Extraskeletal Ewing\'s sarcoma

Clinical History

A 17-year-old woman presented with a history of left shoulder pain irradiating into the left arm and the back of her head with associated ptosis of the left eye. Examination confirmed weakness of the left arm, measured as 4/5 proximally and 3/5 distally on the Medical Research Council scale.

Imaging Findings

Computed tomography (CT) followed by a magnetic resonance imaging (MRI) scan of the neck and thorax showed an expansive paraspinal lesion adjacent to the left lung apex with an “hourglass” expansion into the upper thoracic left posterolateral aspect of the spinal canal through the T1-T2 neuroforamen. There was widening of the neuroforamen with bone scalopping but no bone infiltration was demonstrated. The intraspinal component remained extradural with compression of the thecal sac. About two thirds of the lesion were extraspinal. The mass was iso- to slightly hyperintense to muscle on T1 weighting and hyperintense on T2 weighting. Diffuse heterogeneous contrast enhancement was seen on CT and MRI images with small internal vessels. A hypointense aspect of the intraspinal component was noted on the gadolinium enhanced T1 weighted image, suggestive of necrosis.

Discussion

Our patient presenting an enhancing soft-tissue paraspinal mass with intraspinal-extradural extension, several differential diagnostics were taken into consideration. The observed neural foraminal widening was evocative of a neurogenic tumour. On the other hand, the heterogeneous contrast enhancement and possible necrosis were considered suspicious for a different aetiology such as small round cell tumour or metastasis. Haematologic malignancy was thought to be less likely in the differential diagnostics list.

Our patient showing acute neurological deficits, immediate surgical resection was envisaged after exclusion of distant primary tumour or metastases. A near complete resection of the mass in the spinal canal was achieved. Resection of its paravertebral component, however, was only partially accomplished.

Histology of the resected specimen confirmed a small blue round cell malignant tumour of high cellularity. The possibility of a malignant peripheral nerve sheath tumour (MPNST) was first discussed. However, the morphology of the tumour cells and a CD99 positive cell membrane were not consistent with this diagnosis. Fluorescence in situ hybridisation (FISH) was used for detecting a possible translocation of the EWSR1 gene. Analysis of 50 cells by three readers confirmed translocation of the EWSR1 gene in 87% of all analysed nuclei. A diagnosis of extraskeletal Ewing’s sarcoma (EES) was given.

In 1921, James Ewing (1866-1943) described a tumour which he referred to as diffuse endothelioma of bone [1]. Subsequently, it was called Ewing’s tumour. In total, it comprises 6% of all malignant bone tumours [2].
Rarer is EES, also called primary Ewing’s sarcoma of soft tissue or extraosseous Ewing’s sarcoma, defined as a Ewing’s sarcoma in which no underlying bone involvement is found. It’s an uncommon mesenchymal tumour that has to be differentiated from other small round cell malignant tumours on the basis of immunohistochemistry [2-3].

The majority of EES cases occur in patients between 10 and 30 years of age with a male preponderance. The most common sites affected are the soft tissues of the lower extremity and the paravertebral region [3]. However, EES has also been reported in the abdominal wall [4].

On imaging EES is typically iso- to hyperintense to muscle on T1 weighted MRI images and hyperintense to muscle on T2 weighted MRI images. Large tumours may show heterogenous areas of necrosis and haemorrhage. Calcification is rarely seen on CT [3].

Very few data are available addressing optimal surgical and oncologic treatment modalities of EES.

Differential Diagnosis List

Final Diagnosis

Extraskeletal Ewing's sarcoma

URL:	https://eurorad.org/case/10022
DOI:	10.1594/EURORAD/CASE.10022
ISSN:	1563-4086