The document provides a detailed overview of the anatomy of the foramen magnum, including its location, components, and relationships with surrounding structures such as the occipital bone, vertebrae, and cranial nerves. It describes the bony, muscular, neural, and vascular relations associated with the foramen magnum, including ligaments and arteries, and highlights the significance of the area in neurosurgery. Additionally, it outlines the connections and pathways of cranial and cervical nerves in relation to the foramen magnum.

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:
1) Squamosal 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

8. • 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,

9. • 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 .

10. ATLAS

11. AXIS

12. Vertebral artery groove

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

14. LIGAMENTS

15. 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.

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

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

18. Suboccipitalis muscle
• 4 muscles in suboccipital area

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

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

21. 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

22. 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.

24. 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.

25. Cerebellum
• 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

26. 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 .

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

28. • 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 .

29. ARTERIAL RELATIONS
• Vertebral artery
• PSA
• PICA
• ASA
• Meningeal artery.

30. 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
.

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

32. • 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
1. Posterior meningeal A
2. PSA
3. Br. To cervical muscles
4. PICA infrequently

33. Intradural VA
• 4th 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

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

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

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

37. PICA
• Largest
branch of VA,
• Usually fron
intradural
part
• Tonsomedulla
ry Pica which
forms caudal
loop in
relation to
FM

38. MENINGEAL ARTERY
1. Anterior meningeal
2. Posterior meningeal
3. Meningeal br.of pharyngeal & occipital
4. Dorsal meningeal br.of meningohypophyseal
of ICA

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

40. 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.

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

42. Venous relations

43. Surgical approaches

44. Thank you