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Ewing sarcoma

Dr MT Niknejad and Dr Frank Gaillard et al.

Ewing sarcoma is the second most common primary bone tumour of childhood after osteosarcoma, and may present with very variable radiographic features.

Epidemiology

Typically occurs in children and adolescents between 10 and 20 years of age (95% between 4 and 25 years of age), and has a slight male predilection (M:F 1.5:1) 1-2.

Clinical presentation

Presentation is non-specific with local pain being by far the most common symptom. Occasionally a soft tissue mass may be palpable. Pathological fractures also occur.

Pathology

Ewing sarcoma is a small round blue cell tumour with regular sized primitive appearing cells. It is closely related to the soft tissue tumours pPNET, Askin tumourand neuroepithelioma, which collectively are referred to as Ewing sarcoma family of tumours (ESFT) 1. They share not only microscopic appearances but also demonstrate a non-random t(11;22)(q24;q12) chromosome rearrangement.

Location
  • lower limb : 45%
    • femur most common
  • pelvis : 20%
  • upper limb : 13%
  • spine and ribs : 13%
    • sacrococcygeal region most common 4
  • skull / face : 2%

Alternatively 3:

  • long bones : 50 - 60%
    • femur : 25%
    • tibia : 11%
    • humerus : 10%
  • flat bones : 40%
    • pelvis : 14%
    • scapula
    • ribs : 6%

As far as location within long bones, the tumor is almost always metaphyseal or diaphyseal 2-3:

  • mid-diaphysis : 33%
  • metadiaphysis : 44%
  • metaphysis : 15%
  • epiphysis : 1 - 2%

Radiographic features

Ewing sarcomas tend to be large poorly marginated tumours, with over 80% demonstrating extension into adjacent soft tissues. It should be noted that pPNET often extend into bone, making the distinction difficult.

Plain film and CT

The appearance of these tumours is very variable, but usually have clearly aggressive appearance. Common findings include 2:

They occasionally demonstrate other appearances, including Codman triangles, spiculated (sunburst) or thick periosteal reaction and even bone expansion or cystic components. 

Soft tissue calcification is uncommon, seen in less than 10% of cases 2.

MRI
  • T1 : low to intermediate signal
  • T1 C+ (Gd) : heterogeneous but prominent enhancement
  • T2 : heterogeneously high signal, may see hair on end low signal striations
Nuclear medicine

Ewing sarcomas demonstrate increased uptake on both Gallium67-citrate and Technetium99m methylene diphosphonate scans 6.

Treatment and prognosis

Systemic chemotherapy is the mainstay of treatment with surgery and / or radiotherapy playing a role depending of the location and size of the tumour.

What was once a uniformly fatal tumour now has respectable survival rates, although these vary with location. Spinal tumours for example have up to 86% long term survival compared to 25% of sacrococcygeal tumours 4. The overall 5 year survival is in the order of 50 - 75% of patients with local disease only at the time of presentation 5.

Prognosis is significantly impacted by the presence of distant metastases at the time of diagnosis, which are far more common for the pelvis (25 - 30%) compared to extremities (<10%) 5. Metastases most frequently go to bone or lungs.

Etymology

Named after James Stephen Ewing : American pathologist (1866 - 1943) 8  

Differential diagnosis

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