General
- The fourth ventricle is a broad, tent-shaped midline cavity
- Located
- Ventral to the cerebellum
- Dorsal to the pons and medulla
- Medial to the cerebellar peduncles
- Connections
- Rostrally: through the aqueduct with the third ventricle
- Caudally: through the foramen of Magendie with the cisterna magna
- Laterally: through the foramina of Luschka with the cerebellopontine angles
- Fissures
- AKA precentral cerebellar fissure.
- Extends inferiorly between the cerebellum and midbrain
- V-shaped
- The dorsal half of the midbrain sits within the limbs of the V-shaped notch, and the cerebellum forms the outer margin, with the apex being posterior.
- The trochlear nerves arise in the cerebellomesencephalic fissure below the inferior colliculi and pass anterolateral to exit the anterior part of the fissure.
- The inner wall of the fissure,
- Which forms the outer surface of the superior part of the roof,
- Composed of the
- Lingula
- A thin, narrow tongue of vermis, sits on the outer surface of the superior medullary velum.
- Dorsal surface of the superior cerebellar peduncles
- Rostral surface of the middle cerebellar peduncles.
- The outer wall of the cerebellomesencephalic fissure is formed by
- Culmen
- Central lobule and its wings.
- 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.
- One of the most complex fissures in the brain.
- The ventral wall of the fissure is formed by the
- Posterior surface of the medulla
- Inferior medullary velum
- Tela choroidea
- The dorsal wall of the fissure is formed by the
- Uvula in the midline
- Tonsils and biventral lobules laterally
- Extends superiorly to the level of the lateral recesses and communicates around the superior poles of the tonsils with the cisterna magna, through the foramen of Magendie with the fourth ventricle, and around the foramina of Luschka with the cerebellopontine fissures.
- The rostral pole of the tonsils faces the
- Inferior medullary velum
- Tela choroidea
- Peritonsillar part of the uvula
- Biventral lobule in the superior part of the fissure.
- Telovelotonsillar cleft
- The portion of the Cerebellomedullary fissure between the tonsil, the tela choroidea, and the inferior medullary velum
- Supratonsillar cleft
- Superior extension of the telovelotonsillar cleft over the superior pole of the tonsil
- 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.
Cerebellomesencephalic Fissure
Cerebellomedullary fissure
Borders
Roof
- Tent shaped
- The apex of the roof, the fastigium, divides the roof into
- 1 median part
- Formed by the superior medullary velum
- A thin lamina of white matter that spans the interval between the superior cerebellar peduncles and has the lingula, the uppermost division of the vermis, on its outer surface.
- It is continuous at the fastigium with the inferior medullary velum.
- The superior cerebellar peduncles form smooth longitudinal prominences on each side of the lingula before disappearing into the midbrain beneath the colliculi
- 2 lateral parts
- Aka lateral walls
- Formed by the inner surface of the superior and inferior cerebellar peduncles
- The fibers of the inferior cerebellar peduncle ascend in the posterolateral medulla and turn posteriorly in the inferomedial part of the fiber bundle formed by the union of the three peduncles to line the ventricular surface of the superior margin of the lateral recess and the inferior part of the lateral wall
- The fibers of the superior cerebellar peduncle arise in the dentate nucleus and ascend on the medial side of the middle cerebellar peduncle to form the ventricular surface of the superior part of the lateral wall.
- The rostral portion of each lateral wall, formed by only the superior cerebellar peduncle, is thinner than the caudal portion, which is formed by the three cerebellar peduncles after they have united
- The neural structures separating the ventricular and cisternal surfaces of the superior part of the roof are
- Thinnest in the area of the superior medullary velum and lingula and
- Thickest in the area of the cerebellar peduncles.
- Rostral part of the lower half of the roof is formed by the
- Nodule
- Inferior medullary velum
- A membranous layer
- A thin bilateral semitranslucent butterfly-shaped sheet of neural
- Is all that remains of the connection between the nodule and the flocculi that form the flocculonodular lobe of the primitive cerebellum
- Relations
- Tissue that blends into the ventricular surface of the nodule medially and stretches laterally across, but is separated from, the superior pole of the tonsil by a narrow, rostral extension of the cerebellomedullary fissure.
- It blends into the dorsal margin of each lateral recess and forms the peduncle of each flocculus.
- The inferior medullary velum is continuous at the level of the fastigium with the superior medullary velum.
- Caudally it is attached to the tela choroidea.
- Caudal part is formed by the
- A thin arachnoid-like membrane
- In which the choroid plexus arises
- It consists of two thin, semitransparent membranes, each having a thickness comparable to arachnoid, between which is sandwiched a vascular layer composed of the choroidal arteries and veins.
- The choroid plexus projects from the ventricular surface of the tela choroidea into the fourth ventricle.
- Forms the caudal part of the inferior portion of the roof and the inferior wall of each lateral recess
- The tela choroidea sweeps inferiorly from the telovelar junction around the superior pole of each tonsil to its attachment to the inferolateral edges of the floor along narrow white ridges, the taeniae, which meet at the obex.
- Cranially, the taeniae turn laterally over the inferior cerebellar peduncles and pass horizontally along the inferior borders of the lateral recesses.
- The tela choroidea does not completely enclose the inferior half of the fourth ventricle, but has three openings into the subarachnoid space:
- Paired foramina of Luschka located at the outer margin of the lateral recesses
- Foramen of Magendie located at the caudal tip of the fourth ventricle.
- The cisternal (external) surface of the caudal half of the roof faces and is intimately related to the cerebellomedullary fissure
- 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.
- Ventricular and cisternal surface
- The ventricular and cisternal surfaces are formed by the same structures, the tela choroidea and the inferior medullary velum, except in the rostral midline, where the ventricular surface is formed by the nodule and the cisternal surface is formed by the uvula.
- 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.
- Enlarged view.
- 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.
- Another dissection
- The cerebellomedullary fissure extends upward between the tonsils and medulla. Both tonsils have been removed by dividing the peduncle of the tonsil.
- Removing the tonsil exposes the inferior medullary velum and tela choroidea forming the lower part of the ventricular roof.
- The inferior cerebellar peduncle ascends along the posterolateral medulla.
- The choroid plexus arises on the inner surface of the tela choroidea. The taeniae are the site of attachment of the tela choroidea along the inferolateral margins of the ventricle floor. The telovelar junction is the site of attachment of the inferior medullary velum to the tela choroidea. The nodule, on which the inferior medullary velum arises, is hidden deep to the uvula.
- The tela, in which the choroid plexus arises, has been removed to expose both lateral recesses.
- The superior cerebellar peduncle forms the lateral wall of the upper half of the ventricle.
- The inferior cerebellar peduncle forms the anterior and upper margin of the lateral recess.
- The middle cerebellar peduncle, which forms a large prominence on the lateral surface of the pons, is separated from the ventricular surface by the superior and inferior cerebellar peduncles.
- This is the telovelo approach view
Superior part (thicker)
Inferior part (thinner)
Tela choroidea
- Rostrally end of the roof narrows to the aqueduct
- Laterally the roof narrows to the lateral recess → foramen of luschka
- Caudally it tapers to a narrow caudal apex at the level of the foramen of Magendie.
- The cisternal (external) surface of the structures forming the superior part of the roof also form the anterior wall of the cerebellomesencephalic fissure.
- Oblique view into the fourth ventricle.
- 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.
Floor
- Most of the cranial nerves arise near its floor.
- The dorsal and ventral cochlear nuclei, the site of placement of the auditory brain stem implant and fibers related to the vestibulocochlear nerve, are in the floor of the recess.
- The facial colliculus is an elevation on the floor of the fourth ventricle in the pons under which is located the abducens nucleus (cranial nerve VI) and the axons of the facial nerve nucleus (VII), which arc around the abducens nucleus.
- “The facial axons come to look for sex (CN6) then runs away as it only see seven (CN7).”
- Two pairs of small swellings can be seen in the floor of the 4th ventricle, the lateral and medial ridges.
- The lateral ridges constitute the vagal trigone and indicate the location of the underlying dorsal motor nucleus of the Vagus.
- The medial ridges constitute the hypoglossal trigone and indicate the location of the underlying hypoglossal nucleus
2 lateral recesses
- Are narrow, curved pouches formed by the union of the roof and the floor that extends laterally below the cerebellar peduncles to open through the foramina of Luschka into the cerebellopontine angles.
- Borders
- Ventral wall
- Formed by the junctional part of the
- Ventricular floor AND
- Rhomboid lip
- A sheet like layer of neural tissue that extends laterally from the floor
- Unites with the tela choroidea to form a pouch at the outer extremity of the lateral recess.
- Rostral wall
- Formed by the caudal margin of the cerebellar peduncles.
- The inferior cerebellar peduncle courses upward in the floor ventral to the lateral recess and turns posteriorly at the lower part of the pons, to form the ventricular surface of the rostral wall of the recess.
- Dorsal margin
- The peduncle of the flocculus interconnecting the inferior medullary velum and the flocculus of the vermis crosses in the dorsal margin of the lateral recess.
- Caudal wall
- Formed by the tela choroidea
- Stretches from the lateral edge of the ventricular floor to the peduncle of the flocculus.
- Outside/ lateral to the lateral recess
- The flocculus is superior to the outer extremity of the lateral recess.
- CN9/10 arise ventral to lateral recess
- CN7 arises rostral to the lateral recess
- 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.
3D view
Cerebellar peduncle
Superior cerebellar peduncle: (brachium conjunctivum)
- Forms the lateral wall of the upper half of the ventricle.
- Consists predominantly of efferent fibres arising in cerebellar nuclei (mainly the dentate nucleus).
- Main afferent: Ventral (anterior) spinocerebellar tract
- Pass along the upper and lateral margin of the rhomboid fossa (Fourth ventricle).
- The fibres of the peduncle enter the midbrain and cross to the opposite side before ending in the red nucleus and the thalamus
- Fibres Entering cerebellum (afferents)
Tracts | Origin | Termination | Function |
Ventral (anterior) spinocerebellar tract | Secondary neurons in intermediate gray matter of lumbosacral spinal cord (Fibers cross locally and then re-cross in the pons to return to the ipsilateral side.) | Vermis and intermediate part of anterior lobe of cerebellum (ipsilateral; terminates as mossy Fibers) | Proprioception and exteroception (lower limb) |
Tectocerebellar fibres | Visual input | ||
Trigeminocerebellar fibres | Proprioception from mesencephalic nucleus | ||
Hypothalamocerebellar fibres | Hypothalamus | Somatic visceral integration | |
Coerulocerebellar fibres | Locus ceruleans | Noradrenergic modulation of cerebellar learning |
- Fibres exiting cerebellum (efferents)
- Efferents arise from
- Emboliform nuclei
- Globose nuclei
- Dentate nuclei
Tracts | Origin | Termination | Function |
Cerebellorubral fibres → Rubrospinal tract | Emboliform nuclei Globose nuclei Dentate nuclei | Red nucleus and thalamus | Fine motor coordination and muscle tone |
Cerebellothalamic fibres → thalamocortical → Corticospinal tract | Emboliform nuclei Globose nuclei Dentate nuclei | Fine motor coordination and muscle tone | |
Cerebelloreticular → reticulospinal trasct | Fastigial Nuclei Globose nuclei | Reticular formation and vestibular nuclei (projection is mostly contralateral) | Somatomotor and autonomic modulation |
Cerebello-olivary fibres | GABAergic feedback | ||
Cerebellohypothalamic fibres | Hypothalamus | Cerebellar autonomic modulation |
- 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.
- Enlarged view.
- The dentate nucleus appears to wrap around the rostral pole of the tonsil.
Middle cerebellar peduncle: (brachium pontis)
- Largest of the three peduncles
- Forms a large prominence on the lateral surface of the pons,
- It is separated from the ventricular surface by the superior and inferior cerebellar peduncles.
- The rostral surface of the middle cerebellar peduncles appear to wrap around the caudal margin of the superior cerebellar peduncles.
- Interpeduncular sulcus
- Shallow groove
- Marks the junction of the superior and the middle cerebellar peduncles.
- It continuous
- Anteriorly with the pontomesencephalic sulcus
- Transverse groove between the pons and midbrain
- Superiorly with the lateral mesencephalic sulcus
- Longitudinal fissure dorsal to the cerebral peduncle.
- Course
- Begins as a lateral continuation of the ventral part of the pons (demarcated on the surface by the attachment of trigeminal nerve)
- Fibres, which arise in pontine nuclei, cross to the opposite side. The fibres of the peduncle form a thick bundle that passes laterally and backwards to enter the white core of the cerebellum through the horizontal fissure.
- Entering the cerebellum, the fibres are placed lateral to those of the inferior peduncle (the superior peduncle being still more medial in position).
- Afferent fibres only: which transmit the impulses mainly from pontine nuclei to the opposite cerebellar hemisphere (pontocerebellar fibres).
- Fibres entering cerebellum
- 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.
Tracts | Origin | Termination | Function |
Pontocerebellar fibres | Basal pontine nuclei. Relay cerebropontine to pontocerebellar projections (source of 90% of the axons in middle peduncle) | Lateral regions of posterior and anterior lobes of cerebellum (contralateral to the origin of these fibers in pons; terminate as mossy fibers; branches to dentate nucleus, also contralateral to the origin in pons) | Cortico-ponto-cerebellar pathway for motor planning |
Few serotoninergic fibres | Modulates the responses of other neurotransmitters |
Inferior cerebellar peduncle: (brachium conjuctiva)
- Forms the anterior and upper margin of the lateral recess.
- Aka restiform body + juxtarestiform body
- Connects the posterolateral part of the medulla ↔ cerebellum
- Course
- Peduncle passes upwards and laterally along the inferolateral margin of the rhomboid fossa (Fourth ventricle).
- Near the upper end of the medulla, the peduncle lies between the superior cerebellar peduncle (on its medial side) and the middle cerebellar peduncle (laterally).
- The inferior peduncle then turns sharply backwards to enter the while core of the cerebellum.
- Juxtarestiform body:
- Over the medial part of the inferior cerebellar peduncle
- Fibres that pass through the vestibular nuclei before entering the cerebellum.
- Fibres entering the cerebellum
Tracts | Origin | Termination | Function |
Posterior spinocerebellar tract | Proprioception and exteroception (lower limb) | ||
Cuneocerebellar tract (posterior external arcuate fibres) | Proprioception and exteroception (upper limb) | ||
Olivocerebellar fibres | Dorsal olivary nucleus Medial accessory olivary nucleus Principle olivary nucleus | Cerebellar cortex | Climbing fibres from inferior olivary and accessory olivary nucleus for cerebellar learning |
Par-olivocerebellar fibres | Same as above | ||
Reticulocerebellar fibres | Lateral reticular nucleus Paramedian reticular nucleus | Feedback from entire central nervous system: spinal cord to cortex | |
Vestibulocerebellar fibres | Information about head position in its movement | ||
Anterior external arcuate fibres | From arcuate nuclei and pontobulbar body, both of which are displaced pontine nuclei (cortico-arcuato-cerebellar pathways and cortico-pontobulbar-cerebellar circumolivary bundle) | ||
Fibres of striae medullares | Same as above | ||
Trigeminocerebellar fibres | Trigeminal nuclei (sensory/mastication) | Exteroception (main sensory and spinal nuclei) |
- Fibres Exiting the cerebellum
- All efferent going through the inferior cerebellar peduncle arises from the from the fastigial nucleus
Tracts | Origin | Termination | Function |
Cerebello-olivary fibres | Fastigial nucleus | GABAergic feedback | |
Cerebellovestibular fibres | Fastigial nucleus | Regulates body equilibrium | |
Cerebelloreticular fibres | Fastigial nucleus | Somatomotor modulation |
- 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.
Multiple views of the 4th ventricle
Abbreviations
- Cer. = cerebellar; fis. = fissure; Inf. = inferior; med. = medullary; Ped. = peduncle; plex. = plexus; T = tonsil; Tonsillobivent. = tonsillobiventral; Sup. = superior; vel. = velum; XI = 11th cranial nerve.
- The fourth ventricle and rhomboid fossa viewed from an inferior trajectory.
- The tonsils are resected.
- The LR (lateral recess of 4th ventricle) is located at the lateral corners of the rhomboid fossa. When followed laterally, it will open into the cerebellopontine cistern.
- Right LR (curved green arrow) Note the close relationship between the inferior cerebellar peduncle and the LR.
- Lateral view of the cavity of the fourth ventricle and the LR of the right half of the brainstem and cerebellum.
- The inferior cerebellar peduncle curves over the LR (green arrow) to connect the medulla oblongata to the cerebellum.
- The tonsillobiventral fissure (red dashed arrow) reaches the LR.
- Oblique view of the lower brainstem and cerebellum with the tonsils removed.
- The tela choroidea and the choroid plexus of the fourth ventricle are shown.
- The tela and the inferior medullary velum form the lower half of the roof of the fourth ventricle.
- The tela forms the posterior aspect of the LR.
- Blue probe shows the cavity and trajectory of the LR.
- The Cerebello-Medullary Fissure is opened by elevation of the tonsil.
- This maneuver will expose the LR (yellow arrow).
- The tonsillobiventral fissure (green arrow) is opened in another specimen viewed from below.
- It is clear that the opening of the tonsillobiventral fissure leads to the
- LR. Please compare the different trajectories of the 2 approaches.
- The inferior view of the brainstem and the cerebellum.
- Note the relationship of tonsil to the biventral lobule and the vermis.
- The tonsillobiventral fissure (dashed green lines) runs inferolaterally from the uvulotonsillar junction to reach the cerebellomedullary cistern.
- The PICA emerges from the tonsillobiventral fissure to branch onto the suboccipital surface of the cerebellum, as denoted by the asterisks.
- Tonsillobiventral fissure approach.
- The right tonsillobiventral fissure is split to show the inferolateral trajectory to the LR of the fourth ventricle (green arrow).
- Note the exposed choroid plexus and the flocculus in the cerebellopontine cistern.
- Yellow arrow shows the trajectory of the tCMF approach to the LR.
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
Made with Bullet