Atormac
Home  -  About us  -  Editorial board  -  Search  -  Ahead of print  -  Current issue  -  Archives  -  Instructions  -  Subscribe  -  Contacts  -  Advertise - Login 
 
 
     

 Table of Contents  
TECHNICAL NOTE
Year : 2017  |  Volume : 7  |  Issue : 2  |  Page : 260-262

Computed tomographic analysis of the sagittal orbit-globe relationship


1 Department of Radiology, University of Tennessee Health Science Center, Memphis, TN, USA
2 Department of Surgery, Division of Plastic Surgery, University of Washington Medical Center, Seattle, WA, USA
3 Department of Plastic and Reconstructive Surgery, Case Western Reserve University School of Medicine, Cleveland, OH, USA

Date of Web Publication22-Nov-2017

Correspondence Address:
Zachary R Abramson
Department of Radiology, University of Tennessee Health Science Center, Memphis, TN
USA
Login to access the Email id


DOI: 10.4103/ams.ams_172_16

PMID: 29264296

Rights and Permissions
  Abstract 


Identifying the normal relationship of the orbital rims to the globes is critical in planning surgical correction of craniofacial deformities affecting the orbit. This article illustrates a technical proof of principle and mathematical basis for a computed tomography-based measurement of the sagittal orbit-globe relationship. The technique does not require subject cooperation and is, therefore, optimal for pediatric craniofacial surgical treatment planning and outcome evaluation.

Keywords: Exophthalmometry, maxillofacial computed tomography, orbital anthropometer, orbitometry, sagittal orbit-globe relationship


How to cite this article:
Abramson ZR, Susarla SM, Kumar AR, Choudhri AF. Computed tomographic analysis of the sagittal orbit-globe relationship. Ann Maxillofac Surg 2017;7:260-2

How to cite this URL:
Abramson ZR, Susarla SM, Kumar AR, Choudhri AF. Computed tomographic analysis of the sagittal orbit-globe relationship. Ann Maxillofac Surg [serial online] 2017 [cited 2020 Jul 13];7:260-2. Available from: http://www.amsjournal.com/text.asp?2017/7/2/260/218970




  Introduction Top


Euophthalmos, the normal relationship of the orbital rims to the globes, is critical for the planning and surgical correction of craniofacial deformities that affect the orbit (e.g., Crouzon and Apert syndrome, achondroplasia, etc.).[1] The establishment of a reproducible facial anthropometric measurement is challenging. When measuring the relationship between the globe and the orbit, surgeons are interested in the distance between landmarks in the anteroposterior plane to answer the question, “How deeply recessed are the patient's eyes?” To answer this question, the distance calculated should not be the distance between two anatomic landmarks in three-dimensional (3D) space, but rather the distance only in the A-P direction. Second, the head and face should be oriented with the facial horizontal plane parallel to the true horizontal plane or in the case of a computed tomography (CT)-based method, the axial plane. Any tilting of the head will alter the distance in anteroposterior dimension from the globe to orbital landmarks. Various devices, such as the orbital anthropometer, can be used to assess the relationship between the globes and peri-orbital soft tissue.[2] While this technique has been employed over the decades, it is difficult to perform in infants and young children, as they do not tolerate the time needed for measurement. In this communication, we describe a CT-based method for measuring the sagittal orbit-globe relationship and provides the mathematical basis for the technique.


  Materials and Methods Top


Anatomic landmarks

The anatomic landmarks used in this study have been adapted from traditional anthropometric and cephalometric definitions.[3],[4] They have been modified to be used in a 3D computer environment exhibited by most DICOM viewers. In addition to identifying the nasion (n), there are four peri-orbital soft tissue landmarks for each eye: orbitale superius (os); orbitale inferius (oi); orbitale laterale (ol); anterior cornea (ac). In addition, the bony landmarks Orbitale (Or) and Porion (Po) are used in the reorientation of the axial plane parallel to the frankfort horizontal. landmark and plane definitions are shown in [Table 1].
Table 1: Landmark and plane definitions

Click here to view


Image manipulation and calculations

To make the appropriate measurements parallel to the facial horizontal plane, the axial plane is reoriented to coincide with the facial horizontal plane, which we define as the Frankfort Horizontal plane extrapolated to 3D [Table 1] and [Figure 1]a. Next, for the measurements to be in the AP direction only, the sagittal plane is defined by choosing two points in the mid-sagittal plane (anterior and posterior nasal spines) [Figure 1]b. These two points comprise a vector lying in the facial horizontal plane, parallel to the mid-sagittal plane. A coronal plane perpendicular to this vector can then be defined and used as a reference point for measurements. Next, the fiducial points described above are digitally placed and the distances between these points and the coronal plane are calculated. Finally, subtracting the distance from the anterior cornea to the coronal plane from all of the landmark-coronal plane distances yields the distance from the anterior cornea to other anatomic landmarks in the A-P direction only, parallel to the facial horizontal [Figure 2]. The mathematical basis for this technique is shown in [Table 2].
Figure 1: Defining the coronal plane. First, the axial plane is oriented to the Frankfort horizontal (the plane defined by porion (right arrow) and inferior orbitale (left arrow) (a). Second, two points are chosen in the axial plane parallel to the mid-sagittal plane to define a vector perpendicular to the desired coronal plane (b)

Click here to view
Figure 2: Diagrammatic overview of landmarks and calculations

Click here to view
Table 2: Mathematical basis for calculating the distances from the globe to soft-tissue landmarks which are parallel to the facial horizontal and sagittal planes

Click here to view


Sample calculation

To demonstrate the application of this technique, we applied this to a 13-year-old female who underwent a maxillofacial CT scan following a motor vehicle accident. The scan was acquired without intravenous contrast using helical acquisition with a 320 detector scanner with 0.5 mm collimation (Toshiba Aquilion 320, Toshiba Inc, Tokyo, Japan), with 1 mm bone and soft tissue reconstructions performed in three orthogonal planes. The DICOM viewer used was OsiriX (OsiriX v5.8.5 Foundation, Geneva, Ch).[3] Landmarks were identified by a fellowship trained neuroradiologist. Mathematical calculations were performed in an electronic spreadsheet (Excel 2011, Microsoft Corp, Redmond, WA).


  Results Top


A single DICOM file of a maxillofacial CT belonging to the index patient was imported into the DICOM viewer. The image was reoriented such that the axial plane corresponded to the facial horizontal plane as described above. The technique outlined above was performed, and the resultant measurements are listed in [Table 2]. Negative numbers correspond to the anterior cornea being posterior to the landmark in comparison. For example, n-ac of − 7.6 means the anterior cornea is 7.6 mm posterior to the soft tissue nasion. The sample calculations were performed on a CT scan from a 13-year-old female who experienced head trauma. The CT scan showed a left retrobulbar hematoma associated with multiple facial and skull base fractures causing mild left eye proptosis. Concordantly, the left anterior cornea is noted to be more anterior relative to adjacent soft-tissue landmarks when compared to the right side [Figure 3] and [Table 3].
Figure 3: Computed tomography landmarks placed for an index patient: Right orbitale superius (top arrow), anterior cornea (middle arrow), orbitale inferius (bottom arrow) (a); nasion (arrow) (b); right and left orbitale (arrows) (c)

Click here to view
Table 3: Measurements of the sagittal orbit-globe relationship in sample patient

Click here to view



  Discussion Top


Identifying the normal relationship of the orbital rims to the globes is critical for the planning and surgical correction of craniofacial deformities. This article demonstrates a technical proof of principle of a CT-based method for measuring the sagittal orbit-globe relationship. A single index case demonstrated the utility of this method and the ability to identify asymmetric sagittal orbit-globe relationships.

Fundamental to this technique is the use of mathematical principles to overcome challenges related to head positioning. In a 3D Cartesian coordinate system, any plane in space can be defined mathematically if a single point within the plane and a vector perpendicular to the plane are known. If the perpendicular vector lies in both the facial horizontal and sagittal planes, then the mathematically defined plane perpendicular to this vector is the coronal plane. Once this particular coronal plane is defined, the shortest distance between an anatomic landmark and that coronal plane will be solely in the A-P dimension and parallel to the facial horizontal.

There are limitations to the method demonstrated here. Abnormal anatomy may affect the ability to define the facial horizontal plane using the Frankfort horizontal. In such cases, an alternative method of determining the facial horizontal plane should be used.[5],[6] In addition, The inter and intra-examiner reliability of this technique is unknown. However, the variability of facial landmark placement has been studied and typically is in the realm of 0– 2 mm.[7] This technique requires radiation, however many patients with congenital or acquired craniofacial abnormalities are evaluated with CT already and would therefore not require any additional radiation. The mathematical basis within can apply to magnetic resonance imaging (MRI) as well, however, soft tissue landmarks may be more difficult to identify. MRI typically has a lower spatial resolution than CT, and with longer acquisition times, motion can be a limiting factor, in particular for the anterior cornea measurements.


  Conclusions Top


The CT-based method for measuring the sagittal orbit-globe relationship demonstrated above is a mathematically reliable representation of clinically performed measurements. Clinical measurements are time-consuming, and accordingly are typically only performed on patients with orbital asymmetry, or those with congenital or acquired maxillofacial abnormalities. This virtual technique can be relatively quickly performed, allowing for the creation of a database of normative values, which for practical reasons cannot be easily acquired by conventional techniques. Such normative data when compared to preoperative patient measurements could assist in surgical planning and outcome evaluation.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Mulliken JB, Godwin SL, Pracharktam N, Altobelli DE. The concept of the sagittal orbital-globe relationship in craniofacial surgery. Plast Reconstr Surg 1996;97:700-6.  Back to cited text no. 1
[PUBMED]    
2.
Kohout M, Pai L, Berenguer B, Tayler P, Pracharktam N, Mulliken JB. New instrument for orbital anthropometry. J Craniomaxillofac Surg 1998;26:174-8.  Back to cited text no. 2
[PUBMED]    
3.
Farkas LG, Eiben OG, Sivkov S, Tompson B, Katic MJ, Forrest CR. Anthropometric measurements of the facial framework in adulthood: Age-related changes in eight age categories in 600 healthy white North Americans of European ancestry from 16 to 90 years of age. J Craniofac Surg 2004;15:288-98.  Back to cited text no. 3
[PUBMED]    
4.
Tenti FV. Cephalometric analysis as a tool for treatment planning and evaluation. Eur J Orthod 1981;3:241-5.  Back to cited text no. 4
[PUBMED]    
5.
Madsen DP, Sampson WJ, Townsend GC. Craniofacial reference plane variation and natural head position. Eur J Orthod 2008;30:532-40.  Back to cited text no. 5
[PUBMED]    
6.
Oh S, Ahn J, Nam KU, Paeng JY, Hong J. Frankfort horizontal plane is an appropriate three-dimensinal reference in the evaluation of clinical and skeletal cant. J Korean Assoc Oral Maxillofac Surg 2013;39:71-6.  Back to cited text no. 6
[PUBMED]    
7.
Gwilliam JR, Cunningham SJ, Hutton T. Reproducibility of soft tissue landmarks on three-dimensional facial scans. Eur J Orthod 2006;28:408-15.  Back to cited text no. 7
[PUBMED]    


    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

Top
 
 
Search
Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
Access Statistics
Email Alert *
Add to My List *
* Registration required (free)  

 
  In this article
   Abstract
  Introduction
   Materials and Me...
  Results
  Discussion
  Conclusions
   References
   Article Figures
   Article Tables

 Article Access Statistics
    Viewed1462    
    Printed50    
    Emailed0    
    PDF Downloaded211    
    Comments [Add]    

Recommend this journal