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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:

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posterior fossa

Posterior fossa

Gerhard van derWesthuizen

Medical officer (3 Military Hosp)

Department of Radiology

posterior fossa outline
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
posterior skull base
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
posterior skull base foramina
Posterior skull base -Foramina
  • Internal acoustic meatus
    • Porusacusticus – 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 meningealartery, meningeal branch of ascending pharyngeal artery
  • Hypoglossal canal
    • CN XII
  • Stylomastoid foramen
    • CN VII
  • Foramen magnum
    • Medulla oblangata, CN XI and vertebral arteries
brainstem
Brainstem
  • Midbrain
    • Connects pons and cerebellum with forebrain
  • Pons
    • Relays information from brain to cerebellum
  • Medulla
    • Relays information from spinal cord to brain
midbrain mesenchephalon
Midbrain (Mesenchephalon)
  • “Butterfly-shaped”, passes through tentoriumcerebelli
  • 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
        • Substantianigra- Motor planning, eye movement, reward seeking, learning and addiction
        • Red nucleus – Relay and control centre of cortiomotor impulses.
        • Periaquaductalgray matter – Pain and defensive behaviour
      • White matter tracts
        • Spinothalamic
        • Medial and lateral lemniscusSomatosensory
        • Medial longitudinal fasciculus – Vestibulo-ocular and optokinetic reflexes
midbrain
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 viasuperior cerebellar peduncle (brachium conjuntivum)
    • Inferior – Pons
  • Blood supply via vertebrobasilar circulation
    • Perforating branches of basilar, SCA, PCA.
slide29
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 medullarytegmentum inferiorly.
slide30
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.
slide31
Pons
  • CN nuclei:
    • V – Throughout brainstem and upper cord.
      • Bulk of motor and sensory in pons.
      • Enters and exits at level of midlateralpons
    • VI– In pontinetegmentum, 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-medullaryjunction

VIII – Vestibular along floor of 4thventricle

Cochlear on lateral surface of inferior cerebellar peduncle

      • Exits at ponto-medullary junction, posterior to VII
medulla
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
medulla1
Medulla
  • Ventral medulla:
  • Pyramid
    • Paired; anterior surface; midline ventral median fissure
    • Ipsilateralcorticospinal tracts prior to decussation
  • Olive
    • Lateral to pyramids, venterolateralsulcus (pre-olivary) and posterolateralsulcus (post-olivary)
    • Inferior olivary complex of nuclei
medulla2
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
medulla3
Medulla
  • CN nuclei:
    • IX – Upper and mid medulla (nucleus ambiguus, solitary tract nucleus and inferior salivatory nucleus.
        • Exits medulla in postolivarysulcus above X
    • X – Upper and mid medulla (nucleus ambiguus, solitary tract and dorsal vagal nucleus)
        • Exits postolivarysulcus between IX and XI
    • XI – Lower nucleus ambiguus and spinal nucleus
        • Exits postolivarysulcus inferior to X
    • XII – Mid medulla, hypoglossal eminence in 4th ventricle
        • Exits anterior medulla in pre-olivarysulcus
cerebellum
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.
cerebellum1
Cerebellum
  • Adjacent CSF cisterns
    • CPA cistern
    • Cisterna magna
    • Quadrigeminal plate cistern
    • Superior cerebellar cistern
  • Blood supply
    • SCA
    • AICA
    • PICA
cerebellum lobes and lobules
Cerebellum – Lobes and lobules
  • 2 Hemispheres seperated by shallow median groove superiorly and deep grove inferiorly.
  • Midline posterior cerebellar notch lodges the falxcerebelli.
  • Devided into lobules by fissures
    • Horizontal fissure – Deepest, divides into sup & infvermis.
    • 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
deep cerebellar nuclei
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)
arterial supply vertebrobasilar system
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
arterial supply vertebrobasilar system1
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 vermianartery
    • 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
venous drainage
Venous drainage
  • Three major drainage systems:
    • Superior (galenic) group
      • Drains into vein of Galen, 3 major veins
      • Precentralcerebellar– 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
references
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