in the presence of chronic cavitary pulmonary histoplasmosis as the cavitation disrupts normal architecture leading to bronchopleural fistulae . 10 , 11 , 12 In contrast to histoplasmosis , other mycotic infections such as paracoccidioidomycosis are well documented to have pleural involvement causing pneumothoraxes without respect to acuity . 13 In these cases , it is thought that pleural involvement results in architectural disruption of the lung ultimately leading to the development of pneumothorax .
FIGURE 4
Infectious Disease Society of America ( IDSA ) guidelines suggest that asymptomatic patients with Histoplasma pulmonary nodules do not require antifungal medication . 8 In this case , since the patient was asymptomatic from the infection itself , the historical pneumothoraxes and the excised SPN were not thought to represent acute or symptomatic pulmonary histoplasmosis , negating the need for antifungal therapy .
Management for an SPN should always involve an assessment of the patient ’ s risk factors for malignancy . Recall the many historical findings which place the patient at higher risk of malignancy found in Table 1 . In the absence of risk factors , the physician should be prompted to consider other etiologies for the lung nodule . Imaging characteristics of benign and malignant nodules are summarized in Table 2 . Nodules can take on both malignant and benign features , hence a multidisciplinary approach to the management of SPN is important . 3 In resource-limited settings where organized tumor boards may not be available , there are established predictive models that may assist in clinical decision-making such as the Brock and Mayo Clinic model . 2 Prior literature had described histoplasmosis as the most common fungal infection to mimic lung cancer , making consideration of nodule characteristics uniquely important in endemic areas . 14
CONCLUSION
This case highlights several learning points . First , our case represents a benign cause of a pulmonary nodule , as well as its unusual presentation with recurrent pneumothoraxes . Given that histoplasmosis is not a rarely encountered diagnosis , it is important to consider its wide variety of potential
Grocott Methenamine Silver ( GMS ) stain showing the Histoplasma organisms ( stained dark blue here ).
TABLE 1 : Risk Factors for Pulmonary Nodule Associated Malignancy 3 Smoking and Exposure History
Patient Age Medical and Family History
Tobacco smoking , exposure to organic dust , heavy metal exposure
Older patients are at higher risk of lung cancer
Patients with chronic lung disease are at higher risk of lung cancer ; patients with family history or personal history of lung cancer are at higher risk
TABLE 2 : Imaging Characteristics of Malignant and Benign Pulmonary Nodules 3 , 4 Malignant Characteristics > 6 mm in size Growth of the Nodule on Repeat Imaging Spiculation Upper Lobe Location Pleural Indentation Vascular Convergence Air Bronchograms SUV > 2.5
Benign Characteristics Peri-fissural Location < 6 mm in size Calcification
Smooth / Homogenous Subpleural Location Fat Attenuation SUV < 2.5 on PET
SUV : standardized uptake value ; PET : positron emission tomography
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