[1775] Cellular Congenital Mesoblastic Nephroma: Clinical-Diagnostic Imaging-Pathologic Features

J Hicks, P Bayindir, M Chintagumpala, P Guillerman. Texas Children's Hospital, Baylor College of Medicine, Houston, TX

Background: Congenital mesoblastic nephroma (CMN) is the most common renal neoplasm of infancy. 2 CMN forms exists - classic (low cellularity, resembling myofibroma) and cellular (high cellularity, resembling congenital infantile fibrosarcoma). Cellular CMN is locally aggressive and invasive, and associated with metastatic disease. Cellular CMN shares similar histopathologic features and the tumor-defining translocation [t(12;15), ETV6-NTRK3] with congenital infantile fibrosarcoma.
Design: Pathology archives were searched over a 10 year period for cellular CMNs (n=8, age range 6d to 6 mos, 5M:3F). Clinical presentation was large palpable abdominal mass with hypertention (6/8), hypercalcemia (2/8), hematuria (2/8), and in utero polyhyrdramnios (1/8). Tissue was available for microscopic, ultrastructural, cytogenetic and RT-PCR translocation studies.
Results: Diagnostic imaging showed large renal masses (5.5 to 14.6cm). Tumors crossed the midline and encased major vessels in 2 cases. There was paravertebral, retroperitoneal and intraspinal tumor extension in 1 case. Tumors were Stage 1 or 2 in 5 cases. Tumor weights ranged from 137 to 1,552 gms. Tumors had a fleshy character with some areas of cystic degeneration and hemorrohage. Tumors were highly cellular spindle cell proliferations with minimal supporting stroma. Mitotic rate was brisk. Tumors lacked encapsulation and infiltrated the adjacent normal kidney. 4 tumors infiltrated the renal capsule with extension into perirenal adipose tissue (3/4). Electron microscopy showed spindle cells with infrequent collagen. In the stroma, there was dense granular, amorphous material previously characterized for congenital infantile fibrosarcoma. Cytogenetics and RT-PCR identifed the t(12;15) tranlsocation. Metastastic disease occurred in 2 patients (liver, lung, peritoneum). Chemotherapy was required in 4 patients due to inability to perform a primary resection at diagnosis or due to metastatic disesae. At a mean follow-up peroid of 3.6 years, 1 patient died of disease and 7 are free of disease.
Conclusions: Cellular CMN is distinctive aggressive, invasive neoplasm with metastatic potential. This tumor shares histopathologic, ultrastructural and molecular features with congenital infantile fibrosarcoma. Renaming cellular CMN as Congenital Infantile Renal Fibrosarcoma should be considered in order to provide appropriate workup, therapy and followup for infants with this aggressive primary renal tumor.
Category: Ultrastructural

Monday, March 9, 2009 1:00 PM

Poster Session II # 245, Monday Afternoon