Musculoskeletal #7 – Long case

10-year-old male:

Axial CT brain bone windows

Non-enhanced axial CT brain soft tissue window

Where is the lesion?

Occipital bone within the medullary cavity

What is it like?

Moth-eaten destructive permeative lytic lesion with wide zone of transition.  There is cortical disruption of both the inner and outer table of the skull and a large soft tissue component.

An MRI is performed.
Axial T1Weighted

Axial T2Weighted
Axial Gadolinium enhanced T1Weighted
What does the MRI show?

Destructive bone lesion with a large soft tissue component which is low signal intensity on T1, heterogenous intermediate signal on T2, and heterogeneous intense enhancement in the post contrast image. It causes mass effect on the adjacent brain parenchyma with no gross invasion.

What is the differential diagnosis?

Given the age of the patient the differential diagnosis includes:

* Osteosarcoma: most common primary bone tumor in young adults. Usually involves the metaphyseal regions of long bones but can occur at other sites. Aggressive lesion with sunburst periosteal reaction and calcified osteoid matrix. 

* Ewing's sarcoma: second most common childhood bone tumor. Typically an aggressive permeative tumor which arises within the medullary cavity of the bone and has a large soft tissue component. 

* Metastasis.

What is the most likely diagnosis?

Ewing’s sarcoma

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