If cancer is not the answer: endoscopic ultrasound-guided biopsies in the diagnosis of infections.

The use of endoscopic ultrasound (EUS) with fine-needle aspiration (FNA) was first reported in the 1990s.1 Since then, this minimally invasive method has gained widespread acceptance due to its ability to acquire tissue in difficult-to-access structures. EUS-guided FNA can target a wide range of lesions, including those within the digestive tract wall (subepithelial tumors) and those in proximity to the gastrointestinal lumen in the chest, abdomen, and pelvis. EUS-FNA can obtain samples for cytologic assessment as well as core biopsies via a Trucut needle for histologic analysis. These biopsies may increase the diagnostic yield or enable more detailed analysis in select cases2,3; however, technical limitations of the EUS-guided Trucut needle hinder its widespread use. Although an EUS-guided biopsy can serve many functions, the most common reason to obtain such a biopsy is to distinguish malignant conditions from benign ones, hence the saying: tumor is the rumor, tissue is the issue, and cancer is the answer. However, benign conditions have their own diagnostic challenges for the clinician and pathologist. First, a “negative” biopsy may not be sufficient to exclude cancer. Furthermore, certain clinical circumstances require a specific diagnosis—beyond the exclusion of malignancy—in order to guide appropriate patient management. The case report by Thadani and associates exemplifies how EUS-guided biopsy can help to identify an infectious disease.4 The authors report a rare case of actinomycosis with a mass lesion in the extrahepatic bile duct. They were able to definitively diagnose the infectious organism through direct microscopic identification with EUS-guided FNA. Although this presentation of actinomycosis is extremely rare, endemic fungal infections are frequently diagnosed in a similar fashion. An example is histoplasmosis, which is highly prevalent in the Mississippi and Ohio River Valleys in the United States.5 Clinical manifestations of histoplasmosis range from asymptomatic or transient nonspecific respiratory symptoms to life-threatening sepsis in rare cases. Mediastinal lymphadenopathy is frequently found and may mimic malignancy on computed tomography and positron emission tomography scans. Biopsy with EUS or endobronchial ultrasound guidance is usually safe and easy in this setting. The pathologist may note the following findings (from least specific to most specific): the absence of malignant cells with benign lymph node tissue, granulomatous inflam-mation with or without necrosis, and identification of the infectious agent. The differential diagnosis for granulomas in these cases includes sarcoidosis, other fungal infections, and tuberculosis. Other causes of granulomas in lymph nodes include sarcoid-like reactions to tumors, drug reactions (from anti–tumor necrosis factor therapy), environmental exposures (eg, beryllium, talc), and malignancies that induce a granulomatous response (eg, lymphoma, carcinoma). These causes are less common but should still be considered in the clinical context. Necrotizing granulomatous inflammation caused by infection with Histoplasma capsulatum can typically be distinguished from non-necrotizing granulomas of sarcoidosis, particularly if abundant necrosis is present.6,7 However, the classical appearance is not always seen, and pathologic overlap exists between the 2 conditions (such as focal necrosis in sarcoidosis and non-necrotizing granulomas in histoplasmosis).8,9 Sampling error and poor specimen quality may cause further difficulties. In my clinical practice, I experienced a case in which FNA cytology of an abnormal lymph node suggested non-necrotizing granulomas but histology of an EUS-guided Trucut biopsy of the same lymph node showed necrotizing granulomas. Granulomatous infections can also present with hilar lymphadenopathy and joint pain, mimicking clinical features of acute sarcoidosis and emphasizing that sarcoidosis remains a diagnosis of exclusion.10 Cytopathologic and histopathologic granuloma findings should be interpreted in the context of pretest probability. EUS-FNA is reportedly highly accurate for diagnosing sarcoidosis when infectious causes of granulomatous inflammation are rare.11,12 However, these results cannot be translated to areas that are endemic for fungal infections. As in the case report by Thadani and colleagues, direct visualization of the infectious organism provides a highly specific diagnosis.4 The budding yeasts of H. capsulatum usually require special silver stains (Gomori methenamine) to be seen in necrotizing granulomas. An exception to this rule is disseminated histoplasmosis, in which organisms may be readily identified within macrophages via hematoxylin and eosin stains in histologic preparations or Romanowsky-based stains in cytologic preparations.7 Although other organisms may appear similar, the clinical setting typically facilitates a defini-tive diagnosis.5 EUS can also help diagnose disseminated histoplas-mosis with adrenal gland involvement,13 as in the case of an 86-year-old man who presented to my practice with weight loss, fatigue, night sweats, chills, dry cough, and hypotension. Bilateral adrenal gland masses raised suspicion for malignancy. Transgastric EUS-guided FNA of the left adrenal gland was performed (Figure 1), and cytology showed necrosis and an organism with the typical appearance of H. capsulatum (Figure 2). The patient slowly improved with itraconazole therapy. Figure 1 Transgastric endoscopic ultrasound–fine-needle aspiration (FNA) of the left adrenal gland. Figure 2 Histiocytes with histoplama (left adrenal gland fine-needle aspiration, Diff-Quik stain, 600×). Image courtesy of Dr. Robert A. Robinson, Department of Pathology, University of Iowa Hospitals and Clinics, Iowa City, Iowa. Similarly, tuberculosis is an important differential diagnosis in the setting of granulomatous lymphadeno-pathy. As with histoplasmosis, EUS can provide a minimally invasive method for obtaining a tissue diagnosis if mediastinal lymph nodes are involved.14,15 Caseating or necrotizing granulomas are typical findings and may be histomorphologically identical to findings associated with histoplasmosis.7 However, it is also possible that FNA merely reveals non-necrotizing granulomas, which may make distinction from sarcoidosis and other granu-lomatous reactions difficult unless stains or cultures for acid fast bacilli (AFB) are positive. In a recent series evaluating EUS-guided FNA for suspected tuberculosis of mediastinal lymph nodes, 25 of 46 patients with a final diagnosis of tuberculosis had granulomas with necrosis, 4 patients had necrosis only, and 17 patients had granulomas without necrosis.14 Of the 17 patients with non-necrotizing granulomas, 6 patients had positive AFB stains. AFB cultures, in addition to smears, increase the diagnostic yield and are more likely to be positive if necrosis is present.16 Although EUS-guided FNA is not performed under sterile conditions, bacterial cultures of the aspirates appear to be accurate for diagnosing purulent infections. Frit-scher-Ravens and associates performed EUS-guided FNA in 16 patients with suspected mediastinal abscesses.17 Purulent inflammation or positive gram stains were found on smears in 13 patients and 6 patients, respectively. Culture and sensitivity testing identified the organisms and aided drug therapy in all 16 patients. The control group consisted of 9 patients who underwent EUS-guided FNA for suspicion of infected lesions, though infection was ultimately not found. EUS aspirate cultures were either sterile or had a low bacterial count. In conclusion, both neoplasms and non-neoplastic infectious conditions can be diagnosed with minimal invasion via EUS-guided biopsies. Although diagnosis can be complex in infections due to overlapping cyto-pathology and histopathology and varying sensitivities and specificities for identifying organisms, EUS often obviates the need for highly invasive surgical procedures and should be considered in the diagnostic algorithm. Dr. Gerke thanks Drs. Robert A. Robinson and Chris S. Jensen of the Department of Pathology in the University of Iowa Hospitals and Clinics in Iowa City, Iowa for their critical review of the manuscript.