Myositis Ossificans

This 87-year-old woman presented with left hip pain. MRI images showed an asymptomatic mass in her right hip. She denied any trauma.A radiograph taken after open reduction and internal fixation of the left femur showed no right sided gluteal mineralization.[[{"type":"media","view_mode":"media_crop","fid":"21989","attributes":{"alt":"","class":"media-image","height":"195","id":"media_crop_3511878125593","media_crop_h":"0","media_crop_image_style":"-1","media_crop_instance":"1590","media_crop_rotate":"0","media_crop_scale_h":"0","media_crop_scale_w":"0","media_crop_w":"0","media_crop_x":"0","media_crop_y":"0","title":"Click to enlarge","typeof":"foaf:Image","width":"219"}}]]However, an MRI demonstrated a right gluteal mass which was asymptomatic. There is a prominent edema pattern in the adjacent musculature.[[{"type":"media","view_mode":"media_crop","fid":"21990","attributes":{"alt":"","class":"media-image","id":"media_crop_4247393376024","media_crop_h":"0","media_crop_image_style":"-1","media_crop_instance":"1591","media_crop_rotate":"0","media_crop_scale_h":"0","media_crop_scale_w":"0","media_crop_w":"0","media_crop_x":"0","media_crop_y":"0","style":"width: 217px; height: 116px;","title":"Click to enlarge","typeof":"foaf:Image"}}]]Ultrasound shows a heterogeneous mass with prominent posterior acoustic shadowing.[[{"type":"media","view_mode":"media_crop","fid":"21991","attributes":{"alt":"","class":"media-image","id":"media_crop_7772977793642","media_crop_h":"0","media_crop_image_style":"-1","media_crop_instance":"1592","media_crop_rotate":"0","media_crop_scale_h":"0","media_crop_scale_w":"0","media_crop_w":"0","media_crop_x":"0","media_crop_y":"0","style":"width: 282px; height: 340px;","title":"Click to enlarge","typeof":"foaf:Image"}}]]Comparison axial images taken one month apart demonstrate early peripheral mineralization of the mass.[[{"type":"media","view_mode":"media_crop","fid":"21994","attributes":{"alt":"","class":"media-image","id":"media_crop_7212114068321","media_crop_h":"0","media_crop_image_style":"-1","media_crop_instance":"1593","media_crop_rotate":"0","media_crop_scale_h":"0","media_crop_scale_w":"0","media_crop_w":"0","media_crop_x":"0","media_crop_y":"0","style":"width: 336px; height: 160px;","title":"Click to enlarge","typeof":"foaf:Image"}}]]Diagnosis:  Myositis ossificansMuscle that has sustained trauma undergoes a process of formation of ossification in the musculature. In the first 8 weeks following the injury on MRI, a heterogeneous mass is frequently seen with a profound amount of surrounding edema. With time, a peripheral low signal intensity rim forms corresponding to peripheral ossification. In its early forms, the peripheral ossification may have a somewhat amorphous appearance on CT or radiograph without clear trabecular formation. [below][[{"type":"media","view_mode":"media_crop","fid":"21998","attributes":{"alt":"","class":"media-image","id":"media_crop_6515352428207","media_crop_h":"0","media_crop_image_style":"-1","media_crop_instance":"1594","media_crop_rotate":"0","media_crop_scale_h":"0","media_crop_scale_w":"0","media_crop_w":"0","media_crop_x":"0","media_crop_y":"0","style":"width: 266px; height: 162px;","title":"Click to enlarge","typeof":"foaf:Image"}}]]With aging, less significant trauma is needed to cause these changes. Frequently, patients do not recall a discrete event.Ultrasound is useful to demonstrate acoustic shadowing indicating a dense substance, often calcification, ossification, or marked fibrosis.  Ultrasound can also be used, as in this case, for biopsy to confirm the diagnosis.[[{"type":"media","view_mode":"media_crop","fid":"21999","attributes":{"alt":"","class":"media-image","id":"media_crop_6807843256535","media_crop_h":"0","media_crop_image_style":"-1","media_crop_instance":"1595","media_crop_rotate":"0","media_crop_scale_h":"0","media_crop_scale_w":"0","media_crop_w":"0","media_crop_x":"0","media_crop_y":"0","style":"width: 246px; height: 227px;","title":"Click to enlarge","typeof":"foaf:Image"}}]]Adapted from the teaching files of the Department of Radiology and Imaging at Hospital for Special Surgery. Special thanks to HSS Department of Pathology for their assistance in this diagnosis.References:Bone and Joint Imaging, 3rd Edition. Ed(s) D Resnick and MJ Kransdorf. Elsevier Saunders: Philadelphia,  2005.Musculoskeletal MRI.  Kaplan P, Helms C, Dussault R, Anderson M, Major N.  Musculoskeletal MRI. Philadelphia: Sanders Company; 2001Robert J Pignolo, Pediatric Fibrodysplasia Ossificans Progressiva (Myositis Ossificans) Medscape EMedicine, updated Sept. 2013 

References:

Bone and Joint Imaging, 3rd Edition. Ed(s) D Resnick and MJ Kransdorf. Elsevier Saunders: Philadelphia,  2005.

Musculoskeletal MRI.  Kaplan P, Helms C, Dussault R, Anderson M, Major N.  Musculoskeletal MRI. Philadelphia: Sanders Company; 2001

Robert J Pignolo, Pediatric Fibrodysplasia Ossificans Progressiva (Myositis Ossificans) Medscape EMedicine, updated Sept. 2013