Pediatric Neurosurgery: Brain Anatomy

Pediatric Neurosurgery: Brain Anatomy

• The tentorium separates the posterior fossa from the cerebral hemispheres.
• Supratentorial refers to the area above the tentorium.
• Infratentorial refers to the area below the tentorium and contains the cerebellum, brainstem, and posterior fossa.
• The brainstem's functions include autonomic functions, nerve fiber passage between the brain and spinal cord, maintenance of consciousness (RAS), and motor and sensory control of the head.
• The brainstem consists of the midbrain, pons, and medulla.
• The midbrain regulates eye movements.
• The pons regulates facial movements, hearing, and balance.
• The medulla regulates breathing, heart rhythms, blood pressure (BP), and swallowing.
• Cranial nerves are located in the brainstem.
• The midbrain contains cranial nerves (CN) 3 and 4.
• The pons contains CN 5, 6, 7, and 8.
• The medulla contains CN 9, 10, 11, and 12.
• The Olfactory (CN1) and Optic nerve (CN 2) are not in the brainstem.
• Brain lobes include the frontal, parietal, temporal, and occipital lobes.
• The insular lobe is hidden under the temporal, frontal, and parietal areas.

Brain Tumors

• Brain tumors are the most common solid tumors in children.
• 50% of brain tumors are supratentorial, and 50% are infratentorial.
• Common types of brain tumors include gliomas, medulloblastomas, and astrocytomas.
• Other types of brain tumors include ependymomas, acoustic neuromas, and meningiomas.
• Posterior fossa tumors can result in cranial nerve dysfunction and elevated intracranial pressure (ICP).
• Untreated tumors can lead to brain herniation and death.
• All tumors increase intracranial volume, leading to increased intracranial pressure.
• Infratentorial lesions can lead to hydrocephalus symptoms such as irritability, poor feeding, and bulging fontanelles.
• Brain stem herniation can be fatal if untreated.
• Symptoms of tumors include sunset eyes, cranial enlargement, engorged scalp veins, decreased level of consciousness (LOC), and neurologic deficits.

Head Trauma

• Concussion is a diffuse injury.
• Contusion is a focal injury.
• Epidural Hematoma is associated with the "walk and drop" phenomenon.
• Subdural Hematoma is common in "shaken baby syndrome."
• Linear skull fractures are the most common.
• Depressed skull fractures may require surgery.
• Diastatic skull fractures involve widened suture lines.
• Basilar skull fractures are the most serious, with a risk of CSF leakage and cranial nerve damage.
• Basilar skull fracture symptoms include raccoon eyes, hemotypanum, battle sign, and CSF otorrhea.

Hydrocephalus

• Hydrocephalus is the enlargement of ventricles due to a CSF imbalance.
• CSF imbalance can be caused by increased CSF production, decreased CSF absorption, or obstruction of the CSF pathway.
• Symptoms of hydrocephalus include headache, lethargy, bulging fontanelles, nausea/vomiting, and an increase in head circumference.
• Communicating hydrocephalus involves impaired CSF absorption, with no blockage within the ventricular system.
• Non-communicating hydrocephalus involves a physical obstruction of CSF flow within the ventricular system.
• Obstructive hydrocephalus is noncommunicating, involving a physical block, where ventricles do not communicate.
• Nonobstructive hydrocephalus is communicating, involving no physical block, where ventricles communicate, but CSF absorption or production is abnormal.
• The most common pediatric cause of hydrocephalus is a brain tumor.
• Congenital causes include stenosis of the aqueduct of Sylvius, neural tube defects, and Dandy-Walker syndrome.
• Acquired causes include intraventricular hemorrhage (IVH), tumors, and infections.
• The goal of treatment is to prevent further increases in intracranial contents to prevent brain herniation.
• CSF needs to be drained to relieve pressure.
• Surgical treatments include VP, VA, ventriculopleural, and ventriculojugular shunts, and ventriculostomy.

Hydrocephalus with Stenosis of Aqueduct of Sylvius

• It has a severe X-linked feature.
• It can cause prenatal hydrocephalus.
• Symptoms include intracranial hypertension, adducted thumbs, spasticity, and severe intellectual deficit.
• It has a poor prognosis.

Dandy Walker Syndrome

• It's caused by a genetic mutation that is hereditary or related to environmental exposure to toxins.
• Seizures occur in 15-30% of cases.
• Symptoms usually start around 1 year of age.
• Symptoms include irritability, increased head circumference, vomiting, and seizures.
• Treat with a cerebral shunt.
• It is associated with disorders like kidney disease and liver disease.

Intraventricular Hemorrhage

• Symptoms can include sudden or gradual neurologic deterioration, a full fontanel with a drop in hematocrit, and SIADH.

VP Shunt

• It is usually placed in the right ventricle.
• A catheter is tunneled to the peritoneal area.
• It can develop transient postop ileus.
• A major complication can be an infection of the shunt tubing, leading to meningitis.

Seizure Disorders

• Epilepsy involves sudden, recurring attacks of motor, sensory, or psychic dysfunction that can occur with or without loss of consciousness (LOC) or convulsions.
• Epilepsy can be congenital or related to birth trauma, tumors, or vascular malformations.

Types of Seizures

• Generalized tonic-clonic (grand mal) seizures involve loss of consciousness, muscle stiffening, and jerking movements.
• Chest muscles tighten, impeding the ability to breathe during tonic-clonic seizures.
• Attempting to open a tightly closed jaw during a seizure can cause more harm.
• A tonic-clonic seizure lasting > 5 minutes is a medical emergency.
• Tonic refers to stiffness.
• Clonic refers to jerking motion.
• Absence seizures involve lapses in awareness.
• Absence seizures begin and end abruptly.
• Absence seizures last a few seconds and are more common in children.
• Absence seizures can be brief, making them harder to detect.
• Atypical seizures involve variable responsiveness.
• Atypical seizures are often seen in patients with global cognitive impairment.
• Atypical seizures usually begin in children by age 6.
• Atypical seizures are related to Lennox-Gastaut syndrome.
• Atonic seizures involve a sudden loss of postural tone.
• Atonic seizures occur primarily in children.
• Myoclonic seizures involve shock-like jerking motions.
• A tonic-clonic seizure lasting >5 minutes constitutes a medical emergency.

Anesthetic Considerations for Pediatric Neurosurgery

• Assessment includes signs and symptoms of increased ICP, labs, antibiotics, the location of the defect or tumor.
• The posterior fossa receives 11/12 cranial nerves, excluding CN 1.
• Limited patient access due to small size is a challenge.
• Limited space for lines due to small size is a challenge.
• Surgical positioning aims to optimize surgical exposure, minimize pressure on neural structures, and maintain cerebral blood flow (CBF).
• The risk of venous air embolism (VAE) is increased in certain procedures.
• Awake neurosurgical procedures are usually performed in older children due to compliance issues with younger children.

Induction Considerations

• Premedication might be needed.
• Inhalation induction may be used.
• IV access is needed.
• Induction with increased ICP involves hyperventilation and quick intubation because of increased ICP resulting from laryngoscopy.

Maintenance Considerations

• Nitrous oxide (N2O) increases CBF, with air trapping effects.
• Volatiles increase CBF.
• Opioids can be used.
• Muscle relaxants can be used.

Emergence Considerations

• Deep or awake extubation is possible.
• Elevating the head of the bed (HOB) and maintaining a midline position can decrease ICP (increasing venous drainage).
• Continued intubation versus extubation must be decided.
• Remove head tongs while the patient is deep to prevent coughing and bucking, which can tear the head tongs.

Neural Tube Defects

• Myelodysplasia refers to neural tube defects.
• Spina bifida refers to spinal cord anomalies.
• Meningocele is the herniation of meninges.
• Myelomeningocele is the herniation of neural elements.
• Skin abnormalities can overly the spinal defect.
• Encephalocele is a congenital defect in the skull that usually results in a protrusion of brain tissue.
• Exencephaly is a lethal congenital fetal brain development anomaly characterized by calvarial absence and loss of fetal brain tissue to variable degrees.
• Anencephaly is a congenital absence of most of the brain and spinal cord, resulting from a defect in the anterior closure of the neural groove.
• Anencephaly is fatal and not compatible with life.
• Rachischisis is a congenital defect caused by the failure of the posterior neuropore to close, resulting in an exposed spinal cord.
• Rachischisis can cause severe paralysis and sensory loss below the lesion.
• Rachischisis results in severe disability.
• Arnold Chiari Malformation is a group of congenital malformations involving the brainstem, cerebellum, upper spinal cord, and surrounding bony structures.
• Type 1 Arnold Chiari Malformation is less severe and not associated with a meningomyelocele.
• Type 2 Arnold Chiari Malformation is the most common.
• Type 2 Arnold Chiari Malformation involves compression of the medulla and cerebellar tonsils in the upper cervical spinal canal.
• Type 2 Arnold Chiari Malformation is associated with meningomyelocele.
• Type 3 Arnold Chiari Malformation has features of type 2 and herniation of the cerebellum through the foramen magnum.
• Type 4 Arnold Chiari Malformation is a form of cerebellar hypoplasia.
• Manifestations of type 1-3 Arnold Chiari Malformation include torticollis, vertigo, nystagmus, swallowing difficulties, cerebellar ataxia, urinary frequency, pins and needles, vomiting, and recurrent headache.
• Progressive lower limb spasticity can result.
• Swelling of the optic disk
• Posterior column nerve palsy
• MRI findings can show a narrow foramen magnum, protruding cerebellar tonsils, and increased spinal fluid proteins.

Anesthetic Considerations for Neural Tube Defect Surgeries

• Surgery is normally done in the sitting or prone position.
• There is a risk of VAE with large venous sinuses opening.
• Prevention of VAE includes maintaining fluid status, avoiding negative (sucking) pressure.
• Surgery can be done within the first week of life or in utero.
• The posterior fossa receives 11/12 cranial nerves with the exclusion of CN 1.
• Associated airway problems with Arnold Chiari malformation, encephalocele, and thoracic myelomeningocele.