Kidney tumor

Childhood tumors

Metanephric stromal tumor


Editorial Board Members: Maria Tretiakova, M.D., Ph.D., Bonnie Choy, M.D.
Ellen D’Hooghe, M.D.
Gordan M. Vujanic, M.D., Ph.D.

Last author update: 4 May 2021
Last staff update: 14 March 2023

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PubMed Search: Metanephric stromal tumor

Ellen D’Hooghe, M.D.
Gordan M. Vujanic, M.D., Ph.D.
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Cite this page: D'Hooghe E, Vujanic GM. Metanephric stromal tumor. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/kidneytumormetastromal.html. Accessed March 19th, 2024.
Definition / general
  • Benign pure mesenchymal renal neoplasm
  • Belongs to the group of metanephric tumors
  • First described by Argani and Beckwith in 2000 (Am J Surg Pathol 2000;24:917)
Essential features
  • Rare benign purely mesenchymal renal tumor
  • Belongs to metanephric tumors
  • 67% of patients between 6 months and 10 years (range 2 days to 56 years)
  • Multifocal in ~10% of cases; never bilateral in cases reported to date
  • Characteristic alternating cellularity resulting in a nodular appearance
  • CD34 positive
  • Associated with BRAF V600E mutations
  • Treated with radical or partial nephrectomy
  • Only 1 recurrence and 1 death (related to vascular abnormalities) reported
Terminology
  • Adult mesoblastic nephroma (in the old literature)
ICD coding
  • ICD-O: 8935/1 - stromal tumor, NOS
Epidemiology
  • Rare tumor, < 50 cases reported in the literature (J Pediatr Urol 2020;16:822)
  • Age 2 days to 56 years (median 2 years, mean < 4 years)
  • 67% between 6 months and 10 years
  • 3 adult cases
  • M:F = 1.2:1
Sites
  • Kidney; multifocal in ~10% of cases
  • Never bilateral
Pathophysiology
Etiology
  • Not known
Clinical features
  • Asymptomatic abdominal mass (~53% of patients) (J Pediatr Urol 2020;16:822)
  • Always unilateral in reported cases to date
  • Abdominal discomfort or pain (~21%)
  • Hematuria (17%)
  • High blood pressure (~10%)
Diagnosis
  • No distinguishing imaging features
  • Diagnosed as a renal mass, some with cystic and solid components
  • Biopsy unhelpful
Laboratory
  • No abnormalities
Prognostic factors
Case reports
Treatment
  • Surgery (radical nephrectomy) is regarded as the only mode of treatment necessary
  • Some cases treated with partial nephrectomy
  • No chemotherapy necessary
  • Reference: J Pediatr Urol 2020;16:822
Gross description
  • Centrally located in the renal medulla
  • Lobulated, often cystic (~55% of cases)
  • Multifocal in ~10% of cases
  • 2.5 - 12 cm (median 5 cm)
  • Rarely protrudes into renal pelvis (botryoid growth)
  • In 5 - 6% of cases, renal artery aneurysms found (Int J Surg Pathol 2011;19:667)
Gross images

Contributed by Ellen D’Hooghe, M.D. and Gordan M. Vujanic, M.D., Ph.D.
Gross appearance

Solid and cystic tumor with hemorrhage

Microscopic (histologic) description
  • Well circumscribed and unencapsulated tumor (Am J Surg Pathol 2000;24:917)
  • No major infiltration of the renal parenchyma; instead, has a scallop-like border
  • Nodular appearance on low power view due to alternating cellularity
  • "Onion skin" cuffing around entrapped tubules, which may show:
    • Cystic dilatation
    • Embryonal hyperplasia
    • Intraluminal growth (fibroadenoma-like pattern)
  • Vascular changes:
    • Angiodysplasia of entrapped arterioles
    • Juxtaglomerular cell hyperplasia
  • Heterologous elements in ~20% of cases (glial, chondroid but never skeletal muscle)
Microscopic (histologic) images

Contributed by Ellen D’Hooghe, M.D. and Gordan M. Vujanic, M.D., Ph.D.
Nodularity

Nodularity

Alternating cellularity

Alternating cellularity

"Onion skinning"

"Onion skinning"

Cysts

Cysts


Angiodysplasia

Intratubular growth

Tumor - kidney interface

Angiodysplasia

Intratubular growth

Tumor - kidney interface

CD34

CD34

Positive stains
Molecular / cytogenetics description
Sample pathology report
  • Kidney, total nephrectomy:
    • Metanephric stromal tumor (see comment)
    • Comment: Tumor shows a nodular appearance on the low power view due to alternating hypo and hypercellularity of spindle cells. Entrapped renal tubules are surrounded by concentric layers of the same cells ("onion skinning"). There are some blood vessels showing angiodysplasia. The tumor - kidney interface is clearly demarcated with only subtle infiltration. Tumor does not infiltrate the renal sinus or perirenal fat. Tumor cells show strong and diffuse CD34 positivity. Molecular studies show a BRAF V600E mutation. This is a benign tumor, which requires no further treatment.
Differential diagnosis
Board review style question #1

A 3.5 year old boy presented with an abdominal mass. Imaging studies revealed a left sided renal mass. Total left nephrectomy was performed. The tumor was composed of hypocellular and hypercellular areas of spindled cells. Which finding is most characteristic for this entity?

  1. BCOR+
  2. CD34 positivity of tumor cells
  3. ETV6-NTRK3 gene fusion
  4. Infiltrative tumor - kidney border
Board review style answer #1
B. CD34 positivity of tumor cells

Comment Here

Reference: Metanephric stromal tumor
Board review style question #2
Which of the following is correct regarding metanephric stromal tumor?

  1. It contains a stromal and an epithelial component
  2. It is associated with BRAF V600E mutations
  3. It is treated with surgery and chemotherapy
  4. It never occurs after 3 years of age
Board review style answer #2
B. It is associated with BRAF V600E mutations

Comment Here

Reference: Metanephric stromal tumor
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