Noninfectious Granulomatous Lung Disease: Radiological Findings and Differential Diagnosis

Abstract

Granulomatous lung diseases (GLDs) are a heterogeneous group of pathological entities that can have different clinical presentations and outcomes. Granulomas are histologically defined as focal aggregations of activated macrophages, Langerhans cells, and lymphocytes, and may form in the lungs when the immune system cannot eliminate a foreign antigen and attempts to barricade it. The diagnosis includes clinical evaluation, laboratory testing, and radiological imaging, which especially consists of high-resolution computed tomography. bronchoalveolar lavage, transbronchial needle aspiration or cryobiopsy, positron emission tomography, while genetic evaluation can improve the diagnostic accuracy. Differential diagnosis is challenging due to the numerous different imaging appearances with which GLDs may manifest. Indeed, GLDs include both infectious and noninfectious, and necrotizing and non-necrotizing granulomatous diseases and the imaging appearance of some GLDs may mimic malignancy, leading to confirmatory biopsy. The purposes of our review are to report the different noninfectious granulomatous entities and to show their various imaging features to help radiologists recognize them properly and make an accurate differential diagnosis.

Keywords: chest imaging; differential diagnosis; granulomatous lung diseases (GLDs); high-resolution computed tomography (HRCT); radiology.

Figure 1

Chest X-ray, AP, showing a range of pulmonary parenchymal abnormalities: multiple micronodules with a peribronchovascular distribution, reticulonodular opacities, right lung consolidation, and symmetric hilar lymphadenopathy. According to Scadding classification, the X-ray in the Figure can be classified as stage II (thoracic adenopathy and pulmonary infiltrates), as in 25–65% of patients.

Figure 2

(A): Chest HRCT, axial planes, shows well-defined micronodules, prominent in the right lung, with a perilymphatic distribution along the bronchovascular bundles, interlobular septa, interlobar fissures, and subpleural regions; there are also larger nodules in the middle lung zones and symmetric hilar lymphadenopathy. (B): Original drawing representing the perilymphatic disposition of parenchymal micronodules.

Figure 3

Chest HRCT, axial planes, showing numerous bronchiolocentric GGO, with symmetric distribution.

Figure 4

(A): Chest HRCT, axial planes, patient affected by GPA: CT scans shows bronchiolocentric nodules, several cavitated, surrounded by GGO halo as a result of alveolar inflammation or diffuse alveolar hemorrhage secondary to necrotizing vasculitis. Bilateral pleural effusion can be noted. (B): Chest HRCT, axial planes, patient affected by EGPA: CT scans shows bronchiolocentric nodules with perilesional GGO halo as a result of alveolar inflammation/hemorrhage secondary to necrotizing vasculitis. In these two figures, it is shown that the HRCT differential diagnosis between GPA and EGPA can only be the presence of central cavitation of the lesions. Pleural effusion is more frequent in EGPA, seen in up to 50% of cases, and may be secondary to eosinophilic cardiomyopathy or eosinophilic pleuritis. In this case, it is present in GPA and not in EGPA HRCT.

Figure 5

(A): Chest HRCT, axial planes, shows HP in acute stage with diffuse centrilobular poorly defined small nodules and ground-glass attenuation with prevalence to upper lobes. (B): Original drawing representing the centrilobular disposition of parenchymal micronodules.

Figure 6

Chest HRCT, axial planes, patient affected by chronic aspiration pneumonia. CT scan shows centrilobular micronodules and GGO due to the surrounding parenchyma inflammation, and occlusive aspiration of the medium lobe bronchus, with relative pulmonary atelectasis.

Figure 7

Chest HRCT, axial planes, patient affected by talc granulomatosis (A) and patient affected by aspiration pneumonia (B). In both (A,B), CT shows numerous millimetric micronodules in a centrilobular pattern. The differential diagnosis between aspiration pneumonia and talc granulomatosis, when occlusive bronchus involvement and pulmonary atelectasis are not present, can be very challenging and impossible without a detailed clinical history, bronchoscopy, and BAL.

Figure 8

Chest HRCT, axial planes: CT scan shows GGO, subpleural nodules or consolidations, bronchovascular bundles thickening, interlobular septal thickening, thin-walled cystic airspaces with perivascular distribution, and architectural distortion.

Figure 9

Chest HRCT, axial planes, shows PLCH in early, advanced, and end stage (A–C). (A): In early stage disease, there are nodular lesions corresponding to “florid” granulomas, characterized by brochiolocentric and ill-defined micronodules surrounded by ground-glass opacification secondary to inflammatory interstitial infiltration, nodules with irregular margins and centrilobular distribution, and cavitary nodules with thick walls that later become cysts. (B): In advanced stage disease, cystic lesions usually predominate on nodules: cysts appear round and of small dimension (<10 mm), but in advanced disease they are typically larger and of different shapes with thick-walled cysts (>2 mm thick) that progressively transform into thin-walled cysts (<2 mm thick). (C): In end-stage disease, there is a fibrocystic pattern that maintains the typical upper- and middle-lung zone predominance.