3 Feline Chest X-Ray Findings That Are Easily Missed

ARTICLE ABSTRACT

Cat chest films often look clean, but cats hide cardiac and pulmonary disease differently than dogs. Keep three points in view:

1. A normal heart silhouette does not rule out hypertrophic cardiomyopathy, because the muscle thickens inward without changing the outline;
2. A bronchial or interstitial pattern with a normal heart can mean congestive heart failure or feline asthma, and pro-BNP testing helps tell them apart before you start treatment;
3. Chronic airway disease shows up as bronchial casts, collapsed lung lobes, and hyperinflation, findings that are easy to mistake for metastatic or cardiac disease.

In general, it is easier to take radiographs of cats than dogs. Cats are more uniform in size and morphology, and they don’t pant as you try to snap films at the exact right time. It’s also easier to move their front legs out of the X-ray field, allowing most veterinary teams to obtain excellent, unobstructed views of the chest.

But as we all know, cats are not small dogs, and they suffer from different heart and lung conditions than their canine counterparts. Several conditions in cats can be difficult to differentiate on radiographs, and when you’re talking about the difference between asthma and hypertrophic cardiomyopathy (HCM), proper cat chest X-ray reading becomes critical.

According to Dr. John Mattoon, DVM, DACVR, board-certified veterinary radiologist with Vetology, interpreting subtle findings on feline radiographs can be a daily struggle for many veterinarians. While AI screening tools can help you identify these issues and avoid missed findings on cat X-rays, here are a few key points that can help improve your diagnostic skills.

A cat’s heart can have a normal silhouette and size on radiographs, even when advanced cardiac disease, particularly HCM, is present. In this disease, the heart muscle can thicken internally, making it unlikely that changes will be obvious on routine radiographs.

Dogs with advanced cardiac disease usually have visible changes in heart size and pulmonary vessel size, making diagnosis much easier. But in cats, a normal-appearing heart doesn’t rule out HCM. This distinction becomes important when evaluating a cat with respiratory signs.

When a cat presents with respiratory signs and feline thoracic radiograph interpretation reveals a bronchial, interstitial, or broncho-interstitial pattern with a normal heart, the first question is whether the lung changes are secondary to heart failure or reflect a primary respiratory concern.

In most cases, the leading differentials for these pets are congestive heart failure and feline asthma. But if you make the wrong call and start a cat with HCM on corticosteroids to reduce asthma-related inflammation, you could worsen the condition by causing hypertension.

Feline pro-BNP blood testing can help identify hidden HCM in a cat with lung signs and provide information to guide treatment while awaiting an echocardiogram referral.

If lungworms are a concern in your area, it may be wise to also run a fecal PCR or Baermann test for Aelurostrongylus species.

Many cats with asthma, which is the most common chronic pulmonary issue in our feline friends, have relatively unremarkable thoracic radiographs. Asthma primarily causes airway constriction and air trapping, and mild or early cases may produce no visible changes on feline thoracic radiograph interpretation.

With ongoing disease, however, you might see these telltale signs:

• Bronchial casts: These collections of inspissated mucus that block the small airways can appear as nodular opacities when viewed end-on. In an older cat, this presentation can be mistaken for pulmonary metastatic disease, potentially leading you down the wrong diagnostic path.
• Collapsed lung lobes: Chronic airway obstruction in cats can lead to atelectasis of specific lung lobes (the right middle lobe or the caudal segment of the left cranial lobe). These appear as small triangular opacities that appear as wings extending from the heart. The “batwing sign” can be mistaken for a cardiac or pericardial mass.
• Pulmonary hyperinflation: Cats with asthma can inspire normally, but they can’t expel the air properly. Air becomes trapped inside the lungs, causing hyperinflation on chest radiography. This is a reliable sign of feline asthma, so much so that its absence can help rule out the condition and redirect the diagnostic workup.

Vetology’s AI screening technology reliably identifies 15 feline thoracic radiographic signs, including pleural fluid accumulation, cardiomegaly, pulmonary nodules, interstitial patterns, and bronchial patterns. The screening report serves as a a confirmatory read for the astute clinician evaluating cats with cardiac and pulmonary disease, and the Vetology platform enables escalation to a board-certified veterinary radiologist when additional expertise is needed.