Kidney tumor
Childhood tumors
Congenital mesoblastic nephroma

Topic Completed: 1 December 2011

Minor changes: 8 September 2020

Copyright: 2003-2019,, Inc.

PubMed Search: Congenital mesoblastic nephroma [title] kidney

Mandolin S. Ziadie, M.D.
Page views in 2019: 6,463
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Cite this page: Ziadie MS. Congenital mesoblastic nephroma. website. Accessed September 24th, 2020.
Definition / general
  • Congenital myofibroblastic tumor that resembles infantile fibromatosis / leiomyoma (classic) or fibrosarcoma (cellular)
  • Also called fetal mesenchymal / leiomyomatous hamartoma
  • First described in 1967 (Pediatrics 1967;40:272)
  • Most common pediatric renal tumor in infancy
  • 5% of all pediatric renal tumors (Cancer 2006;106:2275)
  • Age at presentation varies with type (classic, 16 days; cellular, 5 months; mixed, 2 months)
  • Rarely occurs in children older than 2 years of age
  • Frequency: 66% cellular, 24% classic and 10% mixed
Diagrams / tables

AFIP images

Age distribution curve

Clinical features
  • May present in utero with fetal hydrops / polyhydramnios
  • Excellent prognosis (5 year survival of 96%, Pediatr Blood Cancer 2008;50:1130)
  • 5% - 10% recur or metastasize (usually cellular type), usually by age 1 year to lung, brain or rarely bone
  • Poor prognostic factors include: cellular variant (Pediatr Surg Int 2007;23:205) and advanced stage or sinus / vascular involvement (margins and sinus / vascular involvement should be reported)
Case reports
  • Nephrectomy with wide margins
  • Chemotherapy if resection is incomplete in infants 3 months or older, or if tumor ruptures during surgery
Gross description
  • Unilateral
  • Extensive sampling of margin should be performed
  • Classic: mean 5 cm, variably circumscribed, white / yellow whorled mass near hilum, involving over half of kidney with indistinct tumor kidney interface; resembles leiomyoma with whorled cut surface; may be cystic; may involve renal sinus; hemorrhage and necrosis uncommon
  • Cellular: mean 9 cm, necrosis and large cystic areas and hemorrhage
  • Mixed: mean 10 cm, cysts, hemorrhage and necrosis in cellular areas
Gross images

Case of the Week #57

Tan fleshy masses
with hemorrhage,
necrosis and cystic

Images hosted on other servers:

Tan fleshy masses
with hemorrhage,
necrosis and cystic

Rubbery solid
tumor invades the
renal parenchyma

Microscopic (histologic) description
  • Classic: resembles infantile fibromatosis or leiomyoma with fascicles and whorls of bland spindled myofibroblasts and thin collagen fibers; tumor surrounds tubules and glomeruli, has irregular borders; chondroid metaplasia / dysplasia of the entrapped tubules is common; mitoses are rare; necrosis / desmoplasia are not present
  • Cellular: resembles infantile fibrosarcoma with a sheet-like proliferation of plump, atypical spindle cells with abundant cytoplasm, vesicular nuclei and nucleoli; frequent mitotic figures (25 - 30 / 10 HPF) and necrosis; the tumor has a pushing border
  • Mixed: tumors with a combination of the above features
Microscopic (histologic) images

AFIP images

Prominent interlacing bundles

Tumor interdigitates with renal parenchyma

Perirenal invasion
with angiomatous

Embryonal metaplasia of Bowman capsule and entrapped tubules; #2 accompanied by epithelial hyperplasia


Extension into renal sinus
and along structures medial
to the kidney is an important
feature of most lesions

Cellular pattern:

Cellular and classic appearance

Mesoblastic Nephroma

Case of the Week #57

Well circumscribed tumor: low power

Medium power

High power

Infiltrative margin

Glomerular entrapment

Angiomatoid area

Images hosted on other servers:

Resembles fibromatosis

Mitotic figures

Cellular areas have
mitotic figures, cystic
degeneration, hemorrhage
and necrosis

Cytology description
Positive stains
Negative stains
Molecular / cytogenetics description
Differential diagnosis
  • Adult mixed epithelial and stromal tumor: mean age in 50s, usually women, similar morphology and staining pattern, also positive for estrogen and progesterone receptors
  • Clear cell sarcoma: similar age but has clear cells and chicken wire vasculature, tumor cells isolate single nephrons, fine nuclear chromatin and low mitotic rate; negative for smooth muscle markers
  • Metanephric stromal tumor: older age, nodular low power pattern, onion skin cuffing around entrapped renal tubules, heterologous differentiation and vascular changes, CD34+
  • Rhabdoid tumor: more invasive margins, usually epithelioid cells with cytoplasmic inclusions and prominent nucleoli, usually presents with metastases, INI1-
  • Wilms tumor: older age, also has blastema and nephrogenic rests; previously treated tumors may have well differentiated spindle cell stroma
Additional references
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