A 35-year-old woman presents with a 2-year history of progressive painless burns on her shoulders and upper back after touching hot objects unknowingly. MRI of the cervical spine shows a T2-weighted sagittal image with a central hyperintense cavity within the spinal cord at C3–C5 level (marked **A**), and sagittal brain imaging reveals cerebellar tonsillar herniation 7 mm below the foramen magnum. On examination, she has loss of pain and temperature sensation in a cape-like distribution across the shoulders and upper limbs, but light touch and vibration sense are preserved. Which of the following best explains the neuroanatomical basis for the dissociated sensory loss pattern in this patient?

Question

Accepted Answer

A. The expanding syrinx cavity (A) interrupts decussating spinothalamic fibers at the anterior white commissure, while dorsal columns remain intact. ## Why option 1 is correct

The clinical hallmark of syringomyelia is **suspended dissociated sensory loss** — loss of pain and temperature sensation with preserved light touch, vibration, and proprioception. This distinctive pattern occurs because the expanding syrinx cavity at the **anterior white commissure** (where spinothalamic fibers decussate) interrupts pain and temperature pathways while the **dorsal columns** (which carry light touch, vibration, and proprioception) remain anatomically spared. The patient's cape-like sensory loss across the shoulders and upper limbs reflects the rostral-caudal extent of the syrinx at the cervical level. This is the pathognomonic sensory pattern of intramedullary syringomyelia and is directly explained by the location and expansion of the syrinx cavity marked **A** (Greenberg Handbook of Neurosurgery 9e — Chiari & Syringomyelia).

## Why each distractor is wrong

- **Option 2**: Dorsal root ganglia compression does not produce dissociated sensory loss; it causes radicular pain and dermatomal sensory loss, not the suspended cape-like pattern seen here. The syrinx is intramedullary, not compressing nerve roots.
- **Option 3**: Corticospinal tract damage causes motor weakness and upper motor neuron signs (hyperreflexia, Babinski), not selective loss of pain/temperature sensation. The patient's sensory loss is the primary finding, not motor involvement at presentation.
- **Option 4**: Bilateral lateral corticospinal tract compression would cause bilateral lower limb weakness and spasticity, not the dissociated sensory loss pattern. Additionally, this would not spare upper limb sensation as described.

**High-Yield:** Syringomyelia → **suspended dissociated sensory loss** (cape-like) = syrinx at anterior white commissure interrupting decussating spinothalamic fibers while sparing dorsal columns.

[cite: Greenberg Handbook of Neurosurgery 9e — Chiari & Syringomyelia]

Answer

B. The syrinx cavity (A) compresses the lateral corticospinal tract bilaterally, causing bilateral lower limb weakness with preserved upper limb sensation

Answer

C. The syrinx cavity (A) causes selective compression of the dorsal root ganglia, sparing the ventral roots

Answer

D. The syrinx cavity (A) preferentially damages the corticospinal tract, leaving spinothalamic pathways unaffected

Explanation

Why option 1 is correct

Why each distractor is wrong

Practice similar questions