Teaching Case

A 12-year-old male patient presented with a 1-month history of an abdominal mass. He had no abdominal pain, vomiting, constipation, bleeding per rectum or weight loss.

Grey scale ultrasound revealed a 9 by 8 by 7 cm predominantly hypoechoic mass with a focus of linear calcification within the peritoneal cavity, lying between bowel loops. Colour Doppler revealed peripheral vascularity with an arterial waveform. A right-sided hydroureteronephrosis was noted. CT examination showed a mixed density mass lesion appearing to 'arise out of nowhere' lying above and behind the bladder, intraperitoneal in location, and displacing bowel loops but not causing bowel obstruction. The lesion showed peripheral enhancement with central areas of necrosis/haemorrhage. A linear hyperdense area was noted, similar to that on grey scale ultrasound, consistent with calcification. A right-sided hydroureteronephrosis was also seen due to compression of right ureter by the mass.

Desmoplastic small round cell tumour (DSRCT) is a rare, potentially fatal abdominopelvic tumour, first described by Gerald and Rosai [1] in 1989, presenting predominantly in young male patients, with a 4:1 male to female ratio, and with a survival of 2-3 years [2]. Histologically, these tumours are characterised by cluster of poorly differentiated cells with blue cytoplasm lying in desmoplastic stroma [3]. The tumour cells express epithelial, mesenchymal, myogenic and neural markers distinguished by chromosomal translocation t (11;22) (p13; q12) resulting in the fusion of the Ewing’s sarcoma (EWSR1) and the Wilms’ tumour (WT1) genes [4]. The tumour predominantly develops as a primary tumour of the peritoneal cavity with transperitoneal seeding to the omentum, and metastases to liver, lungs, distal nodes, and less commonly to the scrotum and ovaries [5].
Patient presentation is non-specific, usually with an abdominal mass slowly increasing in size with no symptoms of bowel obstruction. Clinically, a hard mass with restricted mobility is palpable. Patients usually have ureteric obstruction leading to hydroureteronephrosis and may present with secondary pyonephrosis. Imaging studies help in identifying the origin of the mass, associated complications, and the presence of metastasis. The tumour is diagnosed by radiological-pathological correlation and needs appropriate, targeted oncological management for longer patient survival.
Imaging features of DSRCT on ultrasound include a large lobulated heterogeneous, predominantly solid mass with central necrotic areas which show vascularity on colour Doppler with or without echogenic foci with distal shadowing due to calcification. Due to its large average size of 11.2cm [7] and predominantly retrovesical location, it has a tendency to cause hydronephrosis due to ureteric obstruction. Features of bowel obstruction are not frequently encountered [6]. On CT, large masses have low attenuation with central heterogeneous areas showing no contrast enhancement, suggesting central necrosis. Foci of calcification can be seen in up to 30% of cases [7, 8, 9]. Liver and nodal metastasis are hypoattenuating [9]. Ultrasound guided biopsy for histopathology and IHC studies is usually taken. The diagnosis is established on histopathology with round cells with blue cytoplasm surrounded by desmoplastic cellular stroma.
The current management is Ewing-sarcoma-based polychemotherapy and debulking surgery. Follow-up scans will help in assessing size reduction, thus confirming response to therapy.
Prognosis of DSRCT remains poor with frequent relapses and incomplete cure [2, 3]. DSRCT must be considered as a differential in young males with abdominal mass.

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