INTRODUCTION

 

Cranio-orbito-zygomatic (COZ) approach is a common skull base approach. Pellerin and colleagues and Hakuba first described the orbitozygomaticapproach to theanteriro and middle cranial fossa as well as the upper third f the clivus and posterior fossa.^1,2

The approach has been used to treat variety of lesions; either skull base pathology^2-4, or even vascular lesions.⁵

Many modifications for this approach evolved describing different cuts of the osteotomies and tailoring according to the lesions. The main variations of the approach include the one-piece and the two-piece COZ craniotomies, and an orbitopterional (OPT) modification that includes removal of the orbital roof alone.^6,7

 

Aim of Work

To describe the general steps of the cranio-orbito-zygomatic craniotomy approach, and to give a detailed description of the trans- key burr hole orbital roof osteotomy modification of the approach.

 

MATERIAL AND METHODS

 

The new surgical modification was applied to eight patients with skull base lesions in which orbitozygomatic approach was indicated. Seven cases are of sphenoid wing meningiomas with different extensions and one case of tentorial meningioma extending to the middle cranial fossa.

 

Surgical Technique

The standard steps for single piece COZ approach are applied. Many authors have a detailed description of the approach.^1,2,8-10 The procedure is done in either the supine position or lateral park bench position (Figure 1). Head is fixed in head clamp and is rotated to the contra-lateral side to a degree dependent upon extent of the pathology. Head extension around 10 degrees helps the brain to fall away from the skull base by its weight (effect of gravity).

Scalp flap is elevated by a fronto-temporal skin incision begins at the inferior border of the zygomatic arch, 1cm anterior to the tragus, then proceeds postero-superiorly and curves anteriorly to end just behind the site where the hairline intersects the contralateral midpupillary line (Figure 1). The flap can be modified according to the lesion extension (Figures 1 and 2). This incision allows a generous exposure of the fronto-temporal area, the superior and lateral rims of the orbit, and the zygoma (Figure 3).

The temporalis muscle fascia is then incised sharply (Figure 3) to avoid injury to the frontal branch of facial nerve (details are described elsewhere in the literature).¹¹ The fascial incision is made forward along the margin of the superior temporal line, leaving a narrow myofascial cuff attached to the bone for later re-approximation (Figure 4).

The zygomatic arch, upper part of the zygoma body, fronto-zygomatic process, superior and lateral orbital ridge is exposed subperiosteally (Figure 3). Temporalis muscle is dissected off the pterion bluntly to avoid later atrophy and dissection continues downwards until the inferior orbital fissure identified. Blunt dissection of the periorbital from the lateral and superior orbital ridges is also done (Figure 4).

For the removal of the single piece bone flap three burr holes are done according to the proposed modifications. First burr hole (Key Burr hole) a key burr hole is made below the temporal line nearly one centimeter behind the fronto-zygomatic suture which exposes the orbital content and the basal frontal dura, as described by Al-Mefty and Shimizu and colleagues.^8,12 This is a very important step for the proposed modification, this burr hole is widened to be around 1 centimeter in diameter. Properly placed hole will expose both the frontal base dura and the periorbital with the intervening thin plate of orbital roof.

A Second burr hole is done lateral to the supraorbital notch. The frontal dura is gently dissected off the frontal base to expose the orbital roof and a small cottonoid is used to maintain the dural away from the orbital roof. In case of hyper-pneumatization of the superior orbital ridge a double holes technique through the anterior and posterior walls of the frontal sinus is done (Figure 5).

The Third burr hole (Orbital roof hole) is done through the second hole in the orbital roof to expose the periorbital. A gentle dissection of the periorbital away from the roof downward and medially is done and a small cottonoid is placed to keep the periorbital off the orbital roof.

The second and third bur holes are optional and in presence of a craniotome they may be not necessary (Figure 4). However, if the cuts will be done using a Gigli saw they are necessary to allow the orbital rim cut.

For orbital roof clearance, the frontal base dura is gently dissected off the orbital roof from lateral to medial through the first key hole towards the third hole in the orbital roof and a small cottonoid is inserted to maintain this plan. Using same technique the periorbital is gently dissected from the under surface of the orbital roof, again from lateral to medial until meet the third hole and the plane is maintained by a cottonoid. This step can be done by direct vision or with help of surgical microscope for better illumination and magnification.

Orbital roof osteotomy is done using a low profile sharp osteotome (Figure 6) and gentle hammering from the lateral edge of the orbital roof through the first key hole until the third hole medially. A second cut is made connecting the second and third holes through the superior orbital edge.

Pterional osteotomy is done from the frontal (second) burr hole an osteotomy cut is tailored according to the extent of the lesion  this involves the frontal bone going posteriorly through the parietal bone then directed downward toward the root of zygoma and then antero inferior to inferior orbital fissure across the sphenoid ridge . A second cut from the first key hole to the inferior orbital fissure.

The Zygomatic osteotomy is done by cutting through the zygomatic arch obliquely at its root. The body of the zygoma is then cut; this cut extends from the inferior orbital fissure to the lateral inferior border of zygoma and the lateral orbital ridge.¹³ This frees the zygomatic bone, which is now only attached to the bone flap by the fronto-zygomatic suture.

Now the whole single piece COZ bone flap is only attached to the skull base along the sphenoid ridge which is thinned out and using gentle force is fractured to get the bone flap free (Figure 7 A and B).

Regular steps are then followed for dural opening and subsequent dealing with the pathology. At the end of the procedure, the bone flap is secured in place using miniplates (Figure 8). The frontal bone bur hole is filled with available bone dust and standard closure steps are followed.

 

 

 

 

Figure 1. Surgical position and scalp flap incision. The flap extended more

posterior than usual to adapt for posteriorly extending lesion.

 

 

 

Figure 2. MRI with contract shows skull base meningioma with adherence

to petrous bone and extension to tent and middle cranial fossa.

 

 

 

Figure 3. Scalp flap elevated to expose frontal bone, parietal bone, temporalis muscle over pterion, superior orbital rim zygomatic arch and body. Note subfascial dissection of temporalis fascia to preserve frontal branch of facial nerve.

 

 

Figure 4. Temporalis muscle dissected. Bone cuts are done. The orbital

ridge is cut using a craniotome, no frontal burr hole required

 

 

Figure 5. Left COZ (cranio-orbito-zygomatic) bone flap secured using miniplates,

temporalis muscle reattached. Note the frontal bur hole.

 

 

 

Figure 6. Fine osteotomes used.

 

 

 

 

Figure 7 A and B. Two different bone flaps according to extent of lesions operated.

 

 

 

Figure 8. Postoperative 3-Dimensional computer scan shows good bone flap reconstruction,

frontal hole filled with bone dust and mini-plates used to secure the flap.Figure 9 A and B. 3 Dimensional CT scan shows minimal orbital

roof bone loss following left COZ approach.

 

RESULTS

 

This technique was applied to 8 cases of middle cranial fossa meningiomas. The orbital roof bone loss is minimal in this modification (Figure 9 A, B). No relation between the modification and technique of surgery or the degree of exposure was observed in this work.

No complications related to the new modification were observed. Ipsilateral eyelid edema seen on the second postoperative day in all patients progressed on third day, and rapidly resolved on conservative treatment. Minor periorbital injuries were seen in all cases with no clinical importance. Two cases of minor injury to basal frontal dura were seen treated conservatively with no consequences. There was one case of mortality due to massive pulmonary embolism. A case of stiffness of the temporomandibular joint (TMJ) treated by surgical release of temporalis muscle done by maxillofacial surgeon.

 

DISCUSSION

 

The orbitozygomatic approach is a modification and extension of the pterional craniotomy to gain a wider exposure of structures at the cranial base. Complete removal of the orbitozygomatic bar increases the angles of exposure, decreases the working depth of the surgical field, and minimizes brain retraction.^6,9

The increase in lesion attack angle using COZ is contributed more to the removal of the superolateral orbital rim rather than the removal of the zygomatic arch.^10,14-17

Gupta and colleagues reported that orbital cut using the standard technique is associated with excessive bone loss.¹⁸ The orbital cut is also reported to be difficult and some surgeons prefer the two piece COZ to avoid complicated orbital osteotomies especially with cases of adherent frontal dura or thick orbital roof.^6,19

With trans- key burr hole orbital roof osteotomy there is minimal loss of orbital floor, so potential complications related to excessive loss of orbital roof bone is avoided. The modification proposed in this work is associated with minor injuries of periorbital and frontal dura, which is not clinically importance.

 

Conclusion

Trans key burr hole orbital roof osteotomy in single piece cranio-orbito-zygomatic approach is surgically easy step that avoid excessive traction on the globe with no major complications. The osteotomy helps to preserve the orbital roof preventing potential complications related to defective orbital floor like pulsating exophthalmos.

 

[Disclosure: Author reports no conflict of interest]

 

REFERENCES

 

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