Endobronchial Ultrasound

Endobronchial ultrasound (EBUS) using Olympus mechanical radial ultrasound miniature probes and catheters, improves diagnostics in the airways, including T-staging and diagnosis of solitary pulmonary nodules (SPN). Catheters incorporating a balloon at the tip allow circular contact in the larger lumen, while radial EBUS probes provide a complete 360° image of the parabronchial structures and enable visualisation of structures up to a distance of 4 cm.

Solitary pulmonary nodules (SPN) are an increasing diagnostic challenge. Multiple approaches may be undertaken to establish a tissue diagnosis, including sputum cytology, percutaneous image-guided aspiration/biopsy and bronchoscopic sampling. To obtain tissue samples for the histological evaluation of peripheral lesions, bronchoscopy under fluoroscopy is the standard procedure. This demands expensive x-ray equipment in the bronchoscopy suite or coordination with the radiology department and causes exposure to radiation for patients and staff.

An important factor affecting the yield is that lesions situated beyond the airway lumen are not visible to the bronchoscopist, resulting in 'blind' biopsies. Fluoroscopy offers some assistance for localising such lesions. However, the two-dimensional projection views often do not show lesions smaller than 3cm. In such lesions, mostly peripheral pulmonary lesions not visible endobronchially, diagnostic yield of routine bronchoscopy may therefore be less than 20%. The highest diagnostic yield for bronchoscopic evaluation of small SPNs appears to be associated with the use of mechanical radial ultrasound miniature probes, or miniprobes, in the diagnostic procedure. EBUS miniature probes employ a flexible catheter housing a mechanically rotated ultrasound transducer, which produces a 360° radial ultrasound image.

EBUS miniature probes in combination with navigation bronchoscopy improve the diagnostic yield of flexible bronchoscopy in peripheral lung lesions without compromising safety. This has been demonstrated for electromagnetic navigation bronchoscopy (ENB) demonstrating the highest diagnostic result when combining ENB and EBUS.

A recent procedural improvement was achieved with the introduction of a GuideSheath as an accessory to the EBUS probe. The sheath acts like a prolonged working channel of the bronchoscope and allows the removal of the probe after visualisation of the solid lesion. With the distal end of the GuideSheath still at the target site, sampling devices can then be brought forward. Specimens can then be obtained through the GuideSheath using regular biopsy forceps.

EBUS miniature probes have proven to be extremely useful, especially for on-the-spot decision making during diagnostic and interventional procedures. In clinical practice, radial endobronchial ultrasound is a routine procedure.

In pre-operative staging, EBUS allows detailed analysis of intraluminal, submucosal and intramural tumour spread, which can be essential for decision making on resection margins. EBUS has proved to be useful in the diagnostics of mediastinal tumour involvement in the large vessels and the oesophageal wall, which is frequently impossible with conventional radiology. A prospective study showed that differentiation of external tumour invasion from compression of the tracheobronchial wall by EBUS is highly reliable in contrast to CT imaging, thus offering the potential for improved T-staging of lung cancer.

In small, radiologically invisible tumours such as Carcinoma in Situ (CIS), the decision for local endoscopic therapeutic intervention is dependent on the tumour’s intraluminal and intramural extent within the multilayer structures of the bronchial wall and the adjacent structures. EBUS bronchoscopy with a miniature probe or miniprobe is a very reliable tool in analysing the extent of these small lesions. Especially for decisions in potentially curative endobronchial therapy such as photodynamic therapy or endoluminal high dose radiation, where diagnosis of limitation of the lesion to the bronchial wall or to the close vicinity is essential. Here, EBUS is superior to all other imaging procedures due to the detailed analysis of the layers of the bronchial wall.

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