Fig. 5
From: Pelvic heterotopic ossification: when CT comes to the aid of MR imaging
A 72-year-old tetraplegic male patient with spinal injury. Different grades of maturity may coexist in the same clinical setting. a Axial CT scan shows an HO formation located within the gluteus minimus muscle with the typical features of maturity: well-structured cancellous bone outlined by cortex and adherent to cortical bone. Immature ossification and amorphous calcifications coexist in various regional muscles. b–d Axial corresponding MR imaging shows the mature ossification with a high-fat bone marrow signal outlined by low signal cortical bone (c) (small arrow). The amorphous calcifications contiguous to the posterior iliac bone (large arrow) are characterised by elevated signal intensity on STIR images (b) and intense contrast-enhancement on T1-weighted fat-saturated (d) compared with unenhanced T1-weighted images (c). The small immature ossification in the gluteus medius muscle (asterisks) is clearly demonstrated by CT (a), while it is not easily recognisable on MR imaging