Letters to the Editor
To the Editor:
Ultrasonographic imaging of the lung parenchyma is generally difficult due to significant artifact from sound reflection by residual alveolar gas. As opposed to ultrasound-guided interventions on other organs (ie, ultrasound-guided radiofrequency ablation for hepatocellular carcinoma, Whipple procedure for pancreatic carcinoma, etc.), this limitation has effectively negated the utility of ultrasonography as a guidance modality for the diagnosis and treatment of lung tumors.1 Unilateral lung flooding has been shown to make the lung amenable to ultrasonographic evaluation without significant cardiopulmonary compromise in porcine models.2,3 Utilization of lung flooding in humans has essentially been limited to the treatment of pulmonary alveolar proteinosis. However, in that context it is generally well tolerated.4 In a recent report, Lesser et al5 demonstrated that lung flooding allowed for ultrasonographic identification of ex vivo lung tumors within resected human lungs, as well as simulated tumors within porcine lungs in vivo. We found their novel work of significant interest. However, the practical utility of ultrasonographic visualization of a tumor within the lung parenchyma is mitigated if diagnostic and/or therapeutic tools are unable to be visualized using the same modality. This prompted us to investigate whether the lung flooding technique would also allow for transthoracic ultrasonographic visualization of a routine endobronchial tool within the distal airways of the lung. We chose standard flexible transbronchoscopic biopsy forceps due to their ubiquity and ease of use.
We requested access to a human cadaver that had already been prepared and utilized for other educational purposes. The cadaver was intubated by direct laryngoscopy with an 8.0 mm cuffed endotracheal tube and the cuff was inflated in the distal bronchus intermedius. The cadaver was placed in reverse Trendelenburg position at approximately 30 degrees. One liter of tap water was instilled through the endotracheal tube using a 60 mL syringe and a short piece of tubing that allowed for a tight seal between the proximal endotracheal tube and syringe. Instillation was discontinued once significant resistance was encountered and the water began to return in a retrograde manner through the endotracheal tube. Posterior transthoracic ultrasonographic examination of the right lower lobe revealed hyperechoic homogenous lung parenchyma consistent with adequate flooding. The bronchoscopy biopsy forceps were then inserted into the right lower lobe through the endotracheal tube. We were able to visualize the forceps as an intensely hyperechoic density within the lung parenchyma and were able to generate motion artifact by moving the forceps (Fig. 1).
We believe that this is the first report of transthoracic ultrasonographic visualization of an endobronchial bronchoscopic tool using the lung flooding technique. Although we recognize that this area of investigation is only in its infancy, we find the recently published study by Lesser and colleagues to be intriguing, and our own report to be complementary and informative. The ability to noninvasively visualize a parenchymal lung lesion, in addition to the endobronchial tools required to access it, has interesting implications for the potential utility of lung flooding with transthoracic ultrasonography as an adjunct to the diagnosis and treatment of lung lesions. We hope that this description generates interest in others and promotes further scientific investigation in this compelling area of research.
Zachary S. DePew, MD*
Akash Verma, MRCP†
Fabien Maldonado, MD‡
‡Division of Pulmonary and Critical Care Medicine, Mayo Clinic, Rochester, MN
†Changi General Hospital, Singapore, Singapore
1. Schirmer BDHolzheimer RG, Mannick JA. Intra-operative and laparoscopic ultrasound. Surgical Treatment: Evidence-Based and Problem-Oriented. 2001.Munich:Zuckschwerdt.
2. Lesser T, Klinzing S, Schubert J, et al.. Lung flooding—a new method for complete lung sonography. Res Exp Med. 1999;198:83–91.
3. Klinzing S, Lesser T, Schubert H, et al.. One-lung flooding for video assisted thoracoscopic surgery in animal experiments on pigs—oxygenation and intrapulmonary shunt. Res Exp Med (Berl). 2000;199:333–340.
4. Selecky PA, Wasserman K, Benfield JR, et al.. The clinical and physiological effect of whole-lung lavage in pulmonary alveolar proteinosis: a ten-year experience. Ann Thorac Surg. 1977;24:451–461.
5. Lesser TG, Schubert H, Bischoff S, et al.. Lung flooding enables efficient lung sonography and tumour imaging in human ex vivo and porcine in vivo lung cancer model. Eur J Med Res. 2013;18:23.