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Metanephric adenoma of kidney

Metanephric adenoma (MA) of the kidney is a type of benign renal neoplasm

Epidemiology

While it can present at any age 6, the peak age of occurrence is thought to be around the 5th to 6th decades 2. There may be a 2:1 female preponderance 2

Clinical presentation

Metanephric adenoma is asymptomatic in many patients. Some patients can have abdominal pain and haematuria. 

Pathology

Metanephric adenoma is histologically characterized by the arrangement of monotonous small blue embryonal epithelial cells in an acinar, tubular, or sheetlike configuration. True cystic forms of metanephric adenoma are rare.

Abundant psammoma bodies are commonly found. There is some pathological overlap with that of Wilms tumours.

Immunochemistry may help in diagnosis and can show positivity to markers such as vimentin, pancytokeratin and cytokeratin-19 3.

 

Associations
  • polycythaemia: a characteristic finding seen in approximately 10% of patients with metanephric adenoma, promptly disappears after surgical resection. 

Radiographic features

General

They are difficult to differentiate from other renal tumours such as renal cell carcinomas on imaging grounds 1. Metanephric adenoma however typically appears as a well-defined, unencapsulated, solitary solid mass. 

CT

It commonly appears as a hyperattenuating mass on unenhanced CT; large tumors appear as heterogeneous, hypovascular masses with frequent foci of hemorrhage and necrosis. Calcification is seen in 20% of cases. 

MRI

Usual signal characteristics include:

  • T1: hypointense signal 2,6-7
  • T2: usually slightly hyperintense 2,6 but sometimes hypointense 7
Ultrasound

Metanephric adenoma appears as an expansile hypoechoic or hyperechoic mass on sonography. 

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