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)

  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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