JPC SYSTEMIC PATHOLOGY

URINARY SYSTEM

January 2024

U-P09

 

Signalment (JPC #1851283): Adult male beagle.

 

HISTORY: Incidental finding in an apparently healthy dog.

 

HISTOPATHOLOGIC DESCRIPTION: Kidney: The renal pelvis is markedly expanded by clear space, and the medulla and cortex are compressed into a 5 mm thick band of tissue (hydronephrosis). There is stromal collapse and close apposition of glomeruli, with loss of approximately 80% of the renal tubules and replacement by dense fibrous connective tissue, abundant macrophages, eosinophils, lymphocytes, plasma cells, and neutrophils. Multifocally, glomerular tufts are shrunken, and contain one or more of the following changes: contain plump parietal and visceral epithelial cells (hypertrophy), parietal epithelium piled up to 3 layers thick (hyperplasia), adherence of visceral epithelium to Bowman’s capsule (synechia), and dilation of the uniferous space by pale eosinophilic homogenous to flocculent fluid (proteinosis). Remaining tubules are shrunken or collapsed (atrophy), with one or more of the following changes: epithelial cells are swollen with vesiculate nuclei (degenerate) or shrunken with hypereosinophilic cytoplasm and pyknotic nucleus (necrosis), lumen contain sloughed epithelial cells or contain brightly eosinophilic amorphous fluid (tubular proteinosis). The renal capsule, and to a lesser extent the perirenal adipose tissue, is irregularly thickened and expanded up to 0.5 mm by a dense band of fibrous connective tissue, numerous small caliber vessels, and abundant macrophages, fewer lymphocytes, plasma cells, eosinophils, neutrophils, and scattered multinucleate giant cells (foreign body and Langhans types) often centered on nematode eggs. Eggs measure approximately 75 x 40 µm, are round to oval with an 8 µm thick, brown, mammillated, anisotropic shell and contain either a larva measuring 20 µm in diameter, or an embryo measuring 30 µm in diameter (operculated egg). The pelvic urothelium is piled up to 15 cell layers thick (hyperplasia) and urothelial cells are often swollen with vacuolated cytoplasm (degeneration).  

 

Adjacent to the kidney are adult nematodes which measure approximately 10 x 5 mm, have a 10 µm thick cuticle, polymyarian-coelomyarian musculature, pseudomembranes attached to the enteron, ventral nerve cord, an intestine lined by many uninucleate columnar cells with a prominent brush border, and a uterus with numerous eggs.

 

MORPHOLOGIC DIAGNOSIS: Kidney: Pyelonephritis, granulomatous and eosinophilic, chronic-active, diffuse, severe, with hydronephrosis, fibrosis, and capsular and perirenal nematode eggs, larvae, and adults, beagle, canine.

 

ETIOLOGIC DIAGNOSIS: Renal dioctophymiasis

 

CAUSE: Dioctophyma renale 

 

GENERAL DISCUSSION: 

• A member of the superfamily Dioctophymoidea 
• Known as the “giant kidney worm,” the largest of all nematodes 
• The parasite has a worldwide distribution; endemic in Canada and the northern US
• Primarily found in mustelids and canids, in the pelvis of the right kidney or free in the abdominal cavity
• Definitive hosts are fish-eating carnivores, especially mink; infections have been recorded most often in mink, dogs, cats, and wild canids

 

PATHOGENESIS:

 

LIFECYCLE:

• Prolonged lifecycle that may take up to 2 years from egg to adult worm 
• Involves one (or two) intermediate hosts (aquatic oligochaete annelid [mud worm]; fish or frog) and one definitive host (carnivore)
  1. Eggs are passed in the urine, embryonate in the environment (1-7 months), and are ingested by the worm intermediate host, where they encyst in the body cavity and develop into L1 and L2 stages
  2. Encysted larva may continue to develop into infective L3 and L4 stages in the worm or in a second intermediate host (fish or frog)
  3. Ingestion of infective L3-L4 larvae by mammals results in larval penetration by the gut and migration across the peritoneal cavity to the kidney
  4. Adult worms live in the renal pelvis, but may also encyst in the peritoneal cavity, uterus, mammary gland, or urinary bladder
• Dogs are considered abnormal hosts:
  1. Very few adults present, only 1/3 of infections have worms of both sexes present, and most are not patent 
  2. 60% of infected dogs only have parasites in the peritoneal cavity, which may encircle a liver lobe and case infarction or rupture +/- hemoperitoneum 

 

TYPICAL CLINICAL FINDINGS:

• Infection is usually asymptomatic
• Hematuria
• Renal failure if bilateral 

 

TYPICAL GROSS FINDINGS:

• Typically unilateral; the right kidney more commonly affected than the left due to proximity of right kidney to stomach
• Hemorrhagic to suppurative pyelitis, ureteral obstruction, and hydronephrosis with an intra-renal red cylindrical worm; up to 45 cm long and 6 mm wide (males) or up 100 cm long and 12 mm wide (females)
• Compensatory enlargement of the unaffected kidney 
• Nematodes may be occasionally observed in the peritoneal cavity with associated chronic perihepatitis and peritonitis 

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Hemorrhagic and purulent pyelitis +/- ureteral obstruction with hydronephrosis 
• Parenchymal collapse, fibrosis, and multifocal lymphoplasmacytic to mixed lymphocytic, plasmacytic, eosinophilic, and neutrophilic inflammation 
• Transitional cell hyperplasia and degeneration in the renal pelvis 
• Nematode: Thick smooth cuticle, polymyarian-coelomyarian musculature, ventral nerve cords, uninucleate columnar intestinal cells, uterus with thick shelled eggs
• Eggs: Thick shelled, pitted, barrel-shaped, embryonated eggs with slightly flattened ends

 

ADDITIONAL DIAGNOSTIC TESTS:

 

DIFFERENTIAL DIAGNOSIS:

• Parasites reported in canine kidneys include:

1. Toxocara canis (U-P05): Initial granulomatous response surrounding an entrapped larva, followed by a focal fibrous scar on the kidney surface or cortex  
2. Pearsonema (Capillaria) plica: Nematode found in the renal pelvis, ureter, and urinary bladder of small carnivores; causes little inflammation
3. Leishmania sp. (U-P03): Glomerulonephritis from immune complex deposition in vessel walls, +/- nonsuppurative interstitial nephritis, amyloidosis, and intrahistiocytic amastigotes

 

COMPARATIVE PATHOLOGY:

 

References:

1. Cianciolo RE, Mohr FC. Urinary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology 
2. Keel MK, Terio KA, McAloose D. Canidae, Ursidae, Ailuridae. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018:248-249.
3. Sula MM, Lane LV. The Urinary System. In: Pathologic Basis of Veterinary Disease. 7^th ed. St. Louis MO: Elsevier; 2022:754
4. Uzal FA, Plattner BL, Hostetter JM. Alimentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. Philadelphia, PA: Elsevier Saunders; 2016:255.

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