Indications

Broadly speaking, an OZ is a modification to the standard pterional craniotomy that allows the surgeon to see backwards, towards the inion, and upwards, toward the vertex of the head. Removal of the rim of the orbit facilitates this upward and backward viewing trajectory with minimal brain retraction.

Removal of the zygoma facilitates retraction of the temporalis muscle downward (i.e. towards the feet) and gives a view parallel with the floor of the middle cranial fossa. This facilitates access to the lateral cavernous sinus. 

In the figure below, the pink dotted line demonstrates the trajectory available to a traditional pterional craniotomy to access the posterolateral corner of the tumor. This trajectory necessarily takes the surgeon across the temporal pole (blue dotted line) and requires significant retraction on the brain. In contrast, the trajectory available with removal of the orbital rim (yellow dotted line) requires almost no temporal lobe retraction at all. 

Common indications include clinoidal or sphenocavernous meningiomas with growth into the underside of the frontal lobe and extending along the cavernous sinus and floor of the middle cranial fossa. Another rare indication is for clipping of a basilar tip aneurysm, where a steep anterior-posterior trajectory is needed (imagine looking through the eye towards the basilar apex), which is facilitated by removal of the rim of the orbit and gentle lateral-to-medial retraction of the orbital contents. 

Equipment

• Foley
• Layla bar
• Greenburg retractor
• Skytron bed (at Mercy) or Mizuho bed (at Presbyterian). These beds are able to go down further than the standard OR bed. 

Monitoring

• SSEPs
• Transcranial MEPs
• 8-channel EEG
• CN5 and 7 EMG (when stripping of the middle cranial fossa floor dura or cavernous sinus is anticipated)

Medications

• No paralytic, no inhaled anesthetics (for tcMEP monitoring)
• 1 g/kg IV mannitol
• 10 mg IV dexamethasone
• 1000 mg IV Keppra
• 2 g Ancef
• 250 mg IV Solumedrol if the optic nerve is involved but this is case and attending dependent

Pinning

Pin as for a classic bicoronal craniotomy. Single pin on the side of the pathology on the mastoid, double pin contralateral to the pathology with the upper pin biased towards the occiput as far back as will safely secure the head. 

Positioning

• Rotate the bed 90 degrees such that the side of the pathology is away from anesthesia, just like for a pterional. 
• Pull the patient up in the bed such that the shoulders are just above the break.
• Pull the patient towards the side of the pathology such that their flank aligns with the edge of the bed. 
• Tuck the ipsilateral arm. 
• No bump is needed. 
• Leave the belly bare in case a fat graft is needed. 

Head Positioning

The goal of head positioning is to have the ipsilateral malar eminence as the highest point in the field. Aside from the malar eminence, the goal of head positioning is to have the long axis of the optic nerve perpendicular to the plane of the floor, i.e. the person positioning should be staring straight down the axis of the ipsilateral eye. 

1. Rotate the head to the side opposite the pathology by about 20 to 30 degrees
2. Extend the neck significantly
3. Attach the Mayfield to the outside attachment of the head clamp

Marking

For most cases, the incision should begin at the ispilateral zygoma and follow the hairline to the contralateral mid-pupillary line. In this case, a 3/4 bicoronal was used for a better cosmetic outcome in the setting of the patient's male-pattern baldness.

Use the strap from a surgical mask to mark a line extending from a point just anterior the ipsilateral tragus, posteriorly towards the occiput, then on a trajectory towards contralateral tragus but not all the way. 

Mark the abdominal fat graft incision. This is marked in case a fat graft is needed in the setting of an air sinus violation (either accidentally or after resection of a heavily pneumatized clinoid). 

Tarsorrhaphy

Use 6-0 Prolene suture in a horizontal mattress. Suturing supplies are in a lumbar drain kit. First stitch goes on the upper eyelid, just above the tarsal plate. Second stitch goes in the lower lid just below the tarsal plate, just above and below the lashes, respectively. 

Make sure you have the CV-11, not CV-1 needle.

When suturing, do not suture with your hand over the eye. Pass the needle through the bottom lid with your hand resting on the cheek and through the top lid with your hand resting on the forehead. This avoids unintentional corneal abrasions. 

Leave the cut ends of the suture long so they are easy to remove at the end of the case. 

​

Prep

Chlorhexidine for the scalp, ophthalmic betadine for the eye and face. 

Draping

Four blue towels in a square for the abdomen. 

One blue towel across the back of the head, just posterior to the incision line. A second blue towel across the face, the edge of which is just above the eyebrows. 

Procedure

Scalp

Begin by using a #10 scalpel blade to incise the scalp straight down to the bone from superior temporal line to ipsilateral superior temporal line. Place Raney clips on the cut edge of the scalp. 

Once you reach the ipsilateral superior temporal line, use a pair of Metzenbaum scissors to develop the subgaleal plane then incise the scalp on top of the scissors. This protects you from cutting into the temporalis muscle and causing significant bleeding. It also preserve the deep temporal fascia in case it is needed for a graft. 

When you get close to the ear, use the Metzenbaum scissors to spread the tissue above the galea to identify and preserve the superficial temporal artery. 

Next, use a broad periosteal elevator to sweep the loose areolar connective tissue off the deep temporal fascia in a posterior-to-anterior direction. Above the superior temporal line, use the broad periosteal to dissect the scalp and pericranium in a single layer, also in a posterior-to-anterior direction. 

Stop elevating the flap once you see the fat pad, about 2-3 cm posterior to the lateral orbital rim. 

Differential Flap

Every OZ requires a differential flap. The purpose of the flap is to protect the frontalis branches of the facial nerve which supply motor function to the frontalis muscle. Aside from causing a cosmetic deformity, a frontalis palsy can also lead to ptosis, especially in older patients. 

This can be done in an interfascial or subfascial method. Dr. Fernandes prefers the interfascial approach. 

Use a #15 scalpel blade to make a straight linear incision in the superficial layer of the deep temporal fascia, on a superior-to-inferior trajectory. The top of the incision crosses the superior temporal line and the bottom stops just shy of the root of the zygoma. 

Use a broad periosteal elevator to develop the plane between the superficial and deep layers of the deep temporal fascia. This plane contains fat and a prominent vein which can be safely coagulated and divided. 

Note that the frontalis branches of the facial nerve, which run in the loose areolar connective tissue between the galea and the superficial layer of the deep temporal fascia, are now protected by a layer of deep temporal fascia. You can now continue to elevate the flap in an anterior-to-posterior direction. 

Once you reach the orbital rim, the dissection plane should carry you directly onto the bone. Continue dissecting the periosteum off the bone of the lateral orbital rim and follow its curvature over the rim and into the orbit, where you will dissect the periorbita from the bone of the orbit. At this stage, the supraorbital bundle comes into view (red circle). This usually passes through a notch in the superior orbit and can be easily mobilized out of the notch to continue the anterior mobilization of the scalp.

 There exists a normal anatomic variant where the supraorbital bundle is fully encased by bone, i.e. a foramen instead of a notch. In that case, you can safely mobilize the supraorbital bundle by cutting the foramen and bundle out of the rest of the skull in a single piece using an osteotome. 

Once the orbital rim is dissected free of soft tissue, carry the dissection plane inferiorly along the zygomatic bone along a superior-to-inferior trajectory (yellow arrow) until you see the zygomaticofacial foramen (red circle). . 

Next, dissect in the subperiosteal plane posteriorly, along the zygomatic arch. Once on the arch, carry the dissection plane superiorly and inferiorly to fully encircle the arch and free its length from the periosteum. 

Temporalis Muscle

You are now ready to make the muscle cuts and elevate the temporalis. First, find the root of the zygoma. With the Bovie, make a horizontal cut in the temporalis, starting just above the root of the zygoma and continuing posteriorly along a line parallel with the root. Continue this line to the posterior border of the temporalis muscle. 

Begin elevating the muscle from the temporal fossa with a curved Adson periosteal dissector. Use the side edge of the curved Adson to dissect in the subperiosteal plane along an anterior-to-posterior trajectory. The goal of dissection is to leave the periosteum on the muscle, which preserves its vascular supply.

The plane will dissect nicely until you reach the superior temporal line, at which point you should use the Bovie to free the muscle from its attachment on the line. Continue releasing the muscle from the superior temporal line with the Bovie along a posterior-to-anterior trajectory to the orbital rim.

Continue dissecting the muscle free from the back side of the orbital rim down to the root of the zygoma. Once the muscle is free, pull it inferiorly and secure it with fish hooks. 

Pterional Craniotomy

With the M8 drill bit, make burr holes at 1) the root of the zygoma, 2) posteriorly, and 3) at the MacCarty keyhole. Use image guidance to verify that the planned location of the MacCarty keyhole will show both anterior fossa dura and periorbita. 

Before turning the craniotomy, use image guidance to verify the location of the ipsilateral frontal air sinus. Ideally, the anteromedial border of the craniotomy should be defined by the supraorbital notch. There are three possibilities: 

1. The sinus is very small and it does not extend laterally past the supraorbital notch. This is the ideal situation. Nothing to do differently. 
2. The sinus is medium sized and extends a small amount lateral to the notch. In this case it might make sense to restrict the medial extent of the craniotomy a little to avoid the air sinus, even if the craniotomy doesn't quite extend to the supraorbital notch as we would like. 
3. The sinus is large and extends well lateral to the notch. In this case you have no choice but to come across the air sinus with your craniotomy.
   1. You will have to exenterate the part of the sinus on the bone flap by drilling followed by Bovie electrocautery to ensure that no mucus rests remain in the flap. 
   2. For the cut end of the sinus that is on the skull, use a Penfield one to dissect the mucosa away from the skull and fold it into the sinus. Then, place a muscle patch in the hole followed by a small pericranial flap or temporalis fascia free graft - the "belt and suspenders" approach

For the craniotomy itself, the only difference from a standard pterional is in the cuts over the orbital rim. All cuts are made with the M8. Use a Penfield 3 to dissect the dura away from the inner table then place a Penfield 1 in the skull along the orbital roof. This defines for you the trajectory of this cut and makes sure it is as close as possible to the roof of the orbit. 

Once the pterional is complete, drill down the cut end of the sphenoid ridge and cut the meningoorbital band. 

Orbitozygomatic Osteotomies

First, dissect the frontal dura and periorbita away from the orbital roof and retract the orbital contents and frontal lobe with brain ribbons. Then, make the cut through the orbital roof with the reciprocating saw. Carry this posteriorly to about the anterior-posterior midpoint of the orbital roof. 

Next, with a 6 mm diamond burr, make the lateral orbital wall cut (red line), connecting the superior (blue) and inferior (yellow) orbital fissures from inside the skull. 

The next cut is across the zygomatic process of the facial bone. This starts by dissecting the periorbita from the lateral orbit and finding the inferior orbital fissure with a Penfield 4. Protect the orbital contents with a brain ribbon. Start the maxillary cut with the tip of the saw in the inferior orbital fissure and make the superior half of the chevron-shaped cut in the zygomatic process of the facial bone (red line). Then, use the reciprocating saw to complete the second half of the chevron. 

The last cut is simply across the zygomatic arch at the root of the zygoma. 

Anterior Clinoidectomy

All parts of clinoid drilling are done with the irrigating MIS drill attachment and a 4 mm diamond burr. 

There are three attachments to the anterior clinoid: 

• Lesser wing of the sphenoid
• Roof of the optic canal
• Optic strut

Follow the lesser wing of the sphenoid medially to find the clinoid. With the diamond burr, make the first cut across the lesser wing. The yellow arrow marks the view of the surgeon. 

Carry this cut further posteromedially to come across the roof of the optic canal. The yellow arrow marks the view of the surgeon. Once the roof of the optic canal and lesser wing are drilled away, the only thing that remains supporting the clinoid is the optic strut. This can be fractured or drilled to complete the clinoidectomy.

Dura

Open the dura in a C-shape. Start with a #15 blade and carry through with Metzenbaum scissors. 

Closure

The mesh is not always used. It was used in this case due to significant squamous temporal bone removal. 

Orders

​​Standard postop craniotomy orders. ICU admission, CT head, SBP cap per attending, Keppra, dexamethasone or Solumedrol per attending. 

Follow-up

Standard postop craniotomy follow up. Two weeks for a wound check, no imaging. 

Quiz Questions

• What are the bony connections of the clinoid? 
  • Roof of the optic canal
  • Lesser wing of the sphenoid
  • Optic strut
• What structure does the optic strut form when viewed from the inside of the sphenoid sinus? 
  • Lateral OCR
• What injury are patients prone to with the optic strut cut of the clinoidectomy? 
  • Carotid injury
• Under which layer do the frontalis branches run? 
  • Under the superficial temporal fascia (which is the lateral continuation of the galea)What is the blood supply to the temporalis muscle?
  •  Deep temporal arteries, branches of the second division of the internal maxillary, a terminal branch of the external carotid.
• What is the blood supply of a pericranial flap? 
  • The supraorbital artery. 
• What structure is at risk if the cut across the zygomatic process of the facial bone is completed lower than the inferior orbital fissure? 
  • The maxillary sinus

• List the layers of the scalp and temporal fascia at the following locations:

  • Above the superior temporal line

    1. Skin
    2. Subcutaneous fat
    3. Galea
    4. Loose areolar connective tissue
    5. Pericranium
  • Below the superior temporal line anteriorly
    1. Skin
    2. Subcutaneous fat
    3. Galea aka superficial temporalis fascia
    4. Loose areolar connective tissue
    5. Superficial layer of the deep temporalis fascia
    6. Deep layer of the deep temporalis fascia
    7. Temporalis muscle
    8. Periosteum
  • Below the superior temporal line posteriorly 
    1. Skin
    2. Subcutaneous fat
    3. Galea aka temporoparietal fascia
    4. Loose areolar connective tissue
    5. Superficial layer of the deep temporalis fascia
    6. Deep layer of the deep temporalis fascia
    7. Temporalis muscle
    8. Periosteum