Proteinosis alveolar: radiologic and pathologic findings

Clinical History

An asymptomatic 20-year-old man being investigated following cervical trauma was found to have an incidental pulmonary abnormality.

Imaging Findings

Plain chest radiograph shows bilateral, symmetric and perihilar ground-glass opacities predominant in upper and middle lung fields (Fig 1).

In concordance with the chest radiograph, computed tomography revealed patchy areas of ground glass opacities with superimposed thickening of interlobular and intralobular lines (crazy paving) (Fig. 2). It extended through both lungs with a predominant perihilar and upper lobe distribution, where it tended to consolidate (Fig 3).

Discussion

Pulmonary alveolar proteinosis (PAP) is an uncommon diffuse lung disease, characterized by the accumulation of surfactant in the distal airways, due to a dysfunction of alveolar macrophages. In some cases it is related to a secondary cause (immunodeficiency disorders, cancer, etc.), but the majority are idiopathic [1].

From the clinical point of view, the typical case is an asymptomatic patient between his/her 20s and 40s, but there is no correlation between radiologic findings and clinical presentation. Symptoms such as cough and dyspnoea can be present.

Computed tomography (CT) usually shows parenchymal involvement that consists of ground-glass opacities associated with superimposed interlobular and even intralobular lines [2]. This pattern, known as 'crazy paving', in PAP tends to be bilateral, perihilar and symmetric. However, many other illnesses can mimic this type of presentation [3] and we must bear in mind some details regarding the differential diagnoses:

-Pneumocystis jiroveci pneumonia should be suspected in severely immunocompromised patients. In early stages, plain chest radiograph can be unremarkable even with a pathologic CT. In a few days it can turn into a consolidation.

-Acute respiratory distress syndrome presents as an acute onset and is usually associated with intense trauma, sepsis or other aggressive factor.

-Cardiogenic pulmonary oedema has lower field distribution and acute onset of typical signs and symptoms of cardiac affection.

-Alveolar haemorrhage syndromes are usually associated with a clinical context of coagulopathies, collagen or inflammatory diseases as vasculitis or lupus.

-Hounsfield units between -35 and -75 suggest lipoid pneumonia (medical history of oil ingestion?). Some studies suggest that ill-defined centrilobular nodules, lower extension and presence of consolidation points to lipoid pneumonia rather than PAP [4].

-Hypersensitivity pneumonitis due to pulmonary toxicity when using some drugs can express as a crazy paving pattern.

-Bronchioloalveolar carcinoma appears in older patients than those who suffer from PAP (generally in older than 50). Bronchorrhea is infrequent but indicative.

-Cryptogenic organizing pneumonia has a subacute onset which consists of non-productive cough and dyspnea. Characteristically responds to treatment with corticoids. Bronchiectasis and thickening of bronchial walls of affected areas are common.

Due to non-specificity of the radiologic findings, bronchoscopy must be performed in order to confirm diagnosis. In our case, tissue obtained by transbronchial biopsy was insufficient, but showed granular PAS positive eosinophilic proteinaceous material. The bronchoalveolar lavage fluid showed abundant large acellular material (Fig. 4).

These findings in the clinical and radiological context suggest the diagnosis of alveolar proteinosis.

Differential Diagnosis List

Final Diagnosis

Alveolar proteinosis.

URL:	https://eurorad.org/case/14055
DOI:	10.1594/EURORAD/CASE.14055
ISSN:	1563-4086