🫀 Spinal Cord Syndromes
Master the tract anatomy first, then every syndrome follows logically. The wiring explains everything.
The Foundation — Know the Wiring First
There are only three tracts you need to understand to derive every spinal cord syndrome from first principles. The key is knowing two things about each: where it travels in the cord (which column), and where it crosses over (decussates). Everything else follows from that.
The Golden Rule — Where a Tract Crosses Determines the Side of the Deficit
If a tract crosses high up in the brain (medulla/brainstem), then a cord lesion will produce a deficit on the same (ipsilateral) side as the injury — because the nerve was already on the correct side by the time it reached the cord.
If a tract crosses immediately within the spinal cord, a cord lesion will produce a deficit on the opposite (contralateral) side — because the crossed fibres come from the other side of the body.
This single rule explains Brown-Séquard syndrome completely.
The Three Tracts — Summary Table
| Tract | Modalities Carried | Location in Cord | Where It Crosses | Side of Deficit After Cord Lesion |
|---|---|---|---|---|
| Corticospinal Tract | Voluntary motor | Lateral columns | Medulla oblongata (pyramidal decussation) | IPSILATERAL (same side as lesion) |
| Dorsal Columns (Fasciculus Gracilis & Cuneatus) |
Proprioception, vibration, fine/discriminative touch | Posterior (dorsal) columns | Medulla oblongata (sensory decussation) | IPSILATERAL (same side as lesion) |
| Spinothalamic Tract | Pain, temperature, crude touch | Anterolateral columns | Spinal cord — within 1–2 levels of entry | CONTRALATERAL (opposite side from lesion) |
The Somatotopic Organisation of the Corticospinal Tract
Within the corticospinal tract, the fibres are layered by body region — a concept called somatotopic organisation. This is crucial for understanding Central Cord Syndrome:
🦾 Arm fibres are located medially (centrally) within the lateral corticospinal tract
🦵 Leg fibres are located laterally (peripherally) within the corticospinal tract
Think of it as the cord being like a cable with the arm wires in the middle and the leg wires on the outside. Crush the centre → arms more affected than legs.