 | 0.42 | 0.42 | 0.09 | 1.46 | 0.988 | 0.48 | 0.61 | 0.05 | 2.25 | 0.973 |
| Small wing right | 1.18 | 0.94 | 0.08 | 5.71 | 0.933 | 0.39 | 0.33 | 0.10 | 1.21 | 0.987 | 0.82 | 1.20 | 0.01 | 3.21 | 0.947 |
Table 5.
Interobserver reproducibility
| Landmarks | X axis | Y axis | Z axis | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Mean (mm) | SD (mm) | Min (mm) | Max (mm) | ICC | Mean (mm) | SD (mm) | Min (mm) | Max (mm) | ICC | Mean (mm) | SD (mm) | Min (mm) | Max (mm) | ICC | |
| Anterior nasal spine | 1.43 | 1.15 | 0.12 | 4.12 | 0.928 | 0.71 | 0.90 | 0.02 | 2.53 | 0.976 | 1.20 | 1.30 | 0.05 | 4.70 | 0.937 |
| Posterior choanae left | 0.78 | 0.82 | 0.19 | 2.65 | 0.987 | 1.09 | 0.77 | 0.16 | 2.80 | 0.939 | 1.36 | 1.04 | 0.11 | 3.27 | 0.947 |
| Posterior choanae right | 0.66 | 0.52 | 0.12 | 1.99 | 0.978 | 1.13 | 0.82 | 0.06 | 2.26 | 0.968 | 1.32 | 0.74 | 0.18 | 2.25 | 0.937 |
| Clival anterior left | 1.18 | 1.19 | 0.06 | 3.87 | 0.967 | 2.48 | 3.10 | 0.12 | 3.47 | 0.961 | 2.01 | 1.60 | 0.20 | 4.87 | 0.943 |
| Clival anterior right | 1.64 | 1.12 | 0.06 | 3.48 | 0.955 | 1.97 | 2.47 | 0.21 | 3.21 | 0.952 | 2.18 | 1.48 | 0.09 | 4.57 | 0.941 |
| Inferior orbital fissure left | 1.07 | 0.74 | 0.24 | 2.68 | 0.942 | 1.52 | 1.40 | 0.12 | 4.19 | 0.951 | 1.14 | 0.72 | 0.11 | 2.46 | 0.926 |
| Inferior orbital fissure right | 0.94 | 0.65 | 0.07 | 2.23 | 0.988 | 1.16 | 1.22 | 0.04 | 3.91 | 0.944 | 0.80 | 0.78 | 0.02 | 2.58 | 0.963 |
| Superior orbital fissure (anterior–superior) left | 0.47 | 0.47 | 0.02 | 1.56 | 0.994 | 0.83 | 0.73 | 0.20 | 3.00 | 0.947 | 0.77 | 0.82 | 0.17 | 2.71 | 0.952 |
| Superior orbital fissure (anterior–superior) right | 0.48 | 0.57 | 0.00 | 2.20 | 0.989 | 0.54 | 0.44 | 0.03 | 1.27 | 0.977 | 0.51 | 0.69 | 0.03 | 2.49 | 0.974 |
| Superior orbital fissure (posterior-inferior) left | 1.07 | 0.96 | 0.08 | 2.54 | 0.970 | 1.97 | 2.92 | 0.33 | 11.00 | 0.962 | 1.00 | 0.65 | 0.24 | 2.59 | 0.925 |
| Superior orbital fissure (posterior-inferior) right | 1.39 | 1.15 | 0.03 | 3.39 | 0.947 | 1.07 | 1.14 | 0.02 | 3.13 | 0.933 | 0.70 | 0.66 | 0.05 | 1.85 | 0.959 |
| Frontomaxillary suture left | 1.42 | 0.90 | 0.11 | 3.31 | 0.985 | 1.21 | 0.93 | 0.29 | 3.04 | 0.996 | 1.98 | 1.33 | 0.03 | 4.74 | 0.946 |
| Frontomaxillary suture right | 1.72 | 0.95 | 0.24 | 3.48 | 0.957 | 1.47 | 1.13 | 0.28 | 4.04 | 0.925 | 1.68 | 1.06 | 0.07 | 2.98 | 0.965 |
| Frontozygomatic suture left | 1.63 | 1.04 | 0.51 | 3.44 | 0.972 | 1.52 | 1.04 | 0.14 | 3.11 | 0.960 | 1.89 | 0.96 | 0.32 | 3.27 | 0.950 |
| Frontozygomatic suture right | 2.08 | 0.58 | 1.02 | 2.99 | 0.975 | 1.79 | 1.06 | 0.24 | 3.75 | 0.973 | 1.59 | 0.70 | 0.58 | 2.88 | 0.961 |
| Lacrimal canal left | 2.49 | 2.05 | 0.26 | 6.29 | 0.923 | 2.58 | 2.23 | 0.32 | 8.42 | 0.969 | 1.77 | 1.06 | 0.43 | 3.99 | 0.954 |
| Lacrimal canal right | 2.19 | 1.34 | 0.20 | 4.46 | 0.959 | 2.40 | 1.64 | 0.15 | 5.64 | 0.934 | 2.07 | 0.89 | 0.43 | 3.48 | 0.938 |
| Paraforamen caecum left | 0.66 | 0.52 | 0.18 | 1.92 | 0.994 | 0.40 | 0.45 | 0.04 | 1.73 | 0.984 | 0.71 | 0.53 | 0.13 | 2.00 | 0.989 |
| Paraforamen caecum right | 0.61 | 0.54 | 0.05 | 1.80 | 0.991 | 0.50 | 0.43 | 0.01 | 1.43 | 0.979 | 1.26 | 1.06 | 0.21 | 3.60 | 0.957 |
| Planum sphenoidale left | 1.22 | 1.07 | 0.07 | 4.00 | 0.972 | 0.81 | 0.82 | 0.01 | 2.69 | 0.950 | 0.90 | 1.04 | 0.06 | 3.14 | 0.941 |
| Planum sphenoidale right | 1.01 | 0.80 | 0.06 | 2.48 | 0.976 | 0.61 | 0.55 | 0.00 | 1.85 | 0.957 | 0.48 | 0.54 | 0.02 | 1.68 | 0.973 |
| Small wing left | 1.37 | 1.42 | 0.02 | 3.97 | 0.971 | 0.56 | 0.49 | 0.02 | 1.54 | 0.986 | 1.17 | 1.16 | 0.01 | 3.66 | 0.941 |
| Small wing right | 1.70 | 0.94 | 0.32 | 3.37 | 0.933 | 0.56 | 0.48 | 0.01 | 1.69 | 0.974 | 1.35 | 1.15 | 0.13 | 3.67 | 0.988 |
Table 6.
Angular and linear measurements change
| Angular measurements (°) | Mean change (mm) | SD (mm) | Min (mm) | Max (mm) |
|---|---|---|---|---|
| Medio-lateral orbital angle (left) | 6.20 | 8.97 | −4.6 | 20.8 |
| Medio-lateral orbital angle (right) | 2.53 | 5.29 | −4.6 | 8.9 |
| Anterior orbital angle | −13.53 | 16.79 | −32.3 | 13.3 |
| Median orbital angle | 0.62 | 4.79 | −5.3 | 8.3 |
| Vertical orbital angle (left) | 1.40 | 5.48 | −3.6 | 11.5 |
| Vertical orbital angle (right) | −2.25 | 6.79 | −13.6 | 4.7 |
| Relative lateral orbital angle (left) | 0.83 | 1.68 | −2.3 | 2.2 |
| Relative lateral orbital angle (right) | −3.67 | 6.53 | −12.4 | 4.4 |
| Relative medial orbital angle (left) | 2.23 | 13.69 | −7.3 | 29.5 |
| Relative medial orbital angle (right) | 3.12 | 11.76 | −3.7 | 26.5 |
| Lateral orbital angle (left) | −3.33 | 3.31 | −8.7 | 1.4 |
| Lateral orbital angle (right) | −3.33 | 13.37 | −25.2 | 7.5 |
| Linear measurements (mm) | ||||
| Anterior orbital width (left) | −2.20 | 4.89 | −11.1 | 3.5 |
| Anterior orbital width (right) | −1.28 | 2.73 | −5.3 | 2.3 |
| Lateral orbital depth (left) | −1.43 | 1.48 | −3.2 | 0.5 |
| Lateral orbital depth (right) | −1.28 | 2.50 | −5.5 | 0.9 |
| Median orbital depth (left) | −7.82 | 6.58 | −17.4 | 1.7 |
| Median orbital depth (right) | −7.07 | 6.15 | −13.9 | 2 |
| Deep orbital height (left) | −0.13 | 0.84 | −1.1 | 1.2 |
| Deep orbital height (right) | −0.38 | 0.42 | −1 | 0.2 |
| Sphenoidal orbital height (left) | −4.85 | 2.95 | −8.6 | 0 |
| Sphenoidal orbital height (right) | −4.25 | 3.33 | −8.1 | 1 |
| Anterior orbital height (left) | −6.68 | 1.95 | −8.9 | −3.3 |
| Anterior orbital height (right) | −3.72 | 4.09 | −7.9 | 3.2 |
| Posterior orbital width (left) | −0.30 | 0.89 | −2 | 0.6 |
| Posterior orbital width (right) | −1.03 | 2.20 | −4.7 | 0.8 |
| Central orbital depth (left) | −4.63 | 3.90 | −12.2 | −1 |
| Central orbital depth (right) | −6.02 | 3.81 | −11.5 | −0.9 |
Based on these results, it is difficult to establish any correlation between the proposed measurements and any orbital volume change.
Discussion
Since the introduction of three-dimensional imagining techniques, the measurement of orbital morphology has been widely used for patients suffering hypertelorism [8], midface hypoplasia [9], orbital fractures [10] as well as, post oncological defects [11]. These measurements were calculated either as a distance between points (landmarks) or as a volumetric value. The first method offers quick results, though frequently, they cannot be compared between different samples or between different clinicians due to the lack of standardized reproducible landmarks. Moreover, the procedure of volumetric measurement requires a manual delineation of a whole series of CT slices, a time consuming task, which results in data simply relating to volume change without any information in the direction [6, 10].
To overcome these drawbacks, the technique of three-dimensional (3D) cephalometric analysis seems a clear solution. The introduction of each 3D cephalometric analysis into everyday workflow will consist of several steps [12]. Guided by protocol, in the first step we have established 11 bilateral and 1 unilateral landmarks and a subsequent reliability assessment, showed them to be sufficiently precise (<2.49 ± 2.05 mm SD). It is important that the landmarks presented were selected on a three-dimensional skull reconstruction which reduces selection time and enables measurements between landmarks which have three different coordinates values, an impossible task in flat/two-dimensional tomographic slices.
For the next step, linear and angular measurements were established (based on previously examined landmarks), these serve for any further analysis on pre and postoperative CT scans. Unfortunately the measurement results show large discrepancies (8.2°; 3.04 mm) with an additional unclear pattern of change (increase and reduction of the same measurements in different patients who underwent the same surgery and distraction protocol). This could be the result of our study limitations.
The first limitation was the fact that our patients have different syndromic defects with diverse severity of midface hypoplasia and additional craniofacial anomalies which could influence landmark localization. One example is the abnormal position of the nasal bones found in Binder syndrome [2]; this could affect the localization of the frontomaxillary suture landmark. Also the Le Fort III osteotomy line crosses three of the proposed landmarks: the frontozygomatic suture where the osteotomy begins; the inferior orbital fissure which could be affected during intraorbital cuts and the lacrimal canal, which lies on the most fragile part of the orbital walls. It should be noted that the lacrimal bone (where lacrimal canal landmark lies) is sensitive to the threshold segmentation process. We used >700 HU values during segmentation which in some cases resulted in porous reconstruction (Fig. 2). A modification of HU values might help to obtain a more detailed reconstruction, however it might also result in more numerous artifacts from metal objects such as orthodontic brackets or distractor devices. Finally the human factor cannot be discounted.
Fig. 2.
Porous structure of lacrymal bone after threshold segmentation
To overcome the difficulties mentioned above, further research should be performed and consider remarks.
The presented landmarks are reproducible and could constitute a base for other linear and angular measurements, however to demonstrate a possible connection between the measurements and a postoperative morphological change, these measurements should be performed on more homogenous and larger group.
If new landmarks are necessary, the location of the osteotomy line and other surgical interventions should be taken into consideration as potentially misleading areas during the selection process.
To shorten the time required for taking these measures, the introduction of automatic landmark selection might be a solution [13, 14]. This could significantly accelerate the analysis process and increase measurement reliability. The extent of accuracy could also be increased through the implementation of pre-measuring calibration [15].
Finally, in most of diagnostic techniques an examined value is compared to a specific pattern- norm value. However our purpose was to create a method for the comparison of pre and post-surgical results, so that the norm was not required, but a study performed on a large group of healthy subjects would enable the establishment of standard value of orbital morphology. This could expand the application of this technique from comparative measurements to differential diagnostics between pathology and acceptable morphology.
Funding
None.
Compliance with Ethical Standards
Conflict of interest
None.
Ethical Approval
This article does not contain any studies with animals performed by any of the authors. All procedures performed in study involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Local ethics committee number 27/2013/V.
Informed consent
Informed consent was obtained from all individual participants included in the study.
References
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