Lumbar vertebral osteomyelitis (sans discitis)

Case contributed by Dr Chris O'Donnell

Presentation

Diabetic with PUO and acute renal failure. Sore left ankle and lower lumbar spine.

Patient Data

Age: 60
Gender: Male

Only subtle soft tissue swelling around the L4 vertebra. No obvious bone erosion or endplate irregularity.

MRI scan performed within 8 hours of the CT

MRI

Minimal generalized reduction in T1 signal in the L4 vertebral body with subtle increased T2 signal on STIR but a heretrogeneous enhancement pattern following IV gadolinium. Small epidural soft tissue mass behind the body of L4 producing marked thecal compression with bilateral psoas inflammatory swelling and locules of fluid (rim-enhancing) especially on the left indicative of abscess. Note endplates (L3/4 and L4/5) are intact and the discs show no enhancement or fluid as usually seen in discitis. Pus was drained from the psoas muscles at surgery.

US guided aspiration of the ankle joint

Ultrasound

Frank pus was aspirated from the ankle joint and grew S. aureus

Case Discussion

This is an unusual case of systemic Staphylococcus aureus infection in a diabetic. Rather than originating in the disc or endplates (spondylodiscitis), infection is located centrally in the vertebral body as osteomyelitis, spreading bilaterally into the psoas muscles and posteriorly into the epidural space. This case highlights the sensitivity of MRI with IV Gad and the insensitivity of CT scanning for the diagnosis of spinal infection.

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