Chest ultrasound (US) is a safe and effective method of evaluating lesions in the chest wall, pleural cavity, mediastinum and the lung periphery.1,2 Using US to guide needle biopsy to obtain specimens for histocytology studies provides real-time imaging of the procedure.3 Performing needle biopsy under US guidance has many advantages over other imaging techniques: it does not expose the patient to radiation, the equipment is easily transported, and the procedure is quick, inexpensive, and can be performed at the bedside.4,5 US-guided techniques are particularly suitable for individuals that are more susceptible to injury from radiation, such as children and pregnant women, and for patients that are difficult to move, such as those admitted to intensive care units.6

Estimates suggest that 40% of pulmonary malignancies appear as masses in peripheral lung tissue, and are potentially accessible to US.7 Despite these advantages, US is rarely used in Spain in the study of malignant chest lesions, and in most hospitals the technique of choice is computed tomography (CT)-guided needle biopsy.4

In our unit, we have routinely used US since 2010 to detect pleural effusion and to guide thoracocentesis. In 2011, we started to use real-time US imaging to guide needle biopsy in pleural, pulmonary and mediastinal lesions.

Most studies involving this technique have been authored by interventional radiologists, and there is scant reference in the literature to the experience of pulmonologists in this context.2,8–10

A review of the literature showed no published series from Spanish hospitals.

The aim of this study was to evaluate the cost-effectiveness and safety of US-guided puncture and/or biopsy in the diagnosis of peripheral chest lesions in an interventional pulmonology unit (IPU).

In 15 (26%) cases, the lesion measured ≤3cm (nodule); in 43 (74%) cases, it measured >3cm.

In 51 (88%) cases, the lesion was located in the lung, in the mediastinum in 3 (5%) cases, in the parietal pleura in 2 (3.5%) cases, and supraclavicular region in 2 (3.5%) cases (Table 1).

Table 2 shows that a conclusive diagnosis (for benign or malignant disease) was obtained in 47 out of 58 (81%) procedures. The most frequent diagnosis was NSCLC (38%). Of the 11 (19%) non-diagnostic cases (Table 3), definitive diagnosis was obtained with CT-guided FNA performed by interventional radiologists (1 case), US-guided FNA performed by interventional radiologists (2 cases), thoracotomy (1 case), bronchoscopy with transbronchial biopsy (1 case), bronchoscopy with transbronchial biopsy (1 case), or on the basis of clinical and radiological follow-up (5 cases). Five cases initially classified as non-diagnostic for malignancy (benign and non-diagnostic) were later definitively diagnosed as malignant by the end of the study.

Table 4 shows the diagnostic yield of US-guided needle biopsy in the best (excluding unsuitable specimens) and worse clinical scenario (including unsuitable specimens and specimens with inflammatory cells).

Lesion size (nodule/mass) did not affect the process of obtaining a definitive diagnosis (P=.91).

No statistically significant differences were found between the specimen collection method (FNA, core biopsy, or FNA+core biopsy) and diagnostic yield (P=.96). Neither were any statistically significant differences found between diagnostic yield from specimens obtained with biopsy (core biopsy alone or with FNA) and those obtained with FNA alone (P=.75). When determining the histological subtype of the 22 patients diagnosed with NSCLC, excluding 2 patients in whom the type of needle used was unknown, no statistically significant differences were found between specimens obtained using FNA and core biopsy (with or without FNA).

No serious complications were associated with any of the biopsy procedures. One patient died shortly after the biopsy due to progression of malignant disease.

This study shows that US-guided needle biopsy performed by an interventional pulmonologist can be used to obtain a specific diagnosis (benign or malignant disease) of peripheral thoracic lesions in contact with the pleura in up to 81% of cases. Diagnostic yield of malignancy is high when sufficient fluid or tissue is obtained for diagnosis.

Our findings also show that US-guided biopsy can be used to establish a diagnosis of benign disease, such as infectious processes, particularly tuberculosis and abscesses. In 5 cases in which malignancy was not diagnosed, the initial cytohistology of the US-guided core biopsy or FNA was non-diagnostic (insufficient or indeterminate sample), and further studies were needed. This is clinically important, as in no patient was the initial specific diagnosis of benign lesion (which ruled out the need for a new, alternative diagnostic procedure) later found to be a false negative. A false negative would have led to a potentially more serious diagnostic error.

Nevertheless, we believe that a diagnosis of benign lesion does not rule out the need for strict clinical and radiological follow-up. This is particularly important in the case of abscesses, as these can also be present in neoplastic lesions.

The safety profile of the study procedure was also excellent. These good results could be due to various factors: (1) the procedure was performed by trained interventional pulmonologists; and (2) ultrasound is a very safe technique, because it allows the technician to puncture lesions that are in contact with the pleura, and to visualize the procedure in real time.2,12,13 CT-guided biopsy, in contrast, has a higher rate of complications,14 one of the reasons for this being the tendency to pierce or lacerate the healthy lung. “In US, you see what you are doing; in CT you see what you have done”.15

Our study has a number of limitations, some of which are related to its retrospective design. Some data, such as the type of needle used, number of punctures made, or the diameter of the lesion as measured by the ultrasound device, were missing from the preliminary procedures.

Diagnoses obtained from US-guided needle aspiration were not later confirmed using the gold standard technique (surgical biopsy) or by other diagnostic procedures (such as CT-guided biopsy) in order to avoid subjecting the patient to invasive procedures that could put them at risk. This is why, despite the intrinsic limitations, final diagnosis was established on the basis of appropriate clinical and radiological follow-up.

Another limitation to our study is the absence during the biopsy procedure of a pathologist capable of making an on-the-spot cytology assessment of the lesion. This would have reduced the number of FNA samples classified as insufficient.16–18 We recommend that a pathologist be present during the procedure to increase the diagnostic yield.

Many studies have shown ultrasound to be as effective as CT in guiding needle biopsy of peripheral pulmonary lesions, with a diagnostic yield based on confirmatory histology of between 84% and 95%, depending on the study.1,4,12,19–21

Most studies in US-guided needle biopsy have been published by interventional radiologists2,8,9; this is one of the first studies describing the results of this technique performed by interventional pulmonologists.

US imaging has a number of limitations, primarily that the entire pleural area cannot be visualized due to the presence of the ribs, and the technique is only suitable for evaluating lesions in contact with the chest wall.4,19 Therefore, only lesions with an good acoustic window can be sampled using this technique.6,12

Unlike CT, the size of the lesion does not seem to affect US-guided biopsy diagnostic yield.20–24

This is because under CT-guided puncture or needle biopsy, the lesion is not punctured in real time, unless a fluoroscopic CT scan is used, and accurate puncture of small lesions is hampered by the ribs and breathing movements. Ultrasound, however, provides dynamic real-time images, thus enabling the technician to more accurately target the lesion while viewing the tip of the needle.15 US-guided biopsy is a short, easily prepared procedure, and punctures can be repeated as required.1 In our series, as in those reported by other authors, we found that lesion size did not significantly affect diagnostic yield in US-guided biopsy.

Core biopsy specimens are larger than those obtained with needle aspiration. This not only facilitates diagnosis, but also allows pathologists to determine tumor subtypes in the case of malignancy, and to perform molecular analysis.19,20 Despite this, we found no statistically significant differences in either diagnostic yield or tumor subtype determination between FNA and core biopsy. This, however, could be attributed in part to the small size of our sample. In this study, we used different needle sizes, based on the findings of previous authors4,25 who found that needle type did not influence diagnostic yield.

Much effort has been devoted to the search for ultrasound descriptors that can be used as predictive factors to discriminate between malignant and benign peripheral pulmonary lesions. Evidence suggests that the best US criteria for characterizing these lesions include contour of the lung surface, margins when lung is aerated, destruction of normal pulmonary architecture, vascular displacement, neovascularization, and invasion of adjacent structures.6,13 Jeon et al.16 showed that the only statistically significant factor affecting diagnostic yield in US-guided transthoracic biopsy was the lesion-pleura contact arc length. Thus, with a contact arc length ≤30mm, diagnostic yield fell from 98% to 85.4%.

The use of ultrasound in respiratory medicine has increased in recent years, in part due to the development of educational programs, such as the Harmonization of Education in Respiratory Medicine for European Specialists (HERMES) initiative. The first syllabus released in connection with this project, in 2006, calls for training in ultrasound imaging techniques to be included in pulmonology training programs.26,27

Despite its advantages, US is rarely used in the study of malignant chest lesions, and in most hospitals the technique of choice is CT-guided needle biopsy.4

Scientific and technological advances in recent years have broadened the scope of application of US. One such example is the development of color Doppler, which, by preventing accidental puncture of large veins, has widened the diagnostic spectrum and improved the safety of ultrasound-guided techniques. Another new strategy involves the use of contrast agent in US, giving a clearer picture of the target tissue in peripheral lung lesions and improving diagnostic outcomes.28

Studies in larger series based on variables such as number of punctures per procedure, presence or absence of disease, lesion access, or learning curves, will give further insight into the different factors affecting diagnostic yield associated with US-guided biopsy techniques.

Meanwhile, studies such as ours illustrate the growing importance of ultrasound in anticipation of further developments that will extend its use among interventional pulmonologists.

Based on its good diagnostic yield and excellent safety profile, US-guided needle biopsy performed by a fully trained technician should be the technique of choice for the diagnosis of thoracic lesions in contact with the pleura,2 provided it is not contraindicated.

The authors declare they have no conflicts of interest.