return to: Otology - Neurotology
Room Set-up
- Patient images; Stenver view mastoid to assess bone thickness overlying superior canal; MRI coronal and axial (post-contrast) showing tumor and confirming operative side.
- Patient clinic notes. Pre-operative note, audiogram, ABR test results and Internal medicine surgical co-management note placed on wall
White board: intra-operative medications (1 gram Ancef Q8hrs, 10 mg Decadron q6 hrs, Mannitol at 0.4 mg/kg given after performing craniotomy). Nursing instructions to call family every 3 hours
ABR settings (0.05 mA stimulation)
Patient positioning with 3 point straps to allow rolling of the bed to improve operative exposure
Electrode placement; NIMS monitor electrodes in the orbicularis occuli and orbicularis oris with ground electrods on the chest; ABR click generator in the operertive side ear canal; 3 ABR electrodes (one on each mastoid and one on vertex). Also note the posteriorly based temporal skin flap design.
- OPERATIVE PROCEDURE
- Incision and Elevation of Skin Flaps
- Two possible incision designs:
- Anterior/inferiorly-based skin flap (MH)
- Incision starts anterior to tragus, extends posteriorly approximately 3-4 cm posterior to pinna, superiorly 5-6 cm, and anteriorly again to the temporal hairline
- Good for extended middle fossa approaches
- Temporalis muscle is then reflected inferiorly
- Posteriorly-based skin flap (BJG)
- Incision starts just behind temporal hairline and a rounded box shape approx 6 cm wide is carried back approximately 6-7 cm.
- Begin as low onto pinna as possible
- Temporalis muscle flap is then reflected anteriorly
- Keep temporoparietal fascia layer attached to scalp during skin flap elevation
- Anterior/inferiorly-based skin flap (MH)
- Harvest a large piece of temporalis fascia prior to elevation of the muscle flap
- leave cuff of fascia on either side of muscle flap
- Elevate muscle flap
- Anterior temporalis flap if posterior-based skin flap
- Inferiorly-based temporalis flap if anterior-based skin flap
- Should be able to see zygomatic root easily after elevation
- Two possible incision designs:
- Craniotomy
- Have anesthesiologist administer 0.4 grams/kg of mannitol now
- Hyperventilate patient to end tidal CO2 of 30
- Center craniotomy on zygomatic root
- 4.5 x 4.5 cm wide bone flap
- Use a 4 mm (BJG) or 5 mm (MRH) cutting burr to remove the majority of the bone.
- Use diamond 4 mm burr, to remove the final layer of bone over the dura.
- Branches of the middle meningeal artery will be encountered, which are controlled with bone wax or bipolar cautery
- Mark bone flap to ensure easy and properly oriented replacement at end of case.
- Elevate bone flap off of dural with Joker elevator.
- Pass bone flap off to scrub nurse
- Keep bone flap moist
- Check exposure: if the bone window is not flush with the tegmen, remove excess bone with rongeur or drill
- Dural Elevation
- Circumferentially elevate the dura from the overlying cranium, using the bipolar cautery liberally to stop bleeding from the dura.
- Place Oxycel cigars under the bone flap anteriorly, posteriorly, and superiorly.
- Elevate the dura along the floor of the middle cranial fossa from posterior to anterior so as not to disrupt the greater superficial petrosal nerve (GSPN). (SEE FIGURE)
- Identify the arcuate eminence, GSPN, and petrous ridge.
- Use cottonoids anteriorly and posteriorly for dural retraction during elevation.
- Brisk bleeding from the middle meningeal artery at the foramen spinosum may be encountered and can be controlled with bone wax and Oxycel packing.
- Place the House-Urban retractor under the lip of the petrous ridge at the anticipated location of the IAC (based upon the arcuate eminence).
- Identification of the IAC
- Begin drilling using a 4-0 diamond burr over the arcuate eminence to identify the location of the superior semicircular canal.
- The SSCC will be perpendicular to the petrous ridge
- The Stenvers x-ray will demonstrate the amount of bone overlying the semicircular canal (SSCC).
- Blueline the superior canal.
- The IAC is located 60° anterior to the blue lined SSCC. (SEE FIGURE)
- Lower the meatal plane over the IAC until it is well-defined
- Begin drilling using a 4-0 diamond burr over the arcuate eminence to identify the location of the superior semicircular canal.
- Tumor exposure
- Drill deep troughs 270 degrees around the IAC, down to the level of the posterior fossa dura
- Develop your exposure working medial to lateral
- Exercise caution when drilling laterally, due to the location of the cochlea and ampulla of the SSCC.
- Skeletonize the IAC up the level of Bill\’\’s Bar.
- Identify the labyrinthine segment of the facial nerve at the transverse crest and decompress the meatal foramen a few millimeters.
- The cochlea is deeper than the plane of the labyrinthine segment of the facial nerve.
- As long as one does not drill deep to the facial nerve anteriorly, the cochlea will not be violated.
- Remove the last flecks of bone from the IAC dura.
- Have audiologist start monitoring ABR
- Tumor Removal
- Open the dura of the IAC over the superior vestibular nerve with a 59-10 Beaver blade or 2.5 mm hook.
- Place a direct auditory nerve electrode between the dura of the IAC and the cochlear nerve for monitoring the cochlear action potentials in real time.
- Identify the separation between the facial nerve and superior vestibular nerve at the transverse crest.
- Separate the facial nerve from the superior and inferior vestibular nerves at this location.
- Avulse lateral ends of the vestibular nerves, and reflect medially.
- Use a 2.5 mm hook to separate the tumor from the facial and cochlear nerves.
- Always work from medial to lateral when possible.
- When tumor has been separated, cut the medial ends of the vestibular nerves along with the tumor, thus removing the tumor.
- Special considerations
- In larger tumors, it is often necessary to debulk the tumor as for TL excision, prior to establishing a plane between the facial nerve and the tumor.
- If the auditory response demonstrates prolongation of latency or a decrease in amplitude, switch strategies or pause tumor dissection for several minutes.
- A cochlear nerve that no longer responds intraoperatively may still have hearing postoperatively; unfortunately, the reverse is also true.
- Closure
- Ensure hemostasis in IAC/CPA
- Document stimulation of facial nerve with Prass Probe on 0.05 mAmp
- Document ABR/Direct Nerve Monitoring after tumor removal
- Repairing temporal bone defect
- Apply bone wax to all opened air cells.
- Place a large temporalis muscle plug (BJG) or abdominal fat (MRH) in the IAC defect.
- Place the previously harvested fascia over the entire temporal bone defect.
- Use the anterior corner of the bone flap, or a piece of the inner table, over the defect to prevent temporal lobe herniation into the middle ear, if it exposed.
- Bolster fascia into place with Oxycel ™ cigar
- Tisseal ™ is optional to further secure fascia
- Craniotomy closure
- Release the House-Urban retractor and allow the temporal lobe to re-expand.
- Relay to anesthesiologist that the EtCO2 can be allowed to rise
- Ensure an accurate neuro pattie count.
- Tack dura to pericranium with at least two 4-0 neurolon sutures to eliminate epidural potential space
- Double check epidural hemostasis
- Replace the bone flap.
- Simply replace and allow to float (BJG)
- Plate back with three plates (superior, anterior, posterior) reabsorbable system (MRH)
9. Close the temporalis muscle with water-tight interrupted 3-0 vicryl sutures.
- Release the House-Urban retractor and allow the temporal lobe to re-expand.
- Close the subcutaneous layer with water-tight interrupted 3-0 vicryl sutures.
- Close the skin with running-locking 3-0 nylon sutures.
- Place a large, tight mastoid dressing centered over surgical area.
MCF Anatomy
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- For POSTOPERATIVE CARE , see Skullbase Post-Operative Care Map
- CPT CODING
- 61591 Middle cranial fossa approach
- 61616 Intradural removal of tumor
- 69990 Use of Operating Microscope
- 95867 Facial Nerve Monitoring
- 62140 ( <5 cm2) or 62141 ( > 5 cm2) cranioplasty
- 15770 Abdominal fat harvest
- *Audiologists bill and code the ABR monitoring separately*
- SUGGESTED READING
- Gantz BJ. Middle Cranial Fossa Technique Lecture Slides
- Chen DA, Arriaga MA, Fukushima T. Technical refinements in retraction for middle fossa surgery. Am J Otol. 1998;19:208-211.
- Gantz BJ, Harker LA, Parnes LS, McCabe BF. Middle cranial fossa Acoustic neuroma excision: results and complications. Ann Otol Rhinol Laryngol. 1986;95:454-459.
- Nadol JB. Cerebellopontine angle tumors. In: Nadol JB, Schuknecht HF, eds. Surgery of the Ear and Temporal Bone. New York, NY. Raven Press, Ltd. 1993:391-413.
- Weber PC, Gantz BJ. Results and complications from acoustic neuroma excision via middle cranial fossa approach. Am J Otol. 1996;17:669-675.