Retrolabyrinthine approach to petrous apex
This approach is considered to be the unsung hero of skull base surgery. This technique is ideally suited for patients with pathologies involving the posterior cranial fossa with retained hearing. Directly accessing the Cerebellopontine angle through temporal bone and avoiding neural structures preserves hearing. This approach allows for mobilization of the sigmoid sinus posteriorly and access to the posterior fossa through the presigmoid space.
This approach provides excellent exposure laterally from the 4th cranial nerve to the upper border of the jugular tubercle. There is only limited access to the ventral brain stem and clivus.
Factors that limit this approach:
1. Poorly pneumatized mastoid
2. Forward lying sinus
3. High jugular bulb
4. Low lying tegmen
This approach can be used by itself for small tumors or in conjunction with other techniques to gain greater exposure. These combined approaches include:
Translabyrinthine approach Infratemporal approach Transcochlear approach Combined transtemporal approaches Retro sigmoid craniotomies
Indications:
1. Resection of CP angle tumors
2. Resection of petrous ridge tumors
3. Vestibular neurectomy
4. Partial resection of the sensory root of 5th cranial nerve
5. Fenestration of symptomatic arachnoid cysts
6. Meningiomas
7. Metastatic lesions
8. Biopsy of brainstem lesions
9. In conjunction with other approaches in extensive skull base surgeries
Procedure:
This surgery is performed under general anesthesia. Patient is placed supine. Surgeon should be seated comfortably during surgery. The patient’s head is rotated 70° away from the surgeon. Hair is removed about 4 cms superiorly and post auricularly in order to site the incision.
Facial nerve monitoring electrodes should be placed and verified for its function. Abdomen is also prepared to harvest abdominal fat. Preoperative antibiotics are also administered on the table. Before starting the surgery, Intravenous mannitol and frusemide are administered to bring down the intracranial tension.
Incision:
A C shaped incision is made with a 15-blade scalpel 3-4 cm posterior to the post aural crease extending up to the mastoid tip.
Skin and subcutaneous tissue flap is elevated anteriorly up to the external acoustic meatus. Next an offset incision is created through the temporalis muscle, fascia and periosteum. This helps later during wound closure as the wound can be closed in layers. This layered closure helps in prevention of CSF leak.
A periosteal elevator is used to elevate the periosteum away from the cranium exposing the mastoid cortex. The following bony landmarks need to be identified:
Root of the zygoma
External auditory meatus
Linea temporalis
Mastoid emissary foramen
Asterion
Henle’s spine
The following triangles should be identified before actual drilling starts:
Fukushima outer mastoid triangle:
Three points of this triangle include:
• Posterior root of zygoma
• Asterion
• Mastoid tip
Fukushima Inner triangle (Trautmann’s triangle)
• Anterior – Superior (anterior) semicircular canal
• Superior – Superior petrosal vein
• Lateral – Sigmoid sinus
• Inferior – Jugular bulb
McEwen’s triangle:
• Flat triangle behind the external auditory canal
