A 42-year-old woman with known pulmonary TB presents with progressive lower back pain and bilateral lower limb weakness. MRI shows destruction of L4 and L5 vertebrae with severe kyphosis and spinal cord compression. Which imaging finding best distinguishes Pott disease from metastatic spinal disease?

Explanation

## Imaging Discriminators: Pott Disease vs. Metastatic Spinal Disease **Key Point:** The pattern of vertebral destruction and preservation of the posterior cortex is the cardinal radiological feature distinguishing Pott disease from metastatic malignancy. ### Comparison Table | Feature | Pott Disease (TB) | Metastatic Disease | |---------|-------------------|--------------------| | **Vertebral destruction** | Anterior body + wedging | Uniform or lytic/sclerotic | | **Posterior cortex** | Preserved (initially) | Often destroyed | | **Pedicles** | Spared | Commonly involved | | **Paravertebral abscess** | Cold abscess, prominent | Soft tissue mass (tumor) | | **Kyphosis** | Severe, progressive | Variable | | **Disc space** | Spared initially | May be involved | | **Epidural extension** | Abscess + granulation tissue | Tumor infiltration | | **Progression** | Insidious (months) | Variable (weeks to months) | **High-Yield:** In Pott disease, the **posterior vertebral cortex and pedicles are characteristically spared** because TB spreads beneath the anterior longitudinal ligament. Metastatic disease often destroys the entire vertebral body, including the posterior cortex and pedicles, because it spreads hematogenously throughout the vertebral body. ### Pathophysiological Basis TB spreads via the **anterior spinal artery** and **Batson's venous plexus**, affecting the anterior vertebral body first. The posterior cortex remains intact until late disease. Metastatic cancer, by contrast, seeds the vertebral body uniformly via hematogenous spread, leading to diffuse destruction. **Clinical Pearl:** A patient with known TB and spinal symptoms showing **anterior vertebral wedging with a cold paravertebral abscess and spared posterior cortex** has Pott disease until proven otherwise. ### Mnemonic — Pott's Posterior Preservation: PPP - **P**osterior cortex preserved - **P**edicles spared - **P**aravertebral abscess (cold) [cite:Robbins 10e Ch 8; Park 26e Ch 9]