Imaging is an essential part of managing many serious fungal infections, especially in deep tissues such as the lungs or CNS

At the moment this page focuses on Aspergillus but feel free to contact us if you would like to contribute information about other yeasts and moulds



Characteristic signs (e.g. reverse halo, signet ring, HAM)

Severity and extent of invasion

Staging of chronic conditions


Inactive fungal nodules or aspergillomas may be monitored to determine when (or even whether) to start antifungal treatment

Response to antifungal treatment may be seen on CT scans (e.g. cavity walls may become thinner upon successful treatment)


Bronchial artery embolization may be required to manage life-threatening haemoptysis in CPA patients in whom the artery has become eroded

Radiology of aspergillosis


Sticky mucus becomes impacted, forming ‘slugs’ that completely block airways until they are coughed up

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Rabbit ears


When air can pass around the plug, you may see the ‘finger-in-glove’ sign (or ‘rabbit-ears’ sign)
High-attenuation mucus (HAM) is virtually pathognomonic for ABPA. It is denser than skeletal muscle and best viewed on a mediastinal setting


Signet ring

bronchiectasis may resemble a signet ring when viewed in cross section, as the airway becomes wider than the adjacent pulmonary artery branch


Allergic bronchopulmonary aspergillosis (ABPA) is a hypersensitivity condition seen in patients with asthma or CF, where the immune system reacts excessively against Aspergillus mould growing in the lungs

Early in the course of disease, radiological signs are often transient and many radiographs appear normal. Infiltrates and consolidation appear during exacerbations as sticky mucus plugs block airways, then disappear when are coughed up

Over time, irreversible dilatation of the airways may occur. Central bronchiectasis is more typical of ABPA, but it is not uncommon for it to extend to the periphery. Varicose and cystic forms are more typical

Occasionally aspergillomas may develop. End-stage patients may show fibrosis and spontaneous pneumothorax

ABPA in asthma: ISHAM diagnostic guidelines (Agarwal et al, 2013) includes “Radiological features consistent with ABPA” as one of the minor criteria

ABPA in CF: Radiological signs of these conditions are largely overlapping. The Cystic Fibrosis Foundation consensus criteria (Stevens et al, 2003) reviews the evidence for each sign in more detail



Fungal hyphae growing within a cavity combine with debris/mucus and collapse to form an aspergilloma, which may move around when the patient is mobilised
Monod sign

When an aspergilloma grows inside an existing cavity, the air around it forms the ‘Monod sign’.

Please note that many people incorrectly call this an ‘air crescent’ (which is a similar sign seen in invasive aspergillosis)


Cavity wall thickness

Cavity walls become thickened as vascular granulation tissue forms, which may become thinner during successful antifungal therapy


Bronchial artery erosion

While not invasive, CPA may lead to erosion of a bronchial artery and haemoptysis requiring embolisation. Some patients keep a stock of tranexamic acid at home  in case of bleeds

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Subacute invasive aspergillosis (SAIA)
Patients with some degree of immunosuppression (e.g. alcoholism, corticosteroids) may have a rapid course of disease with localised invasion. An opacity is visible, which then begins to necrose and eventually collapses, forming ITS own cavity and an ‘air crescent’ (similar to IPA). Previously known as chronic necrosing aspergillosis


Chronic pulmonary aspergillosis (CPA) is a long-term infection where Aspergillus grows saprophytically inside a cavity or other site of structural damage

ITS radiological appearance is highly variable so CT scans are preferable to plain radiographs. Note that patients who have previously lived in a resource-limited setting may have only received X-rays

It is particularly seen in the upper lobes and is more commonly single (but may be multiple or bilateral). It often forms in cavities caused by TB or lung cancer, or alongside conditions such as NTM, bronchiectasis, sarcoidosis or ABPA. It is particularly common in COPD patients whose lung immunity against Aspergillus spores is weakened 

If CPA is inadequately treated, it can eventually lead to extensive fibrosis

Imaging is a crucial component of CPA diagnosis despite ITS variable appearance. ERS diagnostic criteria for CPA (Denning et al, 2016) specify that thoracic imaging must be consistent with CPA, preferably based on CT scan

Halo sign


Ground glass opacity surrounding one or more nodules (‘halo sign‘) may be seen as the mould invades blood vessels, causing haemorrhage
Reverse halo

Alternatively, the ‘reverse halo‘ or ‘atoll sign’ may be seen where granulomatous tissue forms around alveoli affected by inflammation/debris. Also see Greene et al (2007)


Air crescent
As the patient recovers, the necrotic area shrinks back and separates from the adjacent viable parenchyma, forming the ‘air crescent‘ sign



Invasive pulmonary aspergillosis (IPA) is a life-threatening acute infection seen mainly in immunocompromised (especially neutropaenic) patients, particularly in critical care and haemato-oncology settings.

ITS radiological appearance evolves over the course of the infection and typical signs are not seen in all patients, particularly in children (Burgos et al 2008)

Parenchymal lesions
Lesions within the parenchyma are generally caused by dissemination via the blood


Extra-axial lesions


Meningeal lesions are often the result of local spread of infection from the sinuses or mastoid bone. The skull base and orbit can also be affected



Angioinvasive infections may cause haemorrhage (Kourkoumpetis et al, 2012)

Complications such as cerebral infarction, haemorrhage, and hydrocephalus may require urgent intervention


Abscess vs neoplasm

Biopsy is often required to distinguish Aspergillus abscesses from neoplasms, as they can rather thick enhancing walls

CNS abscess

In rare cases, Aspergillus can disseminate to the brain from an initial infection site in the lungs or sinuses, or following previous brain pathology (Janardan et al, 2022). This is mainly seen in immunocompromised patients and causes a range of nonspecific neurological symptoms such as headache, lethargy, seizures, and altered mental status

Radiological appearance is often not distinct from other conditions such as neoplasms or bacterial infections, so a definitive diagnosis generally requires mycological evidence (microscopic identification of fungal elements or culture) from needle aspiration or open biopsy. CSF culture is