1. Posterior fossa Gerhard van der Westhuizen Medical officer (3 Military Hosp) Department of Radiology

2. 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

3. 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

4. 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

13. Brainstem and cerebellum

14. Brainstem Midbrain ▫Connects pons and cerebellum with forebrain Pons ▫Relays information from brain to cerebellum Medulla ▫Relays information from spinal cord to brain

17. 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

18. 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.

24. Axial T2

28. Axial T1

29. 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.

30. Pons Tranverse fibres make up bulk Dorsal surface forms rostral half of 4 th 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.

31. 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 4 th ventricle Cochlear on lateral surface of inferior cerebellar peduncle  Exits at ponto-medullary junction, posterior to VII

37. Axial T1

39. Axial T2

44. Cor T2

45. CPA

46. IAM

48. Medulla Caudal part of brainstem composed of gray matter formations, CN nuclei IX – XII and white matter tracts. Between pons and spinal cord. 4 th 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

49. 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

50. 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

52. 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 4 th ventricle  Exits anterior medulla in pre-olivary sulcus

58. Axial T2

62. 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.

63. Cerebellum Adjacent CSF cisterns ▫CPA cistern ▫Cisterna magna ▫Quadrigeminal plate cistern ▫Superior cerebellar cistern Blood supply ▫SCA ▫AICA ▫PICA

66. 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

69. Cerebellum – Lobes and lobules Vermis lobulesAssociated hemispheric lobules Superior vermis: LingulaWing of lingula Central lobuleWing of central lobule Anterior CulmenQuadrangular lobule lobe Primary fissure DecliveSimple lobule FoliumSuperior semilunar lobule Horizontal fissure Inferior vermis: Posterior TuberInferior semilunar lobule lobe PyramidBiventral lobule UvulaTonsils Posterolateral (dorsolateral) fissure NoduleFlocculus Flocculo-nodular lobe

70. Lobules

71. “Like cats catch dogs for the party up north”

72. Deep cerebellar nuclei Fastigial : ▫Medial group (vermis) ▫Antigravity muscle groups Globose: ▫Posterior intermediate groupIpsilateral Emboliform: motor activity ▫Anterior intermediate group(Rubrospinal) Dentate: Lateral group, largest nucleus ▫Ipsilateral motor activity (Corticospinal)

73. Deep cerebellar nuclei

74. Sag T2

77. Cor T2

80. Axial T1

84. 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

85. 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

90. Variants- Persistent trigeminal artery

91. Variants – Persistent hypoglossal artery

92. Variants – Proatlantal intersegmental artery

93. 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

97. References Netter, F.H. (2011). Atlas of Human Anatomy, 5 th ed. Philadelphia: Saunders Elsevier Ryan, S., McNicholas, M., Eustace, S. (2011). Anatomy for diagnostic imaging, 3 rd 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, 1 st ed. Utah: Amirsys