Tuberculous Spondylitis

= POTT DISEASE

[Percivall Pott (1714–1788), full surgeon at St. Bartholomew's Hospital, London, author of the Chirurgical works and discoverer of coal tar-induced cancer of the scrotum in chimney sweeps]

= destruction of vertebral body + intervertebral disk by tuberculous mycobacterium

Frequency: 5% of patients with tuberculosis; 25–50–60% of all skeletal tuberculosis

Associated with: pulmonary TB in 10%

Age: children / adults of 50 years; M >F

• insidious onset of back pain, stiffness
• local tenderness
• NO pulmonary lesions in 50%

Location: upper lumbar + lower thoracic spine (L1 most common); TYPICALLY more than one (up to 5–10) vertebrae + intervening disks affected

Site: vertebral body (82%) with predilection for anterior part adjacent to superior / inferior subchondral bone plate >>posterior elements (18%)

• RARELY affects posterior elements + pedicles!

Spread:

1. contiguous into adjacent disk by penetrating subchondral endplate + cartilaginous endplate
2. subligamentous spread beneath anterior / posterior longitudinal ligaments to adjacent vertebral bodies → sparing of adjacent disks
3. hematogenous spread via paravertebral venous plexus of Batson: separate foci in 1–4%
4. skip lesions = SPECIFIC but rare sign of TB

• TYPICALLY little / NO reactive sclerosis / local periosteal reaction (DDx: pyogenic infection)
• demineralization = vertebral osteopenia (= resorption of dense margin) of vertebral endplates (earliest change):
  • “gouge defect” = mild contour irregularity of anterior and lateral aspect of vertebral body (= erosion from subligamentous extension of tuberculous abscess)
• collapse of vertebral body:
  • vertebra plana in children
  • angular kyphotic deformity (= gibbus deformity) ← preferential anterior involvement in adults
• vertebra within a vertebra (= growth recovery lines)
• ivory vertebra (= reossification as healing response to osteonecrosis)
• slight narrowing + collapse of intervertebral disk space
  N.B.: vertebral disk space maintained longer than in pyogenic arthritis (disk preserved, but fragmented)
• paraspinal infection:
  • lateral bowing of psoas shadow (on abdominal film)
  • anterior scalloping of vertebral bodies (DDx: lymphoma, abdominal aortic aneurysm)
  • large cold fusiform abscess in paravertebral gutters / psoas (= Pott abscess), commonly bilateral ± anterolateral scalloping of vertebral bodies
  • nearly PATHOGNOMONIC amorphous / teardrop-shaped calcification in paraspinal area between L1 + L5 (DDx: nontuberculous abscess rarely calcifies)
  • abscess may extend into groin / thigh / internal viscus

MR:

• centrosomatic rounded well-limited abscess
• surrounded by bone marrow edema
• normal disk spaces

NUC: 35% (up to 70%) FN rate for bone (gallium) scan

Cx:

1. Kyphoscoliosis
2. Ankylosis of vertebrae with obliteration of intervening disk space ← with healing
3. Osteonecrosis
4. Paralysis ← spinal cord compression from abscess, granulation tissue, bone fragments, arachnoiditis)

Prognosis: 26–30% mortality rate

Imaging features favoring tuberculous spondylitis:

• involvement of >1 segment
• delay in destruction of intervertebral disks
• large calcified paravertebral mass
• absence of sclerosis

DDx:

1. Pyogenic spondylitis (rapid destruction, multiple abscess cavities, no thickening / calcification of abscess rim, little new-bone formation, posterior elements not involved)
2. Brucellosis (gas within disk, minimal paraspinal mass, no kyphosis, predilection for lower lumbar spine)
3. Sarcoidosis
4. Fungal spondylitis
5. Neoplasia / metastasis (multiple noncontiguous lesions, no disk destruction, little soft-tissue involvement, posterior elements involved)