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Findings: Fluid is noted in the posterior dependent portion of the right side of the peritoneum. The fluid is not effacing adjacent structures or organs. It is in an unusual location partially behind the margin of the kidney.
Diagnosis: Congenital anomaly of the retroperitoneum with a benign fluid collection
Discussion:Diagnosis of an abscess depends upon the location and appearance of fluid collections. The attentuation of the fluid is not specific for transeudates, exudates or malignant effusions. The location of the fluid is atypical because the lateral conal fascia on the right apparently didn't fuse normally leaving a space within the posterior renal (Gerota'a) fascia. If the patient is immunocompetent the lack of effacement of adjacent structures is usually reliable to indicate sterility or benignancy.
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