The CT halo sign in invasive aspergillosis


Key Clinical Message

In immunocompromised patients, the pulmonary computed tomography halo sign is highly suggestive of angioinvasive aspergillosis. Early recognition may be life-saving.


A 35-year-old male with myelodysplastic syndrome presented with acute abdominal pain. The next day, he developed right-sided weakness. Labs revealed neutropenia. Imaging showed infarcts within the brain, liver, and spleen. Chest computed tomography (CT) is shown below (Fig. 1).

Figure 1.

Chest CT revealing the halo sign (a nodular opacity surrounded by a ground-glass halo) in the right lung.


What is the diagnosis?


Invasive aspergillosis.


Invasive aspergillosis (IA) is a major cause of morbidity and mortality in severely immunocompromised patients [1]. Risk factors for IA include neutropenia, hematopoietic stem cell and solid organ transplantation, and AIDS [1]. A characteristic finding on chest CT is the halo sign, a solid nodule surrounded by a halo of ground-glass attenuation. In IA, the solid nodule represents a fungal nodule or infarct and the ground-glass halo represents hemorrhage. In an immunosuppressed patient, the halo sign is highly suggestive of angioinvasive fungal infection, most commonly aspergillosis (Fig. 2). An identical appearance may be seen with mucormycosis [2].

Figure 2.

Right frontal cortex, H&E, 200X. Intraparenchymal branching, septate fungal hyphae (arrow) identified as Aspergillus.

The CT halo sign has also been reported with other infections including mycobacterial and some viral infections [2]. Non infectious etiologies of the CT halo sign incude hypervascular metastases and Wegener's granulomatosis [2].

Conflict of Interest

None declared.