Clinical History
A 40-year-old woman with a known osteochondroma in the left distal tibial metaphysis consulted for a growing mass in the same ankle, with tenderness and posterior tibial nerve compression symptoms.
Imaging Findings
Radiographs (Fig. 1) showed the osteochondroma and posterior noncalcified soft-tissue mass in the ankle. An ultrasound (Fig. 2) was performed revealing a solid soft-tissue mass, in close relationship with the posterior tibial nerve.
MRI (Fig. 3) was performed showing an oval lesion within the Kager fat pad with intermediate to high signal intensity on T1W images and heterogeneous signal intensity on T2W images, with areas of both intermediate and high signal intensity. No high-flow vascular channels were noted. The mass showed diffuse contrast-enhancement. The lesion was adjacent to the posterior tibial cortex but not to the osteochondroma. There were no signs of medullary invasion. The posterior tibial nerve could be seen apparently entering the mass. This last feature suggested the possible diagnosis of a neurogenic tumour.
Percutaneous biopsy of the lesion was performed and anatomopathological study revealed findings for an extraskeletal Ewing sarcoma.
Discussion
Extraskeletal Ewing sarcoma (EES) is a highly malignant tumour, likely of neuroectodermal origin, included in the Ewing sarcoma family of tumours, which share a translocation of the long arms of chromosomes 11 and 22 (q24;q12) [1].
When compared with its osseous counterpart, EES is relatively rare and usually affects young patients (mean age is 20 years) [1].
Tumours are often large at diagnosis and rapidly growing. Clinical presentation depends on the location of the lesion, which most commonly affects the paravertebral region and the lower extremities. Metastases are common at presentation, lung and bone being the most frequent sites [2].
Histologically, the tumour consists of undifferentiated small round blue cells, that usually contain glycogen. The tumour can be distinguished from other small round cell tumours by immunohistochemical and cytogenetic or molecular analysis [3].
Imaging presentation is that of a nonspecific soft-tissue mass with prominent contrast enhancement. Large tumours usually show heterogeneous signal intensity on MR images, due to haemorrhage and necrosis. Tumours are usually hyperintense on T2W images with or without intermediate signal intensity areas, as a result of the high cellularity. Fluid levels might also be seen due to haemorrhage. An imaging feature that is nonspecific but can assist in diagnosis is the presence of serpentine high-flow vascular channels [4]. Surface osseous changes (cortical erosion or periosteal reaction), without evidence of marrow space invasion, have also been described in the adjacent bone [4]. Calcification may be present but is not a typical feature [2].
Treatment usually combines chemotherapy and surgery, with or without radiation therapy [1].
In conclusion, EES usually affects young patients and reveals an imaging appearance of a nonspecific soft-tissue mass. Although nonspecific, the presence of serpentine high-flow vascular channels is a radiologic feature that can suggest this diagnosis.
Differential Diagnosis List
Extraskeletal Ewing sarcoma
Neurogenic tumour
Vascular lesion (haemangioma
haemangiopericytoma...)
Synovial sarcoma
Lymphoma
Chondrosarcoma
Undifferentiated pleomorphic sarcoma
Final Diagnosis
Extraskeletal Ewing sarcoma
