NAVLE Canine Medicine and Surgery 4

Question 1

A 7-year-old intact male Labrador Retriever presents with a 3-week history of progressive pelvic limb weakness, fecal tenesmus, and perineal swelling. Rectal palpation reveals a large, doughy mass lateral to the rectum that deviates it medially. Urinalysis shows isosthenuria. Which of the following is the MOST likely cause of the isosthenuria in this patient?

Accepted Answer

Retroflexion of the urinary bladder into the perineal hernia causing partial urethral obstruction and post-renal azotemia

Answer

Perineal hernias in intact male dogs can lead to retroflexion of the urinary bladder into the hernia sac. When the bladder retroflexes, the urethra becomes kinked or obstructed at an abnormal angle, causing post-renal azotemia and secondary isosthenuria due to medullary washout from the obstructive uropathy. This is a life-threatening complication requiring emergency surgical reduction. Benign prostatic hyperplasia is unlikely to cause hydronephrosis acutely, and perianal adenocarcinomas (rather than adenomas) secrete PTHrP — but the scenario describes a perineal hernia anatomy, not a perianal tumor. The isosthenuria in this context is mechanistically linked to the hernia complication.

Question 2

A 5-year-old Golden Retriever is presented for acute-onset cervical pain and tetraparesis. MRI reveals a T2-hyperintense, well-defined intramedullary lesion at C5-C6 with a characteristic 'golf ball on a tee' appearance. CSF analysis shows xanthochromia with elevated protein and no pleocytosis. Which condition BEST explains these findings?

Accepted Answer

Acute non-compressive nucleus pulposus extrusion (ANNPE)

Answer

Acute non-compressive nucleus pulposus extrusion (ANNPE) presents with peracute onset of pain and neurological deficits, often following exercise. MRI shows an intramedullary T2-hyperintense lesion that can have a 'golf ball on a tee' or 'smoke signal' appearance due to the nucleus pulposus material extruded directly into the cord parenchyma. CSF xanthochromia with elevated protein and no pleocytosis is consistent with parenchymal injury without inflammation. FCE also presents acutely and is non-painful after the initial event, but the MRI appearance and CSF xanthochromia better fit ANNPE. Neospora would show pleocytosis, and astrocytoma would be a more gradual progression.

Question 3

A 9-year-old spayed female Bernese Mountain Dog is evaluated for a 6-month history of polyuria/polydipsia, weight loss, and a pendulous abdomen. Bloodwork shows a persistent lymphopenia (400 cells/μL), eosinopenia, elevated ALP (1,800 U/L), and mildly elevated ALT. Urine cortisol:creatinine ratio is elevated on two morning samples. A low-dose dexamethasone suppression test (LDDST) shows less than 50% suppression at 4 hours but greater than 50% suppression at 8 hours. What is the MOST appropriate next diagnostic step?

Accepted Answer

No further testing is needed; the 8-hour suppression pattern is diagnostic for pituitary-dependent hyperadrenocorticism (PDH)

Answer

In interpreting the LDDST, suppression of cortisol to <50% of baseline at the 4-hour or 8-hour time point is diagnostic for PDH (pituitary-dependent hyperadrenocorticism). When there is escape at 4 hours but suppression at 8 hours, this pattern (called 'delayed suppression') is considered diagnostic for PDH with approximately 98% specificity — meaning no further differentiation testing is required. The 8-hour suppression (>50% below baseline) essentially rules out an autonomously functioning adrenal tumor, which would not suppress at any time point. An HDDST would be redundant, and while ultrasound and endogenous ACTH are useful adjuncts, the 8-hour LDDST suppression pattern alone confirms PDH.

Question 4

During exploratory laparotomy on a 4-year-old Border Collie for suspected intestinal foreign body, you discover a 6 cm segment of jejunum that is dark purple-black, lacks peristalsis, and does not bleed when cut. The mesenteric vessels to this segment appear grossly intact. You resect the segment. Intraoperatively, which suture pattern for the jejunojejunostomy anastomosis has been shown to produce the LEAST luminal narrowing in small-diameter bowel?

Accepted Answer

Single-layer simple interrupted appositional pattern

Answer

Single-layer simple interrupted appositional (end-to-end) anastomosis produces the least luminal narrowing because it avoids the inversion of tissue that inherently reduces the anastomotic diameter. Two-layer inverting patterns and continuous inverting patterns (Connell) reduce lumen diameter by folding tissue inward, which is particularly problematic in the small-bore jejunum of dogs. The Gambee pattern is a modified appositional pattern that also reduces inversion, but simple interrupted appositional remains the gold standard for minimizing stricture in veterinary small intestinal surgery. Healing strength and leak rates are comparable or superior for single-layer appositional techniques.

Question 5

A 6-year-old neutered male Dalmatian presents with recurrent urolithiasis. Stones have previously been typed as urate uroliths. The owner reports the dog is fed a standard commercial diet. Which of the following explains why Dalmatians are predisposed to urate urolithiasis compared to other breeds, even when consuming the same dietary purine levels?

Accepted Answer

Dalmatians have a defect in the renal proximal tubular transporter URAT1 (encoded by SLC22A12) that impairs uric acid reabsorption, combined with reduced hepatic uricase activity

Answer

Dalmatians have a dual defect: (1) reduced hepatic uricase activity compared to other dogs (they do have uricase, unlike humans, but at lower functional levels), and (2) a defect in renal tubular uric acid reabsorption mediated by the SLC22A12/URAT1 transporter. This combination results in higher serum uric acid concentrations and markedly elevated urinary uric acid excretion. The SLC2A9 mutation seen in humans causes hypouricemia by increasing renal uric acid excretion, which is a different mechanism. Dalmatians are not uricase-null (option B describes humans), and xanthine oxidase overexpression (option D) is not the established mechanism.

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE Canine Medicine and Surgery 4