2. Introduction….
• Collection of hindbrain abnormalities .
• ranging from simple herniation of the
cerebellar tonsils through the foramen
magnum to complete agenesis of the cer-
ebellum.
3. History….
• 1883, John Cleland (Professor of anatomy in Glasgow,
Scotland) - described hindbrain hernia in a child with
myelodysplasia.
• 1891 and 1896, Hans Chiari- (Professor of Pathology at
German University, Prague, Czechoslovakia) analyzed
data from >40 postmortem examinations of patients
with hindbrain malformations.
• Chiari malformations I, II and III were coined in the
earlier work and Chiari malformation IV was added in
1896 publication.
4. History…..
• 1894, Julius A. Arnold(Professor of Pathology
at Heidelberg, Germany) described a single
myelodysplastic patient with associated
hindbrain herniation.
• Schwalbe & Gerdig included Arnold name in
the eponym & designated it ARNOLD –CHIARI
malformation.
5.
6. Chiari 0…..
• Iskander identified it.
• condition in which the obex, but not the cerebellar tonsils, are
inferiorly located and a syrinx is found within the cervical segments
• posterior fossa may appear “crowded”
• large syringes that resolve with posterior fossa decompression .
• physical barrier to CSF movement but not significant caudal
displacement of cerebellar tonsils beyond pathological point
8. Chiari 1…..
• caudal displacement of cerebellar tonsils >
5mm below the foramen magnum
• brainstem normal in position
• may or may not have syrinx but are usually
associated with syrinx .
• Hydrocephalus in <10 % patients.
9. Sagittal magnetic resonance image of child with Chiari I
malformation. Note the caudalmost extent of the
cerebellar tonsils displaced to the lower border of C2.
11. Chiari 1.5……
• applied to patients who bridge the gap
between CIM and CIIM.
• presence of characteristics of both groups
• not associated with neural tube defects
• caudal displacement of cerebellar tonsils
• brainstem and 4th ventricles are also
displaced like in CIIM
12. Chiari 2…..
• almost always occurs in patients with neural
tube defects (myelomeningocele and
encephalocele)
• caudal migration of cerebellar vermis,
brainstem and 4th ventricle .
• Also choroid plexus, basilar A, PICA also
caudally displaced.
• Syringomyelia, hydrocephalus is common
13. Figure 190-2. Sagittal magnetic resonance image demonstrating the Chiari II
malformation. Note the hindbrain hernia into the neck and small cerebellum. Also note
the absence of significant portions of the corpus callosum, a nearly vertical straight
sinus, and an enlarged massa intermedia.
15. Chiari 3…….
• rarest and extreme form of hindbrain hernia
• confused with occipital encephalocele
• <1% occurrence
• has low occipital and high cervical sacs containing
significant portions of the cerebellum and
brainstem.
• Hydrocephalus is common and severe
neurological and developmental problems
present
• Poor prognosis
19. Chiari 4……
• cerebellar hypoplasia or aplasia
• Post fossa normal in size
• not a form of hindbrain hernia
• its inclusion in chiari malformations is hence
debatable
• more appropriate to include this in the
category of posterior fossa cysts
22. Chiari 1……
• Mc presenting symptom is pain (60% to 70%),
usually occipital and upper cervical area, and
often induced by Valsalva maneuvers such as
laughing, sneezing, and coughing.
• In infants and children, headaches may
manifest simply as crying and irritability.
• weakness or numbness,
• unsteadiness.
23. • Scoliosis
• or otological disturbances- tinnitus,
fluctuating hearing loss, vertigo and nausea.
24.
25.
26. Chiari 2…..
• Caudal displacement of cerebellar vermis, lower
brainstem and fourth ventricle seen exclusively in
patients with myelomeningocele
• Numerous other anomalies associated in various
combinations
• vertical straight sinus
• large venous lakes in the tentorium
• fenestrations in falx, which is often not well
formed – gyri of left and right hemispheres
interdigitate – “Chinese lettering” on axial MRI
27. • hyrdrocephalus (90%),
• Syringomyelia (45-95%)
• Tectal beaking (fusion of colliculi )
• Kinking at the level of cervicomedullary
junction
28.
29.
30. Radiographic signs of CIIM
• Lückenschädel – 85%
• Tentorial hypoplasia with wide incisura &
small post. Fossa – 95%
• Enlargement of foramen magnum (73%)
• Inversion (or transtentorial upward herniation)
of the cerebellum
31. • Luckenschadel or Lacunar skull
– result of abnormal radial growth of the skull, seen in upto 85%of cases
– Focalareasof cortical thinning and scalloped appearance of theskull
– most prominent at birth, mayresolve withage
32.
33.
34.
35.
36. Abnormality of ventricular system
• Third ventricle only mildly dilated and contains
large massa intermedia - 75%
• 4th ventricle – small and non visualized in 70%
- often flattened, elongated and extending
into the cervical canal – banana shaped
cerebellum seen“banana sign”
• Lateral ventricles asymmetrically dilated with
prominence of atria and occipital horns
(colpocephaly)
37.
38. • Frontal horn and anterior portion of the third
ventricle – pointed and acutely angulated causing
frontal pinching of calvarium – “lemon sign”
• Incomplete C1 arch – 70% - missing bone
replaced by fibrous band Klippel-Feil fusion
anomalies of cervical spine
• Basilar impression and C1 assimilation quite
uncommon in CIIM as compared to CIM
• Significant shortening and scalloping of clivus
40. • X ray CVJ and cervical spine.
• Computed Tomography Scanning (CT)
• Magnetic Resonance Imaging (MRI)
• Cardiac gated cine MRI for CSF flow study
41. MRI
• Investigation of choice to assess the degree of
tonsillar descent
• T2 weighted saggital MRI of the spine.
• Helps to screen the whole of the spine and
brain for any other associated anomaly of the
neuraxis or presence of hydrocephalus
42. Csf flow study and motion sensitive
MRI
• cine MRI may demonstrate lack of CSF flow
patterns that can occur in the setting of CIM.
• presence of a CIM and a syrinx resulting from
disturbed CSF flow .
• Repeating the study postoperatively may help
in evaluating the adequacy of the
decompression.
• Minimal practical utility.
45. Hydrocephalus theory…
(Chiari, 1891)
• attributed the congenital hindbrain herniation to ‘
chronic hydrocephalus of the cerebrum’
• with ‘pushing out ‘ of the cerebellum and the
brainstem through the foramen magnum
• * hydrocephalus not universal and children with
hydrocephalus.
• * upward herniation through tentorial notch
along with caudal displacement of hindbrain in
Chiari II with hydrocephalus
46. • Caudal Traction theory
• (Penfield,Coburn,Lichtenstein et al.)
• tethering of the cord by the
myelomeningocele with ‘pulling down’ of the
posterior fossa contents
47. • Cerebral overgrowth theory ( Barry, Patten,
Stewart - 1957 )
• excessive volume of cerebral cortex with
downward displacement of tentorium and
hindbrain in an abnormal small posterior fossa.
Developmental Arrest ( Daniel , Strich - 1958)
• the primary dysgenesis of brainstem impairs the
formation of pontine flexure resulting elongated
and herniated brainstem into upper cervical
canal.
48. • Hydrodynamic theory (Gardner &
Goodall, 1965)
• They postulated that the outlets of the fourth
ventricle were occluded by the Chiari I
malformation and that a water-hammer
pulsation was directed from the fourth
ventricle, through the obex, and into the
central canal of the spinal cord, leading to
pulsatile expansion of the central canal to
form a syrinx
49. Craniospinal Pressure Dissociation
theory
( William , 1969)
• Attributed venous pressure changes rather than arterial
pulsations as the driving force for hydromyelia.
• - increase in the subarachnoid fluid pressures resulted from
increase in venous pressure during coughing and Valsalva ‘s
maneuver due to distended epidural venous plexus
resulting in the cranial flow of CSF with dissipation of
pressure difference.
• - hindbrain herniation prevents this caudal flow of CSF due
to ball valve effect of the tonsils which impact at the
foramen magnum
• - explained the association of foramen magnum obstruction
with progression of syrinx.
• - experimental evidence to demonstrate significant
craniospinal pressure difference which normalized
following decompression.
50.
51. Du Boulay modification of Gardner ‘s theory ,1974.
- craniospinal pressure dissociation secondary to
foramen magnum blockage but prevention of CSF egress
during systole is the driving force for hydromyelia.
• Disproportionate CSF absorption theory (Fischer,
Welch)
• disproportionate amount of CSF absorbed/ drained
from the spinal canal induces a negative pressure
gradient resulting in secondary herniation - acquired
Chiari malformation
• eg. Following Lumboperitoneal shunt insertion.
52. • Taylor’s theory ,1975
• ‘’impaired venous drainage results in central
cord necrosis and secondary cavitation.’’
• But neither physiological evidence of venous
obstruction nor histology of syrinx suggestive
of hemmorhagic necrosis
53. • Ball and Dayan’s theory (1972)
• ‘’Syrinx cavity produced by CSF tracking under pressure from spinal
subarachnoid space into the cord along perivascular (Virchow –
Robin ) spaces.’’
• Pros:
• - explained the separation of syrinx cavity from the central canal
• - communication of syrinx with spinal subarachnoid space
demonstrated using metrizamide myelogram.
• Cons:
• -pressure external to syrinx would tend to collapse rather than
enlarge it.
54. Oldfield’s theory ( 1994)
• It is currently a widely accepted theory.
• - hypothesized that CSF in spinal cord acts from outside the spinal
cord and not from within.
• - Brain expands in systole → Tonsils pushed to spinal canal → ↑
spinal sub arachnoid pressure → CSF forced through peri vascular
and interstitial spaces to canal→ Propulsion of syrinx fluid up and
down → origin and propagation of syrinx.
• - systolic pressure wave imparted to intracranial CSF due to blood
flow to the brain is normally adjusted by sudden CSF movement
from basal cisterns to upper spinal canal.
• - In Chiari I , piston like movement of the cerebellar tonsils down
the foramen magnum results in systolic pressure wave in spinal CSF
• -pressure waves act on the surface of the cord and forces CSF into
the parenchyma along the perivascular and interstitial spaces.
55.
56. • once syrinx formed ,longitudinal propulsion of
fluid with propagation of cavity
• * detected preoperatively with Dynamic cine
phase MRI and intraoperative by ultrasound
showing pulsatile excursion of the cord
surrounding the syrinx .
• - based on this bone and dural decompression of
the foramen magnum alone is adequate
treatment without entering the arachnoid.
57. (Nishikawa et al, 1997)
• suggested that the fundamental defect may
involve
• underdevelopment of the occipital somites
originating from para-axial mesoderm leading
to underdevelopment of the occipital bone
and overcrowding of cerebellum within a too
small posterior cranial fossa causing tonsillar
herniation.
59. Chiari 1…..
• First decide whether the lesion is truly
symptomatic.
• Observation in asymptomatic patients without
an associated syrinx
• No medical treatment
• Surgery: for symptomatic patients and
asymptomatic patients with syrinx
60. • 10% patients with CIM – associated hydrocephalus
CSF diversionary shunt or ETV as the initial form of therapy
• Most common surgical procedure: Posterior fossa
decompression
• Goal: enlarge posterior fossa to recreate cisterna magna,
thereby permitting normal flow of CSF
• Syrinx decrease in size and does not require direct Rx in
majority after this
63. PFD vs PFDD…
• Durham and Fjeld-Olenec : meta-analysis of studies
that directly compare cohorts of pediatric patients who
underwent PFD with PFDD.
• Patients who undergo duraplasty are less likely to
require reoperation (2.1% vs. 12.6%) for persistent or
recurrent symptoms but are more likely to suffer CSF-
related complications
• No statistical difference in clinical outcomes between
the two groups, specifically with regard to symptom
improvement and syringomyelia
64. • clinical improvement were 65% in the PFD
patients and 79% in the PFDD patients
• Syrinx resolution :56% in the PFD patients and
87% in those undergoing PFDD.
• large majority of studies reporting the clinical
efficacy of superior to those of PFD
65.
66. Mx strategy…
• Top to down rule
– Hydrocephalus
– FMD with lax duroplasty
– Shunting of syrinx
67. Various procedures adopted…
• FMD alone
• FMD with lax duroplasty
• FMD with arachnoid adhesiolysis and lax duroplasty
• FMD with tonsillar resection, pexy etc and lax durplasty
• FMD with any of the above and additional removal of
C2.
• FMD = Suboccipital craniectomy encompassing the
foramen magnum rim and C1 posterior arch excision
68. Additional procedures for associated
problems
• Hydrocephalus
– VP shunt
– ETV
• Ventral Bony CMJ compression
– Ventral decompression with or without fusion
• CVJ instability
– Posterior fusion
69. Posterior fossa decompression….
• Prone position and neck flexed
• Incision from below inion to the spinous process of C2
• Avascular plane (nuchal ligament) b/t paraspinous
muscles followed down to bone and subperiosteal
dissection performed
• Moderate suboccipital craniectomy, width of the
foramen magnum followed by removal of posterior
arch of atlas
70. PFD…../PFDD…
• Dura opened
• Arachnoid adhesions obstructing flow removed
and the floor of the 4th ventricle examined
• Portion of occipital pericranium harvested
through a separate incision and duroplasty
performed
• Wound closed in anatomical layers.
71. PFD….
• Encouraging result in long term follow up
• Early treatment tends toward better outcomes
• 85% patients – relief of head and neck pain esp. if
valsalva induced
• Associated syrinx decrease in size or collapse in
majority
• If no improvement in symptoms and size of syrinx in 6
mo reexploration with coagulation or resection of
a cerebellar tonsil
72. • Placement of syringosubarachnoid shunt in
recalcitrant cases not responding to
decompression
• Advanced symptoms – medullary dysfunction,
muscle wasting and dysesthesias in trunk or
extremities – unlikely to resolve but should not
progress
• Mild to moderate scoliosislikelihood of
improvement
73.
74. Skin incision….
• • Extent:
• midline
– Just below inion
• – Just past the C2 spine
75.
76.
77.
78.
79. Bleeding at durotomy….
• Cerebellar dura may have venous lakes
• • Circular or occipital sinus may bleed profusely
• • Control
– Proceed slowly
– Bipolar
– Metal Clips
– Figure of 8 stiches
80. Intra dural exploration…
• Arachnoid opening
• – Under magnification
• – Midline
– Avoid adherant PICA
• – Only sharp dissection
83. Mx of descended tonsils…
• Batzdorf advices the following strategy:
• for mobile tonsils : Bipolar coagulation of the tonsils to
shrink it.
• for gliotic tonsils : amputation of the tonsils.
• for adherent tonsils : subpial resection of the tonsils
(dorsally & laterally to avoid scarring in midline)
• for encased tonsils : midline dissection to the fourth
ventricle with tubular shunt to cervical subarachnoid space.
• for membranous occlusion of the fourth ventricle: division
of the membrane, permanent arachnoid retraction sutures
to maintain seperation of tonsils in the midline.
84.
85. Post op complications..
• Early
• – CSF Leak
• Address HCP
• • Resuture
• Lumbar drain
• – Meningitis – Infective / Chemical
86. Post op complication….
• • Early
• – Lower cranial nerve dysfunction
• – Brainstem dysfuctions
– Hematoma
87. • Late
• – Symptom recurrence
• • Occur after initial improvement
Due to:
– New or enlarging syrinx
– CSF obstruction due to scarring
– Cerebellar ptosis
• – Pain
– Instability
88. Recurrent or unresolved chiari…
• Causes:
• – Inadequate decompression
• – Reformation of arachnoid scars
• – Lack of CSF flow normalization despite adquate
soft tissue and bony decompression
• • Management
– Revision surgery
– Shunting of the syrinx
89. Chiari 2…..
• Adequate shunt function must be established
prior to pursuing decompression of CIIM
• Surgical inspection of shunt fxn – because
ventricle size may remain unchanged
• Inspiratory stridor, sleep apnea, recurrent
aspiration pneumonia, opisthotonos and
progressive spasticity or ataxia must be seriously
probed
90. • Surgery rarely includes removal of foramen
magnum unlike CIM Choroid plexus often in
embryonic extraventricular position
• Crucial goal – patency of foramen of magendie –
if any question stent should be placed
• Outcome: infants with brainstem symptoms are
less likely to have significant improvement
following decompression
94. Chiari 1
• Follow up
• Pts without a syrinx: follow up at 1, 6 & 12
months, then every 12 to 24 months ;no need of
repeat imaging (if there is symptomatic
improvement)
• Pts with syrinx: follow up MRI in 6 to 12
months.No further imaging if symptoms
improve or syrinx decreases in size significantly.
95. • If syrinx does not improve ,additional imaging
at surgeon’s discretion
• When syrinx fails to improve or symptoms are
persistent a second surgery is performed
• Second surgery is more aggressive than the
first
• Unilateral tonsillar coagulation is performed
• Stents are placed if free egress of CSF from IV
ventricle was not achieved.
96. Chiari 2….
• Close follow up
• Pre & post op sleep studies
• Gastrostomy tubes for dysphagia
• CT scan at 3 months to see ventricle size
• Clinical relapse is presumed as a shunt
malfunction
