NAVLE Canine Medicine and Surgery 5

Question 1

A 7-year-old intact male Golden Retriever presents with progressive exercise intolerance, muffled heart sounds, and jugular venous distension. Echocardiography reveals a large pericardial effusion. Cytology of the pericardial fluid shows hemorrhagic fluid with no neoplastic cells identified. Which of the following is the MOST likely underlying etiology?

Accepted Answer

Hemangiosarcoma of the right atrium

Answer

In large-breed dogs, particularly Golden Retrievers and German Shepherds, hemorrhagic pericardial effusion is most commonly caused by hemangiosarcoma of the right atrium/auricle. Despite the hemorrhagic nature, cytology is frequently non-diagnostic because neoplastic cells exfoliate poorly into effusions and are difficult to distinguish from reactive mesothelial cells. Idiopathic pericarditis is the second most common cause but is a diagnosis of exclusion. Mesothelioma and chemodectoma occur but are less frequent than hemangiosarcoma in this breed and presentation.

Question 2

A 4-year-old Labrador Retriever is presented for acute vomiting and hematemesis 36 hours after accidental ingestion of ibuprofen. BUN is 85 mg/dL, creatinine is 6.2 mg/dL, and urinalysis shows glucosuria with isosthenuria. Renal biopsy reveals necrosis of the medullary thick ascending limb. Which mechanism BEST explains this specific distribution of renal injury?

Accepted Answer

Inhibition of prostaglandin-mediated vasodilation in the renal medulla leading to hypoxic necrosis

Answer

NSAIDs inhibit cyclooxygenase, blocking prostaglandin synthesis. In the renal medulla, prostaglandins (particularly PGE2 and PGI2) are critical for maintaining vasodilation against the high medullary osmotic gradient and countercurrent vasoconstrictive environment. The medullary thick ascending limb (mTAL) is metabolically active yet receives relatively hypoxic blood, making it uniquely dependent on prostaglandin-mediated vasodilation. NSAID inhibition causes vasoconstriction and medullary ischemia, selectively damaging the mTAL. This differs from the cortical proximal tubule injury seen with aminoglycosides.

Question 3

A 9-year-old spayed female Border Collie is evaluated for a 3-month history of polydipsia, polyuria, and bilateral symmetric alopecia of the flanks. Serum cortisol post-LDDS test is 3.2 µg/dL at 8 hours (non-suppressed). An HDDS test shows 85% suppression. Abdominal ultrasound reveals bilateral adrenal enlargement. Which diagnosis BEST fits this presentation?

Accepted Answer

Pituitary-dependent hyperadrenocorticism (PDH) with a macroadenoma

Answer

The key discriminator here is HDDS suppression. In pituitary-dependent hyperadrenocorticism (PDH), the pituitary adenoma retains some glucocorticoid feedback sensitivity, and >50% suppression on HDDS is considered diagnostic of PDH. Adrenal-dependent tumors are autonomous and do not suppress with either low- or high-dose dexamethasone. Bilateral adrenal enlargement (bilateral adrenocortical hyperplasia) is characteristic of PDH because bilateral ACTH stimulation drives bilateral hypertrophy. A macroadenoma can cause more severe disease and sometimes poor LDDS response, yet still suppresses on HDDS. Ectopic ACTH is extremely rare in dogs.

Question 4

During a routine splenectomy in a 6-year-old DSH cat for splenic mast cell tumor, the surgeon encounters unexpected difficulty controlling hemorrhage from the short gastric vessels. Intraoperatively, the cat develops a sudden drop in systolic BP to 55 mmHg, bradycardia (HR 48 bpm), and becomes unresponsive. Which drug combination is MOST appropriate as the FIRST intervention?

Accepted Answer

Atropine 0.04 mg/kg IV + epinephrine 0.01 mg/kg IV

Answer

This presentation — profound hypotension + bradycardia + unresponsiveness during mast cell tumor manipulation — is consistent with a massive histamine/tryptase release event (anaphylaxis or mast cell degranulation crisis). The combination of hypotension AND bradycardia (rather than the reflex tachycardia of simple hemorrhage) with intraoperative mast cell tumor handling strongly implicates degranulation. Atropine addresses the vagotonic bradycardia, and epinephrine is the drug of choice for anaphylaxis — it reverses bronchospasm, causes vasoconstriction (α1), and positive chronotropy/inotropy (β1/β2). Vasopressin is a second-line vasopressor but does not address the bradycardia or anaphylactic mechanism. A dopamine CRI has too slow an onset in this acute crisis.

Question 5

A 2-year-old male intact German Shepherd presents with a 3-week history of mucopurulent nasal discharge unilateral to the left nostril, sneezing, and mild epistaxis. Rhinoscopy reveals a pale, irregular mucosal lesion. Biopsy shows pyogranulomatous inflammation with broad, pauciseptate hyphae with right-angle branching on GMS stain. Which organism is MOST likely responsible, and what is the MOST appropriate initial antifungal therapy?

Accepted Answer

Conidiobolus coronatus — itraconazole monotherapy

Answer

Broad, pauciseptate hyphae with right-angle branching on GMS stain in a dog with nasal/facial disease is characteristic of zygomycetes, specifically the Entomophthoromycota order. Conidiobolus coronatus (formerly Entomophthora coronata) causes rhinofacial conidiobolomycosis — pyogranulomatous rhinitis with broad hyphae that are difficult to culture. Aspergillus produces narrower, septate hyphae with acute-angle branching. Pythium is an oomycete (not a true fungus) presenting as GI/subcutaneous disease, and its hyphae are similar but the clinical presentation differs. Rhinosporidium produces sporangia, not hyphae. Itraconazole is the recommended first-line treatment for Conidiobolus, though prognosis is guarded.

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE Canine Medicine and Surgery 5