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