Retroperitoneal neoplasms within the perirenal space in infants and children: differentiation of renal and non-renal origin in enhanced CT images.

To retrospectively demonstrate the specific CT findings of retroperitoneal neoplasms to diagnosis and differential diagnosis renal and non-renal tumors within the perirenal space in infants and children.We retrospectively reviewed the clinical data and CT images of 42 consecutive patients with surgically and pathologically proven retroperitoneal neoplasms within the perirenal space. The patients were divided into renal tumors group (n=16) and non-renal tumors group (n=26). The former included nephroblastoma (n=15) and renal lymphoma (n=1), while the latter included neuroblastoma (n=12), retroperitoneal teratoma (n=6), adrenal ganglioneuroma (n=4), retroperitoneal lymphoma (n=2), ectopic pheochromocytoma (n=1) and adrenal cortical carcinoma (n=1). The clinical information of these patients and the major CT imaging findings which were related to lesion localization in the two groups were compared and statistically analyzed using Pearson Chi-Square Test and Risk Estimate.The mean diameter of tumors was 9.82±6.13 cm (n=42 range: 2.3-3 2cm). The demographic data and chief clinical symptoms between the renal tumor group and the non-renal tumor group showed no statistically significant differences (P>0.05). 30.8% (8/26) of non-renal tumor patients presented elevated urinary vanillylmandelic acid (VMA) level, while no patient showed elevated VMA in renal tumor group (P<0.05). Some CT imaging signs of the renal tumors including "crescent sign" (odds ratio, OR=52), "beak sign" (OR=84), "embedded organ sign" (OR=84), and "prominent feeding artery sign" (OR=36) showed significantly higher incidence when compared to the non-renal tumors (P<0.001). The sign of "renal displacement and renal axis rotation" (OR=0.059) was seen in 23 of 26 (88.5%) non-renal tumors, but in only 5 of 16 (31.3%) renal tumors (P<0.001). The sign of "extra-renal central plane of tumor" (OR=0.038) was displayed in 24 of 26 (92.3%) non-renal tumors, but in only 5 of 16 (31.3%) renal tumors (P<0.001). The CT findings such as "pseudocapsule" (OR=38.5), "necrosis and cystic change" (OR=11.2), "vascularity" (OR=16.867), "distant metastasis" (OR=5.96), and "inferior vena cava tumor thrombus" which were thought to be characteristic of renal tumors were observed with significant higher incidence in renal tumors group than in the non-renal tumors group (P<0.05); while CT signs of "irregular mass" (OR=0.045) and "intratumoral calcifications" (OR=0.065) were observed with lower incidence in renal tumors group than in the non-renal tumors group (P<0.05).The "crescent sign", "beak sign", "embedded kidney sign" and "renal arteries feeding" are the most specific CT signs suggestive of renal tumors and distinguish them from non-renal origin tumors within the perirenal space. Other CT signs, such as "pseudocapsule", "hypervascular tumors" and "Inferior vena cava tumor thrombus", when present, tumors of renal origin are strongly suggested. On the other hand, CT signs of "irregular mass", "intratumoral calcifications", and associated elevated urinary vanillylmandelic acid strongly suggest the non-renal tumors.