Anatomic Moment

Osseous of the Orbital Apex

David L. Daniels, Leighton P. Mark, Mahmood F. Mafee, Bruce Massaro, Lloyd E. Hendrix, Katherine A. Shaffer, David Morrissey, and Charles W. Horner

The osseous anatomy of the orbital apex may floor of the , with the zygomatic form- be difficult to conceptualize because of the dif- ing its anterior margin. Important anatomic re- ferent shapes and orientations of the optic ca- lationships of the inferior orbital are nal, superior and inferior orbital , and demonstrated when the is viewed laterally . However, knowing this and slightly posteriorly (Fig 2). The sphenoid anatomy is crucial to evaluate complex frac- bone forms the lateral margin of the inferior tures, tumors, and inflammatory processes in- orbital fissure and most of the posterior wall of volving the orbital apex. the pterygopalatine , the latter formed by Evaluating osseous anatomy of the orbital the pterygoid plates, the of the sphenoid apex with computed tomography (CT) requires bone, and a small part of the vertical plate of the knowledge of its three-dimensional appearance . The maxillary bone forms the (1–8). The optic forms an angle of about medial margin of the and 45Њ with the sagittal plane of the head, slightly together with the orbital process of the palatine tapers anteriorly, and is bounded medially by bone, also the anterior wall of the pterygopala- the body of the , superiorly by the tine fossa. The obliquely extending inferior or- superior root of the lesser wing of the sphenoid bital fissure and the more medially positioned bone, inferolaterally by the optic strut (that is, and transversely oriented the inferior root of the lesser wing of the sphe- together form a gently curving opening. The noid bone), and laterally by the anterior clinoid anterior part of the inferior orbital fissure ap- process (Fig 1). Inferolateral to the pears bulbous. The posterior part of the inferior and separated from it by the optic strut is the orbital fissure is best shown in coronal CT, ap- , a gap between the pearing as a thin, obliquely oriented, and ante- greater and lesser wings of the sphenoid bone riorly tapering channel bounded laterally by the that is somewhat comma-shaped, appearing bulbous inferiorly and thin superolaterally (Fig sphenoid bone and medially by the maxillary 1). The fissure’s bulbous part is located anterior bone and communicating inferolaterally with to the . Just inferior and poste- the (Figs 5–8). rior to the superior orbital fissure is the foramen Important osseous landmarks facilitate the rotundum, a parasagittally oriented thin chan- evaluation of the orbital apex in axial and coro- nel at the upper part of the base of the sphenoid nal CT (Figs 3–5). These landmarks include the bone, which has a trough-shaped posterior con- optic strut, which separates the optic canal from figuration (Fig 1). The foramen rotundum com- the superior orbital fissure, and the small seg- municates posteriorly with the middle cranial ment of the sphenoid bone, which separates the fossa and anteriorly with the upper part of the superior orbital fissure from the foramen rotun- pterygopalatine fossa. dum (Figs 3B and D). In addition, the upper- The pterygopalatine fossa and the inferior or- most part of the pterygopalatine fossa, having a bital fissure have a unique relationship. The in- flat posteromedial margin and a posterolateral ferior orbital fissure, its long forming an corner where it communicates with the foramen angle of about 45Њ with the head’s sagittal rotundum, can be demonstrated on axial CT plane, is located between the lateral wall and (Fig 4D).

From the Departments of (D.L.D., L.P.M., L.E.H., K.A.S., D.M., C.W.H.) and Ophthalmology (B.M.), Medical College of Wisconsin, Milwaukee and the Department of Radiology, University of Illinois at Chicago (M.F.M.). Address reprint requests to David L. Daniels, MD, Department of Radiology, Medical College of Wisconsin, Doyne Clinic/DH 151, 8700 W Wisconsin Ave, Milwaukee, WI 53226. AJNR 16:1929–1935, Oct 1995 0195-6108/95/1609–1929 ᭧ American Society of Neuroradiology 1929

AJNR: 16, October 1995 ANATOMIC MOMENT 1935

Acknowledgments 4. Daniels DL, Yu S, Pech P, Haughton VM. Computed tomography and magnetic resonance imaging of the orbital apex. Radiol Clin We thank Scott Erickson, MD, and Phillip Jones for their North Am 1987;25:803–817 help in preparing this Anatomic Moment. 5. Williams PL, Warwick R, Dyson M, Bannister LH, eds. Gray’s Anat- omy. 35th ed. London: Churchill Livingstone; 1989:346–347 6. Potter GD, Trokel SL: Optic canal. In: Newton TH, Potts DG, eds. References Radiology of the Skull and . Great Neck, NY: Medi-Books; 1986;1:487–507 1. Anderson JE. Grant’s of Anatomy. Baltimore, Md: Williams & 7. Wolff E, ed. Anatomy of the and Orbit. 7th ed. Philadelphia, Pa: Wilkins; 1978 WB Saunders; 1976 2. Daniels DL, Pech P, Kay MC, et al. Orbital apex: correlative ana- 8. Zide BM, Jelks GW. Surgical Anatomy of the Orbit. New York, NY: tomic and CT study. AJNR Am J Neuroradiol 1985;6:705–710 Raven Press; 1985 3. Daniels DL, Rauschning W, Lovas J, et al. Pterygopalatine fossa: computed tomographic studies. Radiology 1983;149:511–516