NAVLE Veterinary Pathology and Necropsy Interpretation — Questions and Answers
Question 1: Necropsy of an 8-year-old dog reveals a 4 cm hepatic mass with a tan cut surface, no central necrosis, and a pushing border compressing but not invading adjacent parenchyma. Histology shows well-differentiated hepatocytes in a solid pattern. The most appropriate classification is:
- Hepatocellular carcinoma — aggressive treatment warranted
- Hepatocellular adenoma (hepatoma) — typically benign, wide surgical excision curative (Correct answer)
- Nodular hyperplasia — no treatment required
- Metastatic carcinoma — full staging required
Correct answer: Hepatocellular adenoma (hepatoma) — typically benign, wide surgical excision curative
Hepatocellular adenomas (hepatomas) are well-encapsulated, well-differentiated benign tumors in dogs with a pushing border and no invasion. Hepatocellular carcinoma shows vascular invasion, necrosis, and nuclear pleomorphism. Nodular hyperplasia is typically multifocal and small (≤1 cm). Metastatic carcinoma would show an infiltrative pattern and non-hepatocyte histology.
Question 2: A 6-month-old calf dies acutely. Necropsy reveals a 'paint-brush' hemorrhage pattern on the epicardium, fibrinonecrotic plaques in the abomasum, and hemorrhagic lymph nodes. Which pathologic process most likely caused these lesions?
- Septicemia with gram-negative lipopolysaccharide-mediated disseminated intravascular coagulation (DIC) (Correct answer)
- Vitamin E/selenium deficiency (white muscle disease)
- Copper toxicity with intravascular hemolysis
- Johne's disease with chronic protein-losing enteropathy
Correct answer: Septicemia with gram-negative lipopolysaccharide-mediated disseminated intravascular coagulation (DIC)
Petechial/ecchymotic hemorrhages (paint-brush pattern) on serosal surfaces combined with hemorrhagic lymph nodes and mucosal necrosis are classic findings of endotoxemia-induced DIC in calves, most commonly from gram-negative septicemia (e.g., Salmonella, E. coli). LPS activates the coagulation cascade, consuming clotting factors and causing bleeding diathesis. White muscle disease shows pale streaking of skeletal/cardiac muscle.
Question 3: Histologic examination of a canine skin biopsy shows epidermal hyperplasia, parakeratosis, Munro microabscesses (neutrophil collections in the stratum corneum), and perivascular lymphocytic infiltrate in the superficial dermis. This pattern is most consistent with:
- Pemphigus foliaceus
- Superficial bacterial pyoderma
- Psoriasiform-lichenoid dermatitis (Correct answer)
- Mast cell tumor with epidermal reaction
Correct answer: Psoriasiform-lichenoid dermatitis
Psoriasiform-lichenoid dermatitis in dogs is characterized histologically by epidermal hyperplasia (psoriasiform), parakeratosis, intracorneal neutrophil accumulations (Munro microabscesses), and a lichenoid (interface) or superficial perivascular infiltrate. Pemphigus foliaceus shows acantholytic cells and subcorneal pustules; pyoderma shows suppurative folliculitis.
Question 4: A 10-year-old cat dies of renal failure. Necropsy shows bilaterally small, pale, irregularly pitted kidneys. Histology reveals tubular atrophy, interstitial fibrosis, glomerulosclerosis, and lymphoplasmacytic interstitial infiltrate. The most accurate pathologic diagnosis is:
- Acute tubular necrosis secondary to nephrotoxin
- Chronic tubulointerstitial nephritis (end-stage kidney disease) (Correct answer)
- Feline infectious peritonitis (FIP) pyogranulomatous nephritis
- Renal lymphoma with parenchymal replacement
Correct answer: Chronic tubulointerstitial nephritis (end-stage kidney disease)
Chronic tubulointerstitial nephritis is the most common cause of chronic kidney disease (CKD) in cats. The classic gross appearance is bilaterally symmetrical small, pale, granular kidneys. Histologically the hallmark is tubular atrophy, interstitial fibrosis, and lymphoplasmacytic infiltrate — representing end-stage scarring. Acute tubular necrosis shows tubular swelling and necrosis without fibrosis. FIP nephritis is pyogranulomatous with vasculitis.
Question 5: Cytology of a fine-needle aspirate from a splenic mass in a 9-year-old Golden Retriever shows large cells with abundant cytoplasm containing hemosiderin, erythrophagocytosis, and rare mitotic figures with no distinct cell clusters. The most appropriate interpretation is:
- Round cell tumor consistent with lymphoma
- Extramedullary hematopoiesis — benign, no treatment needed
- Histiocytic sarcoma — aggressive malignancy requiring staging (Correct answer)
- Hemangiosarcoma — poorly exfoliating, cytology likely non-diagnostic
Correct answer: Histiocytic sarcoma — aggressive malignancy requiring staging
Large pleomorphic cells with erythrophagocytosis and abundant cytoplasm on splenic aspirates are characteristic of histiocytic sarcoma, an aggressive malignancy particularly prevalent in Golden Retrievers and Bernese Mountain Dogs. Hemangiosarcoma is notoriously poorly exfoliating on FNA (blood only usually). Lymphoma shows small-to-large lymphocytes. Extramedullary hematopoiesis lacks pleomorphic large macrophagic cells.
Question 6: A horse is found dead in the pasture after a period of colic. Necropsy reveals a segment of jejunum that is dark red-black, wet, and lacks motility when manipulated, with a well-demarcated transition from normal bowel. The mesenteric vessels to this segment contain thrombi. This pattern is most consistent with:
- Large colon displacement — non-strangulating obstruction
- Strangulating lipoma causing small intestinal volvulus
- Strangulating obstruction with venous infarction from mesenteric thrombus (Correct answer)
- Anterior enteritis (proximal duodenojejunitis)
Correct answer: Strangulating obstruction with venous infarction from mesenteric thrombus
Dark red-black discoloration ('red infarction') with a sharp demarcation line and mesenteric thrombosis indicates strangulating obstruction with venous occlusion leading to hemorrhagic infarction. The bowel is non-viable. Strangulating lipomas cause physical constriction but don't typically involve mesenteric thrombi as the primary lesion. Non-strangulating obstructions do not produce immediate full-thickness ischemic necrosis.
NAVLE Veterinary Pathology and Necropsy Interpretation
Necropsy of an 8-year-old dog reveals a 4 cm hepatic mass with a tan cut surface, no central necrosis, and a pushing border compressing but not invading adjacent parenchyma.
Histology shows well-differentiated hepatocytes in a solid pattern.
The most appropriate classification is: