A 28-year-old Indian male presents with a 5-month history of dull aching upper thoracic back pain, progressive kyphosis, constitutional symptoms (low-grade evening fevers, night sweats, weight loss), and recent bilateral lower limb weakness with hyperreflexia and extensor plantars. Examination reveals a visible gibbus deformity and exquisite tenderness over T8-T9. A frontal chest radiograph is shown. The structure marked **A** in the diagram demonstrates the characteristic anterior vertebral body destruction seen in Pott disease. Which of the following BEST explains why the anterior vertebral body is preferentially affected in tuberculous spondylitis?
A. The anterior vertebral body has a richer blood supply from the anterior spinal artery, making it more susceptible to haematogenous seeding
B. The posterior vertebral body is protected by the posterior longitudinal ligament, making it resistant to tuberculous infection
C. Mycobacterium tuberculosis spreads from the subchondral region and preferentially destroys the anterior vertebral body, while intervertebral discs are relatively preserved early in the disease
D. Tuberculous infection of the spine always begins with disc space involvement, which then spreads secondarily to the anterior body
Explanation
Why option 1 is right
The anterior wedge collapse of the T8 vertebral body (marked A) is pathognomonic for Pott disease because Mycobacterium tuberculosis spreads from the subchondral region of the anterior vertebral body and preferentially destroys this region while relatively preserving the intervertebral discs early in the disease course. This pattern of anterior body destruction with disc preservation is a key radiological distinguishing feature of tuberculous spondylitis from pyogenic spondylodiscitis (which typically involves the disc first). The subchondral location explains why the anterior body is the initial site of mycobacterial osteonecrosis.
Why each distractor is wrong
Option 2: While the posterior longitudinal ligament does provide some protection, it does not explain the specific predilection for anterior body destruction in TB. The posterior body can also be affected in advanced disease, and this option does not address the subchondral pathophysiology that drives anterior body involvement.
Option 3: This describes the pattern seen in pyogenic bacterial spondylodiscitis (e.g., Staphylococcus aureus), where disc space involvement is primary. In TB, the disc is relatively spared early because the infection arises in the vertebral body itself, not the disc. This is a classic teaching point to distinguish TB from pyogenic infection.
Option 4: Although the anterior spinal artery does supply the anterior vertebral body, the rich blood supply alone does not explain TB's predilection for this site. The pathophysiology is driven by the specific pattern of mycobacterial spread via subchondral vessels and the organism's tropism for the anterior metaphyseal region, not simply by vascular density.
High-YieldNEET PG
Anterior vertebral body destruction with disc preservation = TB; disc-space involvement first = pyogenic spondylodiscitis.
Garg RK, Somvanshi DS. Spinal tuberculosis: a review. J Spinal Cord Med 2011;34(5):440-454.
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