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Age / Sex : 9 / M
Chief complaint :
Postoperative
imaging follow-up for right humeral supracondylar fracture.
Past history of
osteogenesis imperfecta
What is your impression?
Two weeks later, you can see the final diagnosis with a brief discussion of this case. (Please submit only one answer)
Courtesy : Moon Jin Il, Pusan National University Hospital
Discussion
Answer: Heterotopic ossification
Findings:
Plain
radiograph shows irregular shaped, ill-defined calcified mass with solid
periosteal reaction at right distal humerus. In MR images, this mass is
continuous with periosteal reaction of the humerus. T1-weighted MR image shows iso-signal
intensity of mass compared to muscle and T2-weighted image shows central high
signal intensity and peripheral low signal intensity of mass. Contrast enhanced
T1-weighted images shows enhancement in central portion and peripheral rim of the
mass. There is no diffusion restriction of the mass in DWI and ADC map. Soft
tissue edema is seen around the mass.
Differential Diagnosis: Heterotopic ossification, parosteal osteosarcoma
Diagnosis:
Heterotopic ossification
Discussion:
Heterotopic
ossification is the development of bone in abnormal sites. Clinically,
heterotopic ossification (HO) occurs in rare congenital disorders and, more
commonly, in acquired conditions such as after surgery or related to spinal
cord or head lesions.
Imaging can
assist in the identification of three degrees of HO: amorphous calcifications,
immature calcifications and mature calcifications.
At plain
radiographs and CT imaging, amorphous calcification is poorly defined with no recognisable
trabecular structure; immature ossification shows poorly defined margins and
initial trabecular formation; mature ossification is characterised by a
cortical outline with a well-defined cancellous bone centre.
At MR
imaging, mature HO presents as typical cancellous fat bone that is hyperintense
on T1- and T2-weighted images, outlined by a rim of hypointense cortical bone. Amorphous
calcification and immature HO can present non-specific signal intensity and contrast
enhancement characteristics. In cases of bone process immaturity, the formation
can show hetereogeneous signal, characterised mostly by focal iso-hypointensity
on T1- weighted images and hyperintensity on T2-weighted/ STIR images, with
occasional fluid contents. A certain amount of enhancement after contrast
administration can occur both inside and peripheral to the lesion.
References:
1.
Zagarella A,
Impellizzeri E, Maiolino R, Attolini R, Castoldi MC. Pelvic heterotopic ossification:
when CT comes to the aid of MR imaging. Insights Imaging. 2013
Oct;4(5):595-603.
2.
Ledermann
HP1, Schweitzer ME, Morrison WB. Pelvic heterotopic ossification: MR imaging
characteristics. Radiology, 2002 Jan;222(1): 189–195.
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