Mesoblastic nephroma

Clinical History

A preterm female of 29 weeks gestation was found to have a mass arising from the right kidney on examination.What is the differential diagnosis?And what imaging modalities would assist you in reaching the final diagnosis?

Imaging Findings

Patient was born at 29/40 weeks gestation, by emergency caesarian section for acute polyhydramnios and fetal decelerations. At birth abdominal examination revealed a right sided abdominal mass. Abdominal US and CT scan revealed the mass to be arising from the right kidney.Given the age of the patient and the rarity of Wilms tumour in newborns, a diagnosis of mesoblastic nephroma was suspected.Due to the coexistence of respiratory distress syndrome (ventilatory dependency)and prematurity, elective nephrectomy was planned at 3 months(corrected gestational age of 40 weeks).

Discussion

Mesoblastic nephroma is the most common solid renal tumour in the neonate. It represents 2% of primary renal tumours in childhood. Presentation is usually within the first year of life with a peak incidence at 1-3 months. Males are affected slightly more than females. Mesoblastic nephroma is now recognised as a separate clinical entity, as previously it was believed to be a congenital form of Wilms tumour. It is thought that it arises as a result of disordered nephrogenic mesenchymal proliferation. Clinical presentation, is usually with a palpable abdominal mass, and rarely haematuria. Some cases can be detected by prenatal US. There is an asssociation with polyhydramnios, hyper-reninemia, hydrops fetalis and premature delivery. Imaging studies usually demonstrate a solid intra-renal mass which replaces large areas of renal parenchyma. The mass appears to be of mixed echotexture, because the tumour may contain areas of cystic degeneration, haemorrhage and necrosis. Radiologically (US, CT or MRI) it is not readily possible to distinguish a Wilms tumour from a mesoblastic nephroma. Mesoblastic nephroma is locally invasive with distant metastases being rare, and the recommended curative treatment is nephrectomy. If incompletely excised, local recurrence is common. Prognosis is excellent and is best if the tumour is diagnosed and resected before the age of 6 months. Potentially aggressive variants include the cellular mesoblastic nephroma (histologically proven in our case),where local and distant metastases have been reported. Follow up is recommended in these cases.

Differential Diagnosis List

Final Diagnosis

Right Mesoblastic nephroma

URL:	https://eurorad.org/case/1038
DOI:	10.1594/EURORAD/CASE.1038
ISSN:	1563-4086