FORAMEN MAGNUM ANATOMY.pptx

Foramen Magnum microanatomy based on Rhotons , useful for foramen magnum decompression procedures and CP angle exposure .

1. FORAMEN MAGNUM ANATOMY Dr.B Vinod Mch Neurosurgery resident Gandhi Medical college Hyderabad.

2. The foramen magnum is located in the occipital bone, three parts: S quamosa l part located behind the foramen magnum 2)Basal ( clival ) portion located anterior to the foramen magnum; 3)Condylar part that connects the squamosal and clival parts

3. RELATIONSHIPS Osseous : 3 bony relations Occipital Atlas Axis

4. Occipital bone Anterior (Narrow): Clivus Posterior: Squamous Lateral:Condyles

5. Clivus : Anterior to FM, thick quadrangular plate of bone that extends forward and upward, at an angle of about 45 ° from the foramen magnum. Superior surface concave side to side Separated from petrous bone of temporal by petroclival fissure. Has inferior petrosal sinus on upper surface which ends in jugular foramen . Inferior surface in front of the foramen magnum, a small elevation, the pharyngeal tubercle, gives attachment to the fibrous raphe of the pharynx.

6. Condylar Located lateral to the anterior half of the FM. Oval in shape,face downward and laterally, and have their long axes directed forward and medially. Medial attachment for alar ligaments Above hypoglossal canal ,forward & laterally Posterior : condylar canals, has emmissary veins , that connects vertebral plexus and joins sigmoid sinus Lateral: jugular process , connects squamous & condylar bone Jugular tubercle: superior to hypoglossal canal.& medial to petroclival fissure,caudal to tubercle courses CN 9,10,11

7. Jugular foramen: anterior and superior to FM. 2 parts . Small anteromedial : petrous part,transmits IPS Large posterolateral : sigmoid part,transmits sigmoid sinus. Intrajugular part. Transmits CN 9,10,11,

8. Squamous part: External : External occipital protuberance(Inion) convex 2 nucheal line External occipital crest, rough surface for muscles Internal: concave & has internal protuberance . Superior fossa for occipital lobe Inferior fossa for cerebellar surface . Vermian fossa for vermis .

9. ATLAS

10. AXIS

11. Vertebral artery groove

12. LIGAMENTS Cruciform ligaments : transverse & vertical ALL PLL Atlanto -occipital Axis-occipital

13. LIGAMENTS

14. ALL Runs along anterior surface of VB From C1 to anterior sacrum Attached to VB and intervertebral discs along its length PLL Along posterior surface of VB up c2 Attaches along posterior surface of VB and discs.

15. Tectorial membrane : Upper part of PLL ,that connects C2 to clivus

16. MUSCULAR RELATIONS Posterior muscles Superficial Trapezius Sternocleidomastoid Deep Splenius capitis Semispinalis capitis Longissimus capitis Suboccipitalis muscle.

17. Suboccipitalis muscle 4 muscles in suboccipital area

18. Anterior muscles Longus colli (C1-T3) Longus capitis ( Clivus to C3 to C6 TP) Rectus capitus anterior Rectus capitus lateralis

19. NEURAL RELATIONS Spinal cord Dentate ligament Brainstem Cerebellum Cranial nerves Cervical nerve roots

20. Spinal cord Blends into medulla at level upper limit of dorsal and ventral rootlets forming C1N Easy to identify level on ventral than dorsal because of ventral rootlets are always present. Junction of SC and medulla present at rostral end ventral C1. Medulla occupies FM not SC SC lies immediately below FM

21. Dentate ligament White sheeth attached to spinal cord Lateral projections of spinal piamater between dorsal & ventral rootlets, forming triangle shape ligament ,that anchors the spinal cord along its length to duramater on each side. At CVJ located Anterior – between VA & C1N ventral root Posterior- PSA & CN 11 Most attachments of ligament is at rostral end at level of FM where VA pierces duramater .

22. BRAINSTEM Lower medulla present at C1n ventral Anterior medulla by medullary pyramids faces Anterior clivus Anterior edge of FM Rostral odontoid process Lateral surface of MO by inferior olives. Posterior MO Superior : Midline inferior half of 4V Lateral by inferior cerebellar peduncles Inferior :Gracious fasciculus and cuneatus .

23. C erebellum Rests above the posterior and lateral edge of FM Tonsils- above and posterior edge Biventral and lobules-sits above and lateral Vermis lower part. Cranial nerve Spinal accessory nerve only nerve pass through FM

24. Cervical nerve roots C1N: suboccipital.N Dorsal and ventral root Dorsal root has medial and lateral branches,supplies skin and muscles of posterior region of neck. C1 leaves Vertebral canal between occipital bone and atlas. Dorsal root courses between posterior arch of atlas and VA ,reaches suboccipital traingle and innervate muscles of this traingle and scalp .

25. C1 ventral ramus courses between VA and posterior arch of atlas , pass lateral to lateral mass of C1 ,supplies Rectus capitis lateralis .

26. C2N : Between posterior arch of atlas and lamina of axis. Dorsal root has lateral and medial branches Medial branch forms Greater occipital nerve ,supply semispinalis capitis . Ascends with occipital artery ,supply scalp till vertex and back ear. C2 ventral courses between arch & TP of atlas ,axis .

27. ARTERIAL RELATIONS Vertebral artery PSA PICA ASA Meningeal artery.

28. VERTEBRAL ARTERY Starts at subclavian artery. Ascends through upper six cervical vertebra Enters duramater behind occipital condyles Into FM to front of MO Join Basilar artery at ponto medullary junction .

29. Has extradural & intradural Extradural VA: 1 st segment ,origin to Transverse foramen of C6 2 nd : C6 to C1 infront of cervical roots 3 rd : C1 to duramater entrance .

30. VA after passing TP of C1 lies medial to rectus capitis lateralis Pass medially below C1 lateral mass & A-O joint ,in groove of posterior arch of C1 lies in floor of suboccipital triangle. C1N pass through duramater of VA lower surface,between VA and posterior arch of C1 Terminal extradural gives branches Posterior meningeal A PSA Br. To cervical muscles PICA infrequently

31. Intradural VA 4 th segment Origin :inferior to lateral edge of FM Duramater is thick and funnel shape,4-6 mm length approx. C1 exit & PSA enter spinal canal through this funnel. Initial intradural segment of VA pass superior to C1N,and anterior to PSA, dentate ligament & CN 11

32. Anterior spinal artery Origin anterior medial VA near basilar artery Descends through FM on anterior surface of medulla & Spinal cord. Supplies : Pryamids and dissucations Medial lemniscus Inter olivary bundles Cn 12 Posterior longitudinal fasciculus

33. POSTERIOR SPINAL ARTERY Origin : outside duramater postero -medial of VA Branches at medulla oblongata into ascending and descending branches Ascending (Dura part):supplies, Gracilis cuneatus Cn11 Choroid plexus of foramen magendie

34. Descending branch : supply Spinal cord posteriorly Anastomose with ascending radicular artery of dorsal

35. PICA Largest branch of VA, Usually fron intradural part Tonsomedullary Pica which forms caudal loop in relation to FM

36. MENINGEAL ARTERY Anterior meningeal Posterior meningeal Meningeal br.of pharyngeal & occipital Dorsal meningeal br.of meningohypophyseal of ICA

37. Anterior meningeal artery: Origin immedialty above T.foramen of C3 medial VA Ascends up C2-C1 region At dens apex joins opp side Supplies : Clivus Anterior part of FM Sc Axis, odontoid ,AA joint

38. Posterior meningeal artery Origin posterior superior of VA Course along lateral mass pf C1 Enters FM Ascends near falx cerebelli Divides near torcula into branches Terminates posterior part of tentorium and cerebral falx & posterior fossa dura , Anastomose with ascending pharyngeal A.

39. Ascending pharyngeal artery Branch of ECA Two Branches that Anastomose to dorsal meningeal A via hypoglossal canal With meningeal br of occipital & post meningeal A via jugular foramen

40. Venous relations

41. Surgical approaches

42. Thank you