Presentation:

49 year-old male with history of MRSA bacteremia, severe back pain, and known T10 metastasis.

Key findings:

Diffuse hypointense signal on T1 imaging, hyperintense signal on STIR, and enhancement across T12-L1 vertebral bodies.
Signal abnormality and involvement of the T12-L1 intervertebral disc.
Ventral epidural signal abnormalities at the T12-L1 disc space and minimal associated central canal stenosis.

Focal enhancement of T8 spinous process, right T8-T9 facet joint, and surrounding soft tissue enhancement of right T8-T9 neuroforamen.
Thin dorsal epidural enhancement at T8-T9 vertebral level.

Rim-enhancing fluid collection of the left anterolateral soft tissue at L1-L2 vertebral level, partially visualized.

Other pertinent findings:

Known T10 vertebral body metastatic lesion.
Incidental enhancing lesion along the left neck correlates with biopsy-proven metastatic lymph node from patient's known esophageal cancer.

Diagnosis:

1. Marked discitis/osteomyelitis of T12-L1 vertebral bodies. Epidural disease causes minimal central canal stenosis at this level.

2. Focal enhanced of T8 spinous process and of right T8-T9 facet and neuroforamen is primarily concerning for infection.

3. Suspicion for left anterolateral paraspinal abscess at the level of L1-L2.

4. Known T10 metastasis.

High-yield Sequences:

T1 - Low signal central component due to increased fluid and surrounding lower bone marrow signal secondary to edema.
Cortical bone destruction.
T2 - Hyperintense bone marrow edema.
T1 + Contrast - Enhancement of the involved bone, abscess margins, periosteum, and adjacent soft tissue collections.

Discussion:

Osteomyelitis involves inflammation of the bone almost exclusively secondary to bacterial infection. Most commonly involved locations (in descending order) are the lower limbs, vertebrae (lumbar > thoracic > cervical), radial styloid, and SI joint.

Osteomyelitis in children is more often related to hematogenous spread, favoring the metaphyseal regions. In adult, direct invasion is more common, typically involving the epiphysis or subchondral regions.

Vertebral osteomyelitis and discitis are favored to be secondary to hematogenous seeding. Common complications are sepsis and epidural abscess, however can spontaneously resolve in children especially before 8 years of age.

MRI is the most sensitive and specific modality and is able to detect soft tissue and joint complications. The earliest feature is bone marrow edema.

Differential Diagnosis:

Metastasis
Primary bone neoplasm
LCH
Charcot joint

References:

A pictorial review of osteomyelitis.