Neurosurgery notes/Procedures/Cranial procedures/Approaches/Skull base approaches/Posterior fossa approaches/CPA approach/Presigmoid approaches/Retrolabyrinthine (posterior petrosectomy) approach

Retrolabyrinthine (posterior petrosectomy) approach

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Parent item
Presigmoid approaches
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Combined anterior-posterior petrosectomy

Indications

  • Approach for pathologies of the posterior cranial fossa.
    • Resection of cerebellopontine angle (CPA) and posterior petrous ridge tumors (e.g., meningiomas, vestibular schwannomas).
    • The procedure is ideally suited for patients with specific posterior cranial fossa pathology who have good hearing, as this approach preserves hearing by avoiding the bony labyrinth and neural structures.
  • Vestibular neuronectomy.
  • Select tumors located adjacent to the presigmoid dura.
  • Access to the petroclival region, jugular foramen, and lesions medial to the internal auditory canal, especially when hearing preservation is preferred.

Surgical Steps

Preparation and Setup

  • GA, Supine
  • Surgeon operates sitting.
  • The patient's head is rotated 70 degrees away from the surgeon and secured with adhesive tape.
  • Hair is removed 4 cm superiorly and postauricularly to allow for wide exposure.
  • Facial nerve monitoring electrodes are placed and verified.
  • The ear and the left lower abdominal quadrant (if fat harvest is necessary) are prepared and draped in a sterile fashion.
  • Mannitol and furosemide are administered intravenously before the skin incision to aid in brain relaxation.
notion image

Incision and Exposure of Mastoid Cortex

  • A C-shaped skin incision is made posterior to the postauricular crease, extending down over the mastoid tip.
  • A skin and subcutaneous tissue flap is elevated anteriorly to the external acoustic meatus.
  • An offset incision is created through the temporalis muscle and fascia and the periosteum;
    • this layering technique assists in wound closure and helps prevent cerebrospinal fluid (CSF) leaks.
  • A periosteal elevator detaches the musculoperiosteum from the cranium, exposing the mastoid cortex.
  • All bony landmarks must be identified, including
    • The root of the zygoma
    • External auditory meatus
    • Linea temporalis
    • Mastoid emissary foramen
    • Asterion
    • Spine of Henle.
notion image

Mastoidectomy and Skeletonization

  • A complete mastoidectomy is performed under magnification using a high-speed cutting burr.
  • Bone removal continues down to the mastoid antrum, exposing the lateral semicircular canal.
  • Properly sized diamond drill bits are used to remove bone overlying the middle fossa dura, sigmoid sinus, and posterior fossa dura.
  • Maximal dural exposure is obtained by completely skeletonizing the sigmoid sinus and jugular bulb.
  • The lateral semicircular canal (LSC) and posterior semicircular canal (PSC) should be well defined, along with the entire course of the mastoid segment of the facial nerve, and the presigmoid, middle fossa, and sinodural angle dura.
  • It is critical not to violate the bony labyrinth, as this would result in hearing loss.
  • Any remaining bone over the posterior fossa dura between the PSC and the sigmoid sinus is removed using blunt dissection, taking care to preserve the underlying endolymphatic duct and sac.
  • Gel-foam is utilized to block the aditus ad antrum.
  • The mastoid cavity is copiously irrigated with bacitracin solution to remove all bone dust.
Skeletonization of the mastoid (fn, facial nerve; ss, sigmoid sinus; l, labyrinth; mft, middle fossa tegmen).
Skeletonization of the mastoid (fn, facial nerve; ss, sigmoid sinus; l, labyrinth; mft, middle fossa tegmen).
 

Dural Opening and Cerebellopontine Angle (CPA) Access

  • In the retrolabyrinthine approach the dural flap is designed to preserve the endolymphatic sac and its aqueduct.
  • While this opening, by itself, provides only limited posterior fossa exposure, when combined with a middle fossa craniotomy and division of the tentorium considerably wider exposure than that depicted here can be obtained.
  • ES, endolymphatic sac
  • 7, facial nerve
  • 8, audiovestibular nerve
  • P, Posterior semicircular canal
  • L, lateral semicircular canal.
notion image
  • The dura anterior to the sigmoid sinus is opened with an 11 blade scalpel and microscissors, creating an anteriorly based C-shaped flap.
  • The endolymphatic sac, which appears as a thickened area of dura, can be visualized inferior to the posterior semicircular canal (PSC)
  • The dura is tacked laterally with four sutures to improve exposure of the operative field.
  • A neurosurgical cottonoid patty is placed over the brainstem to create a small amount of tension between the cerebellum and the petrous ridge.
  • The arachnoid adhesions in this location are transected, and CSF is released.
  • The release of CSF causes the cerebellum to fall away from the petrous ridge, allowing visualization of the CPA, the posterior face of the petrous ridge, and cranial nerves (CN) VII and VIII (which are central to the field).
  • This exposure also grants access to CN V anteromedially, CN IX, X, and XI laterally and inferiorly, and the rostral division of the anteroinferior cerebellar artery associated with the CN VII-VIII complex.
Exposure following raising of anterior base dura flap, with retractor in place posteriorly to aid exposure (ss, sigmoid sinus; mft, middle fossa tegmen; vcn, vestibulocohlear nerve).
Exposure following raising of anterior base dura flap, with retractor in place posteriorly to aid exposure (ss, sigmoid sinus; mft, middle fossa tegmen; vcn, vestibulocohlear nerve).
  • The retrolabyrinthine approach is an anterosigmoid posterior craniotomy which preserves the structures of the inner ear.
  • To obtain posterior fossa exposure, bone much be removed a considerable distance behind the sigmoid sinus and the semicircular canals are skeletonized.
notion image

Closure

  • Meticulous hemostasis is achieved.
  • The dura is reapproximated using 4-0 braided suture.
  • The aditus ad antrum, the facial recess, and retrofacial air cells are covered with temporalis fascia.
  • The mastoid is filled with an abdominal fat graft to help prevent CSF leak.
  • The wound is closed in layers.
  • A compressive mastoid dressing is applied and left in place for 72 hours.

Complications

  • Cerebellar edema.
  • Nerve Injuries:
    • Cochlear nerve injury.
    • Facial nerve injury.
  • Intracranial vascular injury.
    • Possible venous injury (sigmoid sinus, jugular bulb) → bleeding/embolus
  • Cerebrospinal fluid (CSF) leak:
    • The reported incidence of CSF leak is 3%-7%.
  • Postoperative headache.
  • Conductive hearing loss:
    • This specific type of hearing loss can occur if bone dust is not properly irrigated and subsequently enters the middle ear.
    • It may also result if an abdominal fat graft, which is used to fill the mastoid cavity during closure, herniates into the epitympanum.

Pros

  • Preserves hearing: Semicircular canals and cochlea are not sacrificed, unlike translabyrinthine/transcochlear approaches.
  • Less cerebellar retraction: Direct route through the temporal bone, potentially reducing risk of cerebellar injury.
  • Minimal neural manipulation: Avoids direct handling of cranial nerves.
  • Foundation for extended exposures: Forms the starting point for combined petrosal and more extensive skull base approaches.

Cons

  • Technically demanding: Requires careful bone removal near critical neuro-otologic structures.
  • Deep and narrow operative field: Can make instrument maneuverability challenging, especially for complex bypasses.