Endobronchial Ultrasound-guided Transbronchial Needle Aspiration in a Geographical Region With Endemic Histoplasmosis Infection

Abstract

Background and Objective 

In a geographical area with high prevalence of calcific granulomatous inflammation, calcified lymph nodes may affect the diagnostic adequacy of endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA). The objective of this study was to describe the diagnostic performance of EBUS-TBNA in a region endemic of histoplasmosis related granulomatous inflammation.

Methodology 

A retrospective review was done for all patients referred for EBUS-TBNA over a 7-month period at 2 institutions. Computed tomographic (CT) chest studies were reviewed in a blinded manner by 2 radiologists. In parallel, CT images from 100 unselected sequential control patients were reviewed. Cytologic analysis of EBUS-TBNA aspirates was compared with a reference standard of definitive pathologic tissue diagnosis or a composite of ≥6-month clinical follow-up.

Results 

The prevalence of calcified lymph nodes in the 100 control patients was 56%. All 61 patients undergoing EBUS-TBNA were included. In total, 97 lymph nodes (mean size=13.8 mm) and 7 masses were biopsied. Definitive lymph node sampling was achieved in 51 of 61 patients (83%). The sensitivity, specificity, and positive and negative predictive values of EBUS-TBNA for malignancy (primary lung cancer staging, restaging, and reevaluation after cancer therapy, small cell lung cancer, lymphoma, and metastatic cancer) were 81%, 100%, 100%, and 84% respectively. On pre-EBUS CT chest scan, 60.6% had nodal calcification. The prevalence of cancer was not different in those with and without nodal calcification (49%). There was no difference in frequency of definitive lymph node sampling in those patients with or without nodal calcification.

Conclusion 

In a geographical area with endemic histoplasmosis-related nodal calcification, there was no evidence of nodal calcification affecting the frequency of EBUS-TBNA definitive lymph node sampling.

Endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) of mediastinal and hilar lymphadenopathy is evolving as a minimally invasive and safe diagnostic tool for the diagnosis and staging of non-small cell lung cancer (NSCLC).^1–5 When added to endoscopic ultrasound-guided biopsy, EBUS-TBNA allows almost complete staging of the mediastinal and hilar nodes.⁶ Two recent meta-analyses reported the sensitivity and specificity of EBUS-TBNA in primary NSCLC staging as 88% to 94% and 100%, respectively.^7,8 EBUS-TBNA also has been established as a diagnostic tool for benign disease such as sarcoidosis^9–11 and may have a role in the diagnosis of lymphoma involving the mediastinum.¹²

Multiple factors have been identified that may affect the diagnostic yield of EBUS-TBNA, which include lymph node size, location, and earlier cancer therapy.^4,5,12–14 The influence of mediastinal and hilar lymph node calcification on the yield and accuracy of TBNA is not known. On commencing an EBUS-TBNA program at 2 adjacent tertiary referral medical centers in an area with high prevalence of histoplasmosis infection,^15,16 a high incidence of mediastinal and hilar lymph node calcification was noted on pre-EBUS radiographic imaging. In this study, we describe the performance of EBUS-TBNA in a population of patients with a high prevalence of dystrophic lymph node calcification in an area with endemic histoplasmosis infection.

METHODS

The study was approved by the institutional review board at both institutions: the University of Arkansas for Medical Sciences and the Central Arkansas Veteran Health Care System. A retrospective analysis of all patients who underwent EBUS-TBNA at both institutions in the period between October 2007 and June 2008 was performed.¹⁷ The decision for the diagnostic procedure was based on the clinical requirement of histologic diagnosis for enlarged mediastinal and/or hilar lymphadenopathy. Contrast chest computed tomographic (CT) scans with upper abdominal imaging and positron emission tomography/CT scans (if available) of all patients were reviewed before the procedure.

In parallel, contrast-enhanced chest CT scans with upper abdominal imaging studies from 100 unselected sequential patients were also reviewed from the 2 centers (n=50 each) for evidence of dystrophic calcification suggestive of earlier granulomatous infection. The presence of calcifications was subdivided into any calcification (including lung parenchyma, splenic and liver parenchyma, and lymph node calcification), or mediastinal and hilar lymph node calcification alone (lymph node).

All EBUS-TBNA procedures were performed by 1 of 2 pulmonologists with or without supervised fellows. The procedure was performed under either general anesthesia with laryngeal mask intubation or conscious sedation with midazolam and fentanyl. All biopsies were performed using a (Olympus XBF-UC 160F) bronchoscope with dedicated 22-gauge needle (NA-202C Olympus Ltd). Airway survey with flexible bronchoscopy was performed before the biopsy procedure. Identified lymph nodes larger than 0.5 cm in short-axis diameter by EBUS were sampled; lymph nodes smaller than 0.5 cm in diameter were sampled at the discretion of the bronchoscopist. A minimum of 2 passes and a maximum of 5 passes from each biopsied lymph node were attained. All cytologic material was reviewed by rapid on-site examination by one of the institutions' cytopathologists and a decision to perform more biopsies or passes depended on the preliminary results and the need to further stage the disease. All complications were recorded and reported.

Cytologic analysis of EBUS-TBNA aspirates was compared with a reference standard of definitive pathologic tissue diagnosis or a composite of ≥6-month clinical follow-up with radiographic imaging by 2 reviewers. Definitive lymph node sampling was defined by the cytologic evidence of lymphoid tissue with or without necrosis, granulomatous inflammation, or tumor. The results were classified as malignant, benign disease (granulomatous inflammation or other), normal/reactive hyperplasia, or an inadequate sample (bronchial epithelial tissue and blood). Summary statistics were used to describe the lymph node characteristics. Sensitivity and specificity were estimated with 95% confidence intervals (CIs). The primary study outcome was the rate of definite lymph node sampling in patients with and without calcifications on a per patient basis.

Counts, binomial proportions, and corresponding 95% continuity-corrected CIs were used to describe the lymph node characteristics. The sensitivity and specificity of diagnostic EBUS-TBNA were estimated. The rate of definitive lymph node sampling on a per nodal basis was also calculated. The baseline characteristics were compared with those in the control group using the Fisher exact χ² tests.

RESULTS

Between October 2007 and June 2008, 61 patients underwent diagnostic EBUS-TBNA procedures. Eleven procedures were performed under general anesthesia. There were no complications related to the procedure and all patients tolerated the procedure. The prevalence of calcifications in the EBUS-TBNA group was similar to that found in both control groups (Table 1), thus a typical prevalence of calcifications for the geographical region.

TABLE 1: Prevalence of Granulomatous Inflammation as Reflected by the Presence of Dystrophic Calcification on CT Imaging in All 61 Patients Undergoing EBUS-TBNA and 100 Randomly Selected Patients From Our 2 Institutions

There was also no difference in the prevalence of malignant disease among patients who had calcifications and those who did not (51% vs. 45%, P=0.854).

A total of 97 lymph nodes and 7 masses were biopsied in 61 patients. The mean lymph node size was 13.8 mm (range: 4.5 to 41 mm, SD: 6.9 mm). Definitive lymph node sampling was achieved in 51 of 61 patients (83%; 76/97 lymph nodes at 78%; Tables 2 and 3). As the 95% CI: 9 (−2.21%, 2.40%) for the difference between the 2 proportions included 0, there did not seem to be an influence of lymph node calcification on definitive lymph node sampling (Table 2). There was also no evidence of a difference in the sampling inadequacy between lymph nodal stations with (33%) or without (19%) calcification; 95% CI for the difference between the 2 proportions was −7.44%, 40.97% (Table 3). Sampling from a lymph node station containing calcification identified cancer (n=12) in 3 patients: 2 patients with small cell cancer (size 25 and 41 mm; Fig. 1) and 1 with hepatocellular cancer (size 36 mm). There was a statistically significant decrease in the sampling adequacy of lymph nodes smaller than 10 mm (n=21) compared with lymph nodes larger than 15 mm (n=23; P=0.03; Table 4). The location of the lymph node did not statistically alter the adequacy of sampling.

TABLE 2: The Influence of Granulomatous Inflammation as Reflected by Dystrophic Calcification on CT Chest Imaging in 61 Patients Undergoing EBUS-TBNA

TABLE 3: The Influence of Lymph Node Calcification on Sampling by EBUS-TBNA in All 97 Lymph Nodes

TABLE 4: The Influence of Lymph Node Size on Lymph Node Sampling

FIGURE 1.: Sixty-one-year-old female patient with small cell lung cancer. A, Endobronchial ultrasound image of an enlarged subcarinal lymph node, positive for small cell lung cancer with endobronchial ultrasound-guided transbronchial needle aspiration. B, Contrast-enhanced axial computed tomographic (CT) chest image displays calcified mediastinal lymph nodes suggestive of healed histoplasmosis infection (arrows). C, Contrast-enhanced axial CT chest image displays calcified hepatic and splenic granulomas suggestive of healed histoplasmosis infection (arrows).

A reference standard was not available in 7 of 61 patients (inadequate follow up n=6, death from another cause n=1). EBUS-TBNA identified a malignant etiology in 22 of 27 cases (Table 5). The diagnoses of cancer in 5 patients with false-negative EBUS-TBNA by the gold standard were NSCLC (n=2), SCLC (n=1), metastatic renal cell carcinoma (n=1), and Hodgkin lymphoma (n=1). The patient with Hodgkin lymphoma had mediastinoscopy as a gold standard. The other 4 patients with false-negative EBUS-TBNA for cancer had a CT-guided lung biopsy confirming cancer diagnosis, with a presumptive diagnosis of metastatic mediastinal disease based on follow-up without confirmatory biopsy. In these 5 patients, 7 lymph nodes and 1 mass were biopsied. Only 1 lymph node station contained calcification and EBUS-TBNA sampling showed normal lymphoid tissue.

TABLE 5: EBUS-TBNA as Compared With Reference Standard

The sensitivity, specificity, positive predictive value, and negative predictive value of EBUS-TBNA for all cancers (primary lung cancer staging, restaging, and reevaluation after cancer therapy, SCLC, lymphoma, and metastatic cancer) were 81%, 100%, 100%, and 84%, respectively.

DISCUSSION

Although many studies have identified the utility of EBUS-TBNA, specific reasons for inadequate sampling have often not been clearly identified.^3–5,9–14 Lymph node-specific factors that may influence EBUS-TBNA yield include its site, size, echogenicity, and the presence of calcification. EBUS-TBNA is one of many modalities available to sample the mediastinum.¹ Thus, it is important to investigate the influence of specific lymph node characteristics that may be identified by prelymph node sampling on the accuracy of EBUS-TBNA and whether another more invasive test, such as mediastinoscopy, may be needed. An earlier study comparing EBUS-TBNA, positron emission tomography, and CT in staging the mediastinum in 102 patients with NSCLC identified 2 false-negative results for EBUS-TBNA.⁵ Lymph node calcification was deemed the cause of the false-negative test in 1 of these patients. In our recent study of factors influencing the result of EBUS-TBNA in a population of patients presenting to a lung cancer institute, lymph node calcification was thought to contribute to inadequate sampling in 2 patients.²⁰ The geographic location of our 2 centers allowed us an ideal opportunity to assess the influence of calcified lymph nodes on EBUS-TBNA in mediastinal and hilar lymph node sampling. The presence of lymph node calcification was not different between the group undergoing EBUS-TBNA and the control group. The natural history of primary histoplasmosis infection involves lymph node granulomatous inflammation and calcification as a host defense mechanism.²¹ The majority of patients with evidence of nodal calcifications in an endemic histoplasmosis region have had a histoplasmosis infection that is asymptomatic (99.5%).¹⁶ The prevalence of mediastinal and hilar nodal calcification secondary to tuberculous in the region is unknown; however, the yearly incidence of Mycobacterium tuberculosis infection in our area is not high (4.7 cases per 100,000) and the estimated latent tuberculosis prevalence is 4.2%.²² Thus, it is probable that the majority of calcified lymph nodes is secondary to histoplasma infection given the high prevalence of earlier histoplasma infection by skin testing.¹⁵ In fact, the presence of a high prevalence of calcified lymph nodes rather than the cause allowed the analysis of EBUS-TBNA in this specific setting.

In this study population, the presence of mediastinal dystrophic calcification did not affect accuracy of EBUS-TBNA in the overall patient population. When EBUS-TBNA was analyzed on a per lymph node rather than per patient basis, the yield of adequate tissue was less in lymph nodes that were calcified (66%) than in those that were not calcified (81%). However, this did not provide evidence to consider them to be different as the 95% CI between the differences did not include 0. It should be noted, however, that this was a fairly small retrospective analysis and thus was not powered to perform any formal statistical hypothesis testing on the primary study outcome. It also should be noted that this is a retrospective analysis and not every calcified lymph node identified on a CT scan was biopsied (not enlarged or not required for biopsy for instance in the staging of NSCLC). The authors admit that in cases with diffuse nodal calcification in which only 1 positive lymph node by on-site evaluation was required (eg, SCLC), a node that was not calcified would have been preferential. Although nodal calcification did not impact the quality of the EBUS image, the authors did attempt to avoid the calcified area of a lymph node when sampling.

However, it is important to note that sampling from a lymph node station containing calcification with EBUS-TBNA identified cancer in 3 patients. Thus, in the radiographic staging of lung cancer in patients with dystrophic lymph node calcification, it is important that cancer treatment is not denied on the basis of lymph node enlargement with or without calcification without definitive lymph node sampling.

The sensitivity of EBUS-TBNA for cancer at our institution was similar to that of other published studies.^2–5 Of note, when comparing studies of EBUS-TBNA for cancer, it is important to define the population that is being studied (primary NSCLC staging vs. all cancer patients). In our population, 5 patients had EBUS-TBNA tests that were false negative for cancer and none of these patients had false-negative sampling from calcified lymph nodes. In agreement with our recent study from an academic cancer institute,²⁰ our study has shown decreased adequacy of sampling smaller lymph nodes.

In conclusion, our results give no reason to conclude that EBUS-TBNA is a not a safe and effective method for sampling lymph nodes in a population of patients with a high prevalence of dystrophic calcification, including mediastinal and hilar lymph node calcification. In patients undergoing cancer staging, who have lymphadenopathy deemed radiographically secondary to the residual effects of granulomatous inflammation, such as histoplasmosis, cancer therapy should be based on definitive lymph node sampling.