Foramen Magnum Meningioma: Presentation, Diagnosis & Treatment

1. F A R R U K H J A V E D
FORAMEN MAGNUM
MENINGIOMA

2. ANATOMY
 The occipital bone surrounds the foramen magnum
and is composed of two parts:
 the posterior squamosal and
 the narrower anterior part (basal extension of
the clivus).

3. ANATOMY
 The foramen magnum (FM) comprises a bony
channel formed:
 anteriorly by the lower third of the clivus, the
anterior arch of the atlas, and the odontoid process.
 the lateral limits are the jugular tubercle (JT), the
occipital condyle (OC), and the lateral mass of the
atlas.
 Lastly, the FM is limited posteriorly by the lower
part of the occipital bone, the posterior arch of the
atlas, and the two first intervertebral spaces.

4. ANATOMY
 Oval shaped, wider posteriorly than anteriorly
 The contents of the foramen magnum consist of:
 the vertebral arteries (VAs) and their meningeal
branches
 the anterior and posterior spinal arteries
 the lower part of the medulla
 the lower cranial nerves (IX, X, and XI)
 the roots of the C1 and C2 vertebrae.
 the cervicomedullary junction
 the cerebellar tonsils, the inferior vermis and the fourth
ventricle.
 surrounded by veins, venous sinuses, and the jugular
bulb.

7. EPIDEMIOLOGY
 account for only 0.3–3.2% of all meningiomas and
between 4% and 15% of all posterior fossa
meningiomas altogether.
 they are slow growing tumors.
 the mean length of symptoms before diagnosis is
30.8 months.

8. CLINICAL FEATURES
 The clinical presentation is insidious.
 Earlier complains are Occipital headache and
cervical pain.
 This pain is described as deep and is aggravated by neck
motion, coughing, and straining.
 As the tumor grows, sensory and motor deficits
develop

9.  There is an asymmetrical deficit defined by
weakness, paresthesis, and spasticity, first in the
ipsilateral arm and progressing to the ipsilateral
leg, then to the contralateral leg, and finally to the
contralateral arm.
 Long tract signs of upper-motor lesions are the
presence of atrophy in the intrinsic muscles of the
hands.
 Later findings include spastic quadriparesis,
respiratory dysfunction and lower cranial nerve
deficits.

10. CLASSIFICATION
 Among the many classifications of meningiomas of
the FM,6-8 the one most frequently used by
neurosurgeons is the classification from Bruneau
and George.
 The main objective of this system is to define the
surgical strategy preoperatively

11. Bruneau and George
Classification
 Based on this classification, meningiomas of the
FM are classified as
 intradural,
 extradural
 intra- and extradural.

12.  According to their insertion on the dura,
meningiomas are:
 anterior if insertion happens on both sides of the anterior
midline,
 anterolateral if insertion occurs between the midline and the
dentate ligament
 or posterior if insertion is posterior to the dentate ligament

13.  The other landmark used for classification is the
relation to the Vertebral Arteries.
 Meningiomas of the Foramen Magnum can develop:
 above the vertebral arteries
 below the vertebral arteries
 on both sides of the vertebral arteries

15.  Intradural meningiomas are the most common type
 most of them arise anterolaterally, these are followed
in frequency by posterolateral tumors.
 Tumors that arise purely posteriorly and anteriorly
are rare.

16. DIAGNOSIS

17.  All patients should undergo a detailed study of their
neurological function, independent of their clinical
neurological examination.
 Preoperative imaging studies allow for planning of
the surgery

18. the following information must be retrieved from
the radiology:
 the nature of the tumor (intra- and/or extradural)
 its location and attachment
 its relationship with the cervicomedullary junction
 its caudal and rostral extension
 the position and possible involvement of the VAs and their
branches
 the shape of the FM
 the dominance of the VAs
 the venous drainage patterns and dominance
 bony involvement

19. MRI
 T1-weighted MRI with contrast enhancement clearly
defines the tumor and the dural attachment site and
discriminates between the tumor and the brain stem.
 T2-weighted MRI provides information on the
arachnoid plane between the tumor and the
cervicomedullary junction

20. CT SCAN
 CT using sagittal, coronal, and axial viewing and
bone window remains the tool of choice for the study
of:
 bone involvement
 the shape of the FM
 the surgical corridor

21. Angiography
 Should be considered in all
patients with suspected
foramen magnum
meningioma to
 demonstrate the vascular
supply of the neoplasm
 define the position of major
vessels with respect to the
tumor
 determine the venous drainage
of the posterior fossa
 eliminate the possibility of an
aneurysm of the posterior
circulation

22. MRI sagital section
 MRI T1:a large anterior foramen
magnum meningioma isointense to
surrounding brain severely
compresses the neuraxis
MRI T2: pocess hyperintense
to surrounding brain

23. homogeneously enhancing tumor arises
predominantly in an anterior location

24.  MRI. Sagittal T2

25.  Contrast-enhanced T1-weighted MRI scans

26. INTRAOPERATIVE MONITORING
 Somatosensory evoked potentials
 auditory evoked responses
 facial nerve monitoring
 monitoring of the X, XI, and XII cranial nerves

27. Surgical Corridor
 the space between the cervicomedullary junction
and the lateral wall of the FM.

28. Surgical approach
 the location of the tumor
 the extent of the tumor (above the foramen
magnum)
 the relation of the tumor with the vertebral artery
and with the origin of posterior inferior cerebellar
artery

29. SURGICAL APPROACHES
Three general approaches to the foramen magnum are
employed:
o Posterior
o Anterior
o Lateral

31. 31
 Posterior approach –
• Tumors located posteriorly or posterolaterally
to the cervicomedullary junction.
 Ant. approach –
• Extradural lesions situated anterior to
foramen magnum.
 Lat. Approach –
• Anterior or anterolateral lesions especially
when involve or are located adjacent to
temporal bone and clivus.

32. Far-Lateral Suboccipital
Approach

33. POSITION
 Pt is kept in the three quarter–prone position.
 The side of the approach is ipsilateral to the lesion.
 If the lesion is placed midline, the side of the
approach is usually the side of the nondominant
vertebral artery and the nondominant jugular bulb.

34. POSITION
 The results of this positioning are the cerebellum
falling away from the operating field and the
contents of the lateral aspect of the FM and
posterior fossa being placed right under the
surgeon’s view.

35. INCISION
 An inverted hockey stick–shaped incision is made as
it provides good exposure of the muscular layers.

36. MUSCULAR STAGE
(1) elevation of the superficial muscles to expose the
suboccipital triangle
(2) dissection of the suboccipital triangle to expose the
VAs.

37.  The first muscular layer:
 the sternocleidomastoid and trapezius muscles.
 The second or middle muscular layer:
 the splenius capitis, longissimus capitis, and semispinalis
capitis muscles.
 the third layer forms the suboccipital triangle:
 the rectus capitis posterior major muscle, the inferior oblique
muscle and the superior oblique muscle.

38. VENOUS NETWORK
 The venous system of the posterior neck is divided
into two connected plexuses:
(1) the suboccipital venous plexus and
(2) the plexus around the VAs.
 This is the main source of bleeding and air embolism
in this region.

39. EXPOSURE OF THE EXTRADURAL VAs
 The VAs is divided into
4 segments:
 V1 is the pre-foraminal
segment.
 V2 is foraminal
segment.
 V3 is from C2 to dura.
 V4 is the intradural
segment of the VAs and
joins the opposite side
vessel to form the
basilar artery

40. MOBILIZATION OF THE VA
 Multiple periosteal attachments of the vertebral
artery into the foramen superiorly and inferiorly may
be present; these should be sharply divided.
 The vertebral artery is mobilized away from the
occipital condyle with a vessel loop and protected.

41.  The V3 segment of the VAs has some branches that
need to be coagulated during the approach.
 the anterior vertebral artery
 the posterior meningeal artery
 Care should be taken not to coagulate a
posteroinferior cerebellar artery (PICA) or a
posterior spinal artery that arises extradurally from
the V3.

42. Osseous Stage: Suboccipital Craniectomy
 The landmarks for
orientation of the
craniotomy are
(1) the asterion
(2) the midline
(3) the posterior border
of the mastoid
(4) the inion and
(5) the superior nuchal
line.

43.  The inferior margin of the transverse sinus is the
upper limit of the lateral suboccipital approach.
 The mastoid air cells are the lateral limit of the
suboccipital approach.

44. Osseous Stage: Hemilaminectomy
 A C1 hemilaminectomy is necessary to lengthen the
dural incision to achieve the desired exposure in this
approach.
 The hemilaminectomy is performed either piecemeal
or using a side cutting bur with a footplate

45. Retrosigmoid Mastoidectomy
 The goal is to expose the transverse and sigmoid
sinuses defining the superior and lateral extent of the
dural incision.

46. Drilling of Occipital Condyle
 Removal of the occipital condyle and associated lip of
foramen magnum allows the additional anterior
visualization and reduces brain stem retraction.

47.  A high-speed drill is used to remove the posterior
portion of the condyle after displacement of the
VAs to avoid injury of the vessel.
 Additional condylar removal provides increased
visualization at the cost of decreased stability of the
atlantooccipital joint.
 Roughly 8 mm of condyle can be safely removed
posteriorly before occipitocervical fusion should be
considered

48. Dural Incision
 The dura is opened in a lazy J-shaped fashion from the
transverse sigmoid junction curving medial and inferiorly so
that it crosses the foramen magnum just posteriorly to the
intradural entry point of the vertebral artery

49.  The cervical dura should be opened in a linear and
paramedian fashion down to at least the upper edge
of the C2 lamina.

50. Intradural Stage
 The first step of the intradural stage, before
beginning tumor resection, is to identify several
important structures.
 The VA is identified by following the course of the V3
segment where it pierces the dura matter.

51. TUMOR EXCISION
 In general, tumors that encase the VAs can be
removed via an arachnoid plane.
 In tumors located below the VAs, the lower cranial
nerves may be identified in the superior part of the
tumor.
 In contrast, the position of these nerves cannot be
anticipated in tumors with superior extension.

52.  The tumor is approached first via the side of the
main vasculature at the dural attachment.
 The tumor is devascularized and removed piecemeal
with protection of the neurovascular structures
involved.
 The bone and the dura involved by the meningioma
attachment are also removed, if possible, to avoid
recurrence.

54. CLOSURE
 A meticulous homeostasis is performed
 The dura is closed in a watertight manner with the
aid of patches from the pericranium or of dural
substitutes.
 The mastoid bone, if open, is filled with bone wax,
pieces of muscle, and fibrin glue.
 To avoid dead space, the posterior part of the
aponeurotic-muscle flap is made and is sutured onto
the dura.

55.  Preoperative contrast-enhanced T1-weighted MRI showed the
presence of a hyperintense lesion located at the anterolateral
surface of the FM and that compressed the brain stem

56.  Postoperative contrast-enhanced T1-weighted MRI confirmed
the gross total resection of the tumor. G, Coronal and sagittal
CT showing complete preservation of the OC

57.  Three-dimensional CT reconstruction showing the
suboccipital approach.

58. COMPLICATIONS
 Haemorrhage
 Psuedomeningocoele
 CSF leakage
 Lower cranial nerve injury especially IX, X and XI.
 Craniocervical instability.

59. THANK YOU