Emergency imaging of dyspneic cats (Proceedings)

Apr 01, 2010

Often our most delicate patients, dyspneic cats demand the utmost efficiency with the minimal stress during imaging. While most radiologist would appreciate 2 or 3 view imaging, the practical clinician will attempt to maximize the stress inherent in radiography with a single view. This session will discuss views, differential diagnoses and "clinical pearls" on radiology of dyspneic cats.

Principles of localization

Reading radiographs accurately requires a method. One method is to quickly review the entire image looking for a recognizable lesion. This "Aunt Minnie" technique serves us so well in so many cases, we are apt to err in using this method to the exclusion of a more complete method. Any method that provides a complete evaluation of all structures is OK with me. I may start with an Aunt Minnie approach but invariably complete the interpretation with a systematic approach.

Emergency radiography

Don't kill the cat! Make it quick and as stress free as absolutely possible. Along these lines make sure to measure the cat in its cage. Place the cassette on the tabletop (if you are still analog!), set the technique on you machine and put on your lead all before removing the stressed patient from their little temporary home. Limit your views to those that the cat will temporarily allow, starting with a lateral, up to a lateral of the neck region as clinically indicated. A four-view series is often necessary to sort through all potential underlying regions.

Where is the problem?

The most important interpretation may be to isolate the primary lesion site. Is the disease pleural? Pneumothorax and pleural free fluid must be diagnosed early and confidently to speed definitive therapy. The next most important decision tree branch is; heart or lung? This can often be quite difficult. Concurrent lesions may prevent complete assessment of the cardiac silhouette and therefore our ability to assess cardiomegaly. Often I would perform an quick echocardiogram rather than perform an elaborate radiographic series or consider post-therapy radiographs just for speed of reaching the final diagnosis. Similarly, primary mediastinal diseases warrant an ultrasound examination early in the process for concurrent fine needle aspiration of the causative mass lesion.

Lung lesions

Let's say that the cat has no pleural or mediastinal disease and obvious increased lung opacity. This is where we use the pattern approach for lung lesion characterization. The twist is that the rules differ from basic dog rules. Most important is the rule of cardiogenic pulmonary edema being predominantly perihilar. In cats it may be perihilar or just as likely ventral, multifocal or solitary. In other words, it is a difficult diagnosis to confidently rule-out until echocardiography is supportive. However concurrent clinical signs, such as a murmur, hypothermia, thrombosis, and radiographic cardiomegaly (next section) are very supportive.

Pneumonia looks like pneumonia, except when we consider atypical locally prevalent causes, such as mycoplasmosis, toxoplasmosis, histoplasmosis, and blastomycosis amongst others. Primary lung neoplasia may be a large solitary mass, a la dog, but more commonly appears as a nonconsolidating alveolar pattern. These lesions can be focal or multifocal, unilateral or bilateral, and can overlap quite readily for the patterns seen with cardiogenic edema an atypical pneumonia.

Finally, how can a discussion of the dyspneic cat be complete without a review of asthma? The two classic manifestations are the hyperlucent, hyperinflated appearance associated with the acute phase and the bronchial pattern seen in the more chronic phase. However, a normal appearing thorax is still a viable manifestation of a severely asthmatic cat. In fact asthma (or the latest "in vogue" term/acronym) is the primary rule-out for a severely dyspneic cat with a normal-appearing thorax. As a consideration, remember that infections, such as mycoplasmosis, can have a substantial immune component to the chronic bronchitis. Mineralization is seen with primary lung neoplasia and atypical pneumonia, but not with edema.