A 27 year old man presented with vague abdominal pain two weeks after trauma to the abdomen by a cricket ball. The pain was felt in the right lower quadrant with an intermittent increase in severity. There were no systemic or other gastrointestinal symptoms. On physical examination there was a firm, non-tender mass in the right lumbar region. The mass was not mobile, not ballottable. Abdominal sonography showed hypoechoic mass lesion on both sides of the spine, extending from the lumbar region up to the pelvis. His complete haemogram (haemoglobin, total leucocyte count, differential leucocyte count, platelet count), serum glucose, renal and liver function tests, chest radiograph, and electrocardiogram were normal; his erythrocyte sedimentation rate was 60 mm/hour.

Computed tomography of the abdomen (figs 1 and 2) showed bilateral, rounded, hypoattenuated, and fluid dense mass lesions (rim enhancing on contrast) within the psoas muscle sheath, extending from lumbar region up to the pelvis. Psoas muscles on both sides showed curvilinear compression. Similar fluid dense lesions were visualised in the gluteal muscles (fig 3). Liver, spleen, kidneys, pancreas, and para-aortic areas were normal.

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Figure 1

Computed tomography of the abdomen showing bilateral, rounded, hypodense lesions within the psoas sheath (arrows). Note curvilinear compression of psoas muscles on both sides.

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Figure 2

Computed tomography of the abdomen showing similar changes as in fig 1 but at a lower level.

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Figure 3

Computed tomography findings showing hypoattenuated fluid dense lesions within gluteal muscles (arrows).