A Iln 0101 88 :1979
SURGICAL ANATOMY OF THE ORBIT EUGENE RONTAL, MD MICHAEL RONTAL, MD
F. T. GUILFORD, MD
SOUTHFIELD, NhcIDCAN
When operating in and around the orbit, the key to a successful operative result is precise, anatomic localization. This study was constructed to give pertinent anatomic measurements to which the maxillofacial surgeon may refer. The safe distances noted from this study are: 1) medially 30 mm from the anterior lacrimal crest; 2) inferiorly 25 mm from the infraorbital foramen; 3) superiorly 30 mm from the supraorbital notch; and 4) laterally 25 mm from the frontozygomatic suture.
To the maxillofacial surgeon the orbit is frequently regarded as an area to be approached with great trepidation. The possibility of injury to the optic nerve, the globe and its associated structures makes this fear a reality. The possibilities of injuries are enhanced by the tight quarters encountered during surgery. Wide surgical exposure is difficult because of the presence of the globe occupying a large portion of the anterior confines in its rigid bony container. Thus, the surgeon is frequently presented with a decision of limiting his surgical exposure in order to prevent injury to the eye. Modem surgical procedures to the orbit require more precise understanding of the surrounding anatomy. While the relationships within the orbit are widely described in most standard anatomy and specialty texts, these relationships have only been elucidated in cross sectional and gross evaluations and have been directed primarily to suppuration of the sinuses.':" A precise knowledge of the orbital measurements will allow the surgeon the flexibility of working from within and from without the orbit and still preserve function. Anthropological measurements of the eyes have been made, but these have been too imprecise for the purposes of the orbital surgeon.' Individual authors have made attempts at measuring distances in the orbit, but these have not looked at the orbit in its entirety.v"
The orbit is a four-walled unit. Each surface has its own clinically important structures which if injured can cause specific and significant debilitating complications. Correspondingly, each wall has a reference point from which distances to these endangered anatomic structures can be measured. This study was constructed to more precisely identify danger areas within the orbit. Anatomic measurements from fixed points on the orbital rim were taken from dried skulls. It is the purpose of this paper to utilize these anatomic measurements to guide the maxillofacial surgeon in constructing a successful therapeutic regime. METHODS AND MATERIALS To study the interrelationships of important structures and landmarks in the bony walls of the orbit, direct measurements were taken from dry skulls. Skulls used were all imported from India and have been cleaned and prepared in the usual manner. These skulls were all determined by dentition to be adult. Males and females were separated by the prominence of the occipital protuberance. Forty-eight orbits (24 skulls) were studied. The measurements were made using calipers and metal scales. All measurements were made by the authors. On each of the four walls of the orbit (medial, inferior, superior and lateral) an easily identified and readily accessible constant structure on the rim was selected. From this landmark measurements were taken to the nearest aspect of the structure measured. The medial wall is bounded superiorly by the frontal lacrimal suture and the frontal
From the Department of Otorhinolaryngology, University of Michigan Medical School, Ann Arbor, Michigan; and the Section of Otolaryngology, Sinai Hospital, Detroit, Michigan. Presented at the meeting of the American Academy of Facial Plastic and Reconstructive Surgery. Inc., Boston, Massachusetts, April 1977.
382
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SURGICAL ANATOMY OF THE ORBIT
TABLE 1. MEASUREMENTS OF THE MEDIAL ORBITAL WALL
Measured from the anterior lacrimal crest to: Anterior ethmoidal foramen Posterior ethmoidal foramen Optic canal - medial aspect Posterior lacrimal crest Measured from the plane of the anterior and posterior ethmoidal foramina to: Maxillary ethmoidal suture Measured from the posterior ethmoidal foramen to: Anterior ethmoidal foramen Optic canal - medial aspect
Mean (mm)
Range
24 36 42 8
20-28 29-40 37-48 5-10
13
7-17
11 7
5-16 3-12
(mm)
is the frontozygomatic suture. From this point readings were taken to the lacrimal foramen; to the superior orbital fissure; to the inferior orbital fissure; and to the superior aspect of the optic canal. Fig. 1. Illustration of medial wall of the orbit. ethmoidal suture (Fig. 1). A key reference point of the medial wall is the anterior crest of the lacrimal fossa. From this point three measurements were taken along the medial wall. These were from the anterior crest of the lacrimal fossa to the foramen of the anterior ethmoidal artery, to the most posterior aspect of the ethmoidal foramina and to the medial aspect of the optic canal. Measurements were also taken from the anterior ethmoidal foramen perpendicular to the maxillary ethmoidal suture. The inferior wall is defined as bounded medially by the lacrimal suture and the maxillary ethmoidal suture and posteriorly ends at the optic canal. The main reference point is the infraorbital foramen. Five separate readings were taken from this point: to the lateral margin of the lacrimal fossa; to the inferior orbital fissure; to the posterior end of the covering of the infraorbital nerve; to the posterior wall of the maxilla; and to the inferior aspect of the optic canal (Fig. 1). The superior wall conforms to the orbital roof and is made up of portions of the zygomatic, frontal and sphenoid bones. The most common point on the superior rim is the supraorbital notch, or foramen. From this point measurements were taken of the superior rim of the optic canal to the superior orbital fissure and to the lacrimal foramen when present. Measurements were also taken from the posterior ethmoidal foramen to the superior orbital fissure (Fig. 1). The lateral wall of the orbit is formed by the zygomatic and sphenoid bones. On the lateral rim, the most constant reference point
From these measurements, sample means, standard deviations of the sample and standard error means were developed. To test differences between left and right and between male and female orbits, the t-test for the difference of two means was used. This indicated that there was no difference between right and left or between male and female orbits with greater than 95% confidence. The above statistical analysis confirmed that it is correct to consider each of the 48 orbits as an independent entity. The distances from the anterior ethmoidal artery to the posterior ethmoidal artery and from the posterior ethmoidal artery to the medial aspect of the optic canal are derived from subtraction of these measurements. RESULTS
Table 1 describes the measurements obtained on the medial wall. In all but one orbit, the anterior ethmoidal artery was found. In that one specimen, a common opening for the anterior and posterior ethmoidal vessels and nerves was noted. Twelve of the 48 orbits had more than one foramen posterior to the anterior opening. It is important to note that the optic canals averaged approximately 4 cm from the anterior lacrimal crest. Further, the skulls examined averaged 7 mm between the posterior ethmoidal foramen and the optic canal itself. The inferior wall measurements are seen in Table 2. While 48 mm was the mean value distance to the optic fora-
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RONTAL ET AL
TABLE 2. MEASUREMENTS OF THE I;\JFERIOR ORBITAL WALL - MEASURED FROM THE INFERIOR ORBITAL FORAMEN
Lateral margin of the lacrimal fossa Inferior orbital fissure Covered portion of the infraorbital nerve Posterior wall of the maxilla Optic canal - inferior aspect
TABLE 4. MEASUREMENTS OF THE LATERAL ORBITAL WALL - MEASURED FROM THE FRONTOZYGOMATIC SUTURE
Mean
Range
Mean
Range
(mm)
(mm)
(mm)
(mm)
25
13 24
8-18 20-27
14 36 48
8-28 26-44 40-54
12-33 28-38 39-46 20-30
men, there was variance up to 5.4 em from the inferior orbital foramen. The distances along the superior orbital wall are seen in Table 3. The distances here were similar to those seen along the medial wall of the orbit. Specifically, the optic canal was encountered at roughly 43~ em from the supraorbital notch. The lateral wall measurements are seen in Table 4. As in the measurements of the other three walls, the optic canal appeared to average between 4 and 5 em from the reference point along the rim of the orbit. DISCUSSION
Earlier in this century, as otolaryngologists treated life-threatening suppurations of the paranasal sinuses, many complete descriptions were made of these cavities. Studies by Mosher,'; Schaeffer,":" Vanalyea" and others 1 0 - 14 discussed the embryologic, childhood, and adult anatomy and its variations. However, these articles do not describe the orbital contents in relation to modern day orbital procedures. By the TABLE 3. MEASUREMENTS OF THE SUPERIOR ORBITAL WALL Mean
Range
(mm)
(mm)
Measured from the supraorbital notch or foramen to: Superior orbital fissure 40 Lacrimal foramen 32 Optic canal - superior aspect 45 Measured from the posterior ethmoidal foramen to: Superior orbital fissure 13
35-45 28-41 40-50
11-17
Lacrimal foramen Superior orbital fissure Optic canal - lateral aspect Inferior orbital fissure
35 43
25
same measure, standard orbital anatomy treatises detail the intraorbital structures without correlation to the surounding extraorbital anatomy. Today, head and neck procedures regularly traverse the orbit and a need has arisen to show the anatomic interrelationships. The precise knowledge will aid diagnosis, plan treatment and avoid loss of ophthalmologic function. The bony walls represent a constant guide to the orbit. Measurements of the pertinent and constant structures of the bony walls become the basis of safe and efficient surgical success.
Medial Wall. The anatomy of the medial wall is the key to an uncomplicated result for seven standard orbital head and neck procedures. These include: 1) ethmoid vessel ligation; 2) exploration of the medial wall fractures; 3) ethmoid sinus exenteration; 4) orbital decompression; 5) transethmoidal sphenoidotomies; 6) closure of cerebrospinal fluid leakage; and 7) transethmoidal, sphenoidal hypophysectomy. Entrance to the medial wall is via the frontal ethmoidal incision. This places the operator on the frontal process of the maxilla. The only constant landmark on this process is the anterior lacrimal crest. It was felt that this was a more constant structure than the maxillo-nasal-lacrimal junction of Kirchner et aJ.15 Beyond 2 em from the anterior lacrimal crest, the anterior ethmoidal artery is found. This is in, or just above, the frontal ethmoidal suture. The anterior ethmoidal vessel found at the upper extent of the medial wall is constant. A horizontal plane passing through this vessel is the key landmark to safe dissection. During subperiosteal dissection, the posterior ethmoidal foramina are found along the plane of the anterior
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SURGICAL ANATOMY OF THE ORBIT
TABLE 5. MAXIMUM DISTANCE FOR SAFE ORBITAL EXPLORATION Distance
Wall
(mm)
M easured from
Medial Inferior Superior Lateral
30
Anterior lacrimal crest Inferior orbital foramen Supraorbital notch Frontozygomatic suture
25 30
25
ethmoidal foramen. Twenty-five percent of our specimens had more than one posterior ethmoid foramen. This is in agreement with other studies. 15, ,,) One orbit had only one ethmoid foramen. As noted by Kirchner et al,'5 it may be important to find all posterior ethmoidal vessels in surgery for epistaxis. The next structure behind the posterior ethmoidal vessels is the optic foramen. The distance between the posterior ethmoidal foramen and the optic nerve is a variable distance but no less than 3 mm. Therefore, no bone should be removed posterior to the medial wall farther back than the last ethmoid foramen. In summary, a measurement of 30 mm from the anterior lacrimal crest to the lacrimal bone should be used as the indication of safe distance for dissection along the medial wall. Dissection beyond this point must be done with great caution (Table 5). Inferior Wall. Orbital floor exploration and maxillectomy comprise the majority of intraorbital operations along the inferior wall. The initial incision in each of these procedures is carried down to the orbital rim. Once at the rim the periosteum should be elevated without transgressing the orbital septum. Entrance through the orbital septum will be evidenced by herniation of orbital fat. Entry through this adipose tissue may cause injury to the inferior oblique and inferior rectus muscles lying anteriorly. The infraorbital foramen is in line with the supraorbital notch and the middle foramen. This roughly corresponds to a point half way along the infraorbital rim. The lateral portion of the orbital floor is safer to explore than the medial, since the inferior rectus and inferior oblique muscles are more medially located within the orbit. Thus, medial floor blowout fractures are more likely to cause entrapment." Safe posterior
385
dissection of the orbit may be accomplished as long as the bony wall is closely followed. The posterior wall of the maxilla lies as close as 26 mm from the infraorbital foramen. This wall should be considered as the maximum safe distance for intraorbital dissection, since beyond this point there are no bony landmarks for reference. The optic foramen lies on an average of 12 mm beyond this point. To injure the nerve directly, dissection must pass superior, medial and posterior from the posterior wall of the maxilla." Emphasis during inferior floor dissection should be placed on maintaining contact with the bone. If this bony contact is lost, the intraorbital, inferior floor dissection beyond 25 mm from the infraorbital foramen should be done with great caution. Superior Wall. The superior wall is the guide to seven basic transorbital wall head and neck procedures. These are: 1) frontal ethmoidectomy; 2) frontal sinus trephine; 3) frontal sinus obliteration; 4) orbital decompression; 5) exploration for fractures; 6) lacrimal gland excision; and 7) orbital exenteration. Other than for orbital decompression the superior orbit is entered through the incisions just below the eyebrow. These incisions must be placed to avoid the supraorbital nerve and the elevator muscle of the upper lid. The supraorbital notch is constantly found in a parasagittal plane connecting the mental foramen with the infraorbital foramen. The levator muscle is avoided by placing the incision as high as possible, dissecting at right angles to the skin down to the superior orbital rim. Within the orbit, the periosteum can be elevated without danger from the frontal ethmoid suture through the frontal zygomatic suture and as far posteriorly as 30 mm. This allows a 5 mm tolerance to the most anterior aspect of the closest superior orbital fissure that we found, and avoids damage to the optic nerve.
Lateral Wall. Along the orbital wall laterally, the basic intraorbital operations are explorations of orbital fractures, lateral orbitotomy (Kronleinw ) and excision of the lacrimal gland. In all lateral intraorbital procedures the danger of damage to the superior
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orbital fissure or the optic nerve is minimal. Through the superior orbital fissure at the orbital apex pass cranial nerves III, IV, VI, the ophthalmic branch of V, and the ophthalmic vein. The fissure is found to lie no closer than 28 mm from the frontal zygomatic suture at the rim. Due to the curved nature of the orbit and the limited access to this area, it would be difficult and unnecessary to
proceed to this depth during any intraorbital procedure." Likewise, the optic nerve lies 8 mm behind the medial edge of the fissure and would also be under minimal danger from this approach. Therefore, as long as a distance of 25 mm from the frontal zygomatic suture is maintained, safe dissection can be carried out on the lateral orbital wall (Table 5).
REFERENCES
1. Hollinshead WH: Anatomy for Surgeons. New York, Harper & Row Publishers, 1968, vol 1, pp 107-182 2. Warwick R, Williams PL: Gray's Anatomy. Philadelphia, W B Saunders Co, 1973, pp 262-265 3. Ritter FN: The Paranasal Sinuses. St. Louis, C V Mosby Co, 1973 4. Warwick R: Anatomy of the Eye and Orbit. Philadelphia, W B Saunders Co, 1976, pp 1-29 5. Nakagawa G: Schemes of the serial frontal sections of the orbit and its contents. Jpn J Ophthalmol 15:152-162, 1971 6. Mosher HP: Symposium on the ethmoid: The surgical anatomy of the ethmoidal labyrinth. Trans Am Acad Ophthalmol Otolaryngol 31:376-410, 1929 7. Schaeffer JP: Sinus maxillaris and its relations in the embryo, child and adult man. Am J Anat 10:313-368, 1910 8. Schaeffer JP: The genesis, development and adult anatomy of the nasal-frontal region of man. Am J Anat 20:125-146, 1916 9. Van Alyea OE: Sphenoid sinus. Arch Otolaryngol 34:225-253, 1941 10. Goodyear HM: Ophthalmologic conditions referable to disease of the paranasal sinuses. Arch Otolaryngol 48:202-208, 1948 11. Dixon FW: Comparative study of the REPRINTS -
sphenoid sinus. Ann Otol Rhinol Laryngol 46: 687-698, 1937 12. Vail HH: Retrobulbar optic neuritis originating in the nasal sinuses. Arch Otolaryngol 13:846-863, 1931 13. Mosher HP: Anatomy of the sphenoidal sinus and the method of approaching through the antrum. Laryngoscope 13:177-214, 1903 14. Van Alyea OE: Frontal cells. Arch Otolaryngol 341: 11-23, 1941 15. Kirschner JA, Yanagisawa E, Crelin ES: Surgical anatomy of the ethmoidal arteries. Arch Otolaryngol 74:382-386, 1961 16. Takahashi R: Clinicoanatomical studies of the canalis orbitocranialis and canalis orbitoethmoidalis in relation to the ethmoid cells, in Takahashi R (ed ): A Collection of Ear, Nose and Throat Studies. Tokyo, Kyoya Co, 1971, pp 174-204 17. Gozum E: Blowout fractures of the orbit. Otolaryngol Clin North Am 9:477-487, 1976 18. Okashi J: Evaluation of the various routes for operation of the paranasal sinuses, especially the ethmoid cells from the standpoint of the angle and field of exposure, in Takahashi R (ed): A Collection of Ear, Nose and Throat Studies. Tokyo, Kyoya Co, 1971, pp 524-542 19. Stellard HB: Eye Surgery. Baltimore, Williams and Wilkins, 1973, pp 862-878
Eugene Rontal, MD, 21700 Northwestern Highway, Southfield, MI 48075.
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SURGICAL ANATOMY OF THE ORBIT EUGENE RONTAL, MD MICHAEL RONTAL, MD
F. T. GUILFORD, MD
SOUTHFIELD, NhcIDCAN
When operating in and around the orbit, the key to a successful operative result is precise, anatomic localization. This study was constructed to give pertinent anatomic measurements to which the maxillofacial surgeon may refer. The safe distances noted from this study are: 1) medially 30 mm from the anterior lacrimal crest; 2) inferiorly 25 mm from the infraorbital foramen; 3) superiorly 30 mm from the supraorbital notch; and 4) laterally 25 mm from the frontozygomatic suture.
To the maxillofacial surgeon the orbit is frequently regarded as an area to be approached with great trepidation. The possibility of injury to the optic nerve, the globe and its associated structures makes this fear a reality. The possibilities of injuries are enhanced by the tight quarters encountered during surgery. Wide surgical exposure is difficult because of the presence of the globe occupying a large portion of the anterior confines in its rigid bony container. Thus, the surgeon is frequently presented with a decision of limiting his surgical exposure in order to prevent injury to the eye. Modem surgical procedures to the orbit require more precise understanding of the surrounding anatomy. While the relationships within the orbit are widely described in most standard anatomy and specialty texts, these relationships have only been elucidated in cross sectional and gross evaluations and have been directed primarily to suppuration of the sinuses.':" A precise knowledge of the orbital measurements will allow the surgeon the flexibility of working from within and from without the orbit and still preserve function. Anthropological measurements of the eyes have been made, but these have been too imprecise for the purposes of the orbital surgeon.' Individual authors have made attempts at measuring distances in the orbit, but these have not looked at the orbit in its entirety.v"
The orbit is a four-walled unit. Each surface has its own clinically important structures which if injured can cause specific and significant debilitating complications. Correspondingly, each wall has a reference point from which distances to these endangered anatomic structures can be measured. This study was constructed to more precisely identify danger areas within the orbit. Anatomic measurements from fixed points on the orbital rim were taken from dried skulls. It is the purpose of this paper to utilize these anatomic measurements to guide the maxillofacial surgeon in constructing a successful therapeutic regime. METHODS AND MATERIALS To study the interrelationships of important structures and landmarks in the bony walls of the orbit, direct measurements were taken from dry skulls. Skulls used were all imported from India and have been cleaned and prepared in the usual manner. These skulls were all determined by dentition to be adult. Males and females were separated by the prominence of the occipital protuberance. Forty-eight orbits (24 skulls) were studied. The measurements were made using calipers and metal scales. All measurements were made by the authors. On each of the four walls of the orbit (medial, inferior, superior and lateral) an easily identified and readily accessible constant structure on the rim was selected. From this landmark measurements were taken to the nearest aspect of the structure measured. The medial wall is bounded superiorly by the frontal lacrimal suture and the frontal
From the Department of Otorhinolaryngology, University of Michigan Medical School, Ann Arbor, Michigan; and the Section of Otolaryngology, Sinai Hospital, Detroit, Michigan. Presented at the meeting of the American Academy of Facial Plastic and Reconstructive Surgery. Inc., Boston, Massachusetts, April 1977.
382
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383
SURGICAL ANATOMY OF THE ORBIT
TABLE 1. MEASUREMENTS OF THE MEDIAL ORBITAL WALL
Measured from the anterior lacrimal crest to: Anterior ethmoidal foramen Posterior ethmoidal foramen Optic canal - medial aspect Posterior lacrimal crest Measured from the plane of the anterior and posterior ethmoidal foramina to: Maxillary ethmoidal suture Measured from the posterior ethmoidal foramen to: Anterior ethmoidal foramen Optic canal - medial aspect
Mean (mm)
Range
24 36 42 8
20-28 29-40 37-48 5-10
13
7-17
11 7
5-16 3-12
(mm)
is the frontozygomatic suture. From this point readings were taken to the lacrimal foramen; to the superior orbital fissure; to the inferior orbital fissure; and to the superior aspect of the optic canal. Fig. 1. Illustration of medial wall of the orbit. ethmoidal suture (Fig. 1). A key reference point of the medial wall is the anterior crest of the lacrimal fossa. From this point three measurements were taken along the medial wall. These were from the anterior crest of the lacrimal fossa to the foramen of the anterior ethmoidal artery, to the most posterior aspect of the ethmoidal foramina and to the medial aspect of the optic canal. Measurements were also taken from the anterior ethmoidal foramen perpendicular to the maxillary ethmoidal suture. The inferior wall is defined as bounded medially by the lacrimal suture and the maxillary ethmoidal suture and posteriorly ends at the optic canal. The main reference point is the infraorbital foramen. Five separate readings were taken from this point: to the lateral margin of the lacrimal fossa; to the inferior orbital fissure; to the posterior end of the covering of the infraorbital nerve; to the posterior wall of the maxilla; and to the inferior aspect of the optic canal (Fig. 1). The superior wall conforms to the orbital roof and is made up of portions of the zygomatic, frontal and sphenoid bones. The most common point on the superior rim is the supraorbital notch, or foramen. From this point measurements were taken of the superior rim of the optic canal to the superior orbital fissure and to the lacrimal foramen when present. Measurements were also taken from the posterior ethmoidal foramen to the superior orbital fissure (Fig. 1). The lateral wall of the orbit is formed by the zygomatic and sphenoid bones. On the lateral rim, the most constant reference point
From these measurements, sample means, standard deviations of the sample and standard error means were developed. To test differences between left and right and between male and female orbits, the t-test for the difference of two means was used. This indicated that there was no difference between right and left or between male and female orbits with greater than 95% confidence. The above statistical analysis confirmed that it is correct to consider each of the 48 orbits as an independent entity. The distances from the anterior ethmoidal artery to the posterior ethmoidal artery and from the posterior ethmoidal artery to the medial aspect of the optic canal are derived from subtraction of these measurements. RESULTS
Table 1 describes the measurements obtained on the medial wall. In all but one orbit, the anterior ethmoidal artery was found. In that one specimen, a common opening for the anterior and posterior ethmoidal vessels and nerves was noted. Twelve of the 48 orbits had more than one foramen posterior to the anterior opening. It is important to note that the optic canals averaged approximately 4 cm from the anterior lacrimal crest. Further, the skulls examined averaged 7 mm between the posterior ethmoidal foramen and the optic canal itself. The inferior wall measurements are seen in Table 2. While 48 mm was the mean value distance to the optic fora-
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RONTAL ET AL
TABLE 2. MEASUREMENTS OF THE I;\JFERIOR ORBITAL WALL - MEASURED FROM THE INFERIOR ORBITAL FORAMEN
Lateral margin of the lacrimal fossa Inferior orbital fissure Covered portion of the infraorbital nerve Posterior wall of the maxilla Optic canal - inferior aspect
TABLE 4. MEASUREMENTS OF THE LATERAL ORBITAL WALL - MEASURED FROM THE FRONTOZYGOMATIC SUTURE
Mean
Range
Mean
Range
(mm)
(mm)
(mm)
(mm)
25
13 24
8-18 20-27
14 36 48
8-28 26-44 40-54
12-33 28-38 39-46 20-30
men, there was variance up to 5.4 em from the inferior orbital foramen. The distances along the superior orbital wall are seen in Table 3. The distances here were similar to those seen along the medial wall of the orbit. Specifically, the optic canal was encountered at roughly 43~ em from the supraorbital notch. The lateral wall measurements are seen in Table 4. As in the measurements of the other three walls, the optic canal appeared to average between 4 and 5 em from the reference point along the rim of the orbit. DISCUSSION
Earlier in this century, as otolaryngologists treated life-threatening suppurations of the paranasal sinuses, many complete descriptions were made of these cavities. Studies by Mosher,'; Schaeffer,":" Vanalyea" and others 1 0 - 14 discussed the embryologic, childhood, and adult anatomy and its variations. However, these articles do not describe the orbital contents in relation to modern day orbital procedures. By the TABLE 3. MEASUREMENTS OF THE SUPERIOR ORBITAL WALL Mean
Range
(mm)
(mm)
Measured from the supraorbital notch or foramen to: Superior orbital fissure 40 Lacrimal foramen 32 Optic canal - superior aspect 45 Measured from the posterior ethmoidal foramen to: Superior orbital fissure 13
35-45 28-41 40-50
11-17
Lacrimal foramen Superior orbital fissure Optic canal - lateral aspect Inferior orbital fissure
35 43
25
same measure, standard orbital anatomy treatises detail the intraorbital structures without correlation to the surounding extraorbital anatomy. Today, head and neck procedures regularly traverse the orbit and a need has arisen to show the anatomic interrelationships. The precise knowledge will aid diagnosis, plan treatment and avoid loss of ophthalmologic function. The bony walls represent a constant guide to the orbit. Measurements of the pertinent and constant structures of the bony walls become the basis of safe and efficient surgical success.
Medial Wall. The anatomy of the medial wall is the key to an uncomplicated result for seven standard orbital head and neck procedures. These include: 1) ethmoid vessel ligation; 2) exploration of the medial wall fractures; 3) ethmoid sinus exenteration; 4) orbital decompression; 5) transethmoidal sphenoidotomies; 6) closure of cerebrospinal fluid leakage; and 7) transethmoidal, sphenoidal hypophysectomy. Entrance to the medial wall is via the frontal ethmoidal incision. This places the operator on the frontal process of the maxilla. The only constant landmark on this process is the anterior lacrimal crest. It was felt that this was a more constant structure than the maxillo-nasal-lacrimal junction of Kirchner et aJ.15 Beyond 2 em from the anterior lacrimal crest, the anterior ethmoidal artery is found. This is in, or just above, the frontal ethmoidal suture. The anterior ethmoidal vessel found at the upper extent of the medial wall is constant. A horizontal plane passing through this vessel is the key landmark to safe dissection. During subperiosteal dissection, the posterior ethmoidal foramina are found along the plane of the anterior
Downloaded from aor.sagepub.com at PURDUE UNIV LIBRARY TSS on May 26, 2015
SURGICAL ANATOMY OF THE ORBIT
TABLE 5. MAXIMUM DISTANCE FOR SAFE ORBITAL EXPLORATION Distance
Wall
(mm)
M easured from
Medial Inferior Superior Lateral
30
Anterior lacrimal crest Inferior orbital foramen Supraorbital notch Frontozygomatic suture
25 30
25
ethmoidal foramen. Twenty-five percent of our specimens had more than one posterior ethmoid foramen. This is in agreement with other studies. 15, ,,) One orbit had only one ethmoid foramen. As noted by Kirchner et al,'5 it may be important to find all posterior ethmoidal vessels in surgery for epistaxis. The next structure behind the posterior ethmoidal vessels is the optic foramen. The distance between the posterior ethmoidal foramen and the optic nerve is a variable distance but no less than 3 mm. Therefore, no bone should be removed posterior to the medial wall farther back than the last ethmoid foramen. In summary, a measurement of 30 mm from the anterior lacrimal crest to the lacrimal bone should be used as the indication of safe distance for dissection along the medial wall. Dissection beyond this point must be done with great caution (Table 5). Inferior Wall. Orbital floor exploration and maxillectomy comprise the majority of intraorbital operations along the inferior wall. The initial incision in each of these procedures is carried down to the orbital rim. Once at the rim the periosteum should be elevated without transgressing the orbital septum. Entrance through the orbital septum will be evidenced by herniation of orbital fat. Entry through this adipose tissue may cause injury to the inferior oblique and inferior rectus muscles lying anteriorly. The infraorbital foramen is in line with the supraorbital notch and the middle foramen. This roughly corresponds to a point half way along the infraorbital rim. The lateral portion of the orbital floor is safer to explore than the medial, since the inferior rectus and inferior oblique muscles are more medially located within the orbit. Thus, medial floor blowout fractures are more likely to cause entrapment." Safe posterior
385
dissection of the orbit may be accomplished as long as the bony wall is closely followed. The posterior wall of the maxilla lies as close as 26 mm from the infraorbital foramen. This wall should be considered as the maximum safe distance for intraorbital dissection, since beyond this point there are no bony landmarks for reference. The optic foramen lies on an average of 12 mm beyond this point. To injure the nerve directly, dissection must pass superior, medial and posterior from the posterior wall of the maxilla." Emphasis during inferior floor dissection should be placed on maintaining contact with the bone. If this bony contact is lost, the intraorbital, inferior floor dissection beyond 25 mm from the infraorbital foramen should be done with great caution. Superior Wall. The superior wall is the guide to seven basic transorbital wall head and neck procedures. These are: 1) frontal ethmoidectomy; 2) frontal sinus trephine; 3) frontal sinus obliteration; 4) orbital decompression; 5) exploration for fractures; 6) lacrimal gland excision; and 7) orbital exenteration. Other than for orbital decompression the superior orbit is entered through the incisions just below the eyebrow. These incisions must be placed to avoid the supraorbital nerve and the elevator muscle of the upper lid. The supraorbital notch is constantly found in a parasagittal plane connecting the mental foramen with the infraorbital foramen. The levator muscle is avoided by placing the incision as high as possible, dissecting at right angles to the skin down to the superior orbital rim. Within the orbit, the periosteum can be elevated without danger from the frontal ethmoid suture through the frontal zygomatic suture and as far posteriorly as 30 mm. This allows a 5 mm tolerance to the most anterior aspect of the closest superior orbital fissure that we found, and avoids damage to the optic nerve.
Lateral Wall. Along the orbital wall laterally, the basic intraorbital operations are explorations of orbital fractures, lateral orbitotomy (Kronleinw ) and excision of the lacrimal gland. In all lateral intraorbital procedures the danger of damage to the superior
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orbital fissure or the optic nerve is minimal. Through the superior orbital fissure at the orbital apex pass cranial nerves III, IV, VI, the ophthalmic branch of V, and the ophthalmic vein. The fissure is found to lie no closer than 28 mm from the frontal zygomatic suture at the rim. Due to the curved nature of the orbit and the limited access to this area, it would be difficult and unnecessary to
proceed to this depth during any intraorbital procedure." Likewise, the optic nerve lies 8 mm behind the medial edge of the fissure and would also be under minimal danger from this approach. Therefore, as long as a distance of 25 mm from the frontal zygomatic suture is maintained, safe dissection can be carried out on the lateral orbital wall (Table 5).
REFERENCES
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sphenoid sinus. Ann Otol Rhinol Laryngol 46: 687-698, 1937 12. Vail HH: Retrobulbar optic neuritis originating in the nasal sinuses. Arch Otolaryngol 13:846-863, 1931 13. Mosher HP: Anatomy of the sphenoidal sinus and the method of approaching through the antrum. Laryngoscope 13:177-214, 1903 14. Van Alyea OE: Frontal cells. Arch Otolaryngol 341: 11-23, 1941 15. Kirschner JA, Yanagisawa E, Crelin ES: Surgical anatomy of the ethmoidal arteries. Arch Otolaryngol 74:382-386, 1961 16. Takahashi R: Clinicoanatomical studies of the canalis orbitocranialis and canalis orbitoethmoidalis in relation to the ethmoid cells, in Takahashi R (ed ): A Collection of Ear, Nose and Throat Studies. Tokyo, Kyoya Co, 1971, pp 174-204 17. Gozum E: Blowout fractures of the orbit. Otolaryngol Clin North Am 9:477-487, 1976 18. Okashi J: Evaluation of the various routes for operation of the paranasal sinuses, especially the ethmoid cells from the standpoint of the angle and field of exposure, in Takahashi R (ed): A Collection of Ear, Nose and Throat Studies. Tokyo, Kyoya Co, 1971, pp 524-542 19. Stellard HB: Eye Surgery. Baltimore, Williams and Wilkins, 1973, pp 862-878
Eugene Rontal, MD, 21700 Northwestern Highway, Southfield, MI 48075.
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