Middle cranial fossa approach to tegmen dehiscence

Considerations

• Pre-operative imaging

  • • Localize the dehiscence - group and anterior vs posterior 

    • Understand the inner table contour

• 1998: Combined Mastoid/Middle Cranial Fossa Repair of Temporal Bone Encephalocele

• 2013: Cerebrospinal Fluid Leakage from Tegmen Tympani Defects Repaired via the Middle Cranial Fossa Approach

• 2014: Combined Approach for Tegmen Defects Repair in Patients with Cerebrospinal Fluid Otorrhea or Herniations: Our Experience

Preparation

• • Hair clipper

  • Chlorhexidine swab

  • 30 ml 1% Lidocaine with 1:100,000 Epinephrine 

  • Neurophysiologist

    • Facial nerve

    • Trigemimal nerve 

Procedure

Sample operative report

Consent reviewed with patient. Patient was sedated in the pre-operative area and then taken into the OR by the anesthesia service. Patient was further sedated and intubated for procedure. *** First a lumbar subarachnoid drain was placed and secured using Tegaderm. After all appropriate lines and monitors were established, patient was rotated 135 degrees to begin patient positioning for procedure. The arms, legs and other pressure points were padded with foam to reduce the chance of positional neuropathy and the body was secured.

The patient was  placed in Mayfield head holder. The scalp was clipped, and a curvilinear line was made with a marking pen from the root of the zygoma, slightly behind the ear and then to midline. The skin was first sterilized with a chlorhexidine prep and then *** 30 ml of local anesthetic with epinephrine was infiltrated into the subcutaneous space. Once everything was in position the surgical fields were then re-prepped with chlorhexidine solution. The patient was covered in sterile drapes.

The surgery began with the scalp incision using a scalpel and Bovie for cautery. The scalp was reflected, and a gauze pad was rolled into a cylindrical tube and placed underneath the skin flap. Hooks were used to retract the skin out of the way. Bovie cautery was used to raise the temporalis muscle off of the skull, and it was also placed under hook retraction. Three burr-holes were made; 1 at the keyhole, another at the temporal floor inferior to the pterion, and the third posteriorly at the most posterior portion of the temporal bone visible in the surgical field. The dura was then dissected away from the bone using a Penfield 3 dissector. The drill with the footplate attachment was used to connect the three burr-holes. A combination of a Penfield 3 and 1 dissectors were used to dissect the remaining portion of dural attachments off of the bone flap. The bone flap was carefully set aside. A series of tack-up holes and 4-0 Vicryl sutures were placed to secure the edges of the bone flap. The residual rim of bone was removed with the side cutting drill to expand the craniotomy to the level of the middle fossa floor.

Once all drilling was complete, the dura over the middle fossa floor was carefully dissected from posterior to anterior to expose the dehiscence. Occasional venous bleeding was meticulously controlled using the Bipolar and bone wax. A Penfield 1 was used to dissect the dura away from the middle fossa floor exposing the tumor attachments and vascular supply. At this point the microscope was brought into the field for the portion of the extradural microscopic dissection. First the dura was removed off of the middle fossa floor starting from the posterior portion of the petrous bone and then swept anteriorly. Foramen spinosum was identified and the middle meningeal was identified and cut. The dura along with the petrous ridge was identified and followed until the trigeminal ganglion was identified. Here foramen ovale was identified. Next the dura was removed from the anterior temporal tip and followed posteriorly until foramen rotundum was identified. Next the dura was slowly removed off of the dura propria, dissecting it off of the gasserian ganglion/meckel's cave. Once this was achieved the dura was opened.

Using the microscope, the surgical field was evaluated and small bleeding vessels were cauterized to ensure a dry surgical field during the case. The dura was flapped towards the temporal floor. Next a temporal lobe retractor was placed. The dehiscence was visible with *** minimal retraction of the temporal lobe *** using only instruments. The repair of the dehiscence was multi-layered, consisting of *** Mimix, temporalis muscle, Mimix, temporalis fascia, Duragen, Tisseal.

The final closure ensued. First, *** a layer of duragen was placed underneath the dura and sewn into place. Then a layer of dural grafts (surgisis) was sewn to and over the dura, extradurally. 4-0 Vicryl sutures were used for closure of the dura. Next the middle fossa floor was waxed copiously to eliminate any of the bone dehiscence. Then tisseel was sprayed onto the floor to reduce risk of post-operative CSF leak. The bone flap was placed and secured using the Stryker plating system. Vancomycin powder was sprinkled over the hardware. The soft tissue closure began with the temporalis muscle. The temporalis muscle was sutured back to its cuff using 2-0 Vicryl sutures. The galea was closed with running 2-0 vicryl suture. The skin was closed with a running 4-0 Prolene suture.

Following this a head-wrap was placed in standard fashion using Bacitracin, Telfa, fluffs, two kerlix wraps, and secured by a flexi-net dressing. The patient was then turned 180 back towards anesthesia and was promptly extubated. The patient was transported to *** in stable condition.

There were were no complications or untoward events in the OR. All counts were correct at the end of the procedure.

Post-op 

• • ICU admission

    • Neurochecks 

    • HOB elevated 

• Antibiotic

  • Cefazolin (trade name Ancef, Kefzol) x 24 hours 

  • Dexamethasone 

    • 4 grams q6 hours x 48 hours 

  • POD 2 

    • Remove outer dressing 

  • POD 14 

    • Remove sutures / staples 

Pearls & Pitfalls

High-Yield

• • Middle fossa structures 

    • Arcuate eminence

    • SCC

    • Foramina - rotundum, ovale, spinosum 

      • Spinosum is most posterior and lateral 

    • Sinuses - sigmoid, transverse, Labbé

• Posterior tegmen dehiscence is more likely than anterior given the relative thinness of the bone 

Links

• Operative Neurosurgery - Tegmen tympani defect

• Otosurgery - Tegmen dehiscence

• Otosurgery - SCD surgery - left middle fossa craniotomy and canal plugging

• YouTube (2:14) - The Middle Fossa Approach and Extended Middle Fossa Approach Video 1

• YouTube (21:26) - Spontaneous cerebrospinal fluid otorrhea repair with the middle fossa approach

• YouTube (25:02) - Left Middle Cranial Fossa Approach and Repair of Superior Semicircular Canal Dehiscence