Veterinary Radiology

Well the new quarter is in session so we are back at Known Case Conference to challenge the residents with reading radiographs.The case moderator knows the answer but the residents have to narrow it down to their best list of differential diagnoses.

We hold KCC rounds after work in a barn on the west side of town. Not just any barn, it’s fully equipped with light boxes, a projector and screen (for digital cases) and wireless internet. And beverages and snacks of course. This week I rode my bike out to the barn on a windy day. A large unidentified  insect blew into my forehead and stung me, so I spent most of the session lamenting how much my head hurt! Anyway here are a few of the case summaries for you.

Case 1 - 8 year old male neutered dog with an acute abdomen

The abdominal radiographs had poor detail, and the contour of the abdominal wall was distended. The spleen was enlarged and curved in a “reverse C” shape on the lateral projection. The proximal extremity of the spleen was visible on the lateral ventral to the cecum, then the body curved caudally and the distal extremity was just caudal to the liver. The small intestine was displaced by this enlarged spleen. Differential diagnoses included splenic torsion, and inflammatory or diffuse infiltrative disease. Diagnosis: Splenic torsion. These have a very characteristic position and shape if there isn’t too much effusion obscuring them. There is no contour change such as with a mass. Check the v/d projection to see that the proximal extremity of the spleen is not visible in its normal position.

Case 2 - 1 year old male neutered German Shorthair Pointer with lethargy.

These thoracic radiographs had an asymmetric interstitial pattern that was most pronounced in the left cranial lung lobe. There was interstitial pattern dorsally as well, and the distribution was patchy. The heart and vessels were normal, as was the pleural space. Differentials included hemorrhage, atypical pneumonia or inflammatory disease, or non-cardiogenic edema. Diagnosis: hemorrhage from rodenticide toxicity. Hemorrhage is often asymmetrically distributed. Dogs with rodenticide toxicity may also have a widened medastinum from accumulation of blood.

Case 3 - 2 year old Australian Shepherd cross with left hind limb lameness.

A lateral radiograph of the spine and pelvis showed an aggressive bone lesion of L5 with permeative osteolysis and marked ventral new bone production. There was also faint periosteal reaction on one of the femurs. On the v/d, the left femoral neck was lytic with an apple core appearance. The left ileal wing was sclerotic with increased periosteal new bone. Differentials for aggressive polyostotic bone lesions: fungal osteomyelitis, bacterial osteomyelitis, neoplasia. The latter two are much less likely than fungal disease. Diagnosis: Coccidiodomycosis. Here’s a different case with coccidiodomycosis of the pelvis.

Just a quick note to say that links to cases may be unavailable over the next 24 hours while the server is assigned a new IP address. I’ll be updating the old links as well, but please send me an email if you have trouble accessing cases Wednesday afternoon.

The freshman class has been asking me all sorts of great questions pertaining to abdominal radiology. I thought I would share some of the questions and answers with you.

What are the radiographic signs for free peritoneal gas?

There are a few different signs to look for when you suspect free peritoneal gas. Serosal surfaces, especially ones that you would not normally see (liver lobes) become visible from the high contrast between gas and soft tissue. You will also see gas that is not contained within the gastrointestinal tract. These gas bubbles often have odd, angular shapes. Gas also tends to rise to the highest point in the abdomen, which is under the diaphragm in both projections. Look for the diaphragm to be outlined by gas on both sides. It is usually highlighted by gas (lungs) on the cranial side, but the caudal side should have stomach wall or liver adjacent to it. When outlined on both sides by gas, the diaphragm will appear as a very thin, sharp, soft tissue line.

Signs to look for:

*increased peritoneal detail

*angular gas bubbles not contained in the GI tract

*diaphragm outlined by gas on both sides

Is there any benefit to fasting an animal prior to radiographing in order to see the GI tract better?

Yes, fasting the animal and taking it outside will ensure that the stomach and colon are empty. The stomach can cause a mass effect in the cranial abdomen when it is full. Radiopaque material in the colon can also obscure portions of the abdomen. An empty GI tract as well as urinary bladder makes for a much better study.

How can I identify the different parts of the diaphragm on a radiograph?

Generally, when the animal is in lateral recumbency, the weight of the abdominal organs push on the dependent crus. If the animal is in left lateral, that would be the left crus. So you will usually see the left crus projected in front of the right in left lateral recumbency. The opposite is true for right lateral recumbency. But there is a lot of variation in diaphragm conformation between animals, and where you center the x-ray beam, so you won’t see these changes every time. Just remember the fundus sits under the left crus, and the caudal vena cava enters the right crus for landmarks.

The cupula is sometimes visible on a lateral radiograph, but is seen better on the v/d as the most cranial part of the diaphragm centered on midline. The two crura can look like “Mickey Mouse” ears.