Posterior fossa

1. Posterior fossa Gerhard van derWesthuizen 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 • 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

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 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

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 viasuperior cerebellar peduncle (brachium conjuntivum) • Inferior – Pons • Blood supply via vertebrobasilar circulation • Perforating branches of basilar, SCA, PCA.

24. Axial T2

25. Axial T2

26. Axial T2

27. 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 medullarytegmentum inferiorly.

30. 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.

31. 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

37. Axial T1

38. Axial T1

39. Axial T2

40. Axial T2

41. Axial T2

42. Axial T2

43. Axial T2

44. Cor T2

45. CPA

46. IAM

47. 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. • 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

49. 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

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