Anterior vs posterior petrosal approach
Anterior petrosal approach
- Most commonly referred as “Kawase” or “Extended middle fossa approach”
- Subtemporal craniotomy
- Anterior petrosectomy (Extradural)
- Transtentorial (middle-to-posterior fossa trajectory)
Posterior petrosal approach
- Most commonly referred as “petrosal approach”
- Mastoidectomy + L-shape subtemporal craniotomy
- Retrolabyrinthine petrosectomy (hearing preservation)
- Presigmoidal transtentorial approach
Various skin incision
Various different approaches to the middle and posterior skull base
Choosing the surgical approach
Craniocaudal location of tumour
- A classification of intradural tumors located ventral to the brainstem and upper cervical spinal cord based upon characteristics relevant to the selection of surgical approach.
- The upper dashed line, separating zone 1 from zone 2, is the level of the tentorium cerebrelli.
- The lower dashed line, demarcating zone 2 from zone 3, represents the lowest portion of the posterior fossa typically accessible via a transtemporal approach.
- Zone 1
- Anatomical Relationships - Brainstem: Midbrain
- Cranial Base: Upper Clivus
- Surgical Approaches: Middle Fossa.
- Zone 2
- Anatomical Relationships - Brainstem: Pons, Upper Medulla
- Cranial Base: Midclivus
- Surgical Approaches: Transpetrosal (Retrolabyrinthine,Translabyrinthine,
- Transcochlear), Retrosigmoid.
- Zone 1+2
- Anatomical Relationships - Brainstem: Midbrain, Pons, Upper Medulla
- Cranial Base: Mid- and upper clivus,
- Transtentorial Route (Via Tentorial Notch, Via Cavum Trigeminale), Largest tumor component (Posterior Fossa, Middle Fossa)
- Surgical Approaches:
- Middle Fossa (MF)
- Transpetrosal/MF
- Retrolabyrinthine/MF
- Translabyrinthine/MF
- Transcochlear/MF
- Middle fossa/transpetrous apex.
- Zone 3
- Anatomical Relationships - Brainstem: Lower Medulla, Spinal Cord
- Cranial Base:
- Lower clivus
- Foramen magnum
- Cervical Spine
- Surgical Approaches:
- Lateral approach to foramen magnum (LAFM).
- Zone 2+3
- Anatomical Relationships - Brainstem: Pons, Medulla, Spinal Cord
- Cranial Base:
- Mid- and Lower clivus
- Foramen magnum
- Cervical Spine if jugular foramen involved
- Surgical Approaches:
- Retrosigmoid/Lateral Approach to the Foramen Magnum (LAFM)
- Transpetrosal/ LAFM
- Retrolabyrinthine/LAFM
- Translabyrinthine/LAFM
- Transcochlear/LAFM
- Transjugular/ LAFM
Size of tumour
- Characteristics of tumors ventral to the brainstem which affect the choice of operative approach.
- (A,B) Tumors confined to the mid-line are best managed with a presigmoid transpetrosal approach to minimize the need for cerebellar and brainstem retraction.
- The amount of petrosectomy performed depends, in part, upon the thickness of the tumor ventral to the brainstem. As a general rule, more bulky tumors which push the brainstem posteriorly require a lesser degree of petrosectomy in order to expose the tumor-brainstem interface.
- (C) Tumors with a substantial lateral component may open a pathway adjacent to the displaced pons, thus allowing a conventional retrosigmoid approach without need for supplemental petrosectomy.
- A pre-sigmoid opening may still be needed when the tumor extends beyond the midline to the side opposite of the main tumor mass.
Possible relationships of the basilar artery to a prepontine tumor.
- The vessel may be situated in one of three positions:
- Posterior to the tumor on the surface of the pons
- Most common location A
- Anterior to the tumor elevated from the pontine surface (B),
- Enveloped by the tumor (C)
- In the later two situations radical tumor removal carries a substantial risk of brainstem ischemia due to interruption of the pontine perforating vessels.
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