Metanephric stromal tumor

Metanephric stromal tumor (MST) is a very rare, benign renal neoplasm that predominantly affect children. 

Epidemiology 

Metanephric stromal tumor is characterized by pure stromal morphology, hyper-differentiation, and no metastasis. The median age of diagnosis was 2 years. Less than fifty cases are reported in the literature, and only three of them are adult cases. More than half of all cases were diagnosed between six months and ten years after patients' first visits ^1,2,3. 

Clinical presentation 

Patients typically present with asymptomatic abdominal mass. A few of them develop occasional hematuria, oliguria, or abdominal discomfort or pain ².

Predisposing Factors 

The prevalence of BRAF V600E mutations in metanephric stromal tumor is in need of further investigation ³.

Pathology

Pathological features 

Metanephric stromal tumor is usually centered in the renal medulla except for one case in which the tumor is originated mainly from the renal cortex. Tumor size averages 5.7 cm (range 2.5- 12 cm) with a protruding white-cream, cystic-solid mass that is well-distinguished from normal renal tissue ^3,4.

Radiographic features 

Ultrasound 

Ultrasound reveals a heterogenous mass that is isoechoic compared to the renal parenchyma. Color Doppler ultrasonography can help detect the displacement of the intrarenal vessels ^2,4. 

Computed tomography 

Contrast-enhanced abdominal computed-tomography shows a lobular mass with both cystic and solid components in the affected kidney. Computed-tomography angiography can also be used to detect extrarenal vasculopathy ^2,5. 

Treatment and prognosis

Surgery is the first-line treatment for metanephric stromal tumor. Nephrectomy, partial nephrectomy, and nephroureterectomy can also be indicated ².