Advanced Neurosurgical Neuroanatomy: Spinal and Vertebral Column Multiple Choice Questions
Question 1: Spinal Cord Segmental Anatomy
A 45-year-old patient presents with a thoracolumbar fracture at T12. During surgical planning, at what vertebral level would you expect the L1 spinal cord segment to be located?
A) At the T12 vertebral body
B) At the upper one-third of T11 vertebral body
C) At the lower one-third of T12 vertebral body
D) At the L1 vertebral body
Correct Answer: B
Explanation: The lumbar spinal cord segments do not correspond to their respective vertebral levels. In 93.8% of cases, the beginning of the lumbar spinal cord segment is found above the T11 spinal nerve root axilla and corresponds to the upper one-third of the T11 vertebral body 1. This anatomical relationship is critical for surgical planning, as the conus medullaris typically terminates between the axilla of the L1 and L2 spinal nerve roots in 93.8% of specimens 1. Understanding this discrepancy prevents inadvertent spinal cord injury during vertebral body procedures at the thoracolumbar junction.
Question 2: Nerve Root Compression Patterns
A patient with L5-S1 disc herniation presents with foot drop. Which specific motor function should be tested to confirm S1 nerve root involvement?
A) Foot dorsiflexion
B) Foot plantarflexion
C) Great toe extension
D) Hip flexion
Correct Answer: B
Explanation: L5-S1 disc herniation typically affects the S1 nerve root, causing weakness in foot plantarflexion 2. The focused neurological examination should include evaluation of foot plantarflexion and ankle reflexes, as these are the primary clinical manifestations of S1 nerve root pathology 2. While foot dorsiflexion tests L5 function and great toe extension tests L5 (extensor hallucis longus), plantarflexion weakness specifically indicates S1 involvement, which is the expected finding with L5-S1 disc herniation.
Question 3: Vertebral Body Erosion Recognition
During preoperative imaging review for a patient with chronic back pain, you identify vertebral body erosion at T10-T12. The patient is hemodynamically stable with isolated radicular symptoms. What is the average diameter of aortic aneurysms associated with vertebral body erosion?
A) 3.5 cm
B) 5.0 cm
C) 7.0 cm
D) 9.0 cm
Correct Answer: C
Explanation: When the diameter of an aortic aneurysm is large (average diameter 7.056 ± 3.39 cm), chronic contained rupture and chronic pressure of a primary pulsatile aneurysm cause vertebral lysis and erosion 3. The most critical diagnostic challenge is that patients with chronic contained rupture of aortic aneurysm are generally hemodynamically stable with isolated symptoms from spinal cord or radicular nerve compression, creating diagnostic uncertainty 3. Abdominal chronic contained rupture is more frequent than thoracic (26/80 thoracolumbar origin with 18/80 thoracic vertebral body erosion), and vertebral body loss up to 30% can be tolerated and naturally mends after aneurysm repair, though every case requires spine specialist evaluation 3.
Question 4: Spinal Tract Anatomy and Clinical Correlation
A patient sustains a unilateral spinal cord injury at T6. On examination, they have ipsilateral loss of vibration and proprioception below the lesion, but contralateral loss of pain and temperature sensation. Which anatomical principle explains this pattern?
A) All ascending tracts decussate at the level of injury
B) Spinothalamic tracts decussate while dorsal columns remain ipsilateral
C) Dorsal columns decussate while spinothalamic tracts remain ipsilateral
D) Both tracts remain ipsilateral to the injury
Correct Answer: B
Explanation: Damage to the unilateral gracilis-cuneatus fasciculi (dorsal columns carrying touch and vibration) correlates with ipsilateral clinical findings, whereas damage to the unilateral spinothalamic tract (pain-temperature) correlates with contralateral clinical findings 4. This creates the classic Brown-Séquard syndrome pattern. The corticospinal tract (upper motor neuron) also produces ipsilateral findings 4. Peripherally, the main descending (corticospinal tract) and ascending (gracilis or cuneatus fasciculi and spinothalamic tracts) pathways compose the white matter, while centrally the gray matter contains laminae 1-5 carrying sensory information in the posterior horn and lamina 9 carrying lower motor neuron information in the anterior horn 4.
Question 5: Neurophysiological Monitoring Interpretation
During anterior cervical discectomy and fusion at C5-C6, you observe a sudden 50% amplitude decrease in somatosensory evoked potentials (SSEPs) with preserved motor evoked potentials (MEPs). What is the most appropriate immediate action?
A) Continue surgery as MEPs are preserved
B) Stop manipulation and notify anesthesia to optimize blood pressure
C) Convert to posterior approach
D) Abandon the procedure immediately
Correct Answer: B
Explanation: Transcranial electric motor evoked potentials and somatosensory evoked potentials provide complementary monitoring during cervical spine surgery, with MEPs detecting motor pathway injury and SSEPs detecting sensory pathway injury 3. Intraoperative improvements of somatosensory evoked potentials correlate with clinical outcome in surgery for cervical spondylotic myelopathy 3. When SSEPs decrease significantly, immediate intervention includes stopping surgical manipulation, optimizing spinal cord perfusion through blood pressure augmentation, and assessing for mechanical compression 3. The combination of transcranial electric motor and somatosensory evoked potential monitoring during cervical spine surgery provides superior detection of iatrogenic injury compared to either modality alone 3.
Question 6: Thoracolumbar Fracture Neurological Assessment
A 32-year-old patient presents with a T12 burst fracture and incomplete spinal cord injury. Which validated assessment tool demonstrates the highest inter-rater reliability for thoracolumbar fractures?
A) Sunnybrook Cord Injury Scale
B) Frankel Scale
C) Functional Independence Measure
D) Modified Japanese Orthopaedic Association Score
Correct Answer: B
Explanation: The Frankel scale demonstrates inter-rater reliability ranging from 94% to 100% in thoracic and lumbar patients, with better agreement compared to the Sunnybrook scale 3. However, both scales are deemed insensitive as significant recovery in motor, sensory, bladder, or walking functions can occur without scale changes 3. The ASIA Impairment Scale (AIS) grade, sacral sensation, ankle spasticity, urethral and rectal sphincter function, and abductor hallucis motor function can be used to predict neurological function and outcome in patients with thoracic and lumbar fractures 3. Patients with lumbar or conus injuries demonstrate the greatest neurologic recovery as graded by ASIA classification, attributed to higher concentration of lower motor neurons and the ability of neurons to develop "root escape" 3.
Question 7: Imaging for Surgical Decision-Making
A 58-year-old patient with cervical spondylotic myelopathy shows T2 hyperintensity within the spinal cord on MRI. What does this finding predict regarding surgical outcome?
A) Excellent prognosis regardless of signal characteristics
B) Poor prognosis if signal is diffuse and bright
C) No correlation with outcome
D) Only relevant if associated with cord atrophy
Correct Answer: B
Explanation: MRI T2-weighted intramedullary high signal intensity in cervical spondylotic myelopathy predicts prognosis based on the type of intensity, with diffuse bright signal correlating with poorer outcomes 3. The severity of stenosis on imaging may predict surgical outcome 3. MRI without contrast is the preferred imaging modality for confirming disc herniation and other spinal pathologies 2. MRI can influence management decisions in up to 25% of patients by revealing posterior ligamentous complex integrity, which is crucial for determining stability 2. The Congress of Neurological Surgeons provides a Grade B recommendation that MRI should be used to assess posterior ligamentous complex integrity when determining the need for surgery in thoracolumbar injuries 2.
Question 8: Cervical Pseudarthrosis Management
A patient develops symptomatic pseudarthrosis 18 months after anterior cervical discectomy and fusion at C5-C6. What is the most evidence-based surgical approach for revision?
A) Anterior revision with plating is superior to posterior fusion
B) Posterior fusion and anterior revision have equivalent outcomes
C) Observation as most pseudarthroses are asymptomatic
D) Interspinous wiring without bone grafting
Correct Answer: B
Explanation: Treatment of anterior cervical pseudarthrosis can be accomplished with either posterior fusion or anterior revision, with studies showing equivalent outcomes between approaches 3. Anterior revision with allograft fusion and plating has demonstrated effectiveness 3. Posterior nerve-root decompression, stabilization, and arthrodesis represent viable treatment options for symptomatic pseudarthrosis 3. The efficacy of anterior cervical plating in the management of symptomatic pseudarthrosis of the cervical spine has been established, with increased fusion rates demonstrated for multi-level procedures 3. Interspinous wiring techniques have been used as salvage operations, though bone grafting typically accompanies these procedures 3.
Question 9: Vertebral Compression Fracture Classification
A 72-year-old patient with known metastatic breast cancer presents with new thoracic back pain and a compression fracture at T8. Using the Spinal Instability Neoplastic Score (SINS), which finding would contribute most significantly toward an "unstable" classification?
A) Posterior element involvement
B) Mechanical pain
C) Vertebral body collapse >50%
D) Junctional location (T1-T5)
Correct Answer: C
Explanation: The Spinal Instability Neoplastic Score (SINS) evaluates spinal stability in patients with metastatic spinal disease through a composite of clinical and radiographic data including location, pain, bone quality, alignment, presence and degree of vertebral compression fracture, and posterolateral involvement 3. The affected spinal segment is classified as stable (0-6), potentially unstable (7-12), and unstable (13-18) 3. The SINS is routinely used by spine oncologic surgeons and spine radiation oncologists and has excellent interobserver and intraobserver reliability 3. Vertebral body collapse >50% contributes 3 points to the score, representing one of the highest individual contributions 3. MRI is imperative for assessing vertebral compression fractures in patients with malignancy history, allowing differentiation between benign and malignant fractures and assessment of thecal sac compression, epidural extension, and paraspinal extension 3.
Question 10: Conus Medullaris Localization
During surgical planning for an L1 vertebrectomy, at what intervertebral disc level would you expect to find the conus medullaris in 93.8% of patients?
A) T12-L1
B) L1-L2
C) L2-L3
D) T11-T12
Correct Answer: B
Explanation: Termination of the spinal cord occurs between the axilla of the L1 and L2 spinal nerve roots in 93.8% of specimens 1. When the conus medullaris is located at the L1-L2 level, the beginning of the lumbar spinal cord segment always corresponds to the body of T11 vertebra 1. The beginning of the sacral spinal cord segment occurs above the L1 spinal nerve root axilla and corresponds to the upper one-third of the L1 vertebral body 1. In all cadavers, the emergence of the T11, T12, and L1 spinal nerve roots occurs at the level of the lower one-third of the same vertebral body 1. This anatomical knowledge is essential for preventing iatrogenic spinal cord injury during vertebral body procedures, particularly vertebrectomy at the thoracolumbar junction.