Discussion
Micheli in 1729 described a fungus as Aspergillus (rough head) because of the microscopic appearance of the spore-bearing structure. The first recognized infection in man due to the fungus of this genus was described by Sluyter in 1847.3 There are approximately 300 species of the genus aspergillus. They are within the environment, but only approximately 8 species are responsible for the vast majority of human disease. Aspergillus fumigatus is the most common pathogen accounting for most of the infections followed by aspergillus niger.4
Aspergillus species can cause various forms of lung diseases like allergic bronchopulmonary aspergillosis which is a hypersensitivity reaction to aspergillus antigens mostly due to aspergillus fumigatus. The incidence of allergic bronchopulmonary aspergillosis varies from 6% to 20% of all patients with asthma.5 Most patients are under the age of 35 years at the time of diagnosis.1 Invasive pulmonary aspergillosis is another form of pulmonary disease which is characterized by proliferation of fungal mycelia in the pulmonary parenchyma. This disease is uncommon and is due to tissue invasion with the fungi.1 Recently it has increased due to growing numbers of patients with impaired immune status associated with malignancy, organ transplantation and autoimmune conditions.6 Factors that predispose to the development of invasive aspergillosis include neutropenia, prolonged and high-dose corticosteroid therapy, advanced AIDS and chronic granulomatous disease.1 Chronic necrotizing pulmonary aspergillosis is caused by aspergillus species which is associated with cavitary infiltrates in chronic lung disease or in mild immunodeficiency state.6.7 This infection cause progressive damage to the lung parenchyma without clear evidence of tissue invasion. The patients are usually middle-aged with evidence of generalized immunosuppression in the form of diabetes mellitus, malnutrition, corticosteroid or radiation therapy.1 When aspergillus colonizes in a pre-existing lung cavity, a fungus ball comprises of fungal hyphae, inflammatory cells, fibrin, mucus and tissue debris to form an aspergilloma.1 Pulmonary aspergilloma develops in pre-existing lung cavities most commonly in patients with prior pulmonary tuberculosis but also in patients with other conditions as sarcoidosis and idiopathic pulmonary fibrosis.8 In the present case also, the patient had cavitary lesions due to past history of pulmonary tuberculosis.
Cysts and cavities are commonly encountered lesions in the lung on chest radiography and computed tomography (CT). Solid contents within a cavity may be seen in infectious processes, such as aspergillosis and in necrotic cancer. CT can show the size, shape and precise position of cysts and cavities when these details are not apparent on chest radiography.7
The hyphae of aspergillus species range in diameter from 2.5 to 4.5 µm and exhibit frequent septation. Aspergillus hyphae tend to branch dichotomously, progressively and primarily at acute angles of approximately 45°, mimicking an arborizing tree branch. Some times in the areas of mycelial growth, hyphae often become tangled, bulbous and distorted which may cause difficulty in identification and diagnosis.4
Fine needle aspiration cytology can be quite helpful in distinguishing malignancy from infection.9 This technique helps in detecting a wide variety of opportunistic pulmonary infections in immunocompromised patients.10 Fungal elements are detected using routine and special stains like Periodic Acid-Schiff.9 This procedure is safe, cost-effective and provides rapid results.10
Treatment of aspergilloma is considered when patients become symptomatic, usually with hemoptysis. Surgical resection is curative but may not be possible in patients with limited pulmonary function. Oral itraconazole may provide partial or complete resolution of aspergillomas in 60% of patients. Successful intracavitary treatment using CT guided percutaneous catheter instillation of amphotericin has been reported in small numbers of patients.8