June 30, 2017

Assessing Noncardiac Thoracic Lesions with Contrast-Enhanced Ultrasonography

Contrast-enhanced ultrasonography demonstrated usefulness as a diagnostic aid for noncardiac thoracic lesions in dogs and cats.
By JoAnna Pendergrass, DVM
Contrast-enhanced ultrasonography (CEUS) may be a useful diagnostic aid for small animal noncardiac thoracic lesions, according to a study conducted by a team of Italian and American researchers. Study results were recently published in BMC Veterinary Research.
 
In veterinary medicine, conventional thoracic ultrasonography enhances diagnostic accuracy in emergency situations (eg, acute dyspnea) and allows for safe and efficient sample collection. Veterinary use of CEUS, though, remains relatively unexplored, with only a few studies evaluating the use of this procedure for small animal noncardiac thoracic lesions.
 
The use of CEUS in human medicine has been more widely studied. For example, human CEUS studies have reported contrast medium distribution differences between benign and malignant lesions, allowing for discrimination between these lesion types. Differences in time to contrast enhancement between benign and malignant lesions have also been reported.

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Study Design
Researchers performed awake thoracic ultrasonography on 40 small animals (28 dogs, 12 cats) with noncardiac thoracic disease. Baseline grey-scale conventional ultrasonography was performed first to localize and characterize the lesions. Lesion characteristics were:
  • Size
  • Shape
  • Margins
  • Echogenicity
  • Echotexture (contrast medium distribution)
 
Next, CEUS was conducted using a bolus intravenous injection of contrast medium. Images were analyzed qualitatively for contrast medium distribution at designated time points: contrast uptake, peak intensity, and washout. Quantitative analysis was performed to measure several perfusion variables in pulmonary lesions, including arrival time (time when contrast enhancement reached >10% of peak intensity).
 
Immediately after CEUS, researchers performed sedated ultrasound-guided fine-needle aspiration (FNA) or tissue core biopsy (TB) to collect tissue samples.
 
Results
Of the 40 lesions examined, 23 were pulmonary and 17 were mediastinal; 32 were malignant and 8 were benign. Malignant and benign lesions were distributed as follows:
  • Pulmonary: 17 malignant; 6 benign (5 pneumonia, 1 abscess)
  • Mediastinal: 15 malignant; 2 benign (1 each, lipoma and abscess)
 
FNA was used more frequently than TB for diagnostic confirmation, limiting histologic classification. Carcinomas and lymphomas were the most common malignant pulmonary and mediastinal lesions, respectively.
 
Conventional Ultrasound
Pulmonary and mediastinal malignant lesions were round or oval and hypoechoic with inhomogeneous contrast enhancement. Benign lesions were either triangular or oval and hypoechoic with homogeneous enhancement.
 
CEUS
No animals experienced adverse reactions to the contrast medium. Nearly all malignant pulmonary lesions displayed inhomogeneous enhancement with variable avascularization, indicating “chaotic neoplastic neoangiogenesis and necrosis,” the researchers wrote. Most benign pulmonary lesions—particularly pneumonia—had homogeneous enhancement with linear hyperechoic structures representing typical pulmonary vessel branching.
 
Malignant mediastinal lesions predominantly displayed inhomogeneous enhancement. Notably, at peak intensity, homogeneity for mediastinal lymphoma varied according to lesion size: homogeneous if smaller than 50 mm and inhomogeneous if larger than 50 mm.
 
At peak intensity, the mediastinal abscess had homogeneous peripheral enhancement with an avascular center. Researchers indicated that this result could represent a possible advantage of CEUS over conventional ultrasonography: the ability to detect subtle differences in lesion characteristics, allowing for more accurate differentiation between malignant and benign lesions. They noted that an abscess could be misdiagnosed as a solid tumor with conventional ultrasonography.
 
Quantitative analysis revealed that arrival time of contrast medium was significantly shorter with benign than malignant pulmonary lesions. Differences in vascularization explain this finding—pulmonary arteries vascularize benign inflammatory lesions, while bronchial arteries are typically responsible for neoplastic angiogenesis.
 
Conclusions
Taken together, these study results suggest the diagnostic usefulness of CEUS for small animal nonthoracic cardiac lesions. Given the study’s small number of cases, though, researchers noted that larger studies will be needed to determine whether CEUS can “outperform conventional ultrasound in discriminating between thoracic lesions.”
 
 
Dr. JoAnna Pendergrass received her Doctor of Veterinary Medicine degree from the Virginia-Maryland College of Veterinary Medicine. Following veterinary school, she completed a postdoctoral fellowship at Emory University’s Yerkes National Primate Research Center. Dr. Pendergrass is the founder and owner of JPen Communications, a medical communications company.

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