General
- Located between the superior and inferior limbs of the angular cerebellopontine fissure formed by the petrosal cerebellar surface folding around the pons and middle cerebellar peduncle
Borders
Lateral (bony) wall
- The borders of the temporal and occipital bone form the POS
- POS houses the IPS
- 4 foramina in the lateral wall
- Meckel's cave
- IAM
- Jugular Foramen
- Hypoglossal canal
Medial (brainstem/cerebellum) wall
- Formed by the BS (Pons) and petrosal surface of cerebellum
- The petrosal fissure and the MCP (at it's base) are continuous with the CPF superiorly and inferiorly
- Superior limb = continuous with cerebellomesencephalic fissure
- Inferior limb = continuous with cerebellomedullary fissure
- Vessels run in fissures
- Flocculus = medial or inferomedial to PF
- 7th/8th complex is slightly anterior to flocculus
- Choroid plexus through Luschka = slightly inferomedial
3 Neurovascular Complexes
Upper complex
- Vessel:
- SCA, closes to CN5
- Brain stem:
- Midbrain
- Superior cerebellar peduncle,
- Nerve
- CN3, 4, 5
- Cerebellomesencephalic fissure
- Tentorial cerebellar surface
Middle complex
- Vessel
- AICA closes to CN7/8
- Brain stem
- Pons
- Middle cerebellar peduncle,
- Nerve
- CN 6,7,8
- Cerebellopontine fissure
- Petrosal surface
- Flocculus
Lower complex
- Vessel
- PICA closes to CN12
- Brainstem
- Medull
- Inferior cerebellar peduncle,
- Nerve
- CN 9, 10, 11, 12
- Cerebellomedullary fissure,
- Suboccipital surface
- Choroid plexus
One part of Brainstem + One artery complex + Different nerves
Contents
Suprameatal tubercle
- Microscopic endoscopic assisted suprameatal tubercle drilling is a feasible procedure that allows the identification of all neurovascular structures in the cerebellopontine angle and petrous apex region
- By drilling off the suprameatal tubercle and part of the petrous apex, Meckel's cave may be opened, the trigeminal nerve mobilized, and the tentorium divided. Thus the parasellar region may be exposed and the posterosuperior space of the cavernous sinus approached
Cerebellopontine angle
A., artery; A.I.C.A., anteroinferior cerebellar artery; Arc., arcuate; CN, cranial nerve; Coch., cochlear; Emin., eminence; Endolymph., endolymphatic; Flocc., flocculus; Inf., inferior; Intermed., intermedius; Jug., jugular; Labyr., labyrinth; N., nerve; Nerv., nervus; P.I.C.A., posteroinferior cerebellar artery; Post., posterior; S.C.A., superior cerebellar artery; Subarc., subarcuate; Sup., superior; Trans., transverse; Vert., vertebral; Vest., vestibular
- Left CAP dissection
- The AICA passes between the facial and vestibulocochlear nerves.
- A dural septum separates the glossopharyngeal and vagus nerves at the jugular foramen.
- CN8 and the flocculus have been elevated to expose the junction of the facial nerve with the brainstem.
- In the retrosigmoid approach, the CN7 junction with the brainstem can be exposed below the vestibulocochlear nerve.
- Posterior wall of the internal acoustic meatus has been removed.
- The cleavage plane between the superior and inferior vestibular nerves is especially prominent.
- The dura lining the internal acoustic meatus has been opened. The transverse crest/falciform crest separates the superior vestibular and facial nerves above from the inferior vestibular and cochlear nerves below.
- Nervous intermedius goes with CN7
- Enlarged view of the nerves within the meatus.
- The cochlear nerve is partially hidden anterior to the inferior vestibular nerve.
- Cleavage plane between the superior and inferior vestibular and cochlear nerves has been started laterally and extended medially to expose the individual nerve bundles.
- The vertical (bill's bar) and transverse crest are exposed at the meatal fundus.
- The common crus and adjacent part of the superior and posterior canals have been exposed.
- The endolymphatic duct and sac are situated inferolateral to the internal acoustic meatus.
- Another dissection showing the relationships of the junction of the posterior and superior canals and common crus to the meatus.
- The endolymphatic duct extends downward and backward from the vestibule and opens into the endolymphatic sac, which sits under the dura in the area below and lateral to the meatus.
- The jugular bulb can be seen through the bone medial to the endolymphatic sac.
- Fundus of the left internal acoustic meatus.
- The multiple cochlear nerve filaments penetrating the tiny openings in the lamina cribrosa at the meatal fundus can easily be torn with traction on the nerve from lateral to medial, therefore, we try to direct the strokes of dissection from medial to lateral when there is an opportunity to preserve hearing.
- Closure after removing the posterior wall of the internal acoustic meatus.
- Bone wax on a microdissector is carefully placed into open air cells in the posterior meatal lip and then a pledget of crushed subcutaneous abdominal fat is laid over the drilled meatal area.
- This has prevented cerebrospinal fluid leaks after removal of the posterior wall of the internal acoustic meatus in more than 200 consecutive operations for acoustic neuroma by the author.
- View of right internal acoustic meatus with the posterior lip removed to show variable direction of facial nerve displacement by acoustic neuroma.
- A. Normal neural relationships with the eighth nerve dividing into its three parts in the lateral meatus.
- The facial and superior vestibular nerves are above the transverse crest
- The cochlear and inferior vestibular nerves are below.
- The facial nerve occupies the anterosuperior quadrant of the lateral meatus.
- B. The facial nerve is displaced directly anteriorly.
- This is a frequent direction of displacement with acoustic neuroma.
- C. Another frequent direction of displacement of the facial nerve is anterior and superior.
- D. The facial nerve is displaced anteriorly and inferiorly by tumor,
- Tumour erodes the superior wall of the meatus above the nerves and grows into the area above the nerves, displacing them inferiorly.
Relationships with various structures
Abbreviations
- A., artery; A.I.C.A., anteroinferior cerebellar artery; Ant., anterior; Bas., basilar; Br., bridging; Ca., caudal; Cer., cerebellar; Cer. Med., cerebellomedullary; Cer. Pon., cerebellopontine; Chor., choroid; F., foramen; Fiss., fissure; Hem., hemispheric; Inf., inferior; Jug., jugular; Lat., lateral; Marg., marginal; Med., medial, medullary; Mid., middle; Ped., peduncle; Perf., perforating; P.I.C.A., posteroinferior cerebellar artery; Pon., pontine; Pon. Med., pontomedullary; Pon. Mes., pontomesencephalic; Rec., recurrent; Ro., rostral; S.C.A., superior cerebellar artery; Subarc., subarcuate; Sulc., sulcus; Sup., superior; Tr., trunk; Trans., transverse; V., vein; Vel., velum; Vert., vertebral.
Neural relationships
Anterolateral view
- CN7 & 8
- Arise from the brainstem near the lateral end of the pontomedullary sulcus,
- location
- Anterosuperior to the choroid plexus protruding from the foramen of Luschka,
- Anterior to the flocculus,
- Rostral to a line drawn along the junction of the rootlets of the glossopharyngeal, vagus, and accessory nerves with the brainstem, and
- Slightly posterior to the rostral pole of the inferior olive.
- Cerebellopontine fissure
- Formed by the cerebellum wrapping around the lateral side of the pons and middle cerebellar peduncle
- Superior limb that passes above the trigeminal nerve
- Inferior limb that extends below the foramen of Luschka.
- Cerebellomedullary fissure
- Which extends superiorly between the medulla and cerebellum,
- Communicates in the region of the foramen of Luschka with the cerebellopontine fissure.
Anterosuperior view
- The cerebrum and tentorium cerebelli have been removed, and the trigeminal, trochlear, and oculomotor nerves have been divided to allow the brainstem to be displaced posteriorly to expose the cerebellopontine angle from above.
- The facial and vestibulocochlear nerves arise at the lateral end of the pontomedullary sulcus anterior to the flocculus, rostral to the glossopharyngeal, vagus, and accessory nerves, and anterosuperior to the choroid plexus protruding from the foramen of Luschka.
- The cerebellopontine fissure, formed where the cerebellum wraps around the lateral side of the pons and middle cerebellar peduncle, has superior and inferior limbs.
- The foramen of Luschka opens into the inferior limb near the facial and vestibulocochlear nerves.
Posterior inferior view (via a suboccipital approach)
- The right cerebellar tonsil has been removed by dividing the tonsillar peduncle to show the relationship of the lateral recess to the facial and vestibulocochlear nerves.
- Flocculus and choroid plexus protrude in the cerebellopontine angle behind the junction of the facial and vestibulocochlear nerves with the brainstem.
- Inferior medullary velum
- Stretches from the lateral side of the vermis to the flocculus and is all that remains of the connection between the flocculus and the nodulus, which form the flocculonodular lobe of the cerebellum.
- Stretches laterally to form the peduncle of the flocculus.
- The tela choroidea forms the caudal part of the roof of the fourth ventricle and has the choroid plexus attached to its inner surface.
- The facial and vestibulocochlear nerves enter the brainstem at the lateral end of the pontomedullary sulcus.
- Tela choroidea has been opened, but the choroid plexus, which arises on the inner surface of the tela in the fourth ventricle, has been preserved.
- The fringelike choroid plexus extends through the foramen of Luschka slightly below and behind the junction of the facial and vestibulocochlear nerves with the brainstem.
- The inferior cerebellar peduncle ascends on the dorsolateral margin of the medulla.
Posterior view via a retrosigmoid approach
- The retractor is on the petrosal surface of the cerebellum.
- The facial and vestibulocochlear nerves arise at the lateral end of the pontomedullary sulcus, anterior to the flocculus, rostral to the glossopharyngeal, vagus, and accessory nerves, and anterosuperior to the choroid plexus protruding from the foramen of Luschka.
- The cerebellopontine fissure, formed where the cerebellum wraps around the lateral side of the pons and middle cerebellar peduncle, has superior and inferior limbs.
Arterial relationships
Anterolateral view
- AICA
- Arises from the basilar artery
- Courses below the facial and vestibulocochlear nerves, and then above the flocculus to reach the surface of the middle cerebellar peduncle.
- Divides into:
- Rostral trunk,
- Larger of the two trunks
- Caudal trunk
- PICA
- Arises from the vertebral artery and
- Passes first between the CN12 rootlets, and then between the CN10 and CN11 nerves on its way to the cerebellar hemisphere.
- SCA
- Passes above the trigeminal nerve.
Anterosuperior view
- The AICA arises from the basilar artery, passes below the facial and vestibulocochlear nerves, gives rise to the subarcuate artery, and divides into a rostral and a caudal trunk.
- The rostral trunk passes above the flocculus to course on the middle cerebellar peduncle, and the caudal trunk supplies the area below the flocculus.
Posterior view via a retrosigmoid approach
- The AICA arises from the basilar artery and divides into a rostral trunk, which passes above the flocculus to reach the surface of the middle cerebellar peduncle, and a caudal trunk, which supplies the area below the flocculus.
- The PICA arises from the vertebral artery and passes dorsally between the vagus and accessory nerves.
- The SCA courses above the trigeminal nerve.
Venous relationships
Anterolateral view
- The veins that converge on the junction of the facial and vestibulocochlear nerves with the brainstem are the veins of the
- Pontomedullary sulcus
- Cerebellomedullary fissure
- Middle cerebellar peduncle
- Retro-olivary veins
- Lateral medullary veins.
- Transverse pontine and transverse medullary veins cross the pons and medulla.
- The median anterior medullary and median anterior pontomesencephalic veins ascend on the anterior surface of the medulla and pons.
- Superior petrosal sinus ← Superior petrosal vein ←
- Middle cerebellar peduncle vein
- Cerebellopontine fissure vein
- Passes above the flocculus on the middle cerebellar peduncle,
- Is formed by the anterior hemispheric veins that arise on the cerebellum.
- Transverse pontine vein
- A bridging vein passes below the vagal rootlets toward the jugular foramen.
Anterosuperior view
- The veins converging on the junction of the facial nerve with the brainstem are the lateral medullary and retro-olivary veins, and the veins of the pontomedullary sulcus, cerebellomedullary fissure, and middle cerebellar peduncle.
- The median anterior pontomesencephalic vein ascends on the anterior surface of the brainstem
- The transverse pontine and transverse medullary veins cross the pons and medulla.
- The vein of the cerebellopontine fissure passes above the flocculus.
- The transverse pontine vein and the veins of the middle cerebellar peduncle and cerebellopontine fissure join to form one of the superior petrosal veins that empty into the superior petrosal sinus.
- A bridging vein passes from the side of the brainstem to the jugular foramen.
- The anterolateral marginal vein crosses the anterolateral margin of the cerebellum.
- The vein of the pontomesencephalic sulcus courses in the pontomesencephalic sulcus below the oculomotor nerve.
Posterior view via a retrosigmoid approach
- The veins that join near the junction of the facial and vestibulocochlear nerves with the brainstem are the lateral medullary veins and the veins of the cerebellomedullary fissure, pontomedullary sulcus, and middle cerebellar peduncle.
- The vein of the cerebellopontine fissure passes above the flocculus along the superior limb of the cerebellopontine fissure and joins the vein of the middle cerebellar peduncle and a transverse pontine vein to form a superior petrosal vein, which empties into the superior petrosal sinus.
- A bridging vein passes behind the vagus nerve. The lateral anterior pontomesencephalic vein ascends on the pons.
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