CLINICAL SCIENCES The Lacrimal Keyhole, Orbital Door Jamb, and Basin of the Inferior Orbital Fissure Three Areas of Deep Bone in the Lateral Orbit Robert Alan Goldberg, MD; Alexander J. Kim, MD; Kristine M. Kerivan Objectives: To calculate the volume of bone in 3 areas 3 areas of potential bone were delineated within it. of the deep lateral orbit that are available for removal in decompression surgery and to demonstrate these 3 ar- Results: The average volumes of the basin of the inferior eas within a 3-dimensional computed tomographic re- orbital fissure, the sphenoid door jamb, the lacrimal key- construction of the orbit. hole, and the total of the 3 regions were 1.2, 2.9, 1.5, and 5.6 cm3, respectively. The 3 areas of bone contributed vari- Design: The 3 areas of bone in the deep lateral orbit were ably to the total, with the door jamb contributing the most designated the lacrimal keyhole, the sphenoid door jamb, and volume of the 3, nearly twice the value of the other 2. There the basin of the inferior orbital fissure. By means of digi- was, however, a significant amount of interpatient vari- tized computed tomographic scans, these 3 areas of bone ability, especially for the door jamb region. were analyzed by measuring preoperative and postopera- tive orbital volumes and predicted bony expansion vol- Conclusion: Orbital decompression surgery of the deep umes in 9 patients (17 orbits) who underwent deep lat- lateral wall can provide adequate volume expansion be- eral orbital decompression surgery. We also calculated the cause of the amount and location of potential space that volume of bone that could be removed from 11 normal exists in the 3 areas of deep bone. orbits. A 3-dimensional computer reconstruction of an orbital computed tomographic scan was created, and the Arch Ophthalmol. 1998;116:1618-1624 RBITAL decompression sion surgery. These areas are conceptual surgery is indicated in rather than anatomical structures, and we Graves orbitopathy for find them helpful in surgical planning. The optic nerve compres- 3 areas of thick bone are designated the sion, corneal exposure, lacrimal keyhole, sphenoid door jamb, and Odisfiguring proptosis, and compressive or- the basin of the inferior orbital fissure.By bitopathy. Traditional lateral orbital de- means of digitized computed tomogra- compression involves removal of the an- phy (CT), these 3 areas of bone were ana- terior portion of the lateral orbital wall and lyzed by measuring preoperative and post- is limited in the degree of orbital expan- operative orbital volumes and predicted sion that can be achieved.1 There is, how- bony expansion volumes in 9 patients (17 ever, considerable room for orbital expan- orbits) who underwent deep lateral or- sion in the lateral part of the orbit if the bital decompression surgery. We also cal- thicker, deep areas of lateral wall are re- culated the volume of bone that could po- moved. These are the surfaces that were tentially be removed from 11 normal removed in the historic neurosurgical ap- orbits. A 3-dimensional computer recon- proaches; they can be successfully re- struction of an orbital CT scan was cre- moved through an orbital approach with ated, and the 3 areas of potential bone were adequate anatomical knowledge. The deep delineated within the 3-dimensional or- lateral wall can be accessed through a coro- bital image. nal, lateral cutaneous (for example, eye- lid crease), or lateral transconjunctival From the Division of Orbital RESULTS and Ophthalmic Plastic (subcanthal) approach. Surgery, Jules Stein Eye We have found it helpful to concep- Eleven normal orbits were sampled to es- Institute, University of tualize the 3 separate areas of thick bone timate the amount of potential bone avail- California–Los Angeles School in the lateral orbit that are amenable to re- able in the deep lateral orbit. The total of Medicine. moval in deep lateral orbital decompres- amount of potential bone available in the 3 ARCH OPHTHALMOL / VOL 116, DEC 1998 1618 ©1998 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 10/03/2021 MATERIALS AND METHODS keyhole (Figure 2). It is a wedge-shaped section of bone in the superior orbit that begins with a full-thickness notch in the superolateral rim. It extends into the entire fossa of CT SCANNING the lacrimal gland. It is limited externally by the tempora- lis muscle, medially by the point at which the orbital roof Volume measurements of orbital bony and soft tissue struc- thins as the thin frontal bone, and posteriorly by the fron- tures were obtained by importing axial orbital CT scans tal cranial fossa and the posterior thick border of the lesser (1.5-mm or 3-mm thickness, contiguous slice) into the NIH wing of the sphenoid; inferiorly it blends into the thick tri- Image computer program (National Institutes of Health, gone of the greater wing of the sphenoid (the door jamb) Bethesda, Md). With the use of NIH Image, consecutive CT (Figure 3). The lacrimal keyhole forms a potential space scan slices were displayed on a computer monitor and a “draw” in which the lacrimal gland and the associated fibroadi- function was used to outline the perimeters of the struc- pose structures can prolapse laterally and superiorly; the tures, either bone or soft tissue, from which computer- lacrimal gland can actually prolapse outside of the orbital generated area measurements were obtained (Figure 1). The boundary, providing substantial volume expansion. The volume of each structure was calculated by multiplying the thick posterior portion of the lesser wing of sphenoid in area of the outlined structure by the thickness of each scan the region that separates the frontal and middle cranial fos- slice; the sum of volumes from the scan slices were added to sae is a rich area of thick bone that is responsible for much compute the volume occupied by the measured structure. The of the decompression achieved by the transcranial ap- scans were measured by 3 independent observers (R.A.G., proach; it can be removed from the orbital side, providing A.J.K., and K.M.K.); a high level of interobserver consis- substantial orbital volume expansion. tency was found, with agreement within 2%. The door jamb is formed of the greater wing of the For 9 patients who underwent bilateral decompression sphenoid. The thick trigone of the greater wing is a large of the lateral wall only, preoperative and postoperative CT marrow-filled bone that laterally borders the inferotempo- scans were analyzed. First, preoperative CT scans were ex- ral fossa (temporalis muscle) and posteriorly borders the amined and the volume was calculated for each of the 3 ar- middle cranial fossa (Figure 4). Not only is this the most eas of deep bone to be removed. These measurements served voluminous bony area of the 3 deep regions of bone, but as predictions of the volume available for potential orbital ex- also this bone lies almost directly posterior to the globe. pansion. Measurements of orbital soft tissue volume were then In the case of a “woody” orbit, removal of the door jamb calculated on each preoperative scan. The postoperative or- can allow posterior displacement of the globe in an orbit bital soft tissue volumes were also calculated. The postop- that has little ability to expand its lateral shape. Therefore, erative scans were also examined to determine the extent of in these fibrotic orbits, the door jamb area may be the only soft tissue expansion into the newly created orbital spaces. area of bone that can effectively reduce proptosis. Inferi- Axial CT scans of 11 orbits with normal bony anatomy orly, the door jamb consists of the thick part of the greater were also examined. The scans were from 7 women and 4 wing of the sphenoid that borders the inferior orbital fis- men, ranging in age from 30 to 84 years. The perimeters sure on its superolateral edge. In a maximal deep lateral of each of the 3 areas of deep bone that could potentially orbital decompression, the inferior orbital fissure is com- be removed for deep lateral orbital decompression were out- pletely deskeletonized. lined, and the volumes of the bony areas were calculated. The basin of the inferior orbital fissure consists pri- Including the 17 preoperative orbits from our 8 surgical marily of zygomatic bone and part of the lateral maxilla patients, a total of 28 orbits were sampled. (Figure 5). The body of the zygoma can be sculpted un- A 3-dimensional reconstruction of a normal orbit high- til there is only a thin rim of bone along the lateral orbital lighting the 3 bony areas available for deep lateral orbital rim and face of the zygoma, allowing a large segment of decompression was obtained by downloading an axial CT space for inferolateral prolapse of orbital adipose tissue. Me- scan (1.5-mm thickness, contiguous slices) into a 3- dially, the basin of the inferior orbital fissure can be re- dimensional graphic computer workstation. The lacrimal moved all the way to the zygomatic-maxillary suture. The keyhole, sphenoid door jamb, and basin of the inferior or- lateral portion of the maxillary sinus roof can also be re- bital fissure were then highlighted, allowing for visualiza- moved, and the sinus can be entered for some additional tion from different angles. prolapse of tissue. Near the inferior orbital fissure the zy- goma thins, and removal of bone in this region typically SURGICAL ANATOMY exposes the buccal fat; the buccal fat can be cauterized both to reduce its volume, allowing outward prolapse of orbital The frontal bone, part of the lesser wing of the sphenoid, tissues, and also to keep the buccal fat from flowing into and a small portion of the greater wing form the lacrimal the surgical field and obstructing further drilling.