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- Should we also ultrasound rabbit lungs?
Roberto Sargo 1 2, Inês Tomé 1 2, Filipe Silva 1 2 3, Mário Ginja 1 2 3
Background
Subclinical respiratory disease is prevalent in rabbits and often goes undetected due to anatomical and behavioral traits that mask symptoms. Computed tomography (CT) is the gold standard for detecting such lung lesions but is costly, less accessible, and requires sedation or anesthesia. Lung ultrasound (LUS), which is noninvasive and more accessible, has shown utility in human and veterinary medicine but has not been validated for detecting subclinical lung disease in rabbits. This study aimed to evaluate the diagnostic accuracy of LUS compared to CT for identifying subclinical pulmonary lesions in rabbits.
Methods
A prospective study was conducted involving thirty five-month-old male New Zealand white rabbits. LUS was performed using a modified Vet BLUE protocol, evaluating four regions per lung. Ultrasound images were scored based on the presence and severity of lung artifacts (e.g., B-lines, tissue signs, shredding). Subsequently, all rabbits underwent thoracic CT under sedation. CT images were processed using threshold masks to quantify and segment lung aeration, categorizing regions into normal, ground-glass opacity (GGO), or consolidation. CT was used as the reference standard to determine the sensitivity, specificity, and overall accuracy of LUS.
Results
CT identified subclinical lung abnormalities in 86.6% (26/30) of rabbits, with 54% of lung regions showing increased attenuation. LUS detected abnormalities in 63.3% of rabbits, with 19% of regions scoring positive. The diagnostic metrics of LUS were: sensitivity 33.33%, specificity 93.48%, positive predictive value 79.07%, negative predictive value 65.48%, and overall accuracy 67.92%. The right lung, particularly the medial and cranial regions, was more frequently affected. LUS was more successful in identifying areas of consolidation than GGO, detecting 89% of CT-identified consolidations.
Limitations
The primary limitations include a small sample size and single-operator image acquisition and interpretation, potentially introducing bias. Additionally, the study focused on a specific rabbit demographic, limiting generalizability. Sedation effects on lung attenuation and artifact production in CT scans were also acknowledged as potential confounders.
Conclusions
LUS demonstrates high specificity but limited sensitivity for detecting subclinical lung lesions in rabbits. It is effective in ruling out pathology when findings are negative but may miss early or mild lesions. While not a replacement for CT, LUS serves as a practical screening tool and could be used adjunctively in clinical practice, particularly where CT is unavailable or not feasible.
Lung ultrasound images of different regions of a study rabbit’s lung, showing identified patterns observed during the study: (a) Normal lung—air-filled zones showing the rib acoustic shadows (*), the hyperechoic pleural line (short arrow), and A-line artifacts representing horizontal reverberation artifacts of the hyperechoic pleural line (long arrows). (b) B-line (*) vertical, hyperechoic artifact that extends from the pleural line to the bottom of the screen without fading. (c) Multiple B-lines (*). (d) Coalescent B-lines (*). (e) Tissue sign (#), hepatization-like appearance of the lung. (f) Shred sign (ψ), subpleural consolidation with an irregular or “shredded” border between the aerated and consolidated lung. Ultrasound was performed using a musculoskeletal preset (15 MHz), with a depth of 3 cm and the focus set at the level of the pleural line.
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