Cellular Mesoblastic Nephroma with Liver Metastasis in a Neonate: Prenatal and Postnatal Diffusion-Weighted MR Imaging
A 30-year-old woman pregnant with a fetus at 30 weeks gestational age was referred to the obstetrics department of our hospitals, due to an increasing fetal abdominal mass. The fetal mass was first detected at 26 weeks gestation on a routine antenatal US at a local clinic. The mother had no contributing medical or surgical history to explain the mass growth. Another fetal US was performed in the emergency room with a 1-5 MHz curved array transducer (IU22, Philips Medical Systems, Best, The Netherlands). This US revealed a huge left abdominal mass that was composed of both solid and cystic areas, and Doppler US also showed increased vascularity. Fetal cardiomegaly and polyhydramnios were also detected.\nA fetal MRI was obtained on the same day using a 1.5T MR scanner (InteraAchieva, Philips Medical Systems, Best, The Netherlands). Single-shot turbo spin-echo sequences (in the axial, coronal, and sagittal planes), coronal T1-weighted images with spectral presaturation inversion recovery, and axial DWI using four b-values (0, 50, 400, 800 smm-2) were obtained. The MRI showed a huge soft tissue mass (about 8 × 9 × 10 cm) in the left fetal retroperitoneum (). This mass not only displaced the abdominal aorta, but also moved the bowel loops to the right. The right kidney was seen in the right renal fossa, but the left kidney was not visualized. Solid portions in the mass had multiple cystic spaces. The solid portions were of low signal intensity on the T1-weighted images and of intermediate signal intensity on the T2-weighted images. On DWI, diffusion restriction was observed in the solid portions of the mass with apparent diffusion coefficient (ADC) value of 1.02 × 10-3 mm2/sec. No hemorrhage or necrosis was observed.\nAn emergency caesarian section to deliver the female infant was performed the next day due to signs of preterm labor and fetal distress. Immediately after birth, an abdominal radiograph showed a large soft tissue mass occupying the neonate's left abdomen. An abdominal US also showed a huge mass with solid and cystic portions in the left retroperitoneum, as previously seen on the fetal MRI (). Additionally, the mass compressed the aorta to the right without evidence of encasement. The right kidney showed diffusely increased parenchymal echogenicity with renal pelvic dilatation.\nFive days after birth, the neonate underwent radical excision of the tumor in the left retroperitoneum. The surgeon reported that the mass originated from the left kidney that crossed the midline and was composed of solid and cystic lesions. The upper and posterior aspect of the mass was severely adhered to the peritoneum, without bowel adhesion.\nOn pathologic review, the mass was grossly found to be composed of solid and cystic portions and confirmed as originating from the left kidney (). On microscopic examination, there were uniform fascicles of spindle cells with increased cellularity and frequent mitosis in the focal area of the tumor, characteristics suggestive of the cellular variant of CMN. Heterogeneous mesenchymal elements, such as cartilage and fat, were also noted. The final pathological diagnosis was mixed CMN with focal cellular variant (less than 10%).\nAt seven weeks of age, local tumor recurrence was detected in the left retroperitoneum on abdominal US. It was observed as a complex cystic mass similar to the primary mass. This local tumor recurrence grew rapidly during the follow-up period. Its longest diameter increased from 5 cm to 8.6 cm in just two weeks. At nine weeks of age, a whole body MRI with DWI showed a recurrent cystic mass in the left retroperitoneum with one newly developed hepatic nodular lesion (). The lesion in the liver showed low signal intensity on the T1-weighted images and high signal intensity on the T2-weighted images. In addition, this hepatic lesion showed diffusion restriction on DWI, although the recurrent lesion did not. The ADC value of the liver lesion was 1.99 × 10-3 mm2/sec and the ADC value of the surrounding liver parenchyma was 2.37 × 10-3 mm2/sec. A chest CT showed no visible metastatic lesions. The patient responded well to a chemotherapy regimen composed of vincristine, dactinomycin, and endoxan. After four months, no tumor was grossly found remaining in both the retroperitoneum and liver on MRI; this finding was also supported by no visible tumor on the operation field, which was performed for intestinal obstruction secondary to adhesions. Therefore, the hepatic nodular lesion was considered as metastasis. So far, during a 7 month follow-up period after the detection of local tumor recurrence, the patient has undergone 8 cycles of chemotherapy without evidence of tumor growth.