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:
▫ Mesencephalon (midbrain)
▫ Rhomboencephalon (pons, medulla and cerebellum)
• Cerebral aquaduct and fourth ventricle
• CSF cisterns containing vertebrobasilar arteries and
veins
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
• 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
Brainstem and cerebellum
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)
• “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
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.
Axial T2
Axial T2
Axial T2
Axial T2
Axial T1
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.
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.
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
Axial T1
Axial T1
Axial T2
Axial T2
Axial T2
Axial T2
Axial T2
Cor T2
CPA
IAM
IAM
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
Medulla
• Ventral medulla:
• Pyramid
▫ Paired; anterior surface; midline ventral median
fissure
▫ Ipsilateral corticospinal tracts prior to decussation
• Olive
▫ Lateral to pyramids, venterolateral sulcus (preolivary) and posterolateral sulcus (post-olivary)
▫ Inferior olivary complex of nuclei
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
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
Axial T2
Axial T2
Axial T2
Axial T2
Cerebellum
• Function: Integrates coordination and finetuning 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.
Cerebellum
• Adjacent CSF cisterns
▫
▫
▫
▫
CPA cistern
Cisterna magna
Quadrigeminal plate cistern
Superior cerebellar cistern
• Blood supply
▫ SCA
▫ AICA
▫ PICA
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 flocculonodular lobe.
• 3 Lobes with 9 lobules:
▫ Anterior – Lingula, central lobule, culmen
▫ Posterior – Declive, folium, tuber, pyramid, uvula
▫ Flocculo-nodular – Nodule
Vermis lobules
Associated hemispheric lobules
Superior vermis:
Lingula
Wing of lingula
Wingand
of centrallobules
lobule
Anterior
Cerebellum – Lobes
Central lobule
Culmen
Quadrangular lobule
lobe
Primary fissure
Declive
Simple lobule
Folium
Superior semilunar lobule
Horizontal fissure
Inferior vermis:
Posterior
Tuber
Inferior semilunar lobule
Pyramid
Biventral lobule
Uvula
Tonsils
lobe
Posterolateral (dorsolateral) fissure
Nodule
Flocculus
Flocculo-nodular lobe
Lobules
“Like cats catch dogs for the party up north”
Deep cerebellar nuclei
• Fastigial :
▫ Medial group (vermis)
▫ Antigravity muscle groups
• Globose:
▫ Posterior intermediate group
• Emboliform:
▫ Anterior intermediate group
• Dentate: Lateral group, largest nucleus
▫ Ipsilateral motor activity (Corticospinal)
Ipsilateral
motor activity
(Rubrospinal)
Deep cerebellar nuclei
Sag T2
Sag T2
Sag T2
Cor T2
Cor T2
Cor T2
Axial T1
Axial T1
Axial T1
Axial T1
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 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
Variants- Persistent trigeminal artery
Variants – Persistent hypoglossal artery
Variants – Proatlantal intersegmental artery
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
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