Pulmonary alveolar microlithiasis

Clinical History

A 29-year-old young man, without complaints, was submitted to a routine chest radiogram.

Imaging Findings

A 29-year-old young man, without complaints, was submitted to a routine chest radiogram, which showed multiple calcific micronodules scattered throughout the lungs, more numerous in the lower lobes, with obliteration of the heart borders. High resolution computed tomography demonstrated innumerable, very small calcifications, diffusely distributed throughout both lung fields, especially in the
lower lobes, with a subpleural and peribronchovascular predominance. Interlobular septal thickening was also present. Ground glass opacification was visible in the middle lobe and lingula. Small areas of emphysema in the peripheral lung account for the black pleural line. The diagnosis of pulmonary alveolar microlithiasis was established and confirmed by transthoracic lung biopsy.

Discussion

Pulmonary alveolar microlithiasis is a rare condition of unknown pathogenesis characterized by widespread intraalveolar calcifications of both lungs. These calcifications represents 0.01-3mm tiny stones or calcipherites [3, 4]. Patients generally present between the ages of 30 to 50 years, although pediatric cases have been reported. There is a strong family history. Most patients are asymptomatic
at the time of diagnosis, with the disease incidentally detected on chest radiographs obtained for other reasons. However, the disease is slowly progressive and there is a tendency for pulmonary fibrosis and cor pulmonale. Patients have normal serum calcium and phosphorus levels. There is no treatment. Chest radiogram shows characteristic findings. Alveolar microlithiasis typically appears as fine, sandlike calcific micronodules (<1mm) scattered throughout the lungs. There is a predominantly symmetric middle and lower lobe involvement. If the micronodules are limited in number they predominate in a subpleural location. When myriad, they become confluent, very dense, obliterating the heart borders and the diaphragm. The heart may appear relatively lucent, when the lungs are very dense. A stripe of relative lucency at the pleural surface, the so-called black pleural line, can also be present. It represents small subpleural areas of emphysema. Overpenetrated films may be necessary to demonstrate the calcifications. High resolution computed tomography demonstrates diffuse, ground-glass increased opacification throughout the lungs. The calcifications are more numerous and dense along the bronchovascular bundles and in the subpleural regions. They can be seen in a perilobular and centrilobular distribution or associated with interlobular septa. The disease may be associated with intraparenchymal cyst or paraseptal emphysema (the black pleural line).

Differential Diagnosis List

Final Diagnosis

Pulmonary alveolar microlithiasis.

URL:	https://www.eurorad.org/case/6286
DOI:	10.1594/EURORAD/CASE.6286
ISSN:	1563-4086