Pulmonary alveolar microlithiasis

Clinical History

A 92-year-old ex-peasant female patient presented at our institute with a fracture of the femoral neck; a preoperative chest radiograph was made. She reported to have been always in good health during her long life but in the last months she had noticed a mild dyspnoea.

Imaging Findings

The preoperative chest radiograph (obtained in supine position as the patient was on a stretcher) (Fig.1) demonstrated diffuse multiple, bilateral, ill-defined calcifications, relatively less extended in the upper left lobe. Linear calcification of the pleural surfaces was also seen. Due to the discrepancy between these marked radiographic findings and the mild symptoms reporteded by the patient (she did not report respiratory disease) a CT evaluation was requested with a 16-detector row equipment. The axial scans with coronal MPR and MinIP reconstructions (Fig. 2, 3, 4) clearly showed the almost ubiquitous distribution of the calcifications with overlapped interstitial fibrosis, intraparenchymal cyst and paraseptal emphysema (more evident at the upper left lobe explIning the relative sparing of lung parenchyma at that level).

Discussion

Pulmonary alveolar microlithiasis (PAM) is a rare disease characterised by the presence of myriad of tiny calculi (calcospherites) within the alveoli of the lungs. The classic radiographic findings consist of multiple small “sand-like” opacities diffusely involving both lung parenchyma, especially the lower lobes, with a subpleural and peribronchovascular predominance. These findings may change as the disease progresses [1].
The natural evolution of PAM in years brings some anatomo-radiographic changes, so that a classification in four stages can be made, starting from a preclinic phase in which the chest radiograph is normal, to a progressive stage characterised by growth in number and volume of the calculi with overlapped interstitial fibrosis, intraparenchymal cyst and paraseptal emphysema.
High resolution CT can define the extension and the gravity of the disease but, depending on the stage of disease, a differential diagnosis with diffuse alveolar septal amyloidosis, tuberculosis, pneumoconiosis and some types of sarcoidosis has to be made. So the final diagnosis is made when multiple tiny calculi called "microliths" are found in the BAL or during transbronchial biopsy [2].
Patients generally present between the ages of 30 to 50 years, although a few paediatric cases have also been reported. There is a strong familiar history (recently the responsible gene of the disease SLC34A2 has been discovered) [3, 4]. Most patients are asymptomatic at the time of diagnosis, with the disease incidentally being detected on chest radiographs obtained for other reasons. However, the disease is slowly progressive and there is a tendency for development of pulmonary fibrosis and cor pulmonale in progressive stages.
Our case demonstrates that the evolution of the disease can be very slow in years and even with such a severe involvement of the lung parenchyma, symptoms may be very blurred and misinterpreted as mild respiratory failure and chronic pulmonary heart.

Differential Diagnosis List

Final Diagnosis

Pulmonary alveolar microlithiasis

URL:	https://www.eurorad.org/case/9269
DOI:	10.1594/EURORAD/CASE.9269
ISSN:	1563-4086