Involves downward displacement of the cerebellar tonsils into the foramen magnum.
Typically diagnosed in adults.
Often associated with syringomyelia of the cervical spinal cord.
Downward displacement of the medulla is usually absent.
Clinical Presentation:
Occipital headache:
Worsens with the Valsalva maneuver.
Signs of foramen magnum compression:
Cranial nerve dysfunction.
Cerebellar syndrome (coordination issues).
Intracranial hypertension:
May present with papilledema.
Diagnosis:
MRI:
Sagittal MRI gives an accurate assessment of tonsillar descent.
CT: Also used for evaluation.
Treatment:
Surgical decompression:
Bony decompression of the occiput and removal of the posterior arch of C1 (and sometimes C2).
The dura is opened, and a dural patch graft is placed to create more space for the neural elements.
Chiari II Malformation
Description:
Associated with myelomeningocele.
Caudal displacement of the medulla, cervicomedullary junction, and fourth ventricle.
Brain Stimulation
Overview
Electrical stimulation is used in the treatment of:
Movement disorders.
Chronic pain.
Epilepsy.
Involves the placement of an electrode, connected to a subcutaneously placed generator.
Movement Disorders
Parkinson's Disease (PD)
Most common movement disorder treated with surgery.
Stereotactic techniques (developed in the 1950s):
Initially used to create lesions in the pallidum and thalamus.
These ablative procedures declined with the introduction of l-dopa but saw resurgence in the 1990s when patients became unresponsive or intolerant to pharmacologic agents.
Deep Brain Stimulation (DBS)
Replaced ablative procedures due to its ability to induce reversible inhibition of neuronal activity.
Adjustable stimulation according to clinical needs.
Target areas:
Subthalamic nucleus:
Preferred target for treating rigidity and akinesia.
Ventralis intermedius nucleus of the thalamus:
Best for addressing tremor.
Chronic Pain States
Spinal Cord Stimulation (SCS)
Used to treat chronic pain, dystonia, and bladder dysfunction.
Trial phase:
Percutaneous wire electrodes attached to an external generator.
If successful, permanent wire or paddle electrodes are implanted and connected to a programmable generator.
Mechanism of action: Unknown, but commonly used for:
Postlaminectomy syndrome (especially when leg pain > back pain).
Chronic regional pain syndrome.
Not routinely effective for cancer pain.
Epilepsy and Depression
Vagus Nerve Stimulation (VNS)
Approved by the FDA for treating intractable seizures and severe depression.
Mechanism of action: Thought to involve afferent stimulation of higher cortical centers:
Hypothalamus.
Amygdala.
Insular cortex.
Cerebral cortex (through the nucleus of the solitary tract).
Effectiveness:
Decreases seizure frequency but rarely leads to being seizure-free.
