Letters to the Editor
To the Editor:
Observation of artifacts during the performance of ultrasound examination is a common occurrence. A basic understanding of the ultrasonographic principles is a must for any operator performing ultrasonographic interventions and the same holds true for endobronchial ultrasound (EBUS) too. Artifacts during performance of EBUS have been described, which usually occur during the image acquisition phase. Herein, we describe our experience with an unusual artifact which we came across while peforming needle puncture of a mediastinal node during convex probe EBUS-transbronchial needle aspiration (TBNA).
A 17-year-old female patient presented to our outpatient clinic with a history of low-grade fever and loss of weight of 3 months’ duration. Three sputum smear examinations for acid-fast bacilli were negative. Tuberculin test was strongly positive and computed tomography thorax examination demonstrated large and necrotic-appearing mediastinal lymphadenopathy. Nodes also demonstrated peripheral rim enhancement (Fig. 1A). The clinicoradiologic diagnosis was tuberculosis (TB), and convex probe EBUS-TBNA was performed to obtain lymph nodal aspirate for diagnosis and performing drug susceptibility testing. The reported prevalence of multidrug-resistant TB among new cases of TB varies from 0.14% to 5.3% in India.
EBUS scope (BF-UC 180 F; Olympus Medical Systems, Singapore) along with a compatible endoscopic ultrasound unit (EU-ME1; Olympus Medical Systems) was used. The procedure was performed under conscious sedation. Enlarged subcarinal and right interlobar lymph nodes were visualized. The scope was positioned for puncture of the subcarinal node. On sonographic appearance, the node was discrete, had well-defined margins, and no central hilar structure was seen. Coagulation necrosis sign was seen. After visualization of the needle sheath, needle puncture was performed (Fig. 1B). As soon as the needle entry was visualized into the node and before the attachment of the suction syringe, a prominent parabolic hyperintensity appeared around the 2 sides of the needle that gradually became more prominent and the apex of the parabola was pointed toward the needle tip (Fig. 1C; Video, Supplemental Digital Content 1, http://links.lww.com/LBR/A108). Seconds after the suction had been attached and needle jabs were performed, the hyperintense parabola disappeared and the suction syringe filled with pus. No blood was seen in the aspirate (Fig. 1D). Subsequently, aspiration from the interlobar node also yielded pus. Cytopathologic and microbiological analysis of the aspirate demonstrated positivity for Mycobacterium tuberculosis, which was sensitive to rifampicin. Patient was started on antitubercular treatment and improved.
Acoustic impedance in ultrasonographic terminology refers to the resistance of a medium to passage of ultrsound waves. Generation of images requires reflection of the ultrasound waves back to the probe for image processing. This reflection occurs at the interface of different tissue types having varying acoustic impedance and the greatest reflection of echoes back to the ultrasound probe occurs at tissue interfaces with greatest difference in acoustic impedance. There is a very large difference between the acoustic impedance of air and soft tissue, which explains as to why air in soft tissue gives a hyperintense signal. In fact, the attenuation coefficient of air is nearly 80 times that of soft tissue.1 Blood, in contrast, appears hypoechoic. Intranodal entry of air is therefore the likely mechanism of appearance of this artifact in our patient. Needle puncture caused decompression of a tense pus-filled lymph node and the intranodal entry of air occurred from around the needle entry site as the appearance suggested. The rapid disappearence of the artifact on connection of suction syringe further confirms the same. Therefore, we have termed this artifact as “Nodal air entry” artifact. On reviewing the published literature on EBUS-TBNA, we did not come across such a description previously.
Commonly described artifacts during EBUS2 are the attenuation artifacts (tadpole tail sign and the acoustic shadow artifact) and reverberation artifacts including the comet tail artifact. Attenuation artifacts occur because of the differential attenuation between the 2 adjacent structures. At the distal border of a low attenuation structure, the echo is higher leading to a brighter appearance of the area distal to the hypoechoic structure (tadpole tail artifact). The reverse of the same is the acoustic shadow artifact wherein the area distal to a high impedance structure is displayed with a lower brightness. As the mediastinal lymph nodes are anatomically in close proximity to air-containing structures (trachea and bronchi), artifacts due to air can occur during EBUS-TBNA. A commonly observed phenomeneon because of the same is the reverberation artifact, wherein loss of contact of the ultrsound probe with the airway leads to multiple equally spaced strong hyperechoic lines on the ultrasound image, because of acoustic waves being repeatedly reflected between the airway wall and the transducer.
Bronchoscopists perfroming EBUS-TBNA should be aware of the various artifacts which can be encountered during the procedure. In fact, during a phenomenon known as Doppler effect, if the orientation of the ultrasound probe is perpendicular to the blood flow in a large vessel, no Doppler visualization of the flow may be visualized.3 This can even lead to needle puncture of great vessels during the procedure and can rarely be associated with serious consequences. Therefore, a basic training in ultrasound principles should be given to all those willing to perform/performing EBUS.
Karan Madan, MD, DM
Anant Mohan, MD
Randeep Guleria, MD, DM
Department of Pulmonary Medicine & Sleep Disorders, All India Institute of Medical Sciences (AIIMS), Ansari Nagar, New Delhi, India
1. Bushberg JT, Seibert JA, Leidholdt EM, et al..The Essential Physics of Medical Imaging.2002:2nd Ed.Philadelphia, PA:Lippincott Williams & Wilkins;469–553.
2. Nishina K, Hirooka K, Wiegand J, et al.Boliger CT, et al..Principles and practice of endoscopic ultrasound.Clinical Chest Ultrasound: From the ICU to the bronchoscopy suite. Prog Respir Res.2009;Vol 37Basel:Karger;110–127.
3. Colt HG, Davoudi M, Murgu S.Scientific evidence and principles for the use of endobronchial ultrasound and transbronchial needle aspiration.Expert Rev Med Devices.2011;8:493–513.