Age / Sex : 24 / M

Chief complaint : Knee pain for 2 months

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 : Sung Mi Sook, The Catholic University of Korea, Bucheon St. Mary’s hospital

Fibrous dysplasia

Discussion

Answer:  

Fibrous dysplasia

Findings:

A juxtacortical intramedullary asymmetric
bone lesion is noted in the anterolateral aspect of proximal tibia. The margin
of the lesion is irregular and sclerotic. The cortex of affected area is
effaced and expansile. The lesion is relatively well enhanced following
contrast administration. There is no evidence of peritumoral edema or soft
tissue edema.

Differential Diagnosis:

Solid aneurysmal bone cyst, nonossifying fibroma, chondroma, low
grade osteosarcoma

Diagnosis:
 

Fibrous
dysplasia

Discussion:

Plain radiography

- scalloping of the endosteum, bony
expansion, typically sharply marginated

- variable radiopacity, depending on the
relative proportion of fibrous and osseous tissue in the lesions;
characteristic ground-glass appearance

- chronic changes secondary to bone
weakening, with bowing of weight-bearing structures, fracture, and remodeling, producing
the characteristic shepherd’s crook deformity, so well-known in the femur.

MRI

- largely isointense to skeletal muscle on
T1WI and typically heterogeneously hyperintense with hypointense, isointense or
markedly hyperintense areas within on T2WI.

Depending on the appearance on both the T1
and T2WI, the heterogeneous areas may be due to calcification, cystic changes,
fatty areas or septations.

- enhancement characteristics: patchy
central enhancement, rim enhancement, homogeneous enhancement.

References:

1. Cortical
lesions of the tibia: characteristic appearances at conventional radiography.

Levine SM,
Lambiase RE, Petchprapa CN. Radiographics. 2003
Jan-Feb;23(1):157-77.

2. Magnetic resonance imaging appearances of fibrous dysplasia. Shah ZK, Peh WC, Koh WL, Shek TW. Br J Radiol. 2005 Dec;78(936):1104-15.