Subacute Osteomyelitis-MRI

 70 yr old diabetic male  has pain in the left hip with fever of  recent onset with no history  of  significant trauma. MRI shows  a relatively well defined , irregular, predominantly fluid signal intensity lesion in the subtrochanteric region  , with  cortical break, soft tissue involvement,  no significant onion peeling or expansion  or endosteal  low signal margin. Though not classical, in the given circumstances,  subacute osteomyelitis of type 2  is possible.

Teaching points by Dr MGK Murthy

1.       Incidence is increasing  in view of liberal use  of antibiotics

3.       Roberts  radiological  classification (1982) is generally accepted . Type 1-metaphyseal (1a is  punched out and 1b is  with sclerotic  margin classical brodies abscess, maximum in incidence), Type2- metaphyseal cortex and appear similar  to osteosarcoma , Type3- diaphyseal, cortical and looks like osteoid  osteoma , Type4- diaphyseal and looks  like ewing’s with periosteal  response, Type 5-epiphyseal and look concentric lucency, Type6-vertebral body and looks destructive.

4.       All bones involved, with lower limbs, specifically tibia more involved than others

5.       If the lesion tethers from epiphysis to metaphysis across the growth plate  serpigenously, it is called “serpentine sign”. Smaller paravertebral abscess, early new bone formation with bony bridging differentiate from TB in spine.

6.       Xray and 3 phase bone scan may help, but CT would help  pick up eccentric nidus of sequestrum (vs central nidus of osteoid osteoma)  and CEMR is  ideal for  complete evaluation.

7.       Bx and curettage if diagnosis is  in doubt (in 1/3 case looks like malignancy), antibiotics in others and followed by surgery if needed are  recommended