Pelvic Ewing sarcoma in an infant.

Clinical History

We present a 14-month-old infant with pain during passive motion of right upper leg and inability to bear weight during first attempts to walk. No external signs of inflammation (rubor, calor) were present. Pregnancy and childbirth were unremarkable. Alkaline Phosphatase (449 U/L) and CRP (34 mg/L) were elevated.

Imaging Findings

Pelvic radiographs (Fig. 1 a, b) showed asymmetry of the iliac wings with deformity and increase in size, as well as suspected soft tissue swelling on the right. The cortical borders were irregular and partially sclerotic. There was suspected widening of the SI-joint and a coarse bony structure. The ipsilateral pubic and ischium bones and the contralateral hemipelvis were normal in appearance. The axial view of the right hip showed a centrally placed femoral head with no abnormalities.
Coronal T1-weighted MR image (Fig. 2 a) demonstrated expansion of the iliac wing, approx. 3.3cm in width with predominantely low, inhomogenous uptake of gadolinium following contrast administration (Fig. 2 b). Axial T2w SPIR images showed a lamellar periosteal pattern (Fig. 3 b) and a radiating, striated pattern posteriorly (Fig. 3 c) with diffuse enhancement of the parosteal soft tissue (Fig. 2 b, 3 d). There was mild effusion in the hip joint.

Discussion

Ewing sarcoma is the second most common primary malignant bone neoplasm in children and adolescents, accounting for approximately 10% of malignant bone tumours. The tumour is of primitive neuroectodermal origin, primarily arising from the bone marrow; the pelvic bone being among the most frequent sites of manifestations, followed by long bone metaphysis. 75% of the patients are younger than 19 years, median age is 14 and manifestation in infancy is extremely rare but has been described [1, 2].
The clinical presentation may resemble osteomyelitis with pain, swelling and signs of infection in laboratory results. Radiographs of any suspected bone/joint problem is the primary diagnostic approach, regardless of age. Anatomy, bony destruction and possible matrix calcification/ossification can be appropriately evaluated on the radiographs. Radiographic appearance again has many similarities with osteomyelitis, with permeative, moth-eaten lucencies, reactive sclerosis and signs of cortical destruction.
As proper thorough clinical examination can be challenging in infants due to pain and anxiety, the clinical differential diagnosis also includes coxalgia, due to septic or idiopathic arthritis, Perthes disease, slipped capital femoral epiphysis and transient hip synovitis which could be quickly excluded based on MRI.
MR imaging excludes a non-aggressive origin with strong evidence of a periosteal reaction and ballooning/expansion of the bone presenting as mass effect, generally not present in osteomyelitis. Soft tissue enhancement on both sides of the affected bone suggests malignant osseous disease favouring Ewing sarcoma with a differential diagnosis of lymphoma, being less likely due to pronounced reactive sclerosis and extraosseous involvement.
Definitive diagnosis is based on biopsy and histological examination in combination with cytogenetics.
The pre-treatment MR imaging has a very important role in evaluation of the primary tumour extension. Since the tumour is generally chemo-sensitive with good radiological response to treatment, there will be significant reduction in tumour volume and gadolinium enhancement. PET may have additional value in determination of treatment response. Tumour load, metastasis, responsiveness to chemotherapy and adequate surgical margins are the major factors influencing the prognosis [3].
Ewing sarcoma in infants must be considered when infiltrative bony destruction with a large soft tissue component is evident.
Plain radiographs followed by MR imaging is the preferred diagnostic examination of choice in evaluation of Ewing sarcoma and osteomyelitis.
Osteomyelitis, leukaemia and lymphoma may present a similar radiographic appearance but are less likely when a large extra-osseous mass is present on MR imaging.
Laboratory parameters such as alkaline phosphatase and CRP are non-specific.

Differential Diagnosis List

Final Diagnosis

Ewing sarcoma

URL:	https://www.eurorad.org/case/11625
DOI:	10.1594/EURORAD/CASE.11625
ISSN:	1563-4086