NAVLE Small Animal Diagnostic Imaging 4

Question 1

A 7-year-old male neutered Labrador Retriever presents with a 3-week history of progressive tetraparesis. MRI of the cervical spine reveals a T2-hyperintense, T1-isointense intramedullary lesion at C4-C5 that does not enhance with gadolinium contrast. The lesion has a 'flame-shaped' appearance on sagittal sequences. Which diagnosis is MOST consistent with these imaging findings?

Accepted Answer

Spinal cord infarction (fibrocartilaginous embolism)

Answer

Spinal cord infarction (fibrocartilaginous embolism, FCE) classically appears as a T2-hyperintense, T1-isointense intramedullary lesion with a characteristic 'flame-shaped' or wedge-shaped appearance on sagittal MRI sequences. Crucially, FCE lesions do NOT enhance with gadolinium because there is no disruption of the blood-brain barrier by a mass—this distinguishes them from most intramedullary tumors. Syringomyelia appears as a fluid-filled cavity (CSF-isointense on all sequences). Astrocytomas and meningiomas typically show some degree of contrast enhancement.

Question 2

On thoracic radiographs of a 9-year-old DSH cat, you identify a soft tissue opacity in the cranial mediastinum that causes tracheal elevation and rightward deviation. Echocardiography confirms the heart is normal. The mass does not move independently from the cardiac silhouette on fluoroscopy. Which of the following is the LEAST likely differential diagnosis?

Accepted Answer

Aortic body chemodectoma

Answer

Aortic body chemodectomas (heart base tumors) are rare in cats and arise at the heart base, not the cranial mediastinum; they typically cause a mass effect at the level of the great vessels rather than causing cranial mediastinal widening with tracheal elevation. Thymoma and mediastinal lymphoma are the two most common cranial mediastinal masses in cats, and cranial mediastinal cysts are an uncommon but recognized entity. The lack of independent cardiac movement on fluoroscopy helps exclude a cardiac origin but does not distinguish between the other differentials.

Question 3

Ultrasound-guided fine-needle aspiration of a splenic mass in a 10-year-old Golden Retriever yields a non-diagnostic sample. On ultrasound, the mass is a 4-cm, cavitary, mixed echogenicity lesion. Contrast-enhanced ultrasound (CEUS) shows rapid arterial enhancement followed by marked washout in the late portal phase, resulting in a 'Swiss cheese' enhancement pattern. Which splenic pathology does this CEUS pattern MOST strongly suggest?

Accepted Answer

Splenic hemangiosarcoma

Answer

Hemangiosarcoma on CEUS characteristically shows rapid, heterogeneous arterial phase enhancement (due to abnormal tumor vasculature) followed by early and marked washout during the portal/late phase—producing the so-called 'Swiss cheese' or heterogeneous enhancement pattern with hypoechoic regions corresponding to necrosis or hemorrhage. Hemangiomas also enhance early but tend to show more uniform, persistent enhancement ('fill-in' pattern). Nodular hyperplasia shows isoenhancement or mild hyperenhancement without early washout. Hematomas show little to no vascular enhancement. Early washout is the key discriminator favoring malignancy.

Question 4

A 5-year-old intact female Boxer presents for abdominal radiographs due to acute vomiting. Radiographs reveal a markedly distended, gas-filled stomach with a soft tissue band ('shelf sign') in the mid-gastric region and the pylorus positioned to the left of midline on the VD projection. A small amount of free peritoneal gas is also noted. Which combination of conditions does this radiographic constellation represent?

Accepted Answer

Gastric dilatation-volvulus (GDV) with gastric perforation

Answer

The combination of marked gastric gas distension, a 'shelf sign' (also called the 'double bubble' or compartmentalization created by torsion of the gastric wall), and pyloric displacement to the LEFT of midline on the VD view is pathognomonic for GDV. In GDV, the pylorus rotates clockwise (viewed from the patient's caudal aspect) to end up cranial and to the left. The presence of free peritoneal gas (pneumoperitoneum) indicates gastric rupture/perforation, which is a grave complication confirming the need for immediate surgical intervention. This constellation—GDV + perforation—carries the worst prognosis.

Question 5

An 8-year-old Cavalier King Charles Spaniel undergoes brain MRI for evaluation of vestibular signs and progressive cerebellar ataxia. Sagittal T2-weighted images reveal caudal displacement of the cerebellar vermis through the foramen magnum with effacement of the cisterna magna. There is no hydrocephalus. Additionally, a longitudinal fluid-filled cavity is identified within the cervical spinal cord parenchyma that is isointense to CSF on all sequences. Which TWO conditions are being described together?

Accepted Answer

Caudal occipital malformation syndrome (COMS) and syringomyelia

Answer

Caudal occipital malformation syndrome (COMS), also called Chiari-like malformation, is extremely prevalent in the Cavalier King Charles Spaniel breed. It is characterized by caudal displacement of the cerebellum through the foramen magnum, effacement of the cisterna magna, and obstruction of CSF flow. This impaired CSF circulation leads to the formation of a syrinx (syringomyelia)—a CSF-filled cavity within the spinal cord parenchyma that is isointense to CSF on all MRI sequences. The combination of COMS + syringomyelia is a well-described clinicopathological entity in this breed. Dandy-Walker involves cerebellar hypoplasia with a cystic posterior fossa, not caudal herniation.

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE Small Animal Diagnostic Imaging 4