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Mesoblastic nephroma

A mesoblastic nephroma (also sometimes known as a congenital mesoblastic nephroma (CMN) or fetal renal hamartoma) is in general a benign renal tumour. It typically occurs in utero or in infancy.

Epidemiology

It is the commonest neonatal renal tumour. Diagnosis is usually in the antenatal period or immediately after birth. The tumour can account for ~ 3-6 % of all renal neoplams in children 3,7. Approximately 50% occur during the neonatal period and 80% of cases are reported within the first month of life.

Clinical presentation

Most common clinical presentation is a palpable abdominal mass, with haematuria occurring less frequently.

Pathology

It is a mesenchymal tumour. Macroscopically the tumour is a solid un-encapsulated mass which often occurs near the renal hilum tends to invade the surrounding structures and renal parenchyma. Haemorrhage and necrosis are infrequent. Histologically, it is typically composed of connective tissue growing between nephrons, usually replacing most of the renal parenchyma.

The classic cytological description of the lesion is that of cellular clusters of spindle cells, mild nuclear pleomorphism, mitotic activity and no blastema.

Sub types

There are two main pathological variants :

Associations

Radiographic features

Plain film

Non specific and not an imaging modality of choice but if performed incidentally in a neonate, may demonstrate a soft tissue mass displacing bowel. Calcification is rare 3.

Ultrasound

Sonographic appearance can vary depending on the pathological variant 6. In general it is a well-defined mass with low-level homogeneous echoes. The presence of concentric echogenic and hypoechoic rings can be a helpful diagnostic feature. A more complex pattern due to haemorrhage, cyst formation and necrosis can also be seen and tends to favour the cellular variant. Colour Doppler interrogation may show increased vasculairty

Antenatal ultrasound may also show evidence of associated polyhydramnios.

CT

Usually not performed in an antenatal situation. Tends to be generally of low attenuation at CT. More content required.

MRI

Best modality for cross sectional imaging antenatally and can better assess anatomical relationships.  

Unless complicated necrosis and haemorrhage (both generally uncommon), general signal characteristics within the mass include

  • T1 - homogeneously hypo-intense 8
  • T2 - homogeneously hypo-intense 8

Complications

Potential complications with large tumours include

Treatment and prognosis

The majority are benign tumours and have a favourable outcome. The cellular variant can at times be aggressive. As a surgical option, a nephrectomy usually suffices as treatment.

See also

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