Chiari Malformations.pptx

chiari or arnold chiari malformations, various types and pathophysiology, radiological and clinical presentation of the types, signs symptoms, investigations and treatment of these malformations both conservative and surgical. considerations and controversiies in management of chiari malformation associated with various conditions.

1. Chiari Malformtions Presented By: Dr. Rahul Jain SR-2 Neurosurgery Moderated by: Dr V. C. Jha Dr Nitish Kumar Dr Gaurav Verma

2. Introduction Collection of hindbrain abnormalities ranging from simple herniation of the cerebellar tonsils through the foramen magnum to complete agenesis of the cerebellum . Focus of treatment for symptomatic patients with Chiari malformations mainly consists of restoring normal cerebrospinal fluid (CSF) dynamics across the craniocervical junction. Wide variability in the clinical presentation, imaging findings, and technical aspects of decompression for each type of Chiari malformation .

3. HISTORY Observationes Medicae , by the Dutch physician and anatomist Nicholas Tulp (1593–1674), reference to hindbrain herniation in a myelodysplastic individual. In 1883 , John Cleland of Scotland reported a single myelodysplastic patient with hindbrain herniation and hydrocephalus Early 1890s , Dr. Hans Chiari , professor of pathologic anatomy at the German University in Prague, used autopsy specimens to describe four congenital anomalies later termed the Chiari malformations (types I–IV ). Julius Arnold (1835–1915), professor of anatomy at Heidelberg, described a single myelodysplastic patient with hindbrain herniation and no hydrocephalus.

4. The term “ Chiari malformation ” is preferred for type 1 malformations (due to the more significant contribution of pathologist, Hans Chiari ). Although the term Arnold-Chiari malformation has been used specifically in reference to hindbrain herniation in myelodysplastic patients, it was Chiari who described and attempted to delineate the pathophysiology of these posterior fossa abnormalities. Therefore it is most appropriate to refer to this abnormality as the Chiari II malformation (CIIM) .

5. Pathophysiology Theories Grouped into the hindbrain dysgenesis and developmental arrest theory ; the caudal traction theory; the hydrocephalus and hydrodynamic theory of Gardner ; the small posterior fossa/hindbrain overgrowth theory ; and the lack of embryologic ventricular distention theory. Nishikawa and colleagues suggested that the underdevelopment of occipital somites within the paraxial mesoderm creates a small posterior fossa and CIM . The association of craniosynostosis and CIM appears strongest in cases of syndromic, multisuture , and lambdoid synostosis. Lambdoid suture closure , typical in Crouzon syndrome, can directly reduce posterior fossa volume.

6. Development of a craniospinal pressure gradient across the foramen magnum may cause or hasten the development of CIM. The gradient results from impaired CSF flow across the foramen magnum. Negative CSF pressure in the spinal compartment relative to the intracranial compartment creates a “ sump effect ” that forces the tonsils down through the foramen magnum. Once CSF flow is blocked at the foramen magnum, low intraspinal pressures can be accentuated and perpetuated by continuous absorption of CSF through spinal pathways, further worsening the clinical situation.

7. Chiari II Malformation may occur because the cerebellar vermis develops before the tonsils, anabnormal pressure differential that develops in utero would cause abnormal displacement of the vermis and brainstem structures , without any tonsillar involvement. Such a pressure differential could occur with fluid leakage from the myelomeningocele. McLone and Knepper gave “ unified theory ” based on the aforementioned assumption that the neural tube defect occurs first, and all the other manifestations, including the Chiari malformation and hydrocephalus , follow secondarily.

8. Leakage of CSF through the spinal defect causes a lack of distention of the primitive cranial ventricular system. In experimental animals, venting fluid from the embryonic ventricular system can cause, for example, disorganization of the developing cerebral cortex and abnormal development of the pontine flexure .

9. Type 1 Chiari malformation AKA primary cerebellar ectopia , AKA adult Chiari malformation since it tends to be diagnosed in the 2nd or 3rd decade of life. Pathophysiology - disruption of normal CSF flow through the foramen magnum. 5-mm or greater Caudal displacement of cerebellum with tonsillar herniation below the foramen magnum and “peg-like elongation of tonsils.”

10. Prevalence ( radiographically): ≈ 0.5 % . Average age 41 years (12-73 yrs ), slight female preponderance ( female:male = 1.3:1 ). Patients may present due to compression of brainstem at the level of the foramen magnum or hydrocephalus or syringomyelia ; 15-30% are asymptomatic . The most common presenting symptom is pain (60%–70 %) especially headache, usually occipital and upper cervical in location, and often induced by Valsalva maneuvers such as laughing, sneezing , and coughing ( tussive headache ).

11. Signs of CIM Downbeat nystagmus considered characteristic. 10% will have a normal neurologic exam with occipital H/A as their only complaint. Some patients may present primarily with spasticity . Three main patterns of clustering of signs

12. Evaluation MRI of brain and C-spine are the diagnostic tests of choice. Cine MRI may demonstrate blockage of CSF flow at FM. Unenhanced CT is poor for evaluating the neural structures, but very good for HCP.

13. Management of CIM

14. Patients with Chiari malformation and hydrocephalus – Treatment of the hydrocephalus with CSF shunting may also resolve the tonsillar descent and syringomyelia . Indications for surgical decompression Since patients respond best when operated on within 2 years of the onset of symptoms (see below ), early surgery is recommended for symptomatic patients .

15. Operative results Pain generally respond well to surgery. Weakness is less responsive to surgery, especially when muscle atrophy is present. Sensation may improve when the posterior columns are unaffected and the deficit is due to spinothalamic involvement alone. Factors that correlate with a worse outcome are the presence of atrophy, ataxia , scoliosis, and symptoms lasting longer than 2 years. Most favorable results occur in patients with cerebellar syndrome.

16. Type 2 (Arnold)–Chiari malformation CIIM occurs in most (>95%) patients with myelomeningocele and is the leading cause of death in treated myelodysplastic patients today. Almost always associated with myelomeningocele, often accompanied by hydrocephalus. Pathophysiology - More likely due to primary dysgenesis of the brainstem with multiple other developmental anomalies . Findings of Caudally dislocated cervicomedullary junction, pons, 4th ventricle and medulla. Cerebellar tonsils located at or below the foramen magnum .

17. Associated neurological anomalies include tectal beaking - secondary to partial or complete fusion of the colliculi into a single backward pointed peak kinking at the level of the cervicomedullary junction caused by the caudal displacement of a portion of the medulla in conjunction with a spinal cord that is held in relative immobility by the denticulate ligaments

18. Other conditions related with CIIM are poorly myelinated cerebellar folia, hydrocephalus: present in most, heterotopias, hypoplasia of falx , microgyria , degeneration of lower cranial nerve nuclei. absence of the septum pellucidum , thought to be due to necrosis with resorption secondary to hydrocephalus Bony abnormalities associated with CIIM are of cervicomedullary junction, assimilation of atlas, platybasia , basilar impression, Klippel – Feil deformity, craniolacunia of the skull.

19. Presentation About one-third of these patients develop brainstem symptoms by age of 5 years. 20% may present as a neurological emergency - dysfunction of the 9 th and 10 th cranial nerves, affecting respiration, swallowing, and vocal cord functions; this is often accompanied by stridor, opisthotonos , and nystagmus . Symptomatic deterioration with progressive brainstem dysfunction may be irreversible and lead to death . This potentially catastrophic syndrome occurs most frequently in infants younger than 2 years, particularly younger than 3 months .

20. Findings include: swallowing difficulties (neurogenic dysphagia) (69 %) apneic spells (58 %) stridor (56 %) aspiration (40%) armweakness (27%) that may progress to quadriparesis Diagnostic evaluation Skull films - Craniolacunia (AKA Lückenschädel ) in 85% (round defects in the skull with sharp borders, separated by irregularly branching bands of bone; not due to increased ICP. Cranial and cervical MRI is the diagnostic test of choice More common in neonates

21. Management of CIIM

22. Expeditious brainstem decompression should be carried out when any of the following critical warning signs develop: neurogenic dysphagia, stridor, apneic spells. Pre-op status and the rapidity of neurologic deterioration a re the most important prognosticators . 68% had complete or near-complete resolution of symptoms, 20% had no improvement (in general, neonates fared worse than older children) Mortality rate is 71% in infants having cardiopulmonary arrest, vocal cord paralysis or arm weakness within 2 weeks of presentation.

23. Before surgical decompression is considered, patients with symptomatic CIIM must have physiologic intracranial pressure . Properly functioning ventricular shunt can often obviate the need for decompression of hindbrain herniation. Tomita and McLone # concluded that shunt revision can reverse acute respiratory arrest . In contrast, lower cranial nerve findings may not improve after the shunt revision but rather only after posterior fossa decompression . # Tomita T, Mclone DG. Acute respiratory arrest: a Complication of malformation of the shunt in children with myelomeningocele and arnold-chiari malformation. Am J Dis Child . 1983. https://doi.org/10.1001/archpedi.1983.02140280040011

24. The Chiari II anomaly is a challenging surgical entity with unusual and highly variable anatomy . Cerebellar tissue usually extends into the lower cervical spine; it may be very adherent to the medulla, and occasionally the two tissues may even seem indistinguishable or fused. The confluence of sinuses can be as low as the rim of the foramen magnum, and the dura may contain large venous sinuses. Helpful preoperative diagnostic studies include BAEPs, swallow study , direct vocal cord visualization by an otolaryngologist, and assessment of pulmonary function including obstructive and central apnea (sleep study), as well as hypercapnic ventilatory drive by a pulmonary specialist . Once adequate shunt function is ensured and when the symptoms are progressive – surgical decompression

25. Chiari III Malformation Rarest and most severe form of the Chiari malformations; even the existence are controversial Herniation of cerebellum and brainstem into a posterior occipital or high cervical encephalocele with other intracranial anomalies that are seen in CIIM. Given the severity of hindbrain herniation, its management is often problematic from both a technical and an ethical perspective; poor prognosis and usually incompatible with life.

26. Chiari IV Malformation Cerebellar hypoplasia or aplasis without cerebellar herniation. Associated with a small posterior fossa. Existence as a distinct clinical entity is debated. Although this was included in Chiari’s classification of rhombencephalic malformations, it is more appropriate to include this in the category of posterior fossa cysts

27. Chiari type 0 Syringohydromyelia without hindbrain herniation. “ Chiari-like” pathophysiology may be present in the absence of tonsillar herniation, which may be intermittent . Crowded foramen magnum, multiple arachnoid adhesions, fourth ventricular arachnoid veil. Abnormal CSF flow at the posterior fossa or foramen magnum Responds to posterior fossa decompression

28. Chiari type 0.5 Cerebellar tonsils descend less than 5 mm below the foramen magnum, but exhibit ventral herniation defined as unilateral or bilateral crossing of the cerebellar tonsils anterior to the horizontal anatomic line bisecting the caudal medulla at the level of the foramen magnum. Symptoms include: dysphagia & sleep apnea in very young children, and exertion induced H/A and paresthesias in older children. Other possible symptoms: ataxia, behavioral changes.

29. Chiari 1.5 Malformation Severe form of Chiari 1. Entire cervicomedullary junction (and obex ) is situated below the foramen magnum. Platybasia Clinical manifestations and response to suboccipital decompression are similar to Chiari I with the exception that syringomyelia persisted in almost twice as many Chiari 1.5 cases (13.6%) as Chiari I (6.9%).

30. Chiari malformation and pregnancy Issues during pregnancy increased ICP during vaginal labor & delivery elevates the risk of acute tonsillar herniation spinal fluid leak with spinal anesthesia or inadvertent entry into subarachnoid space during attempted epidural anesthesia may precipitate tonsillar herniation. Recommendations ( proposed guidelines ) 1 . before pregnancy in a patient with known CIM MRI of brain and cervical spine to assess degree of obstruction lumbar MRI to evaluate for occult spinal dysraphism If symptomatic other than headache or has HCP - operate

31. 2. patients with CIM considering pregnancy or already pregnant MDT team - fetal medicine, anesthesia , and neurosurgery management at a specialized center since there’s increased risk of medical and obstetrical complications including ARDS, stroke , seizures, sepsis, pre-eclampsia and eclampsia. 3. pregnant patients with CIM who are asymptomatic or only have H/A epidural or spinal anesthesia are low risk and should be made available

32. 4 . pregnant CIM patients with more symptoms for vaginal delivery, minimizing Valsalva maneuvers C-section under regional anesthesia or general anesthesia 5. pregnant CIM patients with unshunted hydrocephalus or findings of increased ICP considered high-risk for vaginal delivery and neuraxial anesthesia . C-section under general anesthesia should be considered suboccipital decompression may be considered if the fetus has not reached viability

33. Surgical technique for suboccipital decompression most frequently performed operation is posterior fossa decompression of the cerebellar tonsilsusing a suboccipital craniectomy . usually combined with dural patch grafting and cervical laminectomy, which must be carried down to the bottom of the tonsillar tip, which usually includes C1, and sometimes C2 or C3. Options for grafts: same incision (pericranium), separate incision (e.g., fascia lata), and allograft.

34. Tonsillar herniation is present in all cases (by definition), the most common position being at C1 (62 %). Fibrous adhesions between dura, arachnoid and tonsils with occlusion of foramina of Luschka and Magendie in 41%. The tonsils separated easily in 40%.

35. Posterior rim of the foramen magnum (FM) is the inferior part of the occipital bone. FM is enlarged no higher than ≈ 3cm above the FM and approximately as wide as the FM (also ≈ 3 cm ). Compression is at the foramen magnum, not in the p-fossa, so keep the posterior-fossa exposure small; the emphasis is to decompress the tonsils by opening the FM and the upper cervical spine as far inferiorly as the tonsils extend . Thick constricting dural band is usually found between the C1 arch and foramen magnum and may be lysed separately.

36. Shrinking the tonsils with bipolar cautery. dividing adhesions to separate the tonsils from each other as well as from the underlying medulla . Excessive removal of occipital bone – cerebellar hemispheres to herniate through the FM (“ cerebellar ptosis ” AKA “cerebellar sag).

37. Controversies in management Need for Dural Opening opening of the dural covering of the foramen magnum is thought to be necessary. increased interest in bony decompression alone The surgeon needs to consider the higher reoperation rates with bone-only decompression and share this information with patients.

38. 2. Arachnoid Opening Confirming the adequate flow of CSF through the obex without any veil obstructing the site . Some surgeons feel keeping the arachnoid intact is important to minimize scarring. 3. Dural Closure autograft material (periosteum, and ligamentum nuchae ) and allograft material (cadaveric, animal, or artificial tonsil coagulation or resection ). no consensus on type of dural closure or even lack of closure. Opponents argue that scarring is induced by such maneuvers and can lead to redo operations

39. 4. Open Versus Endoscopic Approaches benefits of this technique over open surgery remain to be elucidated . Some surgeons raise concerns about added surgical time, limited bony removal, and reliance on tonsillar shrinkage to gain adequate decompression, with increased surgical times and potential for postoperative scarring. 5. Extent of Bony Decompression Most surgeons limit the bony exposure to about 2 cm to prevent cerebellar sag. Titanium mesh with or without duraplasty is typically used to address subsequent cerebellar ectopia .

40. 6. Chiari Decompression in Ehlers-Danlos Syndrome CIM has been reported as a comorbidity with Ehlers- Danlos syndrome (EDS ), may be complicated by craniocervical instability or basilar invagination. The term instability is certainly a misnomer, because the increased range of motion with ligamentous laxity is not clinically the same as instability secondary to trauma or rheumatoid disease . some reports showing improvement in symptoms after craniocervical fixation does not provide adequate or sufficient scientific data to recommend this as a first-line treatment. Even after more than a decade of treating this condition, we are still unable to decide which patients will improve with which surgical intervention.

41. 7. Tethered Cord Release tethered spinal cord with CM or syringomyelia – Incidence ranges from 2.2% to 6 %. subgroup of Chiari patients with atypical presentations and thickened filum may benefit from detethering . 8. Scoliosis 25% to 50 % of CIM patients. role for cilia-driven CSF flow in spine morphogenesis, with irregularities in CSF flow being a potential driver for the development of scoliosis.

42. asymmetric anterior horn cell dysfunction caused by syringomyelia results in unbalanced innervation of the paraspinal musculature , predisposing the patient to scoliosis. Presence of a syrinx is responsible for the increased risk of scoliosis in patients with Chiari 1 malformations. In patients with Chiari-related scoliosis , a decompression may lead to stabilization or even improvement of the scoliosis. Nu ber of small case series reported variable rates of improvement ranging from 0% to 73%, with similarly variable rates of progression ranging from 18% to 72% following decompression.

43. In practice , a Chiari decompression first-line treatment for Chiari-related scoliosis in younger patients (i.e., those <10 years of age) and/or patients with smaller Cobb angles (20 to 50 degree). progressive scoliosis – treatment of spinal curvature. Less than 20 degree – observation with 6 mnth standing xrays for skeletal immature patients. Between 20 to 40 degree – spinal bracing Cobb angle > 50 degree – deformity correction with fusion Chiari 1 patients with syringomyelia who undergo scoliosis surgery, lengthening of the spinal column carries a risk of neurological deficit, and a Chiari decompression is often recommended first in an effort to reduce the size of the syrinx.

44. 9. Occipitocervical Fusion subset of Chiari patients have a variety of radiological findings other than tonsillar herniation, including brainstem herniation through the foramen magnum; medullary kinking, retroflexion of the odontoid, an abnormal clival -cervical angle (CXA ), assimilation of the atlas, and/or basilar invagination - complex Chiari malformations key radiological features the degree of odontoid retroflexion – pBC2 distance > 9 mm the CXA < 125 degree

45. Combination of odontoid retroflexion (pBC2 distance >9 mm) and a CXA less than 125 degrees is highly predictive of progressive craniocervical kyphosis and the need for occipitocervical fusion, particularly following disruption of the posterior tension band during a standard Chiari decompression.

46. CXA , Clival -cervical angle pBC2 line McRae’s line

47. 10. Syringomyelia occurs in approximately 50% to 75% of patients with Chiari 1 malformations. How? obstruction of CSF flow across the cervicomedullary junction results in a downward, piston-like movement of the cerebellar tonsils during the systolic phase of the cardiac cycle, which in turn produces a pressure wave that forces fluid into the spinal cord. Posterior fossa decompression with duroplasty successfully improves the symptoms of a syrinx in over two thirds of patients, with an initial success rate of 80% in their own series.

48. Clinical and radiological improvement is expected within 6 months of surgery. Some surgeons prefer to place syringo -subarachnoid and syringo -pleural shunts into the syrinx in addition to performing a decompression in patients with suboccipital headaches and an 8 mm syrinx.

49. Conclusion Chiari presented his series of hindbrain herniations more than 100 years ago. Today , we understand the Chiari malformations to involve an abnormality at the craniocervical junction resulting in impaired neural function and CSF hydrodynamics. However, the pathophysiology of each malformation is likely very different, and the management is tailored to each individual but simple tenets in the management of these patients : (1) patient selection; 2 ) assurance of normal intracranial physiology; 3) restoration of normal CSF dynamic flow from the fourth ventricle to the subarachnoid space and relief of direct brainstem compression are the goals of surgery.

50. References Greenberg 10 th ed Youman and winn 8 th ed Schmidek and Sweets 7 th ed Internet