posterior fossa
DESCRIPTION
Posterior fossa. Gerhard van der Westhuizen Medical officer (3 Military Hosp) Department of Radiology. Posterior fossa - Outline. Calvarium Posterior skull base Brainstem anteriorly Midbrain, pons and medulla Cerebellum posteriorly 2 Hemispheres and midline vermis Divided into: - PowerPoint PPT PresentationTRANSCRIPT
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Posterior fossaGerhard van der WesthuizenMedical officer (3 Military Hosp)Department of Radiology
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Posterior fossa - Outline• Calvarium
▫Posterior skull base• Brainstem anteriorly
▫Midbrain, pons and medulla• Cerebellum posteriorly
▫2 Hemispheres and midline vermis• Divided into:
▫Mesencephalon (midbrain)▫Rhomboencephalon (pons, medulla and cerebellum)
• Cerebral aquaduct and fourth ventricle• CSF cisterns containing vertebrobasilar arteries and
veins
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Posterior skull base• Formed by posterior temporal and occipital
bones• Anterior - Dorsum sellae medially, petrous ridges
laterally• Posterior - Groove for transverse sinus on
occipital bone• Transmits CN 7-12, medulla oblangata and
jugular veins• Multiple foramina and fissures
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Posterior skull base -Foramina• Internal acoustic meatus
▫ Porus acusticus – CN VII & VIII, labyrinthine artery• Jugular foramen
▫ Pars nervosa - anteromedial CN IX, Jacobson’s nerve and inferior petrosal sinus
▫ Pars vascularis - posterolateral Jugular bulb, CN X & XI, Arnold’s nerve, posterior meningeal
artery, meningeal branch of ascending pharyngeal artery• Hypoglossal canal
▫ CN XII• Stylomastoid foramen
▫ CN VII• Foramen magnum
▫ Medulla oblangata, CN XI and vertebral arteries
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Brainstem and cerebellum
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Brainstem•Midbrain
▫Connects pons and cerebellum with forebrain
•Pons ▫Relays information from brain to
cerebellum•Medulla
▫Relays information from spinal cord to brain
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Midbrain (Mesenchephalon)• “Butterfly-shaped”, passes through tentorium cerebelli
• 3 Main parts:▫ Cerebral peduncles
White matter tracts - Corticospinal, corticobulbar & corticopontine tracts
▫ Tegmentum CN nuclei: III – Level of superior colliculus;
IV – Level of inferior colliculus Accessory oculomotor (Edinger-Westphal)
Gray matter nuclei Substantia nigra - Motor planning, eye movement, reward seeking, learning and
addiction Red nucleus – Relay and control centre of cortiomotor impulses. Periaquaductal gray matter – Pain and defensive behaviour
White matter tracts Spinothalamic Medial and lateral lemniscus Somatosensory Medial longitudinal fasciculus – Vestibulo-ocular and optokinetic reflexes
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Midbrain▫ Tectum
Superior colliculus ( visual pathway) Inferior colliculus (auditory pathway)
Cerebral aquaduct passes between tectum and tegmentum
CSF cisterns associated with midbrain Ambient – Lateral, CN IV Quadrigeminal – Posterior, CN IV Interpeduncular – Anterior, CN III.
Connections: Superior – Cerebral hemispheres, basal ganglia and thalami Posterior – Cerebellum via superior cerebellar peduncle (brachium conjuntivum) Inferior – Pons
Blood supply via vertebrobasilar circulation Perforating branches of basilar, SCA, PCA.
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Axial T2
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Axial T2
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Axial T2
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Axial T2
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Axial T1
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Pons•Relays info from brain to cerebellum.•Middle cerebellar peduncle – Brachium pontis•Bulbous midportion of brainstem•Two main parts:
▫Ventral pons – White matter tracts continuous with cerebral peduncles and medullary pyramids.
▫Dorsal tegmentum– CN nuclei, gray matter nuclei and white matter tracts. Continuation of midbrain tegmentum superiorly and medullary tegmentum inferiorly.
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Pons•Tranverse fibres make up bulk•Dorsal surface forms rostral half of 4th
ventricle.•Adjacent CSF cisterns:
▫Prepontine – CN V & VI ▫CP angle – CN VII & VIII
•Blood supply▫Medial branches SCA, perforating branches
of basilar artery, thalamoperforator arteries.
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Pons• CN nuclei:
▫ V – Throughout brainstem and upper cord. Bulk of motor and sensory in pons. Enters and exits at level of midlateral pons
▫ VI – In pontine tegmentum, near midline, anterior to fourth ventricle. Exits anterior at ponto-medullary junction
▫ VII – Ventrolateral aspect of pons Motor, superior salivatory, solitary tract Exits laterally at ponto-medullary junction
VIII – Vestibular along floor of 4th ventricle Cochlear on lateral surface of inferior cerebellar peduncle
Exits at ponto-medullary junction, posterior to VII
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Axial T1
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Axial T1
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Axial T2
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Axial T2
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Axial T2
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Axial T2
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Axial T2
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Cor T2
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CPA
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IAM
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IAM
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Medulla• Caudal part of brainstem composed of gray
matter formations, CN nuclei IX – XII and white matter tracts.
• Between pons and spinal cord.• 4th ventricle and cerebellum posteriorly• Connected to cerebellum via inferior cerebellar
peduncle (restiform body).• 2 Main parts:
▫Ventral – olive and pyramidal tract▫Dorsal tegmentum – CN nuclei and white matter
tracts
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Medulla•Ventral medulla:
•Pyramid▫Paired; anterior surface; midline ventral median
fissure▫Ipsilateral corticospinal tracts prior to
decussation•Olive
▫Lateral to pyramids, venterolateral sulcus (pre-olivary) and posterolateral sulcus (post-olivary)
▫Inferior olivary complex of nuclei
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Medulla• Dorsal tegmentum:
• Multiple white matter tracts.• Gracile and cuneate tubercles
▫Lower aspect of dorsal medulla▫Nuclei gracilis(medial) ; cuneatus (lateral)
• Fourth ventricle terminates in caudal medulla.• Blood supply:
▫Distal vertebral arteries▫PICA ▫Anterior spinal artery
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Medulla• CN nuclei:
▫ IX – Upper and mid medulla (nucleus ambiguus, solitary tract nucleus and inferior salivatory nucleus.
Exits medulla in postolivary sulcus above X
▫ X – Upper and mid medulla (nucleus ambiguus, solitary tract and dorsal vagal nucleus)
Exits postolivary sulcus between IX and XI
▫ XI – Lower nucleus ambiguus and spinal nucleus Exits postolivary sulcus inferior to X
▫ XII – Mid medulla, hypoglossal eminence in 4th ventricle
Exits anterior medulla in pre-olivary sulcus
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Axial T2
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Axial T2
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Axial T2
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Axial T2
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Cerebellum•Function: Integrates coordination and fine-
tuning of movement and regulation of muscle tone.
•2 Hemispheres and midline vermis•Three surfaces – superior,inferior and anterior•Divided into 3 lobes and 9 lobules by
transverse fissures.•3 Cerebellar peduncles•Cortical gray matter, central white matter and
4 paired deep gray nuclei.
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Cerebellum•Adjacent CSF cisterns
▫CPA cistern▫Cisterna magna▫Quadrigeminal plate cistern▫Superior cerebellar cistern
•Blood supply▫SCA▫AICA▫PICA
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Cerebellum – Lobes and lobules• 2 Hemispheres seperated by shallow median groove
superiorly and deep grove inferiorly.• Midline posterior cerebellar notch lodges the falx cerebelli.• Devided into lobules by fissures
▫ Horizontal fissure – Deepest, divides into sup & inf vermis.▫ Primary fissure – Divides superior surface, small anterior
lobe and larger posterior lobe.▫ Posterolateral fissure – Between posterior lobe and flocculo-
nodular lobe.• 3 Lobes with 9 lobules:
▫ Anterior – Lingula, central lobule, culmen▫ Posterior – Declive, folium, tuber, pyramid, uvula▫ Flocculo-nodular – Nodule
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Cerebellum – Lobes and lobules
Vermis lobules Associated hemispheric lobulesSuperior vermis:Lingula Wing of lingulaCentral lobule Wing of central lobule
Anterior Culmen Quadrangular lobule
lobe Primary fissureDeclive Simple lobuleFolium Superior semilunar lobule Horizontal fissure
Inferior vermis: Posterior
Tuber Inferior semilunar lobule lobe
Pyramid Biventral lobuleUvula Tonsils Posterolateral (dorsolateral) fissure Nodule Flocculus Flocculo-nodular
lobe
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Lobules
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“Like cats catch dogs for the party up north”
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Deep cerebellar nuclei• Fastigial :
▫ Medial group (vermis)▫ Antigravity muscle groups
• Globose: ▫ Posterior intermediate group Ipsilateral
• Emboliform: motor activity▫ Anterior intermediate group (Rubrospinal)
• Dentate: Lateral group, largest nucleus▫ Ipsilateral motor activity (Corticospinal)
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Deep cerebellar nuclei
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Sag T2
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Sag T2
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Sag T2
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Cor T2
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Cor T2
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Cor T2
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Axial T1
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Axial T1
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Axial T1
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Axial T1
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Arterial supply – Vertebrobasilar system•V4 segments of bilateral vertebral
arteries enters through foramen magnum.•Courses superomedially posterior to
clivus•Unites – forms basilar artery.•Terminates into 2 posterior cerebral
arteries in interpeduncular/suprasellar cistern above dorsum sellae
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Arterial supply – Vertebrobasilar system• Branches:
▫ Vertebral artery segment V4 Meningeal branch Anterior and posterior spinal arteries Perforating branches to medulla PICA (largest branch)
Lateral, hemispheric branches, inferior vermian artery▫ Basilar
Pontine and midbrain perforating branches Labyrinthine artery AICA
Lateral and medial branches. SCA
Perforating, marginal and hemispheric branches, superior vermian artery▫ PCA’s
Terminal branches of BA. Perforating – Posterior thalamoperforating, thalamogeniculate Choroidal – Medial posterior, lateral posterior Cortical branches – Anterior & posterior temporal Two terminal trunks - Medial: Medial occipital, parieto-occipital, calcarine, posterior
splenial - Lateral: Lateral occipital, temporal
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Variants- Persistent trigeminal artery
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Variants – Persistent hypoglossal artery
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Variants – Proatlantal intersegmental artery
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Venous drainage• Three major drainage systems:
▫ Superior (galenic) group Drains into vein of Galen, 3 major veins Precentral cerebellar – single, between lingula and central lobule Superior vermian – originates near declive, course superiorly
over culmen Anterior pontomesencephalic – anterior to pons and midbrain; in
relation to basilar artery▫ Anterior (petrosal) group
Petrosal vein – in CPA, tributaries from cerebellum, pons and medulla
▫ Posterior (tentorial) group Inferior vermian veins – Paired, paramedian. Curves
posterosuperiorly under pyramids and uvula
![Page 94: Posterior fossa](https://reader035.vdocuments.site/reader035/viewer/2022081421/5681642c550346895dd5f00b/html5/thumbnails/94.jpg)
![Page 95: Posterior fossa](https://reader035.vdocuments.site/reader035/viewer/2022081421/5681642c550346895dd5f00b/html5/thumbnails/95.jpg)
![Page 96: Posterior fossa](https://reader035.vdocuments.site/reader035/viewer/2022081421/5681642c550346895dd5f00b/html5/thumbnails/96.jpg)
![Page 97: Posterior fossa](https://reader035.vdocuments.site/reader035/viewer/2022081421/5681642c550346895dd5f00b/html5/thumbnails/97.jpg)
References • Netter, F.H. (2011). Atlas of Human Anatomy,
5th ed. Philadelphia: Saunders Elsevier• Ryan, S., McNicholas, M., Eustace, S. (2011).
Anatomy for diagnostic imaging, 3rd ed. London: Saunders Elsevier
• Butler, P., Mitchell, A.W.M., Ellis, H. (1999). Applied Radiological Anatomy. Cambridge: Cambridge University Press
• Harnsberger,H.R., Osborn, A.G., (2006). Imaging anatomy – Brain, head and neck, spine, 1st ed. Utah: Amirsys