Fig. 23.3  RP-EBUS image of normal aerated lung tissue with a “snowstorm like” whitish appearance

Fig. 23.4  A typical RP-EBUS image of a malignant tumor showing a concentric homogeneous structure with clear borders

bronchoscope provides a more reliable conduit to pass biopsy tools and obtain samples. When using a standard bronchoscope, with a 2.0 mm working channel and a 1.4 mm RP-EBUS probe, a 1.9 mm guide sheath should be used and when using the 1.7 mm RP-EBUS probe, a 2.7 mm guide sheath and 2.8 mm working channel bronchoscope should be used.

Indication, Application, and Evidence

While previous indications for the use of RP-EBUS included diagnostic evaluation of endobronchial lesions, staging of non-small cell lung cancer (NSCLC), diagnosis of mediastinal lesions, and the diagnostic evaluation of lung nodules it now has evolved into a tool used mainly for the evaluation of peripherally located pulmonary nodules. This transition followed the development and widespread use of the CP-EBUS. As a result, the balloon catheter used to evaluate endobronchial lesions and mediastinal structures has recently been discontinued in the United States. Currently, RP-EBUS is used to assist in verifying the target lesion’s location, provide ultrasound characteristics of the lesion, and improve diagnostic yield when used in combination with other guided bronchoscopy modalities.

In combination with other clinical and radiographic modalities, the RP-EBUS has the ability to provide sonographic characteristics of peripherally located pulmonary nodules that can assist in determining the probability a lung nodule may be malignant [8]. This was frst attempted in 2002 by Kurimoto et al. who analyzed 124 patients with peripheral pulmonary lesions who had both a confrmed histologic diagnosis and a preoperative RP-EBUS. The major characteristics identifed were a homogenous pattern (Type I), hyperechoic dots and linear arcs pattern (Type II), and a heterogeneous pattern (Type III). The nodules with a Type I pattern were found to be benign in 23/25 (92.0%) of the cases and the Type II and III lesions were malignant in 98/99 (99.0%) of the cases [9]. In 2006, Chao et al. applied a similar concept by identifying four RP-EBUS characteristics in 20 patients with known histologic diagnoses of the pulmonary nodules. These characteristics included continuous hyperechoic margin, homogenous or heterogenous internal echoes, hyperechoic dots in the lesion, and concentric circles along the echo probe. They subsequently enrolled 126 patients who were found to have the specifed ultrasound characteristic, but only 93 had a defnitive diagnosis and were included in the

analysis. After multivariate analysis, only the presence of concentric circles on RP-EBUS was statistically signifcant for predicting benign etiology (odds ration [OR] 46.07, p = 0.03, 95% confdence interval [CI] 3.546–598.802) [7]. Additionally, in 2007 Kuo et al. assessed 224 patients with peripheral lung lesions who underwent RP-EBUS and had a defnitive diagnosis at time of analysis. The ultrasound images were reviewed, and three characteristics were selected to describe the pulmonary nodules including a continuous or noncontinuous margin between the lesion and adjacent lung, presence or absence of air bronchogram within the lesion, and homogenous or heterogenous echogenicity of the lesion. The presence of a continuous lung margin, absence of a discrete air bronchogram within the lesion, and a heterogeneous echogenicity of the lesion were all found to be predictive of malignancy. A lesion with none of the three features had a negative predictive value of 93.7% for malignancy and a lesion with two of the three features carried a positive predictive value for malignancy of 89.2% [10].

The ability of RP-EBUS to confrm localization of a peripheral lung lesion has provided an additional tool to improve diagnostic yield and safety when compared to lung biopsy performed percutaneously or by conventional bronchoscopy. Although image-guided percutaneous core biopsies and fne needle aspirations (FNA) have reported sensitivities of 95% and 90%, respectively, they come with signifcant complications [11]. Pneumothoraces secondary to percutaneous biopsy of peripheral lung lesions are reported to be between 15–43% with 4–18% of those patients requiring chest tube drainage [12]. Regarding conventional bronchoscopy, a systematic review of centrally and peripherally located pulmonary lesions biopsied reported a pooled sensitivity of 88% and 78%, respectively, but this was largely dependent on the size of the lesion. For example, peripheral lesions >2 cm had a sensitivity of 63% and 34% for lesions ≤2 cm [13]. In 2002, Herth et al. performed a crossover study on 50 patients with peripheral lung lesions who were randomized to undergo either TBBx using RP-EBUS followed by TBBx with uoroscopy or vice versa.

The group reported no signifcant difference in diagnostic yield between the two methods and a diagnostic accuracy using RP-EBUS of 80% [3]. A similar study published by Paone et al. reported improved sensitivity (79% vs. 69%) and diagnostic accuracy (85% vs. 69%) when performing RP-EBUS-guided TBBx versus TBBx without RP-EBUS [14]. The introduction of a guide sheath has also shown improvement in the diagnostic yield of TBBx when used with RP-EBUS. The technique involves placing the radial probe within a guide sheath which is advanced through the working channel of the bronchoscope and into the periphery of the lung toward the lung lesion. Once the lesion is confrmed on ultrasound, the radial probe is removed leaving the sheath as an extended working channel for biopsy tools to be inserted [15]. Kurimoto et al. were the frst to introduce this technique and reported a diagnostic yield of 76% in lesions 10 mm or less [16]. TBNA is another biopsy tool that has been reported to increase the diagnostic yield when used in combination with RP-EBUS to biopsy peripheral lung lesions. Chao et al. reported a randomized study where they used RP-EBUS with a guide sheath or uoroscopy on 182 patients to locate peripheral lung lesions. The patients were randomized to undergo conventional biopsy sampling (e.g., TBBx and bronchial washing) or conventional biopsy with the addition of TBNA. The addition of TBNA to conventional sampling increased the overall diagnostic yield from 60% to 78% [17]. Many other factors have been described that increase diagnostic yield when using RP-EBUS to biopsy peripheral lung lesions including lesions >2 cm in size, lesions closer to the hilum, visualization on uoroscopy, malignant disease (as compared to benign), having the probe within the lesion rather than adjacent to it, and taking at least 5 biopsy specimens [18–20]. Overall, the use of RP-EBUS has been shown to improve diagnostic outcomes when compared to conventional bronchoscopic techniques, and despite the signifcant heterogeneity among studies it can provide a sensitivity of over 70% [21, 22].

Over time advancements in bronchoscopic technology and platforms have provided new