NAVLE Small Animal Diagnostic Imaging 6

Question 1

On thoracic radiographs of a 7-year-old male Golden Retriever, you observe a soft tissue opacity mass at the right cardiac apex that obscures the cardiac silhouette border. Which radiographic sign is this, and what does it indicate?

Accepted Answer

Silhouette sign; the mass is in contact with and of similar opacity to the cardiac border, indicating it is within the same radiographic plane

Answer

The silhouette sign (Roentgen sign) occurs when two structures of the same radiographic opacity are in contact — their shared border becomes invisible. Here, a soft tissue mass contiguous with the cardiac silhouette will obliterate that border, indicating the mass is in the same radiographic plane as the heart (e.g., right middle lung lobe, pericardial, or cardiac in origin). This is a critical interpretive principle for localizing intrathoracic lesions.

Question 2

An ultrasound of a 10-year-old cat's liver reveals a hyperechoic nodule with a distal 'ring-down' artifact. This artifact pattern is most consistent with which finding?

Accepted Answer

Hepatic mineralization or dystrophic calcification within the nodule

Answer

Ring-down artifact (also called comet-tail artifact in certain contexts) appears as a series of reverberating echoes trailing deep to a reflective interface — classically associated with mineralization, metal, or gas. A hyperechoic hepatic nodule with this artifact is characteristic of dystrophic calcification or mineralized granuloma (e.g., old inflammatory lesion, fungal granuloma). Gas-containing lesions produce true ring-down/comet-tail artifacts but would be expected in a different clinical context. Lipidosis produces diffuse hyperechogenicity, not a discrete nodule with distal artifact.

Question 3

A 4-year-old intact female Doberman Pinscher presents with acute collapse. Echocardiography reveals a large hypoechoic space surrounding the heart with compression of the right atrium during diastole. The most appropriate NEXT imaging step to identify the underlying etiology is:

Accepted Answer

CT angiography of the thorax with IV contrast after stabilization via pericardiocentesis

Answer

In a Doberman with cardiac tamponade, after life-saving pericardiocentesis, CT angiography with IV contrast is the superior next step for identifying the etiology. Hemangiosarcoma of the right auricle and heart base tumors (chemodectoma) are the most common causes. CT provides superior soft tissue characterization, detects small auricular masses invisible on echocardiography (especially post-pericardiocentesis when fluid is removed), and evaluates for concurrent thoracic or abdominal metastatic disease. CEUS can visualize auricular masses but has more limited anatomic coverage. Repeat echo alone after 48 hours is inferior — CT is now the standard of care for neoplastic pericardial effusion workup.

Question 4

On a lateral abdominal radiograph of a vomiting 8-year-old Shih Tzu, you identify a mineralized opacity within the pyloric antrum. The opacity has a faceted, angular appearance with multiple distinct densities on the orthogonal view. What is the most likely diagnosis?

Accepted Answer

Choleliths that have migrated through a biliary-enteric fistula into the pylorus

Answer

Faceted, angular, radiopaque calculi within the stomach or pylorus with distinct layering/multiple density facets are characteristic of choleliths (gallstones) that have migrated into the GI tract via a cholecystoduodenal or biliary-enteric fistula — a rare but well-documented condition called Bouveret syndrome (gastric outlet obstruction by a gallstone). The faceted morphology and mixed mineral densities (mixed cholesterol/calcium bilirubinate composition) are hallmarks of cholecystolithiasis. Simple enteroliths tend to be round/oval and form distally. Neoplastic mineralization is typically amorphous and associated with a soft tissue mass.

Question 5

A 6-year-old male neutered DSH cat undergoes thoracic CT for investigation of pleural effusion. The CT reveals a soft tissue mass at the cranial mediastinum with a measured Hounsfield unit (HU) value of +18 to +25 on pre-contrast images. This attenuation value is most consistent with:

Accepted Answer

A chylous cyst or lymphangioma with proteinaceous fluid content

Answer

Hounsfield unit ranges: pure water = 0 HU, fat = −50 to −100 HU, simple fluid = 0–20 HU, soft tissue = +30 to +70 HU, blood = +50–80 HU. A pre-contrast attenuation of +18 to +25 HU is higher than pure water (0 HU) but lower than true soft tissue. This is characteristic of proteinaceous or chylous fluid — such as a lymphangioma or chylous cyst. Pure bronchogenic cysts measure near 0 HU. Thymoma would have soft tissue components at 35–60 HU. Mediastinal fat would be strongly negative HU. In a cat with pleural effusion, craniomediastinal lymphangioma is a key differential.

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE Small Animal Diagnostic Imaging 6