NCS Neurologic Pathophysiology 3 — Questions and Answers
Question 1: The ischemic penumbra surrounding a core infarct is clinically significant because it represents tissue that is:
- Irreversibly infarcted and cannot be salvaged
- Functionally impaired but potentially salvageable with timely reperfusion (Correct answer)
- Already undergoing apoptosis due to glutamate excitotoxicity
- Protected by collateral circulation and will recover spontaneously
Correct answer: Functionally impaired but potentially salvageable with timely reperfusion
The penumbra has reduced blood flow (20–50 mL/100g/min) sufficient to maintain membrane integrity temporarily but not function; reperfusion within the therapeutic window can rescue this tissue.
Question 2: Watershed (borderzone) infarctions typically occur in which clinical scenario?
- Cardioembolic occlusion of the middle cerebral artery
- Severe systemic hypotension causing hypoperfusion at arterial boundary zones (Correct answer)
- Venous sinus thrombosis causing cortical vein congestion
- Vasospasm following subarachnoid hemorrhage
Correct answer: Severe systemic hypotension causing hypoperfusion at arterial boundary zones
Watershed zones at the periphery of major arterial territories receive the least perfusion pressure and are first to infarct when systemic blood pressure drops precipitously.
Question 3: Diffuse axonal injury (DAI) following TBI is caused primarily by:
- Direct cortical contusion at the point of impact
- Rotational acceleration-deceleration forces shearing axons at white-gray matter interfaces (Correct answer)
- Herniation of the brain through the foramen magnum
- Secondary ischemia from elevated intracranial pressure
Correct answer: Rotational acceleration-deceleration forces shearing axons at white-gray matter interfaces
Rotational and angular acceleration-deceleration forces generate shear-strain at sites where tissue density changes (white-gray interfaces), physically disrupting axonal cytoskeleton and transport.
Question 4: Central cord syndrome following hyperextension cervical injury characteristically spares which function?
- Upper extremity motor function
- Lower extremity motor function (Correct answer)
- Bladder control
- Pain and temperature sensation below the lesion
Correct answer: Lower extremity motor function
The corticospinal tract is somatotopically organized with cervical fibers medially and sacral fibers laterally; central hemorrhage/edema damages medial fibers first, sparing leg function more than arm function.
Question 5: Cerebral autoregulation maintains constant CBF over a mean arterial pressure (MAP) range of approximately:
- 20–60 mmHg
- 50–150 mmHg (Correct answer)
- 100–180 mmHg
- 60–90 mmHg
Correct answer: 50–150 mmHg
Intact cerebral autoregulation maintains relatively constant CBF (~50 mL/100g/min) across MAP of 50–150 mmHg through arteriolar vasoconstriction and dilation; outside this range, CBF becomes pressure-passive.
Question 6: After subarachnoid hemorrhage, delayed cerebral ischemia typically peaks at which time interval?
- Within the first 24 hours
- Days 4–14 (Correct answer)
- Day 21–28
- Greater than 4 weeks
Correct answer: Days 4–14
Cerebral vasospasm causing delayed ischemia characteristically develops 4–14 days post-SAH, related to oxyhemoglobin degradation products from the subarachnoid clot inducing arterial smooth muscle contraction.
Question 7: Which mechanism best explains the spinal shock seen immediately after complete spinal cord injury?
- Permanent destruction of all spinal cord neurons below the lesion
- Sudden loss of descending facilitation causing temporary hyperpolarization of spinal neurons (Correct answer)
- Inflammatory demyelination of the white matter below the injury
- Acute venous congestion of the spinal cord parenchyma
Correct answer: Sudden loss of descending facilitation causing temporary hyperpolarization of spinal neurons
Spinal shock results from sudden removal of tonic descending excitatory input (reticulospinal, corticospinal, vestibulospinal), leaving spinal circuits temporarily hyperpolarized and areflexic below the lesion.
NCS Neurologic Pathophysiology 3
The ischemic penumbra surrounding a core infarct is clinically significant because it represents tissue that is: