Monitoring

EMG CN7, BSER, SSEPs

Preop Medications

0.5 mg/kg mannitol, 10 mg dexamethasone, 1000 mg Keppra. 

Positioning

Supine with a bump oriented longitudinally. Gardner tucks the arms ipsilateral to the pathology. Zenonos does not tuck if a bump is used. Instead, wrap the arm in a big purple foam and wrap it with the sheet across the abdomen and secure with 3-inch tape. 

The head is positioned with the sagittal plane roughly parallel to the floor. Translate the head towards the ceiling. Slightly extend the neck to promote venous drainage. 

Pinning

Gardner

Single pin in the forehead at the mid-pupillary line (he doesn't usually like forehead pins but thinks this case is an exception). Double pin in the back, oriented in the axial plane.

Zenonos

Single pin in the forehead at the mid pupillary line. Double pin in the back, oriented in the sagittal plane.

Attach the image-guidance arm on the inside and position anterior to the patient's face, out of the way. 

Marking

A shallow question mark-shaped incision beginning just anterior to the tragus and extending to just below the superior temporal line. The "depth" of the question mark depends on the location of the tegmen defect. If it's very posterior allow the incision to extend further back. 

Zenonos always gives lidocaine with epi after a single prep, then preps again. 

Approach

Skin

Incise through the skin, subcutaneous fat, and galea, stopping at the subgaleal space. Extend the incision inferiorly to the root of the zygoma and superiorly to the superior temporal line. At the inferior edge of the incision, spread with Metzenbaum scissors to find and preserve the STA. 

Use a 4x4 to clear the loose areolar tissue off the temporalis fascia. 

Gardner uses two cerebellar retractors to hold the incision open. Zenonos uses the Greenburg retractor with fish hooks. 

Temporalis fascia

Incise the deep temporalis fascia with a 15-blade, staying superficial to the temporalis muscle. Complete a circular incision through the fascia, going all the way around. Leave a ~1 cm cuff of fascia at the superior and posterior margin. Elevate the temporalis fascia from the underlying muscle by spreading and cutting with the Metzenbaum scissors. Do not leave any muscle on the underside of the fascial graft. Give the temporalis fascia graft to the scrub tech to store in saline until it is used later. 

Muscle

Make an incision through the fascia and muscle with the Bovie straight down to bone. Leave a cuff of fascia on the muscle to facilitate re-approximation later during closure. 

Take a Love-Adson periosteal elevator and elevate the muscle from the bone. Sweep from the inferior-anterior corner to the superior-posterior corner. Take care to elevate the periosteum with the muscle. 

THIS PICTURE IS WRONG. DIRECTION IS ANTERIOR TO POSTERIOR

Bone

Use an M8 to make at least two burr holes in the temporal bone. Can make up to four if you'd like. Both Gardner and Zenonos are okay with more burr holes if it prevents causing a new durotomy. 

One burr hole always goes at the root of the zygoma. The second always goes ~4 cm posterior to the first. Use image guidance to make sure that the posterior burr hole is posterior to the tegmen defect. 

The circles in red are mandatory burr holes. The ones in blue are optional. 

Use a craniotome or M8 to turn the craniotomy. 

Defect repair

Relevant structures/landmarks during dissection of the middle fossa floor:

• Arcuate eminence
• Petrous ridge: there is often a "false" petrous ridge, which is encountered first when dissecting laterally to medially, and a "true" petrous ridge, which is encountered first when dissecting laterally to medially, as a result of the groove created by the superior petrosal sinus
• Greater superficial petrosal nerve (GSPN)
  • First branch of facial nerve
  • Has preganglionic parasympathetic fibers
  • Arises from geniculate ganglion
  • Travels in sphenopetrosal groove
  • Is medial to LSPN and often mistaken for LSPN, so stimulation is useful. Stimulation of GSPN results in antidromic signaling to facial nerve and triggers facial EMG
  • After passing Gasserian ganglion (which contains CN V) GSPN is joined by deep petrosal nerve (has sympathetic fibers) and becomes vidian nerve, which travels in vidian canal to sphenopalatine ganglion
  • Post ganglionic fibers from sphenopalatine ganglion supply lacrimal gland
• Facial nerve (CN VII) and superior vestibular (branch of CN VIII) may be exposed by boney defects
  • Portions of facial nerve exposed: subarachnoid, intracanalicular, labyrinthine, first portion of horizontal (tympanic)
• Foramen spinosum containing middle meningeal artery: outermost lateral structure, anterolateral to carotid canal, lateral to mandibular nerve (CN V3)
• Posterior branch of middle meningeal artery: internal maxillary artery, one of two terminal branches of ECA, gives off MMA which enters through foramen spinosum and makes anterior and posterior branches
• Mandibular nerve (CN V3): innervates tensor tympani attached to malleus via tympanic branch

Use the cartouche dissector at 3 mA to peel the dura from the floor of the middle cranial fossa. Start at the posterior limit of the crani and dissect medially, towards the petrous ridge. Once the dissection reaches the petrous ridge, carry it anteriorly along the medial border. This peels the dura off the greater superficial petrosal nerve (GSPN) from posterior to anterior and minimizes the risk of avulsing the GSPN and damaging the facial nerve. 

Find the tegmen defect. Once the dura is dissected from the floor of the middle cranial fossa and the defect is exposed, call the otology team. 

In the interim, find the dural defects and repair them. Small defects can be repaired with figure-of-eight 4-0 Neurolon suture and muscle patches. Larger defects may require an onlay or inlay dural patch graft which may be sutured in place with 4-0 Neurolon. 

The otology team will repair the bony defect in the floor of the middle cranial fossa with a split-thickness bone graft derived from the craniotomy bone flap. Then, they will place the temporalis fascia graft. 

For large defects, a pedicled periosteal graft can be harvested from the underside of the temporalis muscle and laid against the floor of the middle cranial fossa. 

Closure

Gardner

Burr hole cover in the anterior superior burr hole. Mesh securing the posterior superior and inferior corners. The anterior inferior corner is left free. 

Zenonos

Close the temporalis muscle with 3-0 polys.

Variable use of subgaleal JP drain.

Close the galea with 2-0 polys. 

For skin, Zenonos uses 3-0 Biosyn running baseball covered with a small amount of skin glue. No dressing. 

Gardner will use a running 3-0 Nylon. Dressing with Bacitracin ointment and Telfa stapled to the skin. 

Quiz questions

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

1. Above the superior temporal line
   1. Skin
   2. Subcutaneous fat
   3. Galea
   4. Loose areolar connective tissue
   5. Pericranium
2. 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
3. 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

Under which layer do the frontalis branches run? Under 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.