Stepwise dissection of 4th ventricle, cerebellum and brainstem from anterior to posterior
- The petrosal surface faces forward toward the posterior surface of the temporal bone. The fourth ventricle is located behind the pons and medulla.
- The midbrain and pons are separated by the pontomesencephalic sulcus
- The pons and medulla by the pontomedullary sulcus.
- The trigeminal nerves arise from the mid pons.
- The abducens nerve arises in the medial part of the pontomedullary sulcus, rostral to the medullary pyramids.
- The facial and vestibulocochlear nerves arise at the lateral end of the pontomedullary sulcus immediately rostral to the foramen of Luschka.
- The hypoglossal nerves arise anterior to the olives and the glossopharyngeal, vagus, and accessory nerves arise posterior to the olives.
- Choroid plexus protrudes from the foramen of Luschka behind to the glossopharyngeal and vagus nerves.
- Right cerebellopontine angle following removal of some of the medulla.
- The foramen of Luschka opens into the cerebellopontine angle below the junction of the facial and vestibulocochlear nerves with the lateral end of the pontomedullary sulcus.
- Choroid plexus protrudes from the lateral recess and foramen of Luschka behind the glossopharyngeal, vagus, and accessory nerves.
- The cerebellopontine fissure, a V-shaped fissure formed by the cerebellum wrapping around the pons and middle cerebellar peduncle, has a superior and inferior limb that define the margins of the cerebellopontine angle. The superior limb extends above the trigeminal nerve and the inferior limb passes below the flocculus and the nerves that pass to the jugular foramen.
- The part of the pons and medulla forming the left half of the floor of the ventricle has been removed to expose the fastigium,
- Which divides the ventricular roof into superior and inferior parts.
- Roof of the 4th ventricle: both separated by the fastigium
- Superior part:
- Formed by the superior medullary velum.
- Inferior part
- Rostral part of the lower half of the roof is formed by the nodule and inferior medullary velum
- Caudal part is formed by the tela choroidea, a thin arachnoid-like membrane, in which the choroid plexus arises.
- The cerebellopontine fissure has upper and lower limbs, which meet at a later apex located at the medial end of the petrosal fissure, also called the horizontal fissure, which divides the petrosal surface into upper and lower halves.
- The junction of the pons and medulla, which forms the anterior wall of the left lateral recess, has been removed to expose the choroid plexus protruding through the lateral recess (& foramen of Lushka) into the cerebellopontine angles.
- Enlarged view. The choroid plexus protrudes laterally through the foramen of Luschka into the cerebellopontine angle below the flocculus
- The left half of the medulla has been removed.
- The superior half of the roof is formed by the superior medullary velum, which has the lingula of the vermis layered on its outer surface.
- The lower half of the roof is formed by the inferior medullary velum, which arises on the surface of the nodule, and the tela choroidea in which the choroid plexus arises.
- The choroid plexus is composed of paired L-shaped fringes, which have
- Medial segments
- The medial segments extend longitudinally through the foramen of Magendie.
- Lateral segments.
- The lateral segments extend laterally through the foramen of Luschka
- The right half of the tela choroidea and choroid plexus have been removed to expose the upper pole of right tonsil.
- The right cerebellar tonsil has been removed.
- All of the surfaces of the tonsils are free surfaces except the superolateral margin, the site of the tonsillar peduncle, a bundle of white matter, which attaches the tonsil to the remainder of the cerebellum.
- The inferior medullary velum is a thin membranous layer of neural tissue that arises on the nodule and extends laterally above the rostral pole of the tonsil to blend into the flocculus and form the flocculonodular lobe of the cerebellum.
- The cranial loop of the PICA courses between the rostral pole of the tonsil and the inferior medullary velum.
- Both tonsils have been removed. The inferior medullary velum sweeps laterally from the surface of the nodule
Stepwise dissection of 4th ventricle, cerebellum and brainstem from posterior to anterior
The PICAs pass around the posterior medulla to reach the lower margin of the cerebellomedullary fissure.
- The left PICA courses around the lower pole of the tonsil.
- The right PICA descends well below the tonsil to the level of the foramen magnum before ascending along the medial tonsillar surface.
The PICAs ascend between the tonsils and medulla to reach the interval between the tonsil and uvula and to supply the suboccipital surface.
The posterior medullary segment of the right PICA divides into a
- Medial trunk supplying the vermis and paravermian area
- Lateral trunk supplying the hemisphere.
The cerebellum has been sectioned in an oblique coronal plane to show the relationship of the rostral pole of the tonsil to the inferior medullary velum and dentate nucleus.
The dentate nucleus is located above the posterolateral part of the ventricular roof, near the fastigium, where it wraps around, and is separated from, the rostral pole of the tonsil by the inferior medullary velum.
The left tonsil has been removed while preserving the left half of the inferior medullary velum.
The SCAs course in the cerebellomesencephalic fissure.
The PICA passes between the walls of the cerebellomedullary fissure formed above by the inferior medullary velum and below by the upper pole of the tonsil.
Both tonsils have been removed. The PICAs ascend through the cleft between the inferior medullary velum and rostral pole of the tonsil.
The superior part of the ventricular roof has been removed and the nodule and the inferior medullary velum has been folded downward to expose the floor
The Tela choroidea, in which the choroid plexus arises, has been folded downward to expose the lower part of the floor.
Enlarged view of the left lateral recess and the foramen of Luschka.
The rhomboid lip is a thin layer of neural tissue, which extends laterally from the anterior margin of the lateral recess and, with the tela choroidea, forms a pouch at the outer edge of the lateral recess.
Choroid plexus extends through the lateral recess and foramen of Luschka into the cerebellopontine angle.
The tela has been removed to expose the parts of the floor located above and below the nodule and inferior medullary velum.
The nodule and the inferior medullary velum have been removed to expose the full length of the floor, which is divided in the midline by the median sulcus and craniocaudally into pontine, junctional, and medullary parts.
The superior and inferior peduncles face the ventricular surface.
- The middle cerebellar peduncle is separated from the ventricular surface by the superior and inferior peduncles
Enlarged view of the floor of the fourth ventricle.
The median sulcus divides the floor longitudinally in the midline.
- Each half of the floor is divided longitudinally by an irregular sulcus, the sulcus limitans, which deepens lateral to the facial colliculus and hypoglossal triangles to form the superior and inferior foveae.
- A darkened area of cells, the locus ceruleus, is located at the rostral end of the sulcus limitans.
- The stria medullaris crosses the floor at the level of the lateral recess.
- This striae medullaris is different from the Stria medullaris thalami of the hypothalamus which Connects the septal area, hypothalamus, olfactory area and anterior thalamus to the habenulum
- Calamus scriptorius.
- Stacked area made up of
- CN12
- CN10
- Area postrema
- In the lower part of the floor
- Give the configuration of a pen nib
Another fourth ventricular floor.
The paired veins of the superior cerebellar peduncle course on the outer surface of the superior peduncles and join superiorly to form the vein of the cerebellomesencephalic fissure.
The median posterior medullary vein ascends on the medulla and splits into the paired veins of the inferior cerebellar peduncle at the caudal margin of the floor.
That left vein is hypoplastic. The left vein of the cerebellomedullary fissure passes along the lateral recess and ascends to join the petrosal group of veins in the cerebellopontine angle.
- Do not cut thru the superior medullary velum
- Transvermian vs telovelar
- Durotomy Y shaped favouring one side to prevent cutting thru the occipital sinus
- Transvermian
- Do not retract too much can damage dentate nucleus
Brainstem, petrosal surface, and cerebellopontine fissure
- The cerebellopontine fissure, which might also be referred to as the cerebellopontine angle, is a V-shaped fissure formed where the cerebellum wraps around the pons and middle cerebellar peduncle.
- The superior and inferior limbs meet laterally at the apex located at the anterior end of the petrosal fissure that divides the petrosal surface into superior and inferior parts.
- Cranial nerves V through XI arise within the margins of the cerebellopontine fissure.
- The flocculus and choroid plexus extend laterally from the foramen of Magendie above the lower limb of the fissure.
- The basilar sulcus is a shallow longitudinal groove on the anterior surface of the pons, which accommodates the basilar artery.
- The petrosal fissure extends laterally from the apex of the cerebellopontine fissure.
- CN6 arises in the medial part of the pontomedullary sulcus rostral to the medullary pyramids.
- CN7/8 arise just rostral to the foramen of Luschka near the flocculus at the lateral end of the pontomedullary sulcus.
- CN12 arise anterior to CN 9, 10, 11 and olive
- CN 9, 10, 11 arises posterior to the olives.
- Choroid plexus protrudes from the foramen of Luschka behind the glossopharyngeal and vagus nerves.
- CN 7, 8 join the brainstem 2 or 3 mm rostral to the CN 9 on a line drawn dorsal to the olive along the origin of the rootlets of the CN9, 10, 11 rootlets.
- The rhomboid lip, a thin neural membrane in the ventral margin of the lateral recess, extends laterally behind the CN 9, 10, 11 with the choroid plexus.
- The cerebellopontine angle is the area situated between the superior and inferior limbs of the cerebellopontine fissure.
- Superior limb
- Trigeminal nerve near
- Mid portion
- The facial and vestibulocochlear nerves arise
- Inferior limb
- The glossopharyngeal, vagus, and accessory nerves arise near the inferior limb, dorsal to the olive, and anterior to the choroid plexus protruding from the foramen of Luschka.
- CN12 rootlets arise in front of the olive and the cranial rootlets of the accessory nerve.
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