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Chiari malformation


Introduction

Chiari malformations represent a class of posterior fossa disorders that stem from congenital abnormalities. The Chiari I malformation is the most common type, characterized by tonsillar descent that may or may not be associated with syringomyelia. The overall prevalence of the condition in the general population is estimated to be 1%. The chief complaint from patients with symptomatic Chiari I malformation is pain/headaches, with symptom onset during Valsalva maneuvers such as coughing. Those cases associated with syrinx formation may also present with myelopathy. Around 70% to 80% of patients with Chiari I malformation develop a syrinx and 41% develop arachnoid adhesions. Surgical management is indicated in symptomatic patients and in those with progressive syringomyelia. Resolution of the syrinx may occur after surgical decompression of the foramen magnum. In cases of surgical intervention that fail, revision decompression and lysis of adhesions may be warranted. Not uncommonly, there is an arachnoid veil present at the obex, which may prevent cerebrospinal fluid (CSF) outflow from the fourth ventricle and lead to recurrent symptoms. In this chapter, we present a case of a young patient with worsening headaches with coughing and straining.

Example case

  • Chief complaint : headaches

  • History of present illness : This is a 44-year-old female with no significant past medical history who presents with worsening headaches over the past 6 months. She states that her headaches have worsened over the past half-year and that they worsened with coughing and straining as well as with neck extension. She also complains of decreased coordination in her nondominant left hand. The patient underwent magnetic resonance imaging of the cranio-cervical junction that demonstrated significant caudal cerebellar tonsillar displacement compatible with Chiari malformation ( Fig. 67.1 ).

    Fig. 67.1, Preoperative magnetic resonance image (MRI) of the cervical spine. (A) Sagittal and (B) axial T2 images demonstrating signficant cerebellar tonsil ectopia. There is caudal displacement of the tonsils into the upper cervical canal (10 mm) through the foramen magnum. There is significant compression of the cervico-medullary junction with an associated syrinx spanning from C3 to C7.

  • Medications : none

  • Allergies : no known drug allergies

  • Past medical and surgical history : C-section

  • Family history : noncontributory

  • Social history : accountant, no smoking or alcohol

  • Physical examination : awake, alert, and oriented to person, place, and time; cranial nerves II–XII intact; bilateral deltoids/triceps/biceps 5/5; interossei 5/5; iliopsoas/knee flexion/knee extension/dorsi, and plantar flexion 5/5

  • Reflexes : 2+ in bilateral biceps/triceps/brachioradialis with negative Hoffman; 2+ in bilateral patella/ankle; no clonus or Babinski; sensation intact to light touch

  • Andres Almendral, MD

  • Neurosurgery

  • Clinica Hospital San Fernando

  • Panama City, Panama

  • Gordon Deen, MD

  • Neurosurgery

  • Mayo Clinic

  • Jacksonville, Florida, United States

  • Jorge Eduardo Guzman Prenk, MD

  • Neurosurgery

  • Pontifica Universidad Javeriana

  • Bogota, Colombia

  • Daniel J. Hoh, MD

  • Neurosurgery

  • University of Florida

  • Gainesville, Florida, United States

Preoperative
Additional tests requested

  • CTA

  • Upper limb MEP/SSEP/EMG

None Upper limb MEP/SSEP/EMG None
Surgical approach selected Suboccipital craniectomy, C1 laminectomy, duraplasty and C4-5 laminectomy with C4-6 fusion Suboccipital craniectomy, C1 laminectomy, duraplasty Suboccipital craniectomy, C1 laminectomy, duraplasty Occipital craniectomy and C1 laminectomy
Goal of surgery Decompress cervicomedullary junction and cervical space Decompress cervicomedullary junction Decompress cervicomedullary junction, tonsillar decompression, syrinx resolution Decompress pontomedullary junction, reestablish CSF flow
Perioperative
Positioning Prone, with pins Prone, with pins Prone, Concorde, no pins Prone, with pins
Surgical equipment

  • IOM (MEP/SSEP)

  • Fluoroscopy

  • Surgical microscope

  • IOM

  • Fluoroscopy

  • Surgical microscope

  • Tubular retractor

Surgical microscope
Medications None Maintain MAP >90 None Ketorolac 48 hours after surgery
Anatomical considerations Midline posterior cervical nuchal ligament, vertebral artery, PICA, cerebellar tonsils, arachnoid membrane Spinal cord, vertebral arteries, cerebellar tonsils C2 spinous process, lateral venous plexus, atlanto-occipital membrane Cerebellar tonsils
Complications feared with approach chosen CSF leak Spinal cord injury, vertebral artery injury Spinal instability, chronic pain CSF leak, hydrocephalus
Intraoperative
Anesthesia General General General General
Exposure Occiput-C6 Occiput-C1 Occiput-C2 Occiput-C1
Levels decompressed Occiput-C1 and C4-5 Occiput-C1 Occiput-C1 Occiput-C1
Levels fused C4-6 None None None
Surgical narrative Position prone with Mayfield pins, neck slightly flexed, midline skin incision from above inion to C7 spinous process, triangular pericranial graft is obtained from the occipital area measuring 4–5 cm in length and width, open fascia in Y-shaped incision at nuchal ligament by freeing skin margins from deep fascia, suboccipital craniectomy 3–4 cm from foramen magnum, remove enough bone to completely decompress entire posterior surface of cerebellar tonsils and 2.5–3.0 cm from side to side, remove posterior arch of C1 after separating muscles attached to it, keep muscles attached to C2 and C7, open dura in midline at C1 with care to avoid injuring arachnoid membrane and extend superiorly in Y-shaped fashion above foramen magnum, retract dura, suture pericranial autograft to durotomy margins after sizing by using a cottonoid as a guide, separate muscles from C4-6 spinous process, C4-5 laminectomy, place C4-6 lateral mass screws with fluoroscopic guidance, confirm absence of CSF leak with Valsalva maneuver, layered closure Position prone with Mayfield pins, head and neck neutral with head slightly up, incision from inion to C4, suboccipital decompression followed by C1 decompression, microscope brought in, open dura with Y-shaped opening, free adhesions, explore floor of fourth ventricle, harvest fascia lata, duraplasty with fascia lata, close wound in layers, bedrest night of surgery Position prone in Concorde position without pins, identify midpoint between foramen magnum and C2 spinous process under fluoroscopy, 2.5 cm median skin incision at midpoint, place tubular dilators using Seldinger’s technique, remove rectus capitis posterior major and minor muscles using monopolar cautery, expose occipital midline/posterior rim of foramen magnum/C1/C2 spinous process, dock 22 mm tube on C2 spinous process and occipital midline within 1 cm of foramen magnum, decompress 1 cm of foramen magnum, angle tube upward to complete 2 cm wide plus 1 additional cm of occipital bone, remove posterior arch of C1 with drill, widen channel with high-speed drill, completely resect posterior atlanto-occipital membrane, median dural opening with preservation of arachnoid membrane, duraplasty with synthetic patch, remove tube, layered closure Position prone with Mayfield pins, vertical midline incision, expose occiput to C2, occipital craniectomy and C1 laminectomy, midline vertical opening of dura, microscope-assisted lysis of arachnoid, elevate tonsils to confirm outflow of CSF from fourth ventricle, close dura in water tight fashion with fibrin glue, close muscle and skin in layers, approximate skin with horizontal mattress sutures
Complication avoidance Pericranium for duraplasty, maintain muscles attachments to C2 and C7, preserve arachnoid during dural opening, cervical laminectomy and fusion over cyst Explore floor of fourth ventricle, fascia lata for duraplasty Minimally invasive tubular retractor, leave muscles attached to C2 spinous process, resect posterior atlanto-occipital membrane, preserve arachnoid membrane Elevate tonsils to assess fourth ventricular CSF flow, fibrin glue
Postoperative
Admission ICU ICU ICU Floor
Postoperative complications feared CSF leak, vertebral and PICA injury, infection, medullary lesions Hematoma, spinal cord/brainstem compression, infection CSF leak, hematoma, infection CSF leak, delayed hydrocephalus
Anticipated length of stay 2 days 2 days 2–4 days
Follow-up testing MRI C-spine 6 months after surgery MRI C-spine 3 months after surgery MRI C-spine 4 months, 1 year after surgery

  • Head CT if needed

  • MRI cervical spine 6 weeks after surgery if no improvement

Bracing None None None None
Follow-up visits 1 month, 3 months, 6 months, 1 year after surgery 4 weeks after surgery 2 weeks, 4 months, 1 year after surgery 3 weeks, 6 weeks surgery
CSF , cerebrospinal fluid; CT , computed tomography; CTA , computed tomography angiography; EMG , electromyography; ICU , intensive care unit; IOM , intraoperative monitoring; MAP , mean arterial pressure; MEP , motor evoked potentials; MRI , magnetic resonance imaging; PICA , posterior inferior cerebellar artery; SSEP , somatosensory evoked potential.

Differential diagnosis

  • ▪

    Chiari malformation

  • ▪

    Cranio-cervical junction tumor

  • ▪

    Basilar invagination

  • ▪

    Intracranial mass lesion causing displacement

  • ▪

    Dandy-Walker malformation

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