Chiari malformation and syringomyelia by Dr. Shikher Shrestha, FCPS, NEUROSURGERY, NINAS, Nepal
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Transcript of Chiari malformation and syringomyelia by Dr. Shikher Shrestha, FCPS, NEUROSURGERY, NINAS, Nepal
The Chiari Malformations and Syringohydromyelia
Shikher ShresthaNINAS
Introduction
1890s – Hans Chiari, pathologist described four congenital malformations
Various degrees of involvement of rhombencephalic derivatives in those 4
Three of these (types I to III) – progressively more severe herniation and common pathogenesis involving loss of free movement of CSF out of normal outlet channels of the 4th ventricle
Large majority congenital; but can be acquired as well secondary CIM
Different subtypes..
Chiari O
does not have significant hernia
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
Chiari I
caudal displacement of cerebellar tonsils > 5mm below the foramen magnum
brainstem normal in positionmay or may not have syrinx but are usually
associated with syrinx
Chiari 1.5
applied to patients who bridge the gap between CIM and CIIM
presence of characteristics of both groupsnot associated with neural tube defectscaudal displacement of cerebellar tonsilsbrainstem and 4th ventricles are also displaced
like in CIIM
Chiari II
almost always occurs in patients with neural tube defects (myelomeningocele and encephalocele)
caudal migration of cerebellar vermis, brainstem and 4th ventricle
Syringomyelia is common
Chiari III
rare 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
Chiari IV
cerebellar hypoplasia or aplasia
not a form of hindbrain hernia
its inclusion is hence debatable
Chiari I Malformation
Theory: Difficulty in rapidly equilibriating the CSF pressure wave seen during the Valsalva maneuver
Prolonged intracranial hypertension relative to intraspinal compartment downward migration of the cerebellar tonsils obstruction of normal CSF flow from 4th ventricle to cervical subarachnoid space CIM
Obstruction of Foramen of Magendie by arachnoid veils or septation might also lead to the same
Conditions artificially lowering the intraspinal pressure relative to ICP like lumboperitoneal shunt – iatrogenic/acquired
Some derailment on chromosomes 9 and 15
Previously considered adult disease/ but now more frequently reported in pediatric age group – advent of MRI
Clinical Presentation
S&S related to brainstem compression
S&S related to cerebellar compression
S&S related to spinal cord dysfunction secondary to syringomyelia
Clinical Presentations..
Non radicular occipital or cervical pain
Dysesthesias in the C2 dermatome
Neckpain and headache - exacerbated on exertion or by coughing or sneezing (valsalva induced)
Non verbal children irritability, crying, failure to thrive, opisthotonos
Diagnosis
MRI – CVJ and entire spinal cord
50-75% patients have syringomyelia
CT – bony abnormality; plain films for evaluating stability issues
Dynamic MRI (cine MRI) – for CSF flow around the CVJ
Treatment
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
Treatment
10% patients with CIM – associated hydrocephalusCSF diversionary shunt or ETV as the initial form of therapy
Symptomatic ventral compression out of proportion to dorsal compression ventral decompression (transoral odontoid resection) esp. if there is myelopathy
Most common surgical procedure: Posterior fossa decompression
Goal: enlarge posterior fossa to recreate cisterna magna, thereby permitting normal flow of CSFSyrinx decrease in size and does not require direct Rx in majority after this
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
Posterior fossa decompression..
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.
Posterior fossa decompression.. result
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
Surgical outcome
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 scoliosis likelihood of improvement
Chiari II malformation
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 sinuslarge venous lakes in the tentoriumfenestrations in falx, which is often not well formed – gyri
of left and right hemispheres interdigitate – “Chinese lettering” on axial MRI
hyrdrocephalus (90%)
Split cord malformation (6%)
Syringomyelia (20-95%)
Tectal beaking secondary to partial or complete fusion of colliculi into a single backward pointed peak
Kinking at the level of cervicomedullary junction
Cerebellum small than usual
Radiographic signs of CIIM on CT scan
Lückenschädel – 85%
Scalloping of the posterior surface of the petrous pyramid – 80%
Tentorial hypoplasia with wide incisura & small post. Fossa – 95%
Enlargement of foramen magnum (73%)
Inversion (or transtentorial upward herniation) of the cerebellum
Luckenschadel
Lacunar skull or craniolacunae
May coalesce to form larger Defect - Craniofenestra
CT images
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 sign”
Lateral ventricles asymmetrically dilated with prominence of atria and occipital horns (colpocephaly)
Septum pellucidum frequently absent
Frontal horn and anterior portion of the third ventricle – pointed and acutely angulated – “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
Pathophysiology..
Similar to CIM – difficulty in equilibrating dynamic CSF pulse pressure induced by valsalva
Leaking from myelomeningocele sac lowers intraspinal pressure
Clinical presentation..
Pertaining to brainstem, cerebellar and spinal cord dysfunction
~33% - symptoms of hindbrain herniation prior to 5 yrsWorst outcome if those symptoms before 3 months
Stridor, apnea and dysphagia resulting in aspiration might cause death
Nystagmus – earliest sign of cerebellar dysfunction
Initial spinal cord symptoms (weakness, bowel and bladder dysfunction) – secondary to inadequate formation of the lower spinal cord
Worsening spinal cord dysfunction causes:
CSF diversionary shunt malfunctionsyringomyeliaspinal cord tethering
Scoliosis might be related to syringomyelia
Diagnosis
MRI – cranial and spinal
Plain dynamic cervical spine radiographs instability
Treatment considerations..
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
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
DO NOT mistake medullary kink for vermis
Outcome: infants with brainstem symptoms are less likely to have significant improvement following decompression
Syringohydromyelia
Syringomyelia – any longitudinal fluid collection within spinal cord
Hydromyelia – fluid collection enlarging the central canal
Causes:Chiari malformationsneoplasmsAVMarachnoiditisoccult spinal dysraphismIdiopathic
Types:
Communicating. Eg. (Chiari and occult dysraphism)
Non communicating. Eg (Neoplasm, AVM, arachnoiditis, traumatic)
Terminal syrinx (lower third of spinal cord) – normally not a result of hindbrain herniation
Pathogenesis
Fluid collection begins in ependyma lined central canal
Outpouching in weak area
Grows into the white matter of cord without constraint due to absence of ependyma
Crossing fibers of spinothalamic tract in ventral white commisure vulnerable to syrinx expansion
Symptoms..
Loss of pain and temperature in arm and chest
Diminished or absent DTRs
Spasticity in lower limbs
Wasting of intrinsic muscles of hand and scoliosis
Dysesthetic pain over the thorax and arms – poor prognostic indicator
Acute loss of neurological function may occur with coughing or straining
Valsalva maneuver
expansion of epidural venous complex
symptomatic or asymptomatic
enlargement of syrinx
Diagnosis..
MRI
75% of CIM – syrinx
20-95% of CIIM - syrinx
Exophytic Syrinx
Extreme form of syringomyelia
When ruptured through pia mater and expanded
May be confused with spinal arachnoid cysts
Treatment..
Recommended procedure varies depending on the underlying cause
No medical therapy
Exploration of CVJ should be considered
Residual syrinx reexploration of posterior fossa and exploration for readhesion of the arachnoid and the outlet of fourth ventricle + subpial resection of a tonsil
Stenting or shunting distal end placed in peritoneum or pleura and not in subarachnoid space if arachnoiditis or post traumatic case
Reesetablishment of a patent spinal canal and subarachnoid space in the setting of traumatic disruption through removal of bone fragments or bony realignment
Multicompartmental syrinx – drainage at multiple sites
If syrinx from tumor or AVM treatment of primary cause
Evaluation of any tethering elements (eg. Fatty filum terminale) in terminal syringes
Thank you!!