An experimental investigation of the safe distance for internal orbital dissection

Mapping the Posterior Ledge and Optic Foramen in Orbital Floor Blowout Fractures

Background  The posterior ledge (PL) is a vital structure that supports the implant posteriorly during orbital floor reconstruction. This study describes a technique for mapping the PL in relation to the infraorbital margin (IM) in patients with orbital floor blowout fractures. This study establishes the location of the optic foramen in relation to the PL. Methods  Facial computed tomography (FCT) scans of 67 consecutive patients with isolated orbital floor blowout fractures were analyzed using Osirix. Planes of reference for orbital fractures, a standardized technique for performing measurements on FCT, was used. Viewed coronally, the orbit was divided into seven equal sagittal slices (L1 laterally to L7 medially) with reference to the midorbital plane. The distances of PL from IM and location of optic foramen were determined. Results  The greatest distance to PL is found at L5 (median: 30.1 mm, range: 13.5-37.1 mm). The median and ranges for each slice are as follows: L1 (median: 0.0 mm, range: 0.0-19.9 mm), L2 (median: 0.0 mm, range: 0.0-21.5 mm), L3 (median: 15.8 mm, range: 0.0-31.7 mm), L4 (median: 26.1 mm, range: 0.0-34.0 mm), L5 (median: 30.1 mm, range: 13.5-37.1 mm), L6 (median: 29.0 mm, range: 0.0-36.3 mm), L7 (median: 20.8 mm, range: 0.0-39.2 mm). The median distance of the optic foramen from IM is 43.7 mm (range: 37.0- 49.1) at L7. Conclusion  Distance to PL from IM increases medially until the L5 before decreasing. A reference map of the PL in relation to the IM and optic foramen is generated. The optic foramen is located in close proximity to the PL at the medial orbital floor. This aids in preoperative planning and intraoperative dissection.

A systematic review of the surgical anatomy of the orbital apex

PURPOSE

The orbital apex is the narrowest part of the orbit, housing the link between the intracranial cavity and orbit. Knowledge of orbital apex anatomy is crucial to selecting a surgical approach and reducing the risk of complications. Our purpose is to summarize current knowledge on surgical anatomy and attempt to reach a consensus on definition of the orbital apex.

METHODS

The online databases of Embase, the Cochrane library, Web of Science and PubMed (MEDLINE) were queried in a comprehensive bibliographic search on the (surgical) anatomy of the orbital apex and consisted of a combination of two subjects, using indexed terms and free text: "Orbital Apex" and "Orbital Anatomy."

RESULTS

A total of 114 relevant papers were included in this review. Numerous anatomical variations are described in the literature. Variations of the optic canal include duplication (0.64%) and keyhole anomaly (2.65%). Variations in pneumatization of the anterior clinoid process were unilateral in almost 10%, bilateral in 9%, and normal in 72%. A rare variant of the superior orbital fissure (SOF) is Warwick's foramen, which appears as if the lowest portion of the SOF was separated from the main fissure by a transverse bony bridge.

CONCLUSION

The definition of the orbital apex varies in the literature, and further research would most likely identify additional variations. A universal definition reporting these variations and pathology and imaging findings is essential for determining the optimal surgical approach to the orbital apex.

Morphometric and Volumetric Measurements of Orbit With Cone-Beam Computed Tomography

PURPOSE

The purpose of this study was to determine cone-beam computed tomography (CBCT) as a tool for measuring morphometric and volumetric measurements of the orbit. Also, to assess gender and age variations and compare traditional methods of measurements in dry-skull, cadaveric, and other imaging modalities.

PATIENTS AND METHODS

Morphometric and volumetric values of 98 orbits (49 subjects, 21 men/28 women) were measured using CBCT. Their mean and standard deviation were measured and analyzed. The gender and age variability older and younger than 40 years were evaluated. They were compared with other dry-skull and imaging studies done among different populations.

RESULTS

CBCT could accurately measure the various morphometric and volumetric parameters of the orbit. From the reference point infraorbital foramen (I) to lacrimal fossa (F1), inferior orbital fissure (F2), inferior orbital rim (F3), and the optic canal (F4) were (in mm) (mean ± SD) 22.88 ± 1.08, 32.53 ± 0.88, 7.44 ± 0.71, and 51.45 ± 1.28, respectively. From the reference point, superior orbital notch/foramen (S) to superior orbital fissure (S1), lacrimal fossa (S2), and the optic canal (S3) were 49.29 ± 2.1, 26.39 ± 1.58, and 46.82 ± 0.88, respectively. From the reference point frontozygomatic suture (L) to lacrimal fossa (L1), superior orbital fissure (L2), the optic canal (L3), and inferior orbital fissure (L4) were 18.19 ± 0.88, 39.91 ± 1.44, 47.63 ± 1.11, and 35.19 ± 1.02, respectively. Orbital volume was found to show a significant difference between older and younger than 40 years of age, though not significant compared between men and women.

CONCLUSION

CBCT is a viable tool for morphometric and volumetric measurements of the orbit and other orocraniofacial structures. It can also assess age and gender variability. The low cost, high accuracy, low radiation, and ease of use can help in reproducibility among the different living populations.

Orbital volume measurements from magnetic resonance images using the techniques of manual planimetry and stereology

Introduction:

Current volume measurement techniques, for the orbit, are time-consuming and involve complex assessments, which prevents their routine clinical use. In this study, we evaluate the applicability and efficacy of stereology and planimetry in orbital volume measurements using magnetic resonance imaging (MRI).

Materials and Methods:

Prospective imaging study using MRI. Sheep craniums and human subjects were evaluated. Water-filling measurements were performed in animal skulls, as the standard validation technique. Planimetry and stereology techniques were used in each dataset. Intraobserver and interobserver reliability testing were applied.

Results:

In stereology customization, 1/6 systematic sampling scheme was determined as optimal with acceptable coefficient of error (3.09%) and low measurement time (1.2 min). In sheep craniums, the mean volume measured by water displacement, planimetry, and stereology was 17.81 ± 0.59 cm³, 18.53 ± 0.24 cm³, and 19.19 ± 0.17 cm³, respectively. Planimetric and stereological methods were highly correlated (r = 0.94; P ≈ 0.001). The mean difference of the orbital volume using planimetry and stereology was 0.316 ± 0.168 cm³. In human subjects, using stereology, the mean orbital volume was found to be 19.62 ± 0.2 cm³ with a CE of 3.91 ± 0.15%.

Conclusions:

The optimized stereological method was found superior to manual planimetry in terms of user effort and time spent. Stereology sampling of 1/6 was successfully applied in human subjects and showed strong correlation with manual planimetry. However, optimized stereological method tended to overestimate the orbital volume by about 1 cc, a considerable limitation to be taken in clinical practice.

Is Orbital Floor Reconstruction With Titanium Mesh Safe?

To reconstruct the orbital floor defects there are a lot of reconstruction materials, the surgeon must choose one of them. The authors share their experience with 10 patients suffering from orbital trauma causing orbital floor fracture; those fractures were reconstructed using titanium mesh. No complications were encountered postoperatively apart from 1 patient with ectropion. Titanium mesh is a perfect material for the reconstruction of the orbital fractures, eliminating the need for autogenous bone graft.

Orbital Morphometry: A Computed Tomography Analysis

INTRODUCTION

The human orbit is a complex anatomic region, which plays predominant role in the evaluation of craniofacial complex. A thorough understanding of the relationship of the distance from orbital rim to the important vital structures of the orbital apex is required for the surgeon to perform safe and effective surgery.

OBJECTIVES

To evaluate and compare the depth and distances from various points of the orbital rim to the fissures and foramina of the orbital apex between genders in the local population.

METHODOLOGY

Linear measurements were conducted on 60 orbits from 30 patients who had undergone head computed tomography scan. These measurements were done utilizing the multiplanar reconstruction modes on computed tomography images with minimum slice thickness of 1 mm.

RESULTS

Males have statistically significant larger orbits than females with higher mean measurements in all parameters, except for the distance from posterior ethmoidal foramen to the optic canal which was the same. However, there were no significant differences in all parameters between the right and left orbits.

CONCLUSION

This study provides the absolute limit of safe internal orbital dissection in respect to the local population. Despite males having larger orbits than females, it is clinically negligible.

Anatomical Studies of the Orbital Cavity Using Three-Dimensional Computed Tomography

OBJECTIVE

This study was designed to analyze the morphometric characteristics of the orbital cavity using three-dimensional computed tomography in Asians.

METHODS

Two hundred seventy-six orbits in 142 Asians (74 men and 68 women) were examined and compared according to age, sex, and laterality (right and left).

RESULTS

Mean orbital morphometric values were as follows. Orbital cavity depth was 49.60 mm from optic foramen to orbitale (inferior) and 41.32 mm from optic foramen to lacrimal crest (medial). Anterior and posterior orbital medial wall heights were 17.73 and 12.76 mm, respectively. Medial, middle, and lateral orbital floor lengths were 39.08, 29.56, and 20.08 mm, respectively. Anterior and posterior orbital floor width was 21.87 and 12.00 mm, respectively. For the orbital inferior-medial angle, anterior, middle, and posterior value was 132.11°, 126.24°, and 136.88°, respectively. Inferior orbital cavity depth, anterior orbital medial wall height, and orbital floor length tended to increase with aging, whereas orbital floor width tended to decrease with aging. No significant differences were found in terms of laterality, and values were greater in men than in women.

CONCLUSIONS

This quantitative analysis of orbital measurements will allow surgeons to plan operations more accurately and will help predict outcomes.

Pediatric Orbital Depth and Growth: A Radiographic Analysis

BACKGROUND

Orbital reconstruction requires knowledge of orbital depth in order to prevent optic nerve injury. Numerous analyses of adult orbital dimensions have been undertaken previously in order to characterize this measurement, including skull specimen and computerized tomography studies. However, there is a paucity of information regarding the pediatric orbit.

METHODS

The authors used pediatric magnetic resonance imaging (MRI) studies in order to quantify the change in orbital depth in relationship to patient age, and to develop methods to estimate and calculate orbital depth for individual pediatric patients. MRIs of the head in normal pediatric patients were reviewed retrospectively. Orbital depths were measured and correlated with age and cephalometric dimensions. In a randomly selected subgroup of patients, measurements were repeated by an independent investigator to determine interobserver reliability.

RESULTS

Measurements were obtained in 72 patients ranging from 3 months to 18 years of age (mean=7.8 years). There was a significant exponential relationship between orbital depth and patient age (r=0.81, F(2,69)=143.97, P<0.001). Depth increased more rapidly in the first 6 years of life, but leveled off in the early teen years toward a horizontal asymptote of approximately 45 mm. There was also a significant relationship between orbital depth and the sum of the biparietal width plus the anterior-posterior length (r=0.72, F(2,69)=87.44, P<0.0001). There was high interobserver reliability in measurements between 2 independent investigators (r=0.79, P<0.0001).

CONCLUSION

In children, orbital depth increases predictably with rising age and increasing head size. Knowledge of this growth curve and the relationship between head size and orbital depth can complement careful surgical dissection to improve safety and efficacy in pediatric orbital reconstructions.

Orbital wall reconstruction with titanium mesh: retrospective study of 24 patients

The aim of this study was to evaluate the efficacy and safety of traumatic orbital defect reconstruction with titanium mesh. A retrospective study was made. Evaluations were made after a minimum postoperative follow-up of 12 months, looking for the main complications. Twenty-four patients were included in this evaluation; 19 were male (79.1%) and 5 (20.8%) were female. The main injury etiology was vehicle accidents (50%) followed by other causes. Fourteen patients (58.3%) presented orbital floor fractures, and 10 had more than one wall fractured (41.6%). Permanent infraorbital nerve hypoesthesia was observed in two patients (8.3%), enophthalmos occurred in five patients (20.8%), and exophthalmos was found in two patients (8.3%). Four patients (16.6%) still presented evidence of residual prolapsed intraorbital content, and one of those needed further surgical correction; sinusitis occurred in one patient (4.1%). Titanium mesh is a reliable option for orbital reconstruction, despite some complications found in this sample.

Persistent diplopia after retrobulbar anesthesia

PURPOSE

To determine the causative factors of persistent diplopia after retrobulbar anesthesia.

SETTING

Strabismus Section, Department of Ophthalmology, Seoul National University, Seoul, South Korea.

METHODS

Prism and alternate cover tests in the diagnostic positions of gaze and ductions/versions were performed in 28 patients with persistent diplopia 6 months after retrobulbar anesthesia. The Lancaster test, Bielshowsky head tilt test, double Maddox rod test, fundoscopic examination for torsion, forced duction test, force generation test, tensilon test, thyroid function test, and/or orbit computed tomography were performed when necessary.

RESULTS

Most of the patients (26 patients, 93%) did not have diplopia before retrobulbar anesthesia. Of the 14 patients with extraocular muscles imbalance, 12 patients showed vertical rectus overaction (11 superior recti, 1 inferior rectus) and 2 patients, mild vertical rectus underaction. Nine patients were presumed to have a sensory strabismus related to the preoperative poor vision, but this went unnoticed preoperatively. Three patients showed a small vertical deviation without any specific causative factors.

CONCLUSIONS

Fifty percent of the cases of diplopia were associated with either direct trauma or anesthetic myotoxicity to the extraocular muscles, in which overactions were more common than underactions. Thirty-two percent of the patients were presumed to have sensory strabismus, which suggested the importance of preoperative examination for strabismus as well as providing an explanation about the risk of postoperative diplopia before surgery.

Demographics and treatment options for orbital roof fractures

OBJECTIVE

The purpose of this article was to review the frequency, germane anatomy, management modalities, and complications associated with the treatment of orbital roof fractures in the pediatric and the adult population.

STUDY DESIGN

A review of the past 30 years of the English-language maxillofacial surgical literature was undertaken. Important concepts were coupled with the authors' experience to provide a synopsis of contemporary thought on this topic.

RESULTS

More than 235 articles in the oral and maxillofacial, plastic and reconstructive, otolaryngology-head and neck, ophthalmologic, oculoplastic, neurologic, and pediatric surgical literature were reviewed and assessed. From this group, 50 articles were found to contain useful information.

CONCLUSIONS

It has been estimated that 1% to 9% of all facial fractures involve the orbital roof. The typical adult with an orbital roof fracture is a man (89%-93%) who has been involved in a high-energy impact and who has sustained concomitant multisystem injuries (57%-77%). Orbital roof fractures most commonly coexist with other craniofacial injuries. In contrast, in pediatric patients with an orbital roof injury, we see nearly equal sex distribution; the typical patient in this case has a frontobasal fracture that is minimally displaced or nondisplaced (53%-93%) and has sustained concomitant multisystem injuries. The pediatric patient is usually managed by means of observation alone (53%-86%). For the adult patient, a subcranial approach to the orbital roof by means of a bitemporal flap or superior blepharoplasty incision offers wide access with minimal morbidity. Currently available titanium microscrew and miniscrew and mesh systems offer a near-ideal modality for orbital roof reconstruction. The coexisting neurocranial, frontal sinus, and supraorbital rim fractures take priority over the management of orbital roof fractures. Complications associated with orbital roof injuries can be categorized as those attributed to the following: concomitant injury, surgical access, postreconstruction volume discrepancy, muscle entrapment, hemorrhage, and/or infection.

Measurement of orbital volume by a 3-dimensional software program: an experimental study

PURPOSE

This study reports a simple method with high accuracy for determining orbital volume from computed tomography (CT) scans.

MATERIALS AND METHODS

The volume of 20 orbits was evaluated in 20 dry skulls by use of a 3-dimensional software program in General Electric High-Speed Advantage CT/I (Milwaukee, WI), and compared with the volume obtained by direct measurement using the water displacement method. Accuracy of volume measurement by this software program was assessed statistically by paired samples t-test.

RESULTS

The mean volume was found to be 28.37 mL +/- 2.15 by direct impression and 28.41 mL +/- 2.09 by the software program. Volume difference between the 2 methods averaged 0.93 +/- 1.08 mL for each orbit (P < .01). The correlation between the techniques was found to be high (r = 0.887, P < .01). There was no significant volume discrepancy between the 2 methods.

CONCLUSION

Measurement by the technique described is an easy and accurate method of assessing the volume of the orbit.

An evaluation of the support provided by common internal orbital reconstruction materials

PURPOSE

The objectives of this investigation were to assess the weight of the combined internal orbital contents, to evaluate the ability of common internal orbital reconstruction materials to resist loads, and to determine whether these materials provide enough load resistance to support the orbital contents.

MATERIALS AND METHODS

The combined exonerated internal orbital contents (globe, fat, extraocular musculature, neurovascular structures, lacrimal apparatus, and musculocutaneous lids) from 16 human orbits were weighed. Five each of 13 different internal orbital reconstruction materials (titanium mesh, bioresorbables, Marlex [CR Bard, Cranston, RI], Medpore [Porex Medical, College Park, GA], Silastic [Dow Coming, Midland, MI], dried calvarium) were evaluated for their ability to resist loads applied by Instron 85.11 mechanical testing device (Canton, MA) when used to reconstruct uniform orbital floor defects in synthetic skulls (Sawbones, Vashon Island, WA). Yield load, yield displacement, maximum load, and displacement at maximum load were measured. A comparison was then made between orbital content weight and the load-resisting capabilities of the various materials.

RESULTS

The weight of the combined internal orbital contents was 42.97+/-4.05 g (range, 37.80 to 51.03 g). All of the materials tested except Marlex mesh met or exceeded the requirements for support of the combined internal orbital contents.

CONCLUSION

Except in the instance of complete loss of the orbital floor, all of the materials tested should provide adequate orbital support.