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!!