Chiari malformation

CHIARI MALFORMATIONS
Dr. Sourabh Jain
Medical college & Hospital
Trivandrum

Introduction
• These comprise a group of abnormalities involving the
rhombencephalon (hindbrain) and the contents of the CV junction.
• Presently there is no consensus regarding the precise definition,
classification, etiology and the surgical management .
• Series of hindbrain anomalies
• Four types
• No anatomical or embryological correlation between them
•

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.

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.

Definitions of Chiari malformations
• Chiari type I
tonsillar herniation below foramen magnum.
no associated brainstem herniation or supratentorial anomalies.
hydrocephalus uncommon.
• Chiari type II / ACM
caudal herniation of brainstem, cerebellar vermis, and fourth ventricles.
associated with myelomeningocele & intracranial anomalies.
hydrocephalus & syringohydromyelia common
• Chiari type III
occipital encephalocele with many of same intracranial anomalies seen with type II
malformation.
• Chiari type IV
hypoplasia / aplasia of cerebellum with no hindbrain herniation

Transitional forms of Chiari malformations
• Chiari type 1.5
tonsillar herniation as seen in Chiari I with addition of an elongated brainstem and fourth
ventricle.
( Iskandar B,1999 )
• Chiari type 0
syringohydromyelia with no evidence of hindbrain herniation. All of these improved,
clinically and radiographically, in the syrinx following posterior fossa decompression.
Functional disturbances of CSF flow across the CV junction.
At surgery arachnoidal veils and adhesions obstructing the Foramen of Magendie with
crowding of tissue at the Foramen of magnum
(Iskandar B. J Neurosurgery 89:212-216,1998)

CHIARI 1.5
Tonsillar herniation + elongation of brainstem
and 4th ventricle.

Chiari I definition?
• Tonsilar herniation below foramen magnum.
• Extent of descent below FM ?
• Analysis of 800 MRI(95 patients-82 controls, 13 patients)
– Asymptomatic patient tonsillar herniation <3mm
– Border line 3-5 mm
– Symptomatic >5mm (diagnosis of Chiari malformation)
– In most cases of Chiari II- saggital diameter of foramen magnum >42mm
(Aboulezz et al. Comput Assist Tomogr. 9:1033-1036,1985)
• Analysis of 200 controls + 25 pt
-<3mm descend asymptomatic
• Sensivity 96%
• Specificity 99.5%
-Mean tonsillar descent 13.12+/- 7.08 mm in symptomatic group
(Barkovich et al. Am J NR ,7:795-799,1986.)

• Analysis of 221 normal patients aged 5 months to 89 years
• Found a trend towards tonsillar ascent with increasing age
• Criteria to distinguish abnormal tonsillar ectopia
- first decade - > 6 mm
- 2nd-3rd decade - > 5 mm
- 4th-8th decade - > 4 mm
- 9th decade - > 3 mm
(Mikulis DJ. Radiology. 183:725-728, 1992)

• Analysis of 364 symptomatic patients
– Tonsillar descent of at least 5mm(332 patients)
– Obliteration of retrocerebellar CSF spaces in all patients
– (65%)- syringomyelia
– All had varying degrees of cranial base dysplasia
– Significant reduction in posterior cranial fossa and total csf volume
– 12% - positive family history of Chiari I or syringomyelia
– Extent of tonsillar descend cannot be the sole criteria for diagnosis
(Milhorat TH et al. Neurosurgery.44:1005-1017,1999.)

Associated anomalies – Chiari l
• Skull
– Basilar skull and cv junction anomalies (50%)
• Underdevelopment of supraocciput and exocciput
• Shortening of supraocciput
• Shorter clivus
• Smaller and shallow posterior fossa
• Empty sella
• Platybasia
• Basilar impression
• Midline occipital keel
• Accessory occipital condyle

• Spine
– Klippel-Feil deformity
– Atlantoaxial assimilation
– Retroflexion of odontoid process
– Thickening of ligamentum flavum
– Scoliosis

• Ventricle and cistern
– Hydrocephalus (3-10%)
– Elongated 4th ventricle
– Retrocerebellar CSF space are obliterated or
diminished

• Meninges
-- Elevated slope of tentorium
– Thickening of arachnoid at foramen magnum
– Constricting dural bands at level of foramen
magnum and posterior arch of atlas
– Veils of arachnoid that obstruct fourth ventricular
outlet

• Spinal cord
– Syrinx (50-75%)

• Brain
– Elongated midbrain, pons and medulla
– Medullary kinking or flattening
– Tonsils- peg like, lose folial pattern, atrophic

CHIARI MALFORMATION II
- Caudal herniation of brainstem, cerebellar
vermis, and fourth ventricles.
- associated with myelomeningocele &
intracranial anomalies.
- hydrocephalus & syringohydromyelia
common

Associated anomalies – Chiari ll
• Skull
– Craniolcunia or luckenschadel- copper beaten appearance
of calvaria
– Anterior scalloped frontal bone (lemon sign )
– Scalloping of pterous and jugular tubercle
– Enlarged FM
– Notched opisthion
– Elongated clivus with concavity
– Lower inion
– Basilar impression
– Assimilation of atlas

Chiari II Supratentorial pathology
• Luckenschadel or Lacunar skull
– result of abnormal radial growth of the skull, seen in upto 85% of cases
– Focal areas of cortical thinning and scalloped appearance of the skull
– most prominent at birth, may resolve with age
– not a result of raised ICP and hydrocephalus

• Spine
– Elongated cervical spine
– Scalloping of odontoid processes
– Incomplete C1 posterior arch
– Klippel-Feil deformity

• Ventricle and cistern
– Hydrocephalus (90%)
– Asymmetry of ventricle
– Colpocephaly- enlargement of atria and occipital horns
– Shark tooth deformity of 3rd ventricle
– Elongated, flat and small 4th ventricle
– Absent inferior medullary velum
– Foramen of Magendie absence or associated cyst

• Meninges
– Abnormal tentorium cerebelli
– Elongated incisura
– Low lying tentorium
– Vertical straight sinus
– low lying torculla
– Fenestrated or hypoplastic falx cerebri
– Thickened arachnoid
– Thickened cephalad dentate ligament
– Arachnoid cyst

• Brain
– Telencephalon
• Corpus callosal agenesis
• Absent septum pellucidum
• Polygyria
• Chinese lettering of occipital and parietal lobe
• Agenesis of olfactory tract/bulb
• Absent cingulate gyrus

• Brain
– Diencephalon
• Interthalamic adhesions
• Elevated hypothalamus
• Elongated pineal gland
• Elongated habenular commissure

• Brain
– Mesencephalon
• Elongated mid brain
• Shortened quadrigeminal plate
• Tectal beaking
• Forked , kinked shortened aqueduct
• Dysgenesis of cranial nerve nuclei

• Brain
– Metancephalon
• Smaller cerebellum
• Towering of cerebellum
• Tonsillar and vermian herniation
• Dysplasia of cerebellum
• Banana sign- curved cerebellum
• Cerebellar inversion
• Elongated and flattened pons
• Dysplastic cranial nerve nuclei

Associated anamolies – Chiari ll
• Brain
– Myelencephalon
• Elongated and flattened medulla (trumpet like )
• Cervicomedullary kink
• Cephalad pyramidal decussation

Genetics of Chiari
• Familial occurrence
• Concordance in twins and triplets
• Association with other genetic disorder
– Spondyloepiphyseal dysplasia tarda
– Hadelu-Cheney syndrome
– Klippel-Fiel syndrome
– achondroplasia

Genetics of Chiari
• Risk of inheritence
– No data available
– Incidence of familial syringomyelia – 2%
– Incidence of familial CM l – 12%
• Pattern of inheritence
– Autosomal dominant with reduced penetrance
– Autosomal recessive
(Milhort et al.Neurosurgery.44:1005-1017,1999)

Acquired Chiari Malformation
• Acquired Chiari I malformation secondary to
spontaneous spinal cerebrospinal
fluid leakage and chronic intracranial hypotension
syndrome in seven cases.
(Atkinson JL et al. J Neurosurgery. Feb;88(2):237-242,1998)
• The acquired Chiari malformation and syringomyelia
following spinal CSF drainage
(Johnston I et al. Acta Neurochir (Wien). 140(5):417,1998)

Chiari III
• : herniation of brainstem and cerebellum into a
posterior encephalocoel.
• Very rare; most severe form. Management
difficult.
• Differentiate from cervical myelomeningocoel.
• Severe neurological, developmental and cranial
nerve defects, seizures and respiratory
insufficiency.
• Treatment- well planned encephalocoel closure

CHIARI 3: occipital encephalocele with
chiari 2

Chiari IV
• : cerebellar hypoplasia or aplasia(1896). Post fossa size
normal.
• No hindbrain herniation.
• Tentorium cerebelli also hypoplastic.

CHIARI 4 :Cerebellar hypoplasia/ aplasia

Chiari I
Chiari I
• HEAD ACHE
Most common symptom (81%)
Sub occipital
Radiation to vertex / neck / retro-bulbar
Heavy crushing / pressure like
↑ed by physical exertion, Valsalva
maneuver, head dependency and
sudden changes In position

Chiari I
• Spinal cord/ syrinx
– sensory
• Numbness: initial complaint, asymmetric, hands/arms
• Dissociated sensory loss: loss of pain and temp, preserved touch and JPS
• Dysesthesia and proprioception disturbances – advanced stage
• Deep and boring/ itching/ burning
• C2 dysesthesia
• Interscapular pain
• All pain exacerbated by cough and sneeze
• Valsalva or severe cough may alter findings
• Charcot joints: <5% of patients

Chiari I
– Motor:
• Difficulty in performing fine motor tasks in UL
• Weakness of hand and/or arm
• Wasting – distal and proximal
• Fasciculations
• Absent DTRs
• UMN lower extremities
• Horners’ – complete or partial
• Bowel and bladder control normal
• Occasionally LMN in lower extremities

Chiari I
• Brain stem/ CSF flow/ FM
– Cough headache
– Neck and arm pain – non dermatomal “deep and boring”
– Down beat nystagmus
– Hoarse voice
– Palatal dysfunction
– Tongue – fasciculations/ atrophy
– Dysphagia
– Hiccups
– Severe snoring
– Respiratory dysrhythmias
– Facial numbness
– Drop attacks
– Dysarthria

Chiari I
• Cerebellar:
– Nystagmus: horizontal or rotary on lateral gaze
– Ataxia: appendicular
– Dysmetria

Chiari II
• Commonly presents in infancy, childhood and adolescence
• May stabilize or improve after 6 to 12mths
• Risk of apneic attacks, dysphagia with aspiration pneumonia,
life threatening vocal cord paralysis
• Leading cause of death in treated myelodysplastics within first
2 yrs of life

Clinical features
Brain stem
45%
cerebellar
7%
spinal cord
48%
Chiari II

Chiari II
• Brain stem
– Nystagmus: first, coarse, lat gaze evoked
– Poor sucking/ dysphagia/ aspiration
– Arching of head/ fixed retrocollis/ ophistotonus
– “Good baby” – feeble cry
– Inspiratory wheeze or stridor on agitation (cf: epiglottitis)
– Apneic spells – cyanosis/anoxic seizures – exhausted- sleeps
– Vocal cord abductor palsy (b/w cyanotic attacks)
– Gag: blunted or absent
– VII nerve paresis
– Dysconjugate eye movements
– Mirror movements

Chiari II
– Spasticity of upper extremities: severe/ progressive
– Weakness of lower extremities: myleomeningocoele
– Persistent cortical thumb
– Suspended dissociated sensory loss (pain/ temperature)
– Upper extremity weakness and wasting of hand muscles
– Scoliosis

Chiari II
• Cerebellar:
– Nystagmus: horizontal or rotary
– Appendicular ataxia: “falls so much”, gait changes
– Dysmetria: inability to feed himself

Comparison of Chiari I & II anomalies
Findings Chiari I Chiari II
Caudal dislocation
medulla
unusual yes
Caudal dislocation into
cervical canal
tonsil Inferior vermis, medulla,
4th ventricle
Spina bifida May be present Rarely absent
Hydrocephalus May be absent Rarely absent
Medullary kink absent Present in 55%
Course of upper cervical
nerves
normal cephaled
Age of presentation Young adults infancy
Usual presentation Cervical pain Progressive
hydrocephalus,
respiratory distress

PATHOGENESIS OF CHIARI
MALFORMATION and
SYRINGOMYELIA

Isolated
Congenital
Syndromic
↑ICT conditions
Acquired ↓Skull vol
Pressure gradient
CHIARI 1

Theories
• 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 and no dysraphism do not have herniation
* upward herniation through tentorial notch along with
caudal displacement of hindbrain in Chiari II with
hydrocephalus
•

• Cerebral Dysgenesis theory ( Cleland,1883 )
dysplastic changes in brainstem,, cerebellum,, corpus callosum based on
chick embryo studies.
• Caudal Traction theory ( Penfield, Coburn,Lichtenstein et al.)
tethering of the cord by the myelomeningocele with ‘pulling down’ of the
posterior fossa contents
*reverse herniation seen in CIIM
* abnormal relation of the nerve roots to cord normal in thoracic
segments
* tension within the caudal segments dissipated over four segments (
Goldstein & Kepes ,1966 )
*cervicomedullary kink and other anomalies not explain

Theories
• Cerebral overgrowth theory ( Barry, Patten, Stewart - 1957 )
attributed 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.

Theories
• Hydrodynamic theory (Gardner & Goodall, 1965)
failure of the rhombic roof to perforate resulting in the gentle undampened ‘waterhammer
‘ effect of the arterial pulsation of the choroid plexus
dissipated through a patent obex into the central canal resulting in progressive spinal cord
cavitation.
Pros:
* animal studies to support the same by occlusion of the fourth ventricular outlet.
* compensated hydrocephalus with communicating syringomyelia in 14/15 patients of
myelodysplasia in whom VP shunt resulted in neurological improvement with resolution of
the syrinx . ( Hall et al.)
Cons :
* hydrocephalus present in some.
* fourth ventricular obstruction not present in all.
*obex rarely communicates with syrinx.

• Craniospinal Pressure Dissociation theory ( William , 1969)
Attributed venous pressure changes rather than arterial pulsations as the driving
force for hydromyelia.
Proposed that
- 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
Pros:
- explained the association of foramen magnum obstruction with progression of
syrinx.
- experimental evidence to demonstrate significant craniospinal pressure
difference which normalized following decompression.
Cons:
-Only 10% had radiological evidence of communicating syrinx .
- myelography evidence shows cord compression not dilatation
during increase in spinal venous pressure.

Theories
• 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.
- CM usually seen in adults not in children.

Theories
• Aboulker’s theory , 1979
‘’ obstruction at the cisterna magna associated with high venous pressure
caused transmedullary passage of CSF which produces progressive
cavitation “
- initiated by the stenosis of the dural sac at the level of foramen
magnum,thus intracranial CSF doesn’t flow caudally and 30% of the spinal
fluid unable to ascend up resulting in edema progressing to cavitation.
Pros:
- metrizamide scan suggests transneural migration into the cavity.
- communication of syrinx with spinal subarachnoid space.
Cons:
-documentation of venous hypertension in spinal cord not convincing.
• .

Theories
• 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

Theories
• Mesoderm “ too small posterior fossa ” theory
( Marin Padilla ,1981)
- experimentally treated hamsters with excess Vitamin A
- resulted in underdevelopment of occipital squamosa with small
posterior fossa with consequent cephalocranial disproportion.
- barrier against the growth of the neural structures with displacement
upward and downward outside the confines of the fossa.
- radiographic morphometric measurements in 364 symptomatic CIM
concluded paraxial mesoderm disorder with underdevelopment of
posterior fossa cranium/compression of normal hindbrain (Milhorat TH et
al. ,1999)

Theories
• 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.
Aboulker –fluid enter along dorsal nerve roots.

Theories
• Mclone and Knepper’s Unified theory (1989)
-based on assumption that neural tube defect primary with secondary
manifestations of Chiari and hydrocephalus.
-in-utero abnormal pressure differential results in vermian herniaton without
tonsillar involvement, development of vermis predates that of cerebellar
hemisphere and tonsils(Osaka et al.,1978)
- CSF leak through defect results in lack of distension of cranial ventricular system
which is a prerequisite for normal development of cerebral cortex and overlying
skull.

• 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.

-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.

(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.
(Nishikawa M. J Neurosurg 86:40-47, 1997)

• Natural history-varies from spontaneous and complete
regression to progressive devastating neurological
deficits.
• Boman and livanainen(1920-1965)-university of
Helsinki.
• Reported 55 unoperated patients of syringomyelia.
• Slow progression in all cases.
• 3 had disability within 5 years of onset.
• 28 had slow progression with worsening.
• 27 had stationary period for 10 years.
• Patient having chiari malformation not mentioned.

Natural History
• Patients with normal sized cord more likely to
have benign course.
• In case cord dilation present symptoms tend
to progress.

Natural history
• So far 30 cases reported to have resolution of Chiari
malformation with syringomyelia
– Paediatric as well as adult cases
– Duration 1.3 yr to 8 yr
– Complete to partial resolution of syrinx
– Complete to partial resolution of tonsilar descend
– Asymptomatic to static clinical status
Kyoshima K et al, Neurosurgery 53:762-769, 2003

Natural history
• Pathophysiological mechanism
– in children their is enlargement of the posterior fossa with differential growth
between the bone structures and the central nervous system leads to Chiari I
malformation improvement, with restoration of normal CSF flow at the
foramen magnum and consequent resolution of syringomyelia
Castillo Met al,AJNR 16:1158–1160, 1995.
– spontaneous recanalization of CSF pathways at the foramen magnum might
have occurred because of rupture of the arachnoid membranes obstructing
the CSF flow
Klekamp J et al,Neurosurgery 48:664–667, 2001.
– older people,brain atrophy, especially that of the cerebellar tonsils
Mikulis DJet al,Radiology 183:725–728, 1992.
– rupture of the syringomyelic cavity into the spinal subarachnoid space
(fissuring)
Jack CR Jr et al,J Neurosurgery 74:283–286, 1991.

Management of Chiari-Syrinx Complex

Establishment of Diagnosis
• X ray CVJ and cervical spine...
• Computed Tomography Scanning (CT)
• Magnetic Resonance Imaging (MRI)
• Cardiac gated cine MRI for CSF flow study

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
• Septations and flow voids within the syrinx
can be seen

Cardiac gated PC cine MRI for CSF flow
• Definitive role in decision making
– Tonsillar morphology is not equivalent to
symptomatology (Meadows et al J Neurosurg
2000;92:920–26).
– Treatment options following failed FMD

Qualitative Vs Quantitative PCMR
• Presence of CS flow across the FM is not the
only factor
• Quantitative factors involved
– Peak flow velocity
– Duration of flow during systole and diastole

PFD PFD + DUROPLASTY
PFD WITH SHUNTING
THE SYRINX

Indications for surgical Intervention
• Progressive neurological deficit
• Progressive enlargement of syrinx
• Question of close follow-up
• Individualize the treatment

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

• 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.
• Although direct comparisons have not demonstrated a
statistically significant difference in clinical outcomes,
the large majority of studies reporting the clinical
efficacy of PFDD for the most common presentations
have demonstrated rates of improvement superior to
those of PFD

Trends in clinical response to surgery
Well responders
• Headache
• Pain
• Weakness without
atrophy
• Scoliosis
Poor responders
• Sensory
• Atrophy
• Weakness with
atrophy
• Nystagmus
Meadows et al. Neurosurgery Quarterly, Vol. 11, No. 3, 2001

Management Strategy
• Top to down rule
– Hydrocephalus
– FMD with lax duroplasty
– Shunting of syrinx

Selection of Surgical Procedure
• Depends on whether chiari is associated with
syrinx or not.
• Also on the type and degress of tonsillar descent.
• The key is to decompress the posterior fossa and
CVJ adequately, and to establish normal CSF flow
across the region of formen magnum.
• Any associated pathology like hcp and BI will
determine the type and modification of the
procedure

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

Additional procedures for associated
problems
• Hydrocephalus
– VP shunt
– ETV (Missimi et al - NS 2011)
• Ventral Bony CMJ compression
– Ventral decompression with or without fusion
• CVJ instability
– Posterior fusion

Surgical Technique
• Bony decompression
• Dural procedures
• Arachnoid handling
• Dealing with the tonsils

Skin Incision
• Extent:
– Just below inion
– Just past the C2 spine

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

Intradural exploration
• Arachnoid opening
– Under magnification
– Midline
– Avoid adherant PICA
– Only sharp dissection

Morphological variants of tonsils
(described by Batzdorf)
1. Simple tonsillar impaction(mobile tonsils)
2. Adherent tonsillar impaction
3. dense arachnoid scarring (gliotic tonsils)
4. Vascular membrane (encased tonsils)
5. Membranous occlusion of the fourth ventricle

Management of Descended Tonsils
Batzdorf advices the following strategy:
1. for mobile tonsils : Bipolar coagulation of the tonsils
to shrink it.
2. for gliotic tonsils : amputation of the tonsils.
3. for adherent tonsils : subpial resection of the tonsils
(dorsally & laterally to avoid scarring in midline)
4. for encased tonsils : midline dissection to the fourth
ventricle with tubular shunt to cervical subarachnoid
space.
5. for membranous occlusion of the fourth ventricle:
division of the membrane, permanent arachnoid
retraction sutures to maintain seperation of tonsils in
the midline.

Wound closure
• Layered closure
– Muscle
– Facia
– Subcuticular
– Skin

Postoperative complications
• Early
– CSF Leak
• Address HCP
• Resuture
• Lumbar drain
– Meningitis – Infective / Chemical
• Non autologous graft
• Dura not closed
• Meticulous and clean procedure

Postoperative Complications
• Early
– Lower cranial nerve dysfunction
– Brainstem dysfuctions
– Hematoma

Postoperative Complications
• Late
–Symptom recurrence
• Occur after initial improvement
• Due to:
– New or enlarging syrinx
– CSF obstruction due to scarring
– Cerebellar ptosis
–Pain
–Instability

Shunting of syrinx
• Indication:
– Persistent symptoms
• Non resolution of syrinx
– PCMR shows normal flow study
• Options:
– SSS
– SPS
– TPS
– Terminal ventriculostomy

Recurrent or Unresolved Chiari
Failed procedure
• Causes:
– Inadequate decompression
• Bony
• Soft tissue
– Reformation of arachnoid scars
– Lack of CSF flow normalization despite adquate
soft tissue and bony decompression
• Management
– Revision surgery
– Shunting of the syrinx

Intraoperative color doppler after FMD
– Adequacy of CSF flow
• Bidirectional flow across FM
• Waveform exhibiting dual variations
– vascular
– respiratory
• A peak velocity of 3-5 cm/sec
(Milhorat, 2003, NS)
Intraoperative adjuncts for adequate
posterior fossa decompression

• There are subcategories of patients in whom the
condition was more complex ; these patients in
whom the condition is more complex these
patients require more surgical intervention than
others.
• Grabb and colleagues in 1999 showed that
odontoid retroflexion, manifested by a pBC2
distance (maximum perpendicular distance to
basion-inferoposterior point of the C2 body)
greater than 9mm defined a patient that required
craniocervical fusion procedures.

• To identify a CCM, the initial craniospinal MRI
must be evaluated for
• Chiari 1.5 M
• Odontoid retroflexion, measured by pBC2
• CXA (abnormal clival –cervical angle)
• BI
• Assimilation of atlas
• Medullary kinking

• Illustration of SOD, odontoid reduction,
craniocervical fusion plates and rods, C2
pars screws, occipital screws.

Follow up
• Chiari I
• 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.

• 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.

• Chiari II
• 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

• Simple tenets in management:
• Patient selection
• Normal intracranial physiology before
suboccipital decompression
• Restoration of normal CSF dynamic flow from
fourth ventricle to SAS & relief of direct
brainstem compression are the goals of
surgery.

Chiari malformation

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