Congenital mesoblastic nephroma (CMN) accounts for approximately 5% of paediatric renal tumours with the highest peak of incidence during the first 3 postnatal months. CMN almost always has a favourable prognosis. Therefore, CMN needs to be correctly diagnosed and differentiated, principally histologically, from other pediatric neoplasms. We present a clinicopathologic study of 5 cases of CMN.

Atypical congenital mesoblastic nephroma presenting in the perinatal period. Pediatr Surg Int. 2007 Mar;23(3):205-9. Epub 2006 Nov 9.

Congenital mesoblastic nephroma (CMN) is a rare tumour of infancy having an overall good prognosis. The less common, atypical CMNs have cellular elements in them and tend to have an unpredictable course. Occurrence in the perinatal period may further change the outcome. By reporting three patients presenting in the perinatal period with atypical CMN, an attempt is made in this paper to characterize the clinical behaviour of these variant tumours. Though one of our patients had an uneventful course, the other two had several complications including polyhydramnios, prematurity, hypertension, haemodynamic instability and tumour spillage. The course was complicated by recurrence in the latter two and refractoriness to chemotherapy and death in one. That the atypical subset of CMNs occurring in the perinatal period can have a stormy course is well illustrated by this report. Possible prognostic factors are evaluated and the sparse reports of similar cases in the literature are reviewed and compared.

Congenital mesoblastic nephroma presenting with massive hematuria and hemorrhagic shock: report of one case.Acta Paediatr Taiwan. 2006 May-Jun;47(3):135-8.

Congenital mesoblastic nephroma (CMN) is a rare benign tumor that occurs during the neonatal period and early infancy. The vast majority of these tumors present as asymptomatic palpable abdominal masses. We describe an unusual presentation of a CMN in a 10-month-old male infant who presented with massive hematuria and the development of hemorrhagic shock. Abdominal ultrasound showed a heterogeneous solid complex mass measuring 4.8 x 3.5 cm arising from the upper pole of the left kidney. The patient was resuscitated using intravenous fluids and blood transfusions because persistent massive bloody urine leading to progressive shock occurred the night of the admission day. Preoperative diagnosis was possible Wilms tumor of the left kidney. The histopathological findings were consistent with the character of a cellular variant of CMN. The patient was free of recurrence and metastasis at the 2-year follow-up examination. Our case report suggests that CMN is a rare benign renal tumor during infancy and may present with unusual massive hematuria and shock.

Expression of ETV6-NTRK in classical, cellular and mixed subtypes of congenital mesoblastic nephroma.Histopathology. 2006 May;48(6):748-53.

AIM: Congenital mesoblastic nephroma (CMN) is the commonest renal tumour of infancy, with classical, cellular and mixed histological subtypes described. A specific ETV6-NTRK3 fusion-gene product is reported in association with the cellular variant. The aim was to investigate the relationship between the presence of this product and morphological phenotype using paraffin-embedded archival material. METHODS AND RESULTS: Cases of CMN from a single centre during a 15-year period (1989-1994) were identified, anonymized and blindly classified using morphological criteria. RNA was extracted from frozen and paraffin sections for both conventional reverse transcriptase-polymerase chain reaction (RT-PCR) and quantitative real-time RT-PCR. Fifteen samples were analysed; two were non-informative and three expressed ETV6-NTRK3 using both techniques, two showing similar expression, whilst one showed expression two orders of magnitude lower, from a cellular tumour. All fusion positive cases were previously classified as cellular subtype. Six patients had mixed-subtype tumours in which the cellular components, morphologically indistinguishable from cellular tumours, were fusion negative, as were all classical cases. CONCLUSIONS: Real-time PCR Taqman assays, using both fixed and frozen tissue, provide highly reproducible detection and quantification of fusion transcript expression. Differences in expression levels may explain previous conflicting data on fusion gene detection in these tumours.

Prenatal diagnosis of congenital mesoblastic nephroma. A case report. Arch Pediatr. 2005 May;12(5):561-3.

Antenatal ultrasounds allow the detection of renal tumors, especially renal mesoblastic nephromas, but only the pathological analysis of the surgical specimen can confirm this diagnosis postnatally. OBSERVATION: We report the prenatal discovery of a mesoblastic nephroma because of premature labour. Postnatal early surgery was decided because of possible complications in this premature infant. Histology revealed mesoblastic nephroma. COMMENTS: We point out the diagnostic elements of congenital mesoblastic nephroma, especially in what is related to arterial hypertension and hypercalcemia, histology and cytogenetics.

Multicystic congenital mesoblastic nephroma.Int J Surg Pathol. 2002 Jan;10(1):59-63. 

This report describes an unusual example of congenital mesoblastic nephroma cellular variant that presented in a 1-week-old neonate as a multicystic tumor of the kidney. Extensive pseudocystic cavitation resulted from progressive accumulation of ground substance in a loosely myxoid tissue composed of stellate- and spindle-shaped cells that compressed and infiltrated renal tissue. The cells of the tumor were positive for vimentin and smooth muscle actin. The patient is alive and well 16 years after surgery. Differential diagnosis from segmental cystic dysplasia, cystic intralobar nephrogenic rest, cystic nephroma, cystic partially differentiated nephroblastoma, cystic nephroblastoma, and cystic clear cell sarcoma of the kidney, all of which may present at this age, is discussed.

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