Pediatric Myositis

  • Etiology:
    — Due to bacterial or viral or fungal or parasitic organism
    — Can be blood borne or secondary to osteomyelitis or subcutaneous infection
  • Imaging MRI:
    — T1WI post contrast: Best to differentiate inflammed edematous muscle from soft tissue abscess which has ring enhancement around low signal central fluid collection
    — T2WI: Involved muscle is expanded and edematous with edema in adjacent fascial planes and subcutaneous tissues, signal change may cross fascial boundaries and involve more than one muscle group, when signal change approaches a joint look for a joint effusion and if present suspect it is infected
    — STIR: Hyperintense
  • DDX:
  • Complications: Abscess
  • Treatment:
  • Clinical:

Radiology Cases of Myositis

MRI of myositis of the calf
Axial STIR MRI of the calves (above) shows diffusely bright signal in the expanded and edematous muscles in the posterior compartment of the left calf. Sagittal STIR MRI of the left calf (below) shows the length of involvement throughout the entire posterior compartment of the left calf.
MRI of myositis of the hip
Axial (above left and below left) and coronal (above right) T2 with fat saturation MRI of the pelvis shows bright signal in the expanded and edematous left obturator internis and left gluteus medius muscles, which on coronal T1 MRI with contrast (below right) are shown to faintly enhance.