# False-positive asynchronous-abdominal curtain sign mimicking pneumothorax in cats with severe pulmonary hyperinflation—case report

## TL;DR

Two cats showed a false-positive ultrasound sign for pneumothorax due to severe lung overinflation, not actual air in the chest.

## Contribution

Identifies pulmonary hyperinflation as a novel cause of false-positive asynchronous-abdominal curtain sign in cats.

## Key findings

- A-ACS was observed in two cats without pneumothorax but with severe pulmonary hyperinflation.
- Medical treatment resolved respiratory issues and normalized the A-ACS and diaphragmatic movement.
- Pulmonary hyperinflation likely causes false-positive A-ACS due to diaphragmatic flattening.

## Abstract

The asynchronous-abdominal curtain sign (A-ACS) is a suggestive ultrasound artifact for pneumothorax in veterinary medicine. However, its specificity has not been fully established.

We describe two dyspneic cats displaying a prominent A-ACS despite the absence of findings strongly supportive of pneumothorax. Both cases had severe pulmonary hyperinflation secondary to expiratory flow limitation (feline lower airway disease and suspected anaphylaxis). Sonographic assessment revealed A-ACS and reduced diaphragmatic excursion. Medical management targeting bronchoconstriction and inflammation resulted in complete resolution of respiratory signs, normalization of the abdominal curtain sign (ACS), and improved diaphragmatic excursion in the monitored case.

These findings suggest that severe pulmonary hyperinflation may represent a cause of false-positive A-ACS, likely resulting from diaphragmatic flattening and altered cardiophrenic mechanics.

Clinicians should consider pulmonary hyperinflation in cats presenting with A-ACS to avoid misdiagnosis of pneumothorax and unnecessary interventions. Moreover, this sign may offer valuable insights into respiratory dynamics in feline obstructive airway disease.