JPC SYSTEMIC PATHOLOGY
URINARY SYSTEM
January 2018
U-N06 (NP)

SIGNALMENT:  9-month-old female Fisher 344 rat.

HISTORY:  This rat received a single injection of dimethylnitrosamine at one day of age.

HISTOPATHOLOGIC DESCRIPTION:  Kidney:  Effacing and replacing approximately 70% of the cortex and medulla is an unencapsulated, infiltrative, poorly differentiated neoplasm composed of spindle to stellate cells.  Spindles cells are arranged in streams and tightly packed whorls that surround and entrap tubules, glomeruli and cystic spaces, and infiltrate adjacent normal cortex on a fine collagenous to myxomatous matrix. Stellate cells are arranged in loose streams widely separate and replace preexisting tubules, glomeruli and cystic spaces, and extend to the renal pelvis.  Neoplastic cells have indistinct cell borders, scant to moderate eosinophilic fibrillar, occasionally vacuolated cytoplasm, and oval to elongate nucleus that is vesiculate, and has 1-2 variably distinct nucleoli.  Mitoses within the stellate cells average 1 per 10 HPF. Mitoses within the spindle cells average 1 per HPF and there is occasional single cell necrosis characterized by shrunken cells with hypereosinophilic cytoplasm and pyknosis.  Entrapped glomeruli are atrophied and surrounded by a dilated Bowman’s space. Entrapped tubules are scattered throughout the neoplasm are variably dilated and cystic, lined by epithelium that is either attenuated or hyperplastic, and multifocally contain homogenous eosinophilic material (proteinaceous fluid) or basophilic granular material (mineral) and occasionally neutrophils and cellular debris (cellular casts). Within the adjacent renal cortex, tubules contain one or more of the following changes: degeneration, characterized by swollen vacuolated cytoplasm and faded nuclei; or regeneration, characterized by basophilic nuclei and rare mitotic figures.  Multifocally, there are moderate numbers of mildly dilated tubules, and the interstitium is mildly expanded by small numbers of lymphocytes and plasma cells (interstitial nephritis).

MORPHOLOGIC DIAGNOSIS:  Kidney:  Renal mesenchymal tumor (RMT), Fisher 344 rat, rodent.

SYNONYMS:  Renomedullary interstitial cell tumor, malignant mesenchymal tumor

GENERAL DISCUSSION:

PATHOGENESIS:

TYPICAL GROSS FINDINGS:

TYPICAL LIGHT MICROSCOPIC FINDINGS:

ULTRASTRUCTURAL FINDINGS:

DIFFERENTIAL DIAGNOSIS:

COMPARATIVE PATHOLOGY:

This tumor is found only in laboratory rodents and humans

REFERENCES: 

  1. Breshears MA, Confer AW. The urinary system, In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2016:671.
  2. Cianciolo RE, Mohr FC. Urinary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer's Pathology of Domestic Animals. 6th ed. Vol 2. Philadelphia, PA: Elsevier Saunders;2016:447.
  3. Hard GC. Mesenchymal tumor, kidney, rat. In: Jones TC, Mohr U, Hunt RD, eds. Urinary System. Heidelberg, Germany: Springer-Verlag; 1986:61-71.
  4. Hard GC. Tumours of the kidney, renal pelvis and ureter. In: Turusov VS, Mohr U, eds. Pathology of Tumours in Laboratory Animals. 1. Lyon, France; International Agency for Research on Cancer; 1990:307-311.
  5. Meuten DJ, Meuten TLK. Tumors of muscle. In: Meuten DJ, ed. Tumors in Domestic Animals. 5th Ames, IA: Wiley Blackwell; 2017:650-651.
  6. Meuten DJ, Everitt J, Inskeep W, Jacobs RM, Peleteiro M, Thompson KG. Histological classification of tumors of the urinary system of domestic animals. In: Schulman FY, ed. World Health Organization International Histological Classification of Tumors of Domestic Animals. Vol. XI. Second Series. Washington, DC: Armed Forces Institutes of Pathology; 2004:22-23.
  7. Mohr U, ed. Urinary System. In: International Classification of Rodent Tumors. Part I: The Rat. Lyon, France; International Agency for Research on Cancer; 1992:13-17.
  8. Murphy WM, Grignon DJ, Perlman EJ. Kidney tumors in adults. In: Tumors of the kidney, bladder, and related urinary structures, AFIP Atlas of Tumor Pathology. Fascicle 1. Fourth Series. Washington, DC: American Registry of Pathology; 2004:194-195.
  9. Tsuda H, Krieg K. Neoplastic lesions in the kidney. In: Mohr U, Dungworth DL, Capen CC, eds. Pathobiology of the Aging Rat. Vol. 1. Washington, DC: ILSI Press; 1992:235-240.


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