Kidney tumor
Childhood tumors
Congenital mesoblastic nephroma


Topic Completed: 10 December 2020

Minor changes: 10 December 2020

Copyright: 2003-2021, PathologyOutlines.com, Inc.

PubMed Search: Mesoblastic nephroma[TI] kidney[TIAB]

Ellen D’Hooghe, M.D.
Gordan M. Vujanic, M.D., Ph.D.
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Cite this page: D'Hooghe E, Vujanic GM. Congenital mesoblastic nephroma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/kidneytumormesoblastic.html. Accessed January 15th, 2021.
Definition / general
  • Mesoblastic nephroma is a mesenchymal / myofibroblastic renal tumor of low grade malignancy
  • It typically occurs in infancy, often congenital but not always
  • First described by Bolande et al. in 1967 (Pediatrics 1967;40:272)
Essential features
  • Most common renal tumor in the first month of life
  • 90% of cases diagnosed in the first 9 months of life
  • Virtually never after 3 years of age
  • Adult mesoblastic nephroma does not exist
  • 3 histologic subtypes: classic (~25% of cases), cellular (~65%) and mixed (~10%)
  • Cellular type: ETV6-NTRK3 gene fusion in ~70% of cases
  • Classic type: EGFR internal tandem duplication mutation
  • Most important prognostic factor is completeness of surgical resection
Terminology
  • Historic synonyms: renal leiomyomatous hamartoma, congenital mesoblastic nephroma
  • Although "congenital" is a part of the WHO stated name for this tumor, it is sometimes a misnomer as the tumor is not always present from birth
ICD coding
  • ICD-O: 8960/1 - Mesoblastic nephroma
  • ICD-10: D41.0 - Neoplasm of uncertain behavior of kidney
Epidemiology
Sites
  • Kidney; never bilateral, never multifocal
Pathophysiology
  • Unknown
Etiology
  • No recognized risk factors
  • No familial cases have been reported
  • Cellular type associated with t(12;15)(p13;q25) in ~70% of cases (Pediatr Blood Cancer 2018;65:e26925)
  • Classic type associated with EGFR internal tandem duplication mutation (Histopathology 2020;77:611)
  • Not associated with nephrogenic rests
Clinical features
  • Abdominal mass (~75% of patients) (Pediatr Blood Cancer 2017;64:e26437)
  • ~15% detected prenatally, usually associated with polyhydramnios
  • Hypertension (~20%)
  • Hematuria (~10%)
  • Never presents as metastatic or bilateral disease
  • Virtually never associated with syndromes or anomalies typical for Wilms tumor
Diagnosis
  • Imaging techniques cannot distinguish it from other renal tumors (J Pediatr Surg 2008;43:1301)
  • Biopsy not recommended
  • Diagnosis made on nephrectomy
Laboratory
Radiology description
  • Unilateral, well demarcated, hypoechogenic mass
Radiology images

Images hosted on other servers:
Large renal mass

Large renal mass

Upper pole mass

Upper pole mass

CT large mass

CT large mass

Prognostic factors
  • Most important prognostic factor is completeness of surgical resection
  • Histologic type is of no prognostic significance
  • Overall survival reported as ~96% but is almost certainly higher since cases with unfavorable outcome are more likely to be reported (Pediatr Blood Cancer 2008;50:1130)
  • Of 12/276 patients with mesoblastic nephroma who died, 5 died of tumor related and 7 of treatment related causes (Pediatr Blood Cancer 2017;64:e26437)
  • Very rare local relapses and metastases; 38 cases reported in the literature (Pediatr Surg Int 2017;33:1183)
    • Relapses and metastases occur within 12 months after the diagnosis (range 1 - 12 months, median 6 months)
    • Local relapses in 27/38 (71%) of these cases
    • 21/27 (76%) had incomplete resection (stage 3)
    • All but 1 patient had cellular type but even then, cellular type had no significant difference in prognosis
    • Metastases developed in 18 children (7 also had local recurrence)
    • Lung metastases in 7/18 (39%), liver in 5/18 (28%), brain in 4/18 (22%) and heart, bone and peritoneum in 5.5% each
    • 38% of patients with metastases died (all who had brain, bone, heart and peritoneum metastases)
Case reports
Treatment
Gross description
    • Always unilateral and solitary (Adv Anat Pathol 2003;10:243)
    • Typically found in the medial renal sinus
    • Classic type:
      • Firm, whorled, leiomyomatous consistency
      • Poorly demarcated from the normal renal parenchyma
  • Cellular type:
    • Usually soft
    • Tumor-kidney junction relatively clearly demarcated
    • Cystic areas
    • Can show hemorrhage and necrosis
Gross images

Contributed by Ellen D’Hooghe, M.D., Gordan M. Vujanic, M.D., Ph.D. and Case #57
Classic type

Classic type

Mixed type

Mixed type

Cellular type

Cellular type

Microscopic (histologic) description
  • Classic type (~25% of cases) (Adv Anat Pathol 2003;10:243, Histopathology 1985;9:741):
    • Intermingling fascicles of spindle cells with low mitotic activity
    • Collagen deposition
    • Often prominent dilated, thin walled vascular spaces
    • No capsule
    • Tumor-kidney border is irregular with finger-like protrusions of the tumor into the renal parenchyma
    • Islands of hyaline cartilage can be seen at the tumor-kidney interface
    • Entrapped islands of renal parenchyma
    • Foci of extramedullary hematopoiesis common
  • Cellular type (~65% of cases):
    • High cellularity of plump cells with vesicular nuclei, moderate amount of cytoplasm
    • Sheet-like growth pattern
    • High mitotic activity (which is of no prognostic significance)
    • No capsule
    • Clear tumor-kidney border but subtle infiltration into the renal parenchyma
    • Isolated entrapped tubules, which may be mistaken for neoplastic tubules
  • Mixed type (~10% of cases):
    • Features of both types in a variable proportion
  • Staging criteria are as for nephroblastoma
    • Vast majority are stage 2 due to tumor's infiltrative growth into the renal sinus or perirenal fat
Microscopic (histologic) images

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

Classic type

Classic type vessels

Classic type vessels

Entrapped normal renal parenchyma

Entrapped normal renal parenchyma

Extramedullary hematopoiesis

Extramedullary hematopoiesis

Islands of cartilage

Islands of cartilage

Cellular type

Cellular type


Cellular type

Cellular type

Single entrapped tubule

Single entrapped tubule

Tumor-kidney interface

Tumor-kidney interface

Mixed type

Mixed type

Sinus invasion

Sinus invasion

Perirenal fat invasion

Perirenal fat invasion

Cytology description
  • Fine needle aspiration is not indicated
Positive stains
Negative stains
Molecular / cytogenetics description
Sample pathology report
  • Right kidney, total nephrectomy:
    • Mesoblastic nephroma, cellular type, stage II (due to renal sinus and perirenal fat invasion) (see comment)
    • Comment: Tumor shows dense cellularity with plump cells with vesicular nuclei and with a high mitotic activity. Tumor is infiltrating the renal sinus and perirenal fat but is not reaching the resection margins. Lymph nodes are free of tumor.
Differential diagnosis
Board review style question #1

An 11 month old boy presents with an abdominal mass noticed by parents. Imaging studies show a right sided renal mass. Total right nephrectomy is performed. The tumor is composed of undifferentiated cells with no particular pattern, shown above. Which finding is most characteristic for this entity?

  1. BCOR+
  2. BRAF V600E mutation
  3. ETV6-NTRK6 gene fusion
  4. INI1 loss
Board review style answer #1
C. ETV6-NTRK6 gene fusion. This is a mesoblastic nephroma, cellular type.

Comment Here

Reference: Congenital mesoblastic nephroma
Board review style question #2

What is the most important prognostic factor for mesoblastic nephroma?

  1. Age at presentation
  2. Completeness of resection
  3. Genetic abnormalities
  4. Histologic type
Board review style answer #2
B. Completeness of resection

Comment Here

Reference: Congenital mesoblastic nephroma
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