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Neuroradiology Case of the Week

Case 241

Jeremy Duda, BA, Sam McCabe, MD, and P-L Westesson, MD, PhD, DDS

Clinical Presentation: A 13-year-old girl with a tender neck mass associated with fatigue. The patient underwent biopsy and was diagnosed with Ewing’s sarcoma/PNET. She later underwent debridement of the mass and began chemotherapy, and now presents to evaluate interval response to therapy.

Imaging Findings: Axial and coronal MR images obtained pre- and post-gadolinium contrast demonstrate an 8.6 x 10 x 12.5 cm mass involving the soft tissues of the posterior left portion of the neck, from the shoulder to the base of the skull. The margins are well defined without evidence of invasion into adjacent structures. The lesion is hypointense and homogenous on T1 axial images. There is heterogeneous enhancement, especially involving deeper portions compared with the periphery of the mass. On T2 weighted fat saturation the mass is hyperintense with focal areas of decreased signal, suggestive of necrosis and cystic degeneration. Weighted imaging suggests an heterogeneous soft tissue mass containing fluid and areas of necrosis.

Diagnosis: Extraosseous Ewing’s sarcoma

Discussion: Ewing’s sarcoma is a malignant tumor that typically arises in the diaphyses of long bones, accounting for 1% of childhood tumors. However, extraosseous and familial manifestations of the disease have led to the recognition that Ewing’s represents a range of neuroectodermal tumors with similar histological characteristics: poorly differentiated tissue comprised of sheets of small round blue cells. 85% of tumors contain a characteristic translocation t(11;22) (q24;q12) producing a fusion gene involved in transcription.
     Patients present with a painful, erythematous, rapidly enlarging swelling along with constitutional symptoms. When involving the skeleton a pathologic fracture often leads to diagnosis, whereas other sites may present only after several months of symptoms. Ewing’s sarcoma arising outside the skeleton is quite rare, and often arises in the lower extremity or paravertebral region. The tumor often invades local structures including muscle and bone, and metastasizes to lung and bone.
     Ewing’s involving bone may appear radiographically as an osteolytic lesion with periosteal reaction, or on MR demonstrating a soft tissue mass with marrow infiltration. Radiographic findings in extraosseous Ewing’s has a nonspecific appearance and may be differentiated from malignant fibrous histiocytoma and liposarcoma by its absence of calcifications on x-ray and absence of fat on MR. Cross sectional imaging is no more helpful in defining the identity of an extraosseous Ewing’s in the absence of biopsy, although the tumor usually has a well defined border representing a pseudocapsule that may compress adjacent tissues. MR’s primary function is to assess local invasion and tumor response to therapy while CT is a staging tool.
     Definitive diagnosis is made by histological examination of a biopsy specimen. 20-25% of patients present with overt metastases, and their prognosis is poor, but almost all patients have microscopic metastatic disease, necessitating the use of chemotherapy in all cases.
     Overall prognosis has improved with development of treatment modalities consisting of chemotherapy, radiotherapy, and surgical debulking or excision. Patients with either skeletal or extraskeletal Ewing’s without metastases have long-term survival rates of up to 80%.

References:

1. O’Keefe F, Lorigan JG, Wallace S. Radiological features of extraskeletal Ewing’s sarcoma. Br J Radiol. 1990 Jun;63(750):456-60. [Medline]
2. Kennedy JG, Eustace S, Caulfield R, Fennelly DJ, Hurson B, O'Rourke KS. Extraskeletal Ewing's sarcoma: a case report and review of the literature. Spine. 2000 Aug 1;25(15):1996-9. [Medline]
3. Kennedy JG, Frelinghuysen P, Hoang BH. Ewing sarcoma: current concepts in diagnosis and treatment. Curr Opin Pediatr. 2003 Feb;15(1):53-7. [Medline]