Report and follow-up on two new patients with Congenital Mesoblastic Nephroma
Authors: Serra Gregorio , Cimador Marcello , Giuffrè Mario , Insinga Vincenzo , Montante Claudio , Pensabene Marco , Piro Ettore , Salerno Sergio , Schierz Ingrid Anne Mandy , Corsello Giovanni 
Published: January 2023

Abstract
Background
Tumors are rare in neonatal age. Congenital mesoblastic nephroma (CMN) is a usually benign renal tumor observed at birth, or in the first months of life. It may also be identified prenatally, and associated with polyhydramnios leading to preterm delivery. Effective treatment is surgical in most cases, consisting in total nephrectomy. In literature, very few studies report on the neonatal management of such a rare disease, and even less are those describing its uncommon complications.
Cases presentation
We report on two single-center newborns affected with CMN. The first patient is a preterm female baby, born at 30+1 weeks of gestation (WG) due to premature labor, with prenatal (25 WG) identification of an intra-abdominal fetal mass associated with polyhydramnios. After that clinical stability, weight gain, instrumental (computed tomography, CT, showing a 4.8 x 3.3 cm left renal neoformation) and histological/molecular characterization of the lesion (renal needle biopsy picture of classic CMN with ETV6-NTRK3 translocation) were obtained, a left nephrectomy was performed at 5 weeks of chronological age. The following clinical course was complicated by intestinal obstruction due to bowel adherences formation, and then by an enterocutaneous fistula, requiring multiple surgical approaches including transitory ileo- and colostomy, before the conclusive anastomoses intervention. The second patient is a 17-day-old male term baby, coming to our observation due to postnatal evidence of palpable left abdominal mass (soon defined through CT, showing a 7.5 x 6.5 cm neoformation in the left renal lodge), feeding difficulties, and poor weight gain. He then developed hypertension and hypercalcemia, needing intravenous diuretic treatment and which regressed after nephrectomy (histological diagnosis of cellular CMN with ETV6-NTRK3 fusion), performed at day 26. In neither case was chemotherapy added. Both patients have been included in multidisciplinary follow-up, and presently show regular growth and neuromotor development, normal renal function and no local/systemic recurrences or other gastrointestinal/urinary disorders.
Conclusions
The finding of a fetal abdominal mass should prompt suspicion of CMN, especially if it is associated with polyhydramnios, and alert obstetricians and neonatologists also for the risk of preterm delivery. Although being a usually benign condition, CMN may be associated with neonatal systemic-metabolic or postoperative complications. High-level surgical expertise, careful neonatological intensive care, and histopathological/cytogenetic-molecular definition are the cornerstones for the optimal management of patients. This should also include an individualized follow-up, oriented to early detection of any possible recurrences or associated anomalies, and to improve the quality of life of these children and their families.