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CP angle.pptx
- 2. Outline • Anatomy of the CP angle • Imaging Characteristics • Differential Diagnosis • Pathology of the CP Angle • Surgical Approaches
- 4. Anatomy White arrow: 6th CN C: cochlea V: Vestibule Black arrows: cochlear and inferior vestibular nerves P: inferior cerebellar peduncle
- 5. Anatomy: CP angle 3 Neurovascular Complexes 1. Upper Complex: SCA 2. Middle Complex: AICA 3. Lower Complex: PICA
- 7. Anatomy: CP angle AICA Segments ▪ Green: Anterior Pontine ▪ Contacts rootlets of CN 6 ▪ Orange: Lateral pontomedullary ▪ Blue: Flocculonodular ▪ Red: Cortical
- 8. Anatomy: CP angle AICA Segments ▪ Green: Anterior Pontine ▪ Contacts rootlets of CN 6
- 9. Anatomy: CP angle AICA Segments ▪ Orange: Lateral pontomedullary ▪ Related to: ▪ Internal auditory meatus ▪ CN 7, 8 ▪ Choroid plexus protruding from foramen of Luska
- 10. Anatomy: CP angle AICA Segments ▪ Orange: Lateral pontomedullary ▪ This segment is divided into 3 parts: ▪ Premeatal ▪ Meatal ▪ Postmeatal
- 11. Anatomy: CP angle AICA Segments ▪ Orange: Lateral pontomedullary ▪ Nerve Related Branches: ▪ Labyrinth artery CN 7, 8 and the vestibulococclear labyrinth ▪ Enters the IAC ▪ Recurrent Perforating artery brainstem ▪ Subarcuate artery petrous bone in the region of the semicircular canals.
- 12. Anatomy: CP angle AICA Segments ▪ Blue: Flocculonodular ▪ May pass rostral or caudal to flocculus ▪ Often hidden by flocculus or lips of the cerebellopontinue fissure ▪ Red: Cortical ▪ Predominantly supplies the petrosal surface
- 13. CP Angle: Neural Relationships
- 17. CP Angle Pathology • Presentation • Differential Diagnosis • Vestibular schwannoma • Meningiomas • Epidermoids
- 18. Presentation • Sensorineural hearing loss • Tinnitus • Vestibular disturbances • Headache • Facial numbness • Facial weakness • Nausea/vomiting • Diplopia • Lower CN palsies (9, 10, 12): hoarseness, dysphagia • Facial spasm
- 19. Differential Diagnosis ▪ Followed by (most common least common): • Vestibular schwannoma (most common 80%) • Meningiomas • Epidermoids • Schwannomas of other nerves • Glomus jugulare tumors • Glial tumors • Metastatic lesions
- 20. Vestibular Schwannoma • Vestibular schwannoma is the most accurate term. • Neuroma is a misnomer, the cellular makeup is more consistent with a schwannoma • Most lesions arise from the vestibular portion of the 8th cranial nerve. • Other synonyms • Acoustic neuroma • Acoustic schwannoma • Neurinoma • Neurilemmoma
- 21. Vestibular Schwannoma • 6-8% of all intracranial tumors • Most common neoplasm of the CP angle • WHO grade I lesion • The superior vestibular nerve is the most common site of origin (70%).
- 22. Vestibular Schwannoma SPORADIC • Unilateral • VS constitute 95% of all schwannomas. • Present during the 4th and 5th decades of life. • Displaces CN 8 NF-2 • Bilateral (pathognomonic) • Chromosome 22 • Often present at a younger age. • SCREENING: any patient <40yo with unilateral VS should be evaluated for NF2.
- 23. Vestibular Schwannoma: Imaging Characteristics • Avidly enhancing mass in the IAC-CPA • Centered on the porus accousticus
- 25. Vestibular Schwannoma: Pathology • VS arise in the region of the Obersteiner-Redlich zone. • Approximately 8-12mm from the pons • Abrupt transition where oligodendrocyte myelin meets Schwann cell myelin. • Oligodendrocytes stain lighter than Schwann cells
- 26. Vestibular Schwannoma: Pathology Antoni A: compact regions Antoni B: loose regions “Schools of fish” swimming in different directions.
- 27. Epidermoid • Account for 1% of intracranial tumors and about 7% of CPA tumors. • Peak age of occurrence is 40 yrs. • Synonyms • Cholesteatoma • Pearly tumor • Ectodermal inclusion cyst
- 28. Epidermoid • Usually arise from ectoderm trapped within or displaced into the CNS • Epithelial cell rests are carried into the CPA with the developing otic vesicle. • May produce aseptic meningits caused by rupture of the cyst contents. • May lead to hydrocephalus • Mollaret’s meningitis: (rare variant) which includes large cells in the CSF that resemble endothelial cells (possible macrophages).
- 29. Epidermoid • Imaging • XR • Scalloped margins • MRI • T1-hypointense • T2-hyperintense • Some tumors show rim enhancement • Restricted diffusion on DWI as a result of restriction of water movement • CT • Bone erosion is seen in 30%
- 31. Epidermoid: Pathology • Lined by stratified squamous epithelium and contain keratin (from desquamated epithelium), cellular debris, and cholesterol. • Grows at a linear rate (similar to skin) • Cyst contents may be liquid or may have a flaky consistency.
- 33. Epidermoid • Treatment • Surgical goal is to remove as much tumor as possible, but often have to leave capsule adherent to critical structures. • Perioperative steroids and copious irrigation may reduce the risk of post-op hydrocephalus and aseptic meningitis.
- 34. Meningioma
- 35. Surgical Considerations • Audiology • Facial Nerve Function • Neuromonitoring
- 36. Audiology • Audiometric and Audiologic Studies • Gardener and Robertson modified hearing classification Class Description Pure tone audiogram (dB) Speech discrimination I good-excellent 0-30 70-100% II serviceable 31-50 50-59% III nonserviceable 51-90 5-49% IV poor 91-max 1-4% V none Not testable 0
- 37. Surgical Considerations: House and Brackmann Grading Scale
- 38. Surgical Considerations: Neuromonitoring Brainstem function Somatosensory evoked potential (SEP) Contralateral brainstem auditory evoked potentials (BAERs) Facial nerve function Facial electromyography in frontalis, orbicularis oculi, and mentalis muscles Intraoperative stimulation of CN 7 Cochlear nerve function Ipsilateral BAERs Direct electronic monitoring of cochlear nerve
- 39. Brainstem Auditory Evoked Responses (BAERs) I. Cochlear nerve II. Cochlear nuclei (pons) III. Superior olivary complex IV. Lateral lemniscus V. Inferior colliculus (midbrain) VI. Medial geniculate body VII. Auditory radiations
- 40. Brainstem Auditory Evoked Responses (BAERS)
- 41. Surgical Approaches • Posterior to the sigmoid sinus • Retrosigmoid • Transpetrosal • Multiple variations • Pre-sigmoid: petrosectomy • Retrolabyrinthine approach • Translabyrinthine approach • Transcochlear approach
- 43. Surgical Approaches: Retrosigmoid • Most common approach. • Tumors <2.5 cm to avoid too much cerebellar retraction. • Right sigmoid sinus is usually dominant compared to the left.
- 44. Surgical Approaches: Retrosigmoid • C-shaped skin incision, 4 cm posterior to the posterior edge of the mastoid process. • 2 burr holes with one at the junction of the transverse/sigmoid sinus.
- 45. Surgical Approaches: Retrosigmoid • May need to drill away some of the mastoid to expose the sigmoid sinus. • May need to expose the foramen magnum for access to the cisterna magna • Initial dural opening at the anterior-inferior aspect.
- 46. Surgical Approaches: Retrosigmoid • Petrosal vein can usually be saved in small to medium sized tumors. • Subarcuate artery must be sacrificed. • Stimulate tumor capsule at this point to look for the facial nerve.
- 48. Surgical Approaches: Retrosigmoid • Multiple cochlear nerve filaments penetrate the small openings of the lamina cribrosa • These can be easily torn. • Direct traction and strokes of dissection from medial lateral
- 49. Surgical Approaches: Transpetrosal • Can be used for large tumors (>4cm), particularly those that extend up through the tentorial notch • Includes some degree of a posterior petrosectomy • Retrolabyrinthine approach • Translabyrinthine approach • Transcochlear approach • Most of the operation is performed through the pre-sigmoid and subtemporal space, although can also be combined with a retrosigmoid approach especially for lesions with inferior extension. • Boundaries • Superior: CN 4 • Inferior: Jugular bulb • Posterior: Sigmoid sinus • Anterior: Bony labyrinth
- 50. Surgical Approaches Coding Skull Base Codes • Retrolabyrinthine approach • Translabyrinthine approach • Transcochlear approach Craniotomy Codes • Retrosigmoid
- 51. Various petrosectomy options employed during a transpetrosal approach.
- 53. Surgical Approaches:Transpetrosal Retrolabyrinthine • Retrolabyrinthine Petrosectomy • The integrity of the labyrinth is maintained to preserve hearing. • Posterior and superior semicircular canals are skeletonized. • Provides good access to CP angle and lower clivus
- 56. Surgical Approaches: Transpetrosal Translabyrinthine • Typically not utilized in patients with “50/50” hearing or better. • Indicated for tumors >2.5 cm in size regardless of hearing status. • Exposure includes the lateral aspect of the pons, ventral aspect of the lateral cerebellar hemisphere and cranial nerves 5, 6, 7, 8. • The root entry zone of the lower cranial nerves can also be seen to a variable degree depending on the anatomy and location of the jugular bulb.
- 57. Surgical Approaches: Transpetrosal Translabrinthine • Translabyrinthine Petrosectomy • Sacrifices hearing • Semicircular canals are skeletonized and drilled away. • Drilling continues forward so that the IAC is skeletonized. • Bone overlying the labyrinth and mastoid segments of the facial nerve is also thinned.
- 58. Surgical Approaches: Transpetrosal Translabyrinthine ADVANTAGES • Early identification of the facial nerve theoretically resulting in a higher preservation rate. • Less risk to the cerebellum and lower CNs. • Patients don’t get as “ill” from blood in the cisterna magna (essentially an extracranial approach). • Shorter reach for the surgeon. DISADVANTAGES • Sacrifices hearing • Limited access to lower portion of the CP angle.
- 59. Surgical Approaches: Transpetrosal Translabyrinthine • C-shaped incision 4 cm posterior to the postauricular sulcus allowing the pinna to be retracted anteriorly. • Mastoidectomy is performed with high speed drill and the sigmoid sinus is skeletonized.
- 60. Surgical Approaches: Transpetrosal Translabyrinthine • Labyrinthectomy • Opening of the lateral, superior and posterior semicircular canals
- 61. Surgical Approaches: Transpetrosal Translabyrinthine • Skeletonizing the IAC (up to 270° around the canal)
- 62. Surgical Approaches: Transpetrosal Translabyrinthine • Opening of the dura and removal of the tumor
- 63. The spine of Henle approximates the deep site of the lateral semicircular canal.
- 66. Surgical Approaches: Transpetrosal Transcochlear • Transcochlear Petrosectomy • Provides the maximum area of exposure by completely removing the petrous bone. • Sacrifices hearing and facial nerve. • EAC is transected and oversewn. • Semicircular canals are drilled away and the posterior IAC is skeletonized. • Facial nerve canal is completely skeletonized and opened to allow removal of the facial nerve. • The GSPN is then divided to permit posterior transposition of the facial nerve. • This allows the complete removal of the IAC and cochlear apparatus. • Drilling is continued until the ICA is skeletonized up to the siphon