Role of Imaging in Pulmonary Aspergillosis

Imaging plays a pivotal role in the evaluation of pulmonary aspergillosis. High-resolution computed tomography (HRCT) of the chest is the imaging modality of choice for diagnosing pulmonary aspergillosis, guiding treatment decisions, and monitoring the response to therapy. HRCT can also help differentiate among various types of aspergillosis such as allergic bronchopulmonary aspergillosis (ABPA), chronic pulmonary aspergillosis (CPA), and invasive pulmonary aspergillosis (IPA). ABPA often presents with consolidation, nodules, and central bronchiectasis. Classically, mucus plugging giving finger-in-glove appearance can be seen in ABPA on both chest X-ray and CT. Identifying high-attenuation mucus (HAM) on CT is considered pathognomonic of ABPA. It is important to note that the diagnosis of ABPA is primarily serological in predisposed individuals (having bronchial asthma or cystic fibrosis), and imaging may be completely normal. CPA occurs in patients with minimal or no immune suppression and primarily affects individuals having pre-existing underlying structural lung disease. Imaging is essential in diagnosing CPA and typically reveals one or more cavities with or without fungal ball, pericavitary opacities, pleural thickening, and other signs of volume loss. IPA occurs almost exclusively in immunocompromised individuals. It can manifest in two forms, angioinvasive aspergillosis, characterized by multiple nodules with CT halo sign (a central nodule surrounded by a peripheral ground-glass opacity); and airway-invasive aspergillosis, characterized by peribronchial consolidation and centrilobular nodules with tree-in-bud appearance. Ultrasound (USG), magnetic resonance imaging (MRI), and positron emission tomography-computed tomography (PET/CT) are complementary imaging tools that are used in specific clinical indications.