This week’s KCC was a time honored tradition called Stump the Stars. Yes, this time the faculty were on the other side of the table and the residents were calling the shots. They came up with cases that were challenging and novel, and challenged us to come up with a dignosis. It brought back memories of oral boards exams and we all dredged up our best report skills to attempt to set a good example. What kinds of cases did we get?
Case 1
This was an older dog with chronic lameness. There were radiographs of three distal extremities. All had productive changes surrounding the phalanges and destructive changes involving the interphalangeal joints. Differential diagnoses included infectious and non-infectious inflammatory disease. Cold agglutinin was suggested, as well as autoimmune disease although the carpal and tarsal joints were spared. Diagnosis: osteomyelitis due to mycoplasma infection.
Case 2
5 year old female neutered Golden Retriever with weight loss. Thoracic radiographs showed a hilar mass and atelectasis of the left cranial lung lobe with a mediastinal shift. A CT exam showed a mass surrounding and compressing the left main stem bronchus with peripheral enhancement. There were also interstitial infiltrates in the right lung lobes. Differentials included lymph node abscess and tumor. The faculty were divided on this one but lymph node abscess won out by a show of hands. Diagnosis: lymph node abscess, Nocardia cultured from aspirate.
Case 3
Mature dog with hemoptysis. When these radiographs went up, two radiologists shouted out the answer. But the residents told them that was not the diagnosis, and there was an excellent description of a left cranial lung lobe with alveolar pattern, a gas bubble within that lobe that changed position on the opposite lateral, and an extrapleural sign. Differentials included hemorrhage due to coagulopathy, and lung lobe abscess due to migrating foreign body. Diagnosis: Lung lobe torsion. The radiologists were right the first time! It turns out the residents wanted to know how the faculty would deal with the case excluding the correct diagnosis. We didn’t get an explanation for the extrapleural sign though. Give them an inch…
What about my case? OK, I admit it, I got stumped. Two of the eight radiologists present got the diagnosis so it still counts as a point for the faculty. I’d tell you about it but it might end up as an ACVR case challenge next year so I’ve been sworn to secrecy. Great job by the residents!
On Case 2,
Why did they think it would be a lymph node abscess rather than a tumor? Was there any radiographic reason?
On the radiographs it looked like a hilar mass, so there was no way to tell. But on the CT the peripheral enhancement was a thin, even wall surrounding the mass, and the central portion was around 5 HU which is almost as low as water (0 HU). There was no enhancing tissue within the center of the mass. So the position, enhancment pattern, and attenuation of the material in the center of the mass pointed towards and abscess, and the dog was 5 years old making neoplasia slightly less likely.
Thanks Allison.
Could you have a tumor or granuloma that would look this way on CT or can you rank these differentials much less likely given the CT findings? Was lymph node vs. pulmonary abscess the primary differential because of location? Could a bronchial cyst do this?
Yes, a tumor could certainly look like that. I think all of us had infectious/inflammatory (lymoh node abscess) and tumor as the two differentials, and the fact that about half ranked one first vs. the other speaks to the similarities of the findings. Both could be very near the carina and main stem bronchus, be peripherally enhancing, and fluid filled in the center. To me the complete lack of tissue in the center is less typical of a tumor, and more likely in an abscess. The signalment of the dog also swayed me to list abscess first. Given it’s age, I think a congenital anomaly is also reasonable though less likely. (This dog had disease in the opposite lung as well). Good questions!