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Abnormal curtain signs identified with a novel lung ultrasound protocol in six dogs with pneumothorax

Boysen S, McMurray J, Gommeren K. Front Vet Sci. 2019 Aug 28;6:291. doi: 10.3389/fvets.2019.00291. PMID: 31555674; PMCID: PMC6722189.

Background Lung point of care ultrasound is a rapid and useful diagnostic technique to identify or exclude pneumothorax (PTX) in the emergency setting. Currently, PTX can be ruled out by identification of a glide sign, lung pulse or B lines, while PTX can be identified by reappearance of a glide sign or presence of a lung point.
Rational and Objective Currently, interpretation of ultrasonographic artifacts due to PTX can be equivocal and diagnosis might be challenging in some cases. The objectives of this case series were to describe a new ultrasonographic protocol and describe presence of a curtain sign (CS) and two abnormal CS in dogs with PTX. The CS is defined as a vertical edge between normally aerated lung and abdominal contents.
Trial Design Case series  
Patient population and location
  • Six client owned dogs presented with spontaneous or traumatic PTX
  • University teaching hospital
Methods Dogs were scanned with the probe orientated perpendicular to the ribs starting at the 6th intercostal space in the mid height of the thorax, sliding caudally until visualizing the CS. The probe was then slid dorsally until reaching the hypaxial muscles, sliding ventrally again until the pleural line reappeared. The Armenise protocol was then followed until visualization of the CS in the mid thorax, at which point the probe was then slid ventrally until the heart was visualized. At this point of contact the probe was orientated parallel to the ribs to identify presence of pleural effusion. Patients were scanned in sternal or lateral recumbence or standing. In a healthy patient, during inspiration the vertical edge and the abdominal contents slide caudally synchronously. An asynchronous CS was defined as sliding of the abdominal contents caudally during inspiration, while the vertical edge moved in the opposite direction or had minimal movement.   A double CS was defined as two vertical edges appearing during inspiration between the thorax and the abdomen when the probe was positioned in the mid to dorsal caudal lung regions.
Results
  • Six dogs, weighing 13 kg to 38 kg, presented with spontaneous (3) or traumatic (3) PTX were described.
  • PTX was confirmed with radiography, and computed tomography was additionally performed in 3 dogs. In 5 patients PTX was bilateral and in one dog PTX was unilateral.
  • In all dogs a normal synchronous CS was detected ventrally and an asynchronous CS and a double CS were detected in the mid to dorsal caudal thorax. An absent glide sign dorsally and a lung point were detected bilaterally in 4 dogs. One dog had an equivocal glide side bilaterally and a lung point could only be observed in one hemithorax. The remaining dog had unilateral PTX with an absent glide sign and a lung point with ventral B-lines on the affected side.  
Limitations
  • Small sample size
  • Lack of blinding
  • No statistical comparisons with other PTX ultrasound artifacts were made due to small number of patients.
Clinical Relevance and Conclusions
  • This is the first report of an abnormal CS in dogs with PTX. This novel ultrasound protocol includes scanning the thoraco-abdominal border, and the artifacts described seem to be a very useful additional tool to identify PTX in small patients.
  • Further research assessing specificity and sensitivity for PTX compared to other ultrasonographic artifacts and imaging modalities will help evaluate its usefulness in clinical practice.  

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