Kidney tumor
Benign adult tumors
Renomedullary interstitial cell tumor

Topic Completed: 19 May 2020

Minor changes: 1 June 2020

Copyright: 2003-2020,, Inc.

PubMed Search: Renomedullary interstitial cell tumor

Rachelle Gietzen, M.D.
Eduardo Eyzaguirre, M.D.
Page views in 2019: 2,756
Page views in 2020 to date: 2,687
Cite this page: Gietzen R, Eyzaguirre E. Renomedullary interstitial cell tumor. website. Accessed October 24th, 2020.
Definition / general
  • Benign kidney tumor
  • Asymptomatic, commonly found incidentally
  • Arise from renomedullary interstitial cells
  • Also known as medullary fibroma
Essential features
  • Frequently found at autopsy, incidentally on imaging or resection for other reasons
  • Arising from medullary interstitial cells
  • Small, well circumscribed, single or multiple gray-white nodules in the renal medulla
  • Spindle or stellate cells in basophilic stroma with entrapped tubules
  • Prior terms include medullary fibroma and renal hamartoma
ICD coding
  • ICD-10: D30.00 - Benign neoplasm of kidney
Clinical features
  • Asymptomatic, found incidentally during surgery (0.2%), autopsy (16 - 46%) or radiologic investigation (Urology 2014;83:1104)
  • May be symptomatic in case reports (e.g. urosepsis or hematuria) (Urology 2014;83:1104)
Radiology description
Radiology images

Images hosted on other servers:

Incidental tumor

Prognostic factors
Case reports
Gross description
  • Well circumscribed, homogenenous white / gray-white nodules usually in the medulla
  • Small (1 - 13 mm), median tumor size 4 mm and up to 5 cm has been reported in case reports (Hum Pathol 2018;82:46)
  • Arises from medulla but occasionally from the cortex (Urology 2014;83:1104)
  • Surrounding kidney tissue showed that 47% had normal renal parenchyma, 28% showed slight glomerulosclerosis, 19% moderate and 7% severe glomerulosclerosis (Am J Surg Pathol 2016;40:1693)
Gross images

AFIP images

Multiple small tumors

Images hosted on other servers:

Firm, well circumscribed tumor

White tumor

Microscopic (histologic) description
Microscopic (histologic) images

Contributed by Eduardo Eyzaguirre, M.D.

Medullary based tumor

Small stellate cells

Positive stains
Negative stains
Electron microscopy description
  • Resembles renomedullary interstitial cell of kidney with large cytoplasmic lipid droplets (Hum Pathol 1972;3:559)
Sample pathology report
  • Kidney, right, laparascopic complete nephrectomy:
    • Renal cell carcinoma, clear cell type (see synoptic report)
    • Renomedullary interstitial cell tumor
  • Kidney, right, mass, needle core biopsy:
    • Renomedullary interstitial cell tumor
Differential diagnosis
  • Metanephric stromal tumor:
    • Concentric rings or collarettes of stromal cells around entrapped renal tubules and blood vessels
    • Unencapsulated infiltrative tumor of spindle and epithelioid cells
    • Rare in adults
  • Scar:
    • History of poor renal function, renal stones or prior procedures
    • Not well circumscribed
    • Less basophilic
    • More likely to be associated with inflammation
Board review style question #1

An 85 year old man underwent nephroureterectomy for low grade papillary urothelial carcinoma of the renal pelvis. A 3 mm white, solid, medullary based incidental lesion is noted on gross examination. Which of the following is true for this tumor?

  1. They are uncommon tumors seen more frequently in children
  2. They are typically medullary based tumors composed of stellated interstitial cells immersed in a basophilic matrix with entrapped renal tubules
  3. Although the majority are benign, rarely metastasis have been described
  4. Frequently, they present with hematuria and flank pain
Board review answer #1
B. This is a renomedullary interstitial cell tumor. They are typically medullary based tumors composed of stellated interstitial cells immersed in a basophilic matrix with entrapped renal tubules.

Reference: Renomedullary interstitial cell tumor

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Board review style question #2
Which is true about renomedullary interstitial cell tumors?

  1. Often, these tumors are unifocal, found within the cortex and more than 10 mm in size
  2. They are asymptomatic and often found incidentally during nephrectomy or at autopsies
  3. They are CD34 and ER positive and desmin and smooth muscle negative
  4. Congo red stain is characteristically positive in all tumors
  5. Specialized myofibroblast is the probable cell of origin
Board review answer #2
B. They are asymptomatic and often found incidentally during nephrectomy or at autopsies

Reference: Renomedullary interstitial cell tumor

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