Case report
A 6-year old boy was admitted to the hospital due to a 3-day right lower abdominal distension, the child’s family complained that the child got a pain and discomfort in the right lower abdomen after getting up in the morning of July 4, 2016. The family found that the right lower abdomen was raised, accompanied with obvious tenderness as well as slight nausea, the body temperature was 37.5℃. They went to the emergency room of a local hospital. Abdominal ultrasound and CT indicated that the right lower abdomen was occupied with a huge mass. Therefore, they came to our hospital for further diagnosis and treatment. There was no past or family history of kidney diseases or renal trauma. Physical examination showed a swelling in the right upper abdomen with a palpable mass of about 10cm in size, with unclear boundary, poor mobility. Laboratory examinations of complete blood count, serum biochemistry, and urinalysis were normal. Additional imaging with magnetic resonance imaging (MRI) demonstrated a 11.7×11.7×9.8cm size heterogeneous mass originating from the lower pole of the right kindey with a clear boundary. On T2WI, the mass showed mixed signals with multiple low signal separations (Fig. 1A,B ). The mass was dominated with low intensity accompanied patchy hyperchromatic areas on T1WI (Fig. 1C ); DWI showed high signal mixed up with patchy higher signal shadow (Fig. 1D ); ADC presented uneven mixed signals (Fig. 1E ). The tumour constricted pelvic canal junction and caused mildly dilated right renal pelvis and calyceal system. Besides, pancreatic head, duodenum and abdominal aorta were compressed to the left, ascending colon and transverse colon, meanwhile were pushed leftward and downward. The contralateral kidney was normal. The patient underwent right nephrectomy due to suspicion of Wilms’ tumor and the mass was pathologically diagnosed as an IMT (Fig. 2A ), in which spindle cells were admixed with variable amounts of neutrophils, plasma cells, and lymphocytes on a mucinous background (Fig. 2B ). Immunohistochemistry demonstrated positive labeling for SMA, CD34, CD99, while Ckp, P53 and Ki-67 (30%) were focally positive, but no staining for HMB45, Calponin, Nelan-A, S-100, CD10, or EMA. The remaining renal parenchyma and adrenal gland were unremarkable. Surgical margins were clear and no histologic evidence of extension into the renal vein, artery or ureter. The patient recovered well after operation, and no recurrence or metastasis was noted during follow-up.