A 6-year-old child presents with progressive gait abnormality, recent-onset urinary incontinence (regression after toilet training), and asymmetric cavovarus foot deformity. On examination, a midline lumbar tuft of hair with a small dimple is noted. Sagittal T2 MRI of the lumbosacral spine shows the conus medullaris terminating at L3 with a thickened filum terminale (3 mm) demonstrating T1 hyperintensity. The structure marked **A** in the diagram represents the underlying pathology. Which of the following best describes the PRIMARY mechanism of neurologic dysfunction in this condition?

Explanation

## Why abnormal tension on the spinal cord from anatomic restriction at the caudal end is right The clinical anchor defines tethered cord syndrome (marked **A**) as a clinical syndrome of progressive neurologic dysfunction caused by abnormal tension on the spinal cord from anatomic restriction at the caudal end. In this case, the thickened filum terminale (3 mm, normal <2 mm) with fatty infiltration (T1 hyperintensity) and low-lying conus at L3 (abnormal; normal is at or above L2) create mechanical tethering. As the child grows, differential growth between the vertebral column and the tethered cord increases traction stress, leading to progressive ischemia and neuronal dysfunction. This explains the classic presentation: progressive gait abnormality, foot deformities, and urinary incontinence with regression—all hallmarks of progressive traction-related cord dysfunction. (Nelson Pediatrics 22e, Greenberg Neurosurgery 9e) ## Why each distractor is wrong - **Demyelination of the dorsal root ganglia secondary to chronic inflammation**: Tethered cord syndrome is a mechanical traction disorder, not a primary demyelinating or inflammatory condition. Dorsal root ganglia involvement is not the primary pathophysiology. - **Acute vascular occlusion of the anterior spinal artery at the level of the conus**: Tethered cord causes progressive chronic ischemia from traction, not acute vascular occlusion. The mechanism is mechanical tension, not thrombosis. - **Syrinx formation with subsequent cavitation and cord necrosis independent of mechanical tethering**: While syringomyelia (marked **D** in the diagram) can be a secondary finding in tethered cord, it is not the primary mechanism. The primary pathology is tethering itself; syrinx formation is a consequence, not the cause. **High-Yield:** Tethered cord = progressive traction-induced neurologic dysfunction; conus below L2-L3 is abnormal; filum >2 mm is thickened; cutaneous stigmata (hair patch, dimple) are clinical clues in 50–70% of cases. [cite: Nelson Pediatrics 22e — Spinal Dysraphism; Greenberg Neurosurgery 9e]