Pelvic heterotopic ossification: MR imaging characteristics.

Area of Science:

• Radiology
• Medical Imaging
• Orthopedic Imaging

Background:

• Heterotopic ossification (HO) is the abnormal formation of bone in non-skeletal tissues.
• Accurate staging of HO is crucial for understanding its pathophysiology and guiding treatment.
• Magnetic resonance (MR) imaging offers detailed soft tissue characterization, but its role in HO maturation assessment requires further elucidation.

Purpose of the Study:

• To characterize the magnetic resonance (MR) signal intensity patterns of pelvic heterotopic ossification (HO) across different maturation stages.
• To correlate MR signal characteristics with established CT/radiographic grading of HO.

Main Methods:

• Retrospective analysis of 1.5-T pelvic MR imaging in 36 patients with pathologically proven HO.
• HO was graded 1-4 based on CT/radiographic findings (fluid, calcification, immature, mature ossification).
• MR signal intensities (T1, T2, contrast enhancement) were evaluated at identified HO sites.

Main Results:

• A total of 141 HO sites were analyzed, with varying distributions across grades 1-4.
• Increasing HO grade correlated with decreased T2 signal intensity (70% to 4%) and contrast enhancement (100% to 20%).
• T1-weighted imaging showed increased fat and cortical bone signal intensity with maturation (0% to 86%).

Conclusions:

• Pelvic heterotopic ossification (HO) exhibits distinct MR signal intensity changes with progressive maturation.
• T2 signal intensity and contrast enhancement diminish as HO matures.
• T1-weighted signal intensity, reflecting fat and cortical bone, increases with HO maturity.