Alveolar sarcoidosis

Clinical History

A 33-year-old female patient presented with productive cough, fevers, night sweats, polyarthralgia and anterior uveitis. Serum angiotensin converting enzyme level was elevated. Bronchial washings were negative for bacteria (including mycobacteria), fungi and pneumocystis jiroveci. Cytology of the lavage fluid revealed 87% macrophages and no evidence of malignancy.

Imaging Findings

On chest radiograph there are multiple nodular airspace opacities in both lungs (Figure 1); the lesion in the right lower zone lung shows central hypo-attenuation. There is symmetrical hilar shadows lymph node enlargement. Enlarged nodes are present in the aorto-pulmonary window. There is no pleural abnormality.
Chest CT reveals multifocal consolidation with fine nodularity surrounding a number of the lesions (Figure 2). In the right lower lobe there is consolidation surrounding a central area of ground-glass attenuation (the ‘reversed halo’ sign). On the soft tissue windows, there is symmetrical hilar and mediastinal (subcarinal, paratracheal, subaortic, para-aortic and pre-vascular) lymph node enlargement (Figure 3).

Discussion

The presentation is non-specific, but biopsy showed numerous discrete non-caseating granulomata without lymphocytic inflammation, suggesting sarcoidosis, a systemic granulomatous disease. The most frequent sites of involvement include lymph nodes, skin, lungs and eyes, although virtually any organ can be affected.

In patients with a compatible clinical history, thoracic imaging (usually in the form of chest radiograph) is used for confirmation and staging. CT is only necessary in cases of atypical clinical and/or chest radiographic findings; high clinical suspicion of sarcoidosis without typical imaging findings; and suspected complications, including airway disease, fibrosis and mycetoma [1].

The common chest radiograph finding is symmetrical bilateral hilar and right paratracheal lymph node enlargement. About 60% of the patients will also display some pulmonary involvement on chest X-ray. High-resolution CT is superior for detecting and characterizing parenchymal disease. There is a wide range of reported findings [2].

Airspace opacities are non-specific findings on chest radiography and CT. The list of possible diagnoses is broad but the typical causes of this radiological pattern include infection, intra-alveolar blood and some tumours. This radiological pattern is an uncommon finding in patients with sarcoidosis and is also a misnomer: in contrast with other pathologies which cause a pattern of consolidation, histological examination in patients with this appearance on imaging indicate that the predominant abnormality is significant thickening of the interstitium, with displacement of alveolar air [3].

The reversed halo sign was first reported in patients with cryptogenic organizing pneumonia. [4] However, it is now known that this pattern can also be seen in tuberculosis, invasive fungal infection, sarcoidosis, adenocarcinoma, Wegener’s granulomatosis and also pulmonary thromboembolism [5]. It has been suggested that the combination of an irregular halo with peripheral nodularity, should raise the possibility of a granulomatous disease (including tuberculosis and sarcoidosis) [5-6].

Patients with sarcoidosis, without findings of overt lung fibrosis usually respond well to corticosteroid therapy. However, some will relapse and a subset of patients will show progression to lung fibrosis despite treatment.

The take home points are:
1) Sarcoid lung involvement may present as airspace or alveolar opacities. This is caused by predominant interstitial thickening, as opposed to filling of the alveoli.
2) Sarcoidosis is a cause of the reversed halo sign.

Differential Diagnosis List

Final Diagnosis

Sarcoidosis, pulmonary involvement

URL:	https://www.eurorad.org/case/11491
DOI:	10.1594/EURORAD/CASE.11491
ISSN:	1563-4086