CIRCLE OF WILLIS
Vertebral arteries – come together to form a single basilar artery, which branches into 2 posterior cerebral arteries
Posterior communicating arteries – connect middle cerebral arteries to posterior cerebral arteries
Anterior cerebral arteries – branches off middle cerebral arteries and are connected to each other through the 1 anterior communicating artery
NERVE INJURY
Neurapraxia – no axonal injury (temporary loss of function, foot falls asleep)
Axonotmesis – disruption of axon with preservation of axon sheath, will improve
Neurotmesis – disruption of axon and axon sheath (whole nerve is disrupted), may need surgery for recovery
Regeneration of nerves occurs at a rate of 1 mm/day
Nodes of Ranvier – bare sections; allow salutatory conduction
ANTIDIURETIC HORMONE (ADH)
Release controlled by supraoptic nucleus of hypothalamus, which descends into the posterior pituitary gland
Released in response to high plasma osmolarity; ADH increases water absorption in collecting ducts
Diabetes insipidus (↓ ADH) – ↑ urine output, ↓ urine specific gravity, ↑ serum Na, and ↑ serum osmolarity
• Can occur with ETOH, head injury
• Tx: DDAVP, free water
SIADH (↑ ADH) – ↓ urine output, concentrated urine, ↓ serum Na, and ↓ serum osmolarity
• Can occur with head injury
• Tx: fluid restriction, then diuresis
HEMORRHAGE
Arteriovenous malformations – 50% present with hemorrhage; are congenital
• Usually in patients < 30; sudden headache and loss of consciousness
• Tx: resection if symptomatic
• Can coil embolize these prior to resection
Cerebral aneurysms – usually occur in patients > 40; most are congenital
• Can present with bleeding, mass effect, seizures, or infarcts
• Occur at branch points in artery, most off middle cerebral artery
• Tx: often place coils before clipping and resecting aneurysm
Subdural hematoma – caused by torn bridging veins
• Has crescent shape on head CT and conforms to brain
• Higher mortality than epidural hematoma
• Tx: operate for significant neurologic degeneration or mass effect (shift > 1 cm)
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Epidural hematoma – caused by injury to middle meningeal artery
• Has lens shape on head CT and pushes brain away
• Patients classically lose consciousness, have a lucid interval, and then lose consciousness again
• Tx: operate for significant neurologic degeneration or mass effect (shift > 0.5 cm)
Subarachnoid hemorrhage (nontraumatic)
• Caused by cerebral aneurysms (50% middle cerebral artery) and AVMs
• Symptoms: stiff neck (nuchal rigidity), severe headache, photophobia, neurologic defects
• Tx: goal is to isolate the aneurysm from systemic circulation (clipping vascular supply), maximize cerebral perfusion to overcome vasospasm, and prevent rebleeding; use hypervolemia and calcium channel blockers to overcome vasospasm
• Go to OR only if neurologically intact
• Can get subarachnoid hemorrhages with trauma as well
Intracerebral hematomas – temporal lobe most often affected
• Those that are large and cause focal deficits should be drained
Symptoms of ↑ ICP – stupor, headache, nausea and vomiting, stiff neck
Signs of ↑ ICP – hypertension, HR lability, slow respirations
• Intermittent bradycardia is a sign of severely elevated ICP and impending herniation
• Cushing’s triad – hypertension, bradycardia, slow respiratory rate
SPINAL CORD INJURY
Cord injury with deficit → give high-dose steroids (↓ swelling)
Complete cord transection – areflexia, flaccidity, anesthesia, and autonomic paralysis below the level of the lesion
Spinal shock – hypotension, normal or slow heart rate, and warm extremities (vasodilated)
• Occurs with spinal cord injuries above T5 (loss of sympathetic tone)
• Tx: fluids initially, may need phenylephrine drip (alpha agonist)
Anterior spinal artery syndrome – most commonly occurs with acutely ruptured cervical disc
• Bilateral loss of motor, pain, and temperature sensation below the level of lesion
• Preservation of position–vibratory sensation and light touch
• About 10% recover to ambulation
Brown-Sequard syndrome – incomplete cord transection (hemisection of cord); most commonly due to penetrating injury
• Loss of ipsilateral motor and contralateral pain/temperature below level of lesion
• About 90% recover to ambulation
Central cord syndrome – most commonly occurs with hyperflexion of the cervical spine
• Bilateral loss motor, pain, and temperature sensation in upper extremities; lower extremities spared
Cauda equina syndrome – pain and weakness in lower extremities due to compression of lumbar nerve roots
Spinothalamic tract – carries pain and temperature sensory neurons
Corticospinal tract – carries motor neurons
Rubrospinal tract – carries motor neurons
Dorsal nerve roots – are generally afferent; carry sensory fibers
Ventral nerve roots – are generally efferent; carry motor neuron fibers
BRAIN TUMORS
Symptoms: headache, seizures, progressive neurologic deficit, and persistent vomiting
Adults – ⅔ supratentorial
Children – ⅔ infratentorial
Gliomas – most common primary brain tumor in adults and overall
• Glioma multiforme – most common subtype, uniformly fatal
Lung – #1 metastasis to brain
Most common brain tumor in children – medulloblastoma
Most common metastatic brain tumor in children – neuroblastoma
Acoustic neuroma – arises from the 8th cranial nerve at cerebellopontine angle
• Symptoms – hearing loss, unsteadiness, vertigo, nausea, and vomiting
• Tx: surgery usual
SPINE TUMORS
Overall, most are benign; #1 tumor overall neurofibroma
Intradural tumors are more likely benign, and extradural tumors are more likely malignant
Paraganglionoma – check for metanephrines in urine
PEDIATRIC NEUROSURGERY
Intraventricular hemorrhage (subependymal hemorrhage)
• Seen in premature infants secondary to rupture of the fragile vessels in germinal matrix
• Patients go on to get intraventricular hemorrhage
• Risk factors: ECMO, cyanotic congenital heart disease
• Symptoms: bulging fontanelle, neurologic deficits, ↓ BP, and ↓ Hct
• Tx: ventricular catheter for drainage and prevention of hydrocephalus
Myelomeningocele
• Neural cord defect – herniation of spinal cord and nerve roots through defect in vertebra
• Most commonly occurs in the lumbar region
MISCELLANEOUS
Wernicke’s area – speech comprehension, temporal lobe
Broca’s area – speech motor, posterior part of anterior lobe
Pituitary adenoma, undergoing XRT, patient now in shock
• Dx: pituitary apoplexy
• Tx: steroids
Cervical nerves roots 3–5 innervate diaphragm
Microglial cells – act as brain macrophages
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