Archived case 217 · February 24-March 3, 2017
A 62-year-old male presents with complaints of shortness of breath and cough. Past medical history is significant for stem cell transplant two months ago.
What are the pertinent findings on the non-contrast-enhanced CT images? What is your main differential diagnosis?
Axial non-contrast enhanced CT of the chest in soft tissue and lung windows demonstrates a heterogeneous and hyperdense consolidation, largely involving the RLL parenchyma. There are indistinct margins with a zone of ground-glass attenuation surrounding the consolidation, so-called CT halo sign (classically relates to hemorrhage). A small pleural effusion is present. There is no discrete lymphadenopathy. The partially seen intravascular stent in the descending aorta is related to a remote traumatic aortic injury. Answer Diagnosis: Pulmonary nocardiosis
Pulmonary nocardiosis
Nocardia is a gram-positive, branching, beaded bacillus which is weekly acid-fast. Nocardia usually is an “opportunistic pathogen,” with the majority of infections occurring in patients with immunosuppressive conditions (transplant, antineoplastic therapy, AIDS, etc.).
Several different infectious and non-infectious diseases are associated with the presence of the halo sign:
· Fungal infections, including (depending on the host): aspergillosis, mucormycosis, histoplasmosis, blastomycosis, cryptococcosis
· Actinomycosis and other bacterial infections
· Mycobacterial infections, including Mycobacterium tuberculosis and ? non-tuberculosis mycobacterial infections
· Lung malignancy (primary or secondary)
· Systemic diseases: granulomatosis with polyangiitis ?
The most common acute parenchymal findings in PN is airspace opacities and nodules, while masses, lymphadenopathy and pleural disease are less common. The most common manifestation of PN is homogenous consolidation, followed by nodules and cavitation.
In 50% of pulmonary infections, bacteremia and dissemination may occur. Brain imaging is recommended in all patients with nocardiosis to exclude metastatic infection.
References:
1. The Diagnostic Value of Halo and Reversed Halo Signs for Invasive Mold Infections in Compromised Hosts. Georgiadou et. Al., Clinical Infectious Diseases 2011;52(9):1144–1155
2. Nocardiosis: Updates and Clinical Overview. Wilson, J . MayoClinProc. April2012;87(4):403-407
Pulmonary nocardiosis: computed tomography features at diagnosis. Kevin et.al., J Thorac Imaging. 2011 Aug;26(3):224-9.Original case written by its authors at Virginia Commonwealth University and published at this address as part of a weekly teaching collection. Reproduced here as an archive.