Pulmonary aspergillosis is a fungal infection of the lung. There are two ways of fungal infection in human body, one is primary infection, which is caused by inhalation of a large amount of material and soil contaminated by fungal spores, and is less common: the other is a conditional pathogenic or secondary infection, where the patient often has a systemic disease that is the basis of the primary pathology, such as severe infection, malignant tumor, hematological disease, liver cirrhosis, etc. On the one hand, the immune function is suppressed due to the disease itself: on the other hand, the long-term use of hormones, immunosuppressants and anti-tumor cytotoxic drugs, etc., further decreases the immune function of the body, leading to the development of fungal disease. Long-term application of high doses of extensive antibiotics inhibits the growth of bacteria, which can also enable the propagation of insensitive fungi, leading to the development of pulmonary fungal disease. Fungal pathogenicity is weak, healthy human body has strong resistance to fungi, only when the body resistance is reduced to invade the tissue, multiplying to cause disease.
Pathology.
Fungal invasion of lung tissue can cause a series of inflammatory reflections, the basic pathological changes are coagulative necrosis, cellular infiltration and abscess formation. Chronic infection is pulmonary fibrosis or granuloma formation.
Clinical features.
The clinical manifestations of pulmonary aspergillosis are non-characteristic and may include fever, cough, dyspnea, hemoptysis and chest pain. The possibility of fungal infection should be thought of in suspicious patients, especially for pulmonary lesions of unknown origin and febrile illness. Detailed medical history must be taken, including contact history, travel history, and occupational history.
Typology, CT manifestations and differential diagnosis.
I. Allergic bronchio-pulmonary aspergillosis (ABPA)
It is a non-infectious inflammatory disease that occurs almost exclusively in patients with asthma and is also known as asthmatic pulmonary eosinophilia. After the allergic person inhales a large number of Aspergillus spores, the organism is metamorphosed to Aspergillus, the mucus secreted by the bronchus increases, the viscosity increases, the Aspergillus mycelium increases the viscosity of the mucus, and the secretion in the bronchial lumen is not easily discharged then the mucus plug is formed.
CT manifestation: Bronchial mucus embolism is the main pathological and CT manifestation of ABPA, often involving the upper lobe bronchi, almost always located in the lung segment or sub-lung segment bronchial cavity, manifested as (1) V-shaped, Y-shaped, grape-shaped or finger-loop shadows, concentrated in the direction of the lung door, with clear edges; (2) official cavity expansion and wall thickening (inflammatory reflection), may appear orbital signs or annular shadows; (3) mucus embolus cough out, leaving columnar (3) after coughing up the mucus plug, the columnar or cystic bronchial dilatation remains while the distal bronchus remains normal, strongly suggesting the diagnosis of ABPA; (4) the lung tissue distal to the lesion may show pulmonary atelectasis or hyperinflation due to lateral branch ventilation. There may also be exudative alveolitis changes: single or multiple patchy hyperdense shadows in the lung parenchyma, mostly in the upper lobes, which may be transient, wandering or persistent for a longer period of time.
Differential diagnosis.
Bronchial mucus embolism is the predominant pathologic and imaging manifestation of ABPA, often involving the upper lobe bronchi and almost always located in the bronchial lumen of a lung segment or sub-pulmonary segment. There is a long history of bronchial asthma, an increased percentage of eosinophils in the peripheral blood, and Trichophyton sputum can be detected.
1. Congenital bronchial atresia.
Congenital bronchial atresia is also mostly atresia of the proximal bronchus of the lung segment, often forming a well-defined mass, typically in the form of a bronchial branch or with more branches like a finger sleeve, the tip of which points to the lung door, and also in a polygonal shape. Restricted air trapping in the lobes and segments of the lung to which the atretic bronchus belongs is also an important diagnostic basis for congenital bronchial atresia.
Allergic bronchio-pulmonary aspergillosis does not easily form a definite mass shadow, but only a V-shaped, Y-shaped, grape-shaped or finger-loop shadow with clear edges, which is characteristic in patients with bronchial asthma or a history of exposure to fungal dust. Mucus plug coughing out leaves proximal bronchial columnar or cystic dilatation while the distal bronchus remains normal, which is an impossible imaging manifestation of congenital bronchial atresia.
2.Central type lung cancer.
Central type lung cancer can also cause distal bronchial mucus occlusion, but its characteristic imaging manifestations are: bronchial stenosis and/or truncation, and soft tissue mass shadow around the stenosed or truncated bronchus, which are very different from the imaging manifestations of ABPA. Clinical signs and symptoms of blood in sputum, intra-thoracic and distant septal metastases are often present. Sputum cytology or fiberoptic bronchoscopy can be used as further differential diagnosis.
3.Benign tumor in the bronchial lumen.
Benign tumors in the bronchial lumen are very rare, among which misshapen tumors are more common. Those located in the main bronchus and lobe bronchial cavity often cause obstructive pneumonia or pulmonary atelectasis; the bronchial mucus embolism caused by benign tumor in the lung segment bronchial cavity is similar to the imaging performance of ABPA. However, the mass shadow of benign tumors is usually smaller when detected and completely located in the lumen; imaging may show a soft tissue mass shadow with smooth margins in the lumen, narrowing or truncation of the lumen, cup-shaped at the severed end (convexity facing the proximal lumen), and no thickening of the tube wall.
Second, parasitic pulmonary aspergillosis
Parasitic pulmonary aspergillosis is the invasion and parasitism of Aspergillus in the lung pre-existing cavities, cavernous lesions, mycelium and cellular debris in the cavity (cavity) to form – spherical body – that is, Aspergillus ball, also known as mycosphere type pulmonary aspergillosis.
CT manifestations.
Aspergillus ball is spherical, more uniform density, clear boundaries, free state in the cavity, the location can change with the examination position. Mycobacterial ball and cavity (cavity) wall often leaves a crescent-shaped gap between, forming the air crescent sign. This is the characteristic manifestation of parasitic pulmonary aspergillosis.
Differential diagnosis.
1. Spheroid-like lesions in the cavity.
Cavities with blood clots, dried pus, and necrotic tissue can also form contents resembling spheroids, which can be seen in cavities formed by tuberculosis bulb lysis, secondary type tuberculosis, chronic lung abscess, and peripheral type lung cancer, as well as in cavitary diseases such as pulmonary cysts and cystic bronchiectasis. The morphology of spheroids formed from causes other than varicocele is mostly irregular. There is usually no spherical content in the cavity of lung cancer, and occasionally irregular masses may be formed in the cavity due to tumor necrosis.
2.Nodule spheroid subpericardial fissure-like cavity.
Superficially, the larger fissure-like cavity under the envelope of the nodule sphere surrounds the undissolved caseous necrotic lesion – “spheroid within the cavity”, which is very similar to the air crescent sign of parasitic pulmonary aspergillosis. However, the former fissure-like cavity is not completely surrounded by the “cavity spheroid”, and the “cavity spheroid” is closely connected with the rest of the nodule sphere, and cannot move within the cavity (cavity) with the change of body position, which is an important point of differentiation.
III. Invasive pulmonary aspergillosis
Invasive pulmonary aspergillosis (IPA) often occurs in patients with low organism resistance, such as patients with advanced severe disease and immunosuppressed patients (leukemia, lymphoma, organ transplantation), and is an opportunistic lung infection. Aspergillus invades the lung tissue mainly via the airways (rarely this can be transmitted hematologically) causing necrotizing inflammation. Aspergillus parasitic in blood vessels forms varicose nodules (varicocele) surrounded by a ring of hemorrhagic infarction and coagulative necrosis. Hemorrhagic pulmonary infarction results from the formation of thrombus when the branches of the pulmonary artery are invaded. The involvement of larger branches of the pulmonary artery forms a wedge-shaped shadow with pleural base, and most of those invading the tiny vessels around the lesion to make them rupture and bleed are spherical lesions.
CT manifestations.
In the early stage of the disease, single or multiple spherical household patches with blurred margins in one or both lungs, and in the late stage, most cases of necrotic inflammation eventually appear as cavities; the air crescent sign may appear between the varicella nodules (varicella spheres) and the surrounding inflammatory reaction zone; sometimes, in the early stage of varicella infection, before the formation of cavities, a ring-shaped solid area of lower density is shown around the central solid mass (bacterial spheres and coagulated necrotic tissue). The CT value is lower than that of the solid mass and higher than that of the normal lung parenchyma, which is known as the halo sign. The pathologic basis of the halo sign is hemorrhagic pulmonary infarction.
Differential diagnosis.
The pathologic basis of the halo sign is hemorrhagic pulmonary infarction, and although appropriate clinical data coupled with the CT halo sign can be highly suggestive of vascular invasive pulmonary aspergillosis, the halo sign is also not specific to this disease, and close clinical attention must be paid to differentiating it from other diseases with similar imaging. Invasive pulmonary aspergillosis occurs mainly in critically ill patients in advanced stages and in immunosuppressed patients (leukemia, lymphoma, organ transplantation) and is an opportunistic pulmonary infection.
Hemorrhagic pulmonary nodules are also seen in certain hemorrhagic pulmonary metastases such as metastatic angiosarcoma, Kaposi’s sarcoma, Wegener’s granuloma, tuberculosis, and some other infectious lung lesions (candidiasis albicans, trichomoniasis, cytomegalovirus, and herpes zoster virus pneumonia). Mucus-secreting adenocarcinoma may also have similar imaging findings. Close clinical and laboratory examination is required.