NAVLE Small Animal Diagnostic Imaging 5

Question 1

A 7-year-old DSH cat presents with acute dyspnea. Thoracic radiographs show a 'mediastinal mass' with a rounded soft-tissue opacity in the cranial mediastinum. Ultrasound reveals an anechoic, thin-walled structure with no internal vascularity on Doppler. Which diagnosis is MOST consistent with these findings?

Accepted Answer

Mediastinal cyst (branchial or thymic)

Answer

Mediastinal cysts (branchial cleft or thymic remnant cysts) appear as well-defined anechoic structures with thin walls and no internal blood flow on color Doppler. Lymphoma, the most common cranial mediastinal mass in cats, typically shows heterogeneous echogenicity and detectable vascularity. Ectopic thyroid tissue and chemodectomas are vascularized solid masses. The purely anechoic, avascular ultrasound appearance is the key distinguishing feature of a benign cyst.

Question 2

On a lateral thoracic radiograph of a dog, you note the cardiac silhouette contacts the sternum across more than 2.5 intercostal spaces. The trachea is elevated and the caudal vena cava is not visible. Which condition BEST explains this constellation of findings?

Accepted Answer

Peritoneopericardial diaphragmatic hernia (PPDH)

Answer

PPDH is characterized by an enlarged, often misshapen cardiac silhouette that contacts the sternum (sternal contact > 2.5 ICS on lateral view), dorsal tracheal elevation, loss of the diaphragmatic outline, and absence or obscuring of the caudal vena cava. Abdominal organs (omentum, small intestine, liver) within the pericardium create heterogeneous opacity within the cardiac silhouette. Right-sided cardiomegaly alone does not cause sternal contact to this degree or obscure the CVC. PPDH is the most common pericardial disorder in young dogs.

Question 3

During a contrast-enhanced CT of the abdomen in a 9-year-old Golden Retriever, a hepatic lesion shows marked arterial phase enhancement followed by rapid 'washout' (hypoattenuation relative to liver parenchyma in the portal venous phase). What is the MOST likely diagnosis?

Accepted Answer

Hepatocellular carcinoma (HCC)

Answer

The 'arterial enhancement followed by portal venous phase washout' pattern is the hallmark of hepatocellular carcinoma on contrast CT, reflecting the lesion's dependence on arterial blood supply and rapid contrast clearance. Hemangiomas classically show peripheral nodular enhancement that fills in centripetally (similar to human hemangiomas). Nodular hyperplasia typically appears iso- or hypoattenuating without dramatic washout. Biliary cystadenomas are cystic or multilocular and do not enhance in this arterial-dominant pattern. This washout sign carries high specificity for HCC in dogs.

Question 4

A 5-year-old Border Collie is evaluated for progressive ataxia and seizures. MRI of the brain (1.5T) shows bilateral, symmetrical T2 hyperintensity in the thalamus and caudate nucleus with no mass effect and no contrast enhancement. CSF analysis is normal. Which condition is MOST consistent with these MRI findings?

Accepted Answer

Thiamine (vitamin B1) deficiency encephalopathy

Answer

Bilateral symmetrical T2 hyperintensity restricted to the thalamus and basal ganglia (caudate nucleus) without contrast enhancement or mass effect is the classic MRI signature of thiamine deficiency encephalopathy in dogs (and cats). This mirrors the Wernicke's encephalopathy pattern seen in humans. GME typically shows contrast-enhancing, asymmetric multifocal lesions. Neospora lesions are usually multifocal and may enhance. Cerebral infarction causes unilateral, vascular-territory distribution lesions. The bilateral symmetry and selective thalamic/basal ganglia involvement are the key discriminating features.

Question 5

Abdominal ultrasound in a 6-year-old Labrador Retriever reveals a splenic mass with a heterogeneous echotexture containing multiple anechoic cavities and hyperechoic foci casting acoustic shadowing. The surrounding parenchyma shows a 'Swiss cheese' appearance. Which diagnosis does this pattern MOST strongly suggest?

Accepted Answer

Splenic myelolipoma

Answer

Splenic myelolipomas contain mature myeloid elements and adipose tissue, producing a characteristic ultrasound pattern: heterogeneous mass with hyperechoic foci (fat) that may shadow, intermixed anechoic areas, and a 'Swiss cheese' or honeycomb appearance of the splenic parenchyma. Hemangiosarcoma is typically hyperechoic or heterogeneous with blood-filled cavities but lacks the fat-related shadowing foci. Nodular hyperplasia appears as discrete, well-defined hypoechoic nodules. Splenic abscesses can be complex but are associated with clinical signs of sepsis and lack the fat-shadowing component. Myelolipomas are incidental benign lesions.

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE Small Animal Diagnostic Imaging 5