General
- Abbreviation
Abbreviation | Full Form | Abbreviation | Full Form | Abbreviation | Full Form |
A.I.C.A. | Anteroinferior cerebellar artery | Flocc. | Flocculus | Post. | Posterior |
Ant. | Anterior | For. | Foramen | Quad. | Quadrangular |
Cent. | Central | Horiz. | Horizontal | S.C.A. | Superior cerebellar artery |
Cer. | Cerebellar | Inf. | Inferior | Str. | Straight |
Cer.Med. | Cerebellomedullary | Lat. | Lateral | Suboccip. | Suboccipital |
Cer.Mes. | Cerebellomesencephalic | Mid. | Middle | Sulc. | Sulcus |
Cer.Pon. | Cerebellopontine | Med. | Median, Medullary | Sup. | Superior |
Chor. | Choroid | Nucl. | Nucleus | Telovel. | Telovelar |
CN | Cranial nerve | Ped. | Peduncle | Tent. | Tentorial |
Coll. | Colliculus | Pet. | Petrosal | Vel. | Velum |
Dent. | Dentate | P.I.C.A. | Posteroinferior cerebellar artery | Vent. | Ventricle |
Fiss. | Fissure | Plex. | Plexus | ㅤ | ㅤ |
Tentorial, suboccipital, and petrosal cerebellar surfaces.
- The tentorial surface faces the lower surface of the tentorium.
- The anterior vermis is the most superior part of the tentorial surface.
- This surface slopes downward to its posterior and lateral margins.
- The vermian subdivisions of this surface are superior to their corresponding hemispheric parts.
- Anterior part of tentorial surface:
- Two parts
- Vermian part: Culmen
- Hemispheric part: quadrangular lobules
- The anterior part of the superior surface of the cerebellum surrounds the posterior half of the midbrain to form the cerebellomesencephalic fissure.
- Posterior part of the tentorial surface.
- Two parts
- Vermian part: Declive
- Hemispheric part:
- Simple lobules,
- Part of the superior semilunar lobules
- The fissure separating the tentorial surface into anterior and posterior parts is referred to as the tentorial fissure in our nomenclature, but is the primary fissure in older nomenclature.
- The suboccipital surface is located below and between the sigmoid and lateral sinuses and is the surface that is exposed in a wide bilateral suboccipital craniectomy.
- The vermis sits in a large median depression, the posterior cerebellar incisura, between the cerebellar hemispheres.
- According to classical nomenclature, the portions of the vermis within the incisura from above to below are the folium, tuber, pyramid, and uvula.
- The parts of the hemispheric surface from above to below are the superior and inferior semilunar and biventral lobules and the tonsils.
- These lobules extend beyond the suboccipital surface to the other surfaces of the cerebellum.
- Suboccipital fissure
- Divide the suboccipital surface into superior and inferior parts as the suboccipital fissure.
- Made up of
- Prebiventral fissures
- Between the inferior semilunar and the biventral lobules separate the hemispheres into superior and inferior parts,
- Prepyramidal fissure
- Between the pyramid and tuber separates the vermis into superior and inferior parts.
- From below to above the corresponding vermian and hemispheric parts are the uvula and the tonsils, the pyramid and the biventral lobules, the tuber and inferior semilunar lobules, and the folium and the superior semilunar lobules.
- The petrosal (horizontal) fissure,
- The most prominent fissure on the petrosal surface,
- Extends onto the suboccipital surface
- Divides the superior half of the suboccipital surface between the superior and inferior semilunar lobules.
- The cerebellomedullary fissure
- Extends superiorly between the cerebellum and medulla.
- Petrosal surface faces forward toward the petrous temporal bone
- The surface that is retracted to surgically expose the CPA.
- Petrosal fissure divides the petrosal surface into
- Formed by
- Quadrangular lobules
- Simple lobules
- A small part of the superior semilunar lobules.
- Formed by
- Inferior semilunar lobules
- Biventral lobules
- Tonsil.
Superior parts
Inferior parts
- Cerebellopontine fissures
- V-shaped fissures formed where the cerebellum wraps around the pons and the middle cerebellar peduncles.
- These fissures have a superior and an inferior limb, which meet at a lateral apex.
- The petrosal fissure extends laterally from the apex of the cerebellopontine fissures.
Tentorial surface and cerebellomesencephalic fissure.
- The tentorial surface faces the tentorium, which has been removed.
- The surface slopes downward from the apex to the posterior and lateral margins.
- The upper part of the tentorial surface surrounds the posterior half of the midbrain and forms the posterior lip of the cerebellomesencephalic fissure.
- The anterior cerebellar incisura, the notch where the brainstem fits into the anterior part of the tentorial surface, is located anteriorly and the posterior cerebellar incisura, the notch where the falx cerebelli fits into the cerebellum, is located posteriorly.
- Extends downward between the midbrain and the cerebellum.
- The superficial part of the posterior lip is formed by the culmen in the midline and the quadrangular lobule laterally.
- The quadrigeminal cistern extends caudally from the pineal into the cerebellomesencephalic fissure.
- The culmen has been removed to expose the central lobule and its wings, which form part of the posterior lip of the cerebellomesencephalic fissure.
- The central lobule and its wings, the lingula, the superior medullary velum, and medial part of the superior cerebellar peduncles have been removed to expose the fourth ventricle.
- The lower half of the roof is formed in the midline by the nodule and laterally by the inferior medullary velum, which passes laterally above, but is separated from the rostral pole of the tonsils by the cerebellomedullary fissure.
- Some of the middle peduncle has been removed to expose the choroid plexus extending through the lateral recess into the cerebellopontine angle below the facial and vestibulocochlear nerves.
- Oblique view of the lower half of the roof formed by the inferior medullary velum and the tela choroidea in which the choroid plexus arises.
- The inferior medullary velum arises on the surface of the nodule and extends laterally to blend into the flocculus and, with the flocculus and nodule, forms the flocculonodular lobe of the cerebellum.
- The tentorial cerebellar surface faces the tentorium and slopes downward from its apex located below the tentorial apex.
- The cerebellomesencephalic fissure extends forward between the cerebellum and midbrain.
- This surface, in which the vermis is the highest part, differs from the suboccipital surface in which the vermis is folded into a deep cleft, the incisura, between the cerebellar hemispheres. The straight sinus and tentorial edge have been preserved.
- The SCA exits the cerebellomesencephalic fissure and supplies the tentorial surface.
- The right half of the posterior lip of the cerebellomesencephalic fissure has been removed.
- Cerebellomesencephalic fissure
- Anterior wall
- Midline: collicular plate and lingula,
- Laterally: superior cerebellar peduncles.
- The middle cerebellar peduncle wraps around the lateral surface of the superior peduncle. The trochlear nerve arises below the inferior colliculi.
- The right half of the lingula and superior medullary velum have been removed to expose the fourth ventricle.
- Additional white matter has been removed below the right superior peduncle to expose the dentate nucleus in which the superior peduncular fibers arise.
- The dentate nucleus appears to wrap around the rostral pole of the tonsil.
- Additional cerebellum has been removed to expose the nodule and rostral pole of the tonsil. The dentate nucleus wraps around the rostral pole of the tonsil.
- The upper half of the roof is formed by the superior medullary velum, which has the lingula layered on its outer surface.
- The upper part of the lower half of the roof is formed by the nodule in the midline and by the inferior medullary velum laterally.
- The inferior medullary velum
- An almost transparent membrane
- Stretches laterally across the upper pole of the tonsil.
- The left half of the upper part of the roof has been removed.
- The velum arises on the nodule and sweeps laterally above both tonsils.
- The SCA courses within the cerebellomesencephalic fissure.
Suboccipital surface of the cerebellum and the cerebellomedullary fissure
- Suboccipital surface
- Is located below and between the sigmoid and lateral sinuses
- Is the surface that is exposed in a wide suboccipital craniectomy.
- The vermis sits in a depression, the posterior cerebellar incisura, between the hemispheres.
- Cerebellomedullary fissure
- Extends superiorly between the cerebellum and medulla along the inferior half of the ventricular roof.
- The vallecula extends upward between the tonsils and communicates through the foramen of Magendie with the fourth ventricle.
- The PICA supplies the suboccipital surface.
- The lower parts of the vermis behind the ventricle are the pyramid and uvula.
- The right tonsil has been removed to expose the lower part of the roof formed by the inferior medullary velum and tela choroidea.
- The nodule on which the velum arises is hidden in front of the uvula. The uvula hangs downward between the tonsils, thus mimicking the situation in the oropharynx.
- The choroid plexus arises on the inner surface of the tela and extends through the foramen of Luschka behind the glossopharyngeal and vagus nerve.
- The inferior medullary velum arises on the surface of the nodule, drapes across the superior pole of the tonsil, and blends into the flocculus laterally.
- Both tonsils have been removed to expose the inferior medullary velum and tela choroidea bilaterally.
- The telovelar junction is the junction between the velum and tela.
- Cerebellomedullary fissure
- Extends upward between the rostral pole of the tonsil on one side and the tela choroidea and inferior medullary velum on the opposite side.
- The segment of the PICA passing through this cleft is called the telovelotonsillar segment.
- The rhomboid lip is a sheet-like layer of neural tissue attached to the lateral margin of the ventricular floor, which extends posterior to the glossopharyngeal and vagus nerves and joins the tela choroidea to form a pouch at the outer extremity of the lateral recess.
- The right half of the tela has been removed to expose the ventricle and the lateral recess.
- The inferior medullary velum extends laterally to form a peduncle, the peduncle of the flocculus, which blends into the flocculus at the outer margin of the lateral recess.
- The tela has been removed on both sides.
- The lateral wall of the upper half of the ventricle is formed by the superior cerebellar peduncles.
- The inferior cerebellar peduncles ascend along the dorsolateral medulla and form the anterior and rostral margins of the lateral recess.
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
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