A comatose patient is found with both upper limbs flexed at the elbows and wrists, and both lower limbs extended with plantar flexion. This posturing pattern indicates a structural lesion located:
- A Above the red nucleus, interrupting corticospinal fibers while sparing rubrospinal output ✓
- B Below the red nucleus, sparing the rubrospinal tract
- C Within the vestibular nuclei bilaterally
- D In the ventral horn of the cervical cord bilaterally
Correct answer: A. Above the red nucleus, interrupting corticospinal fibers while sparing rubrospinal output
Explanation
Decorticate (flexor) posturing results from lesions above the red nucleus, classically at the level of the diencephalon or rostral midbrain. Corticospinal control of flexors is lost, but the intact rubrospinal tract continues to facilitate upper limb flexion, giving arm flexion with leg extension. Decerebrate (extensor) posturing occurs when the lesion is below the red nucleus, removing rubrospinal influence and leaving unchecked vestibulospinal and pontine reticulospinal extensor tone, which defines option B.
Reference: Ganong's Review of Medical Physiology, 26th ed.
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