pulmonary alveolar microlithiasis

CT findings

of high-attenuation pulmonary abnormalities. Pulmonary alveolar microlithiasis. Axial CT at a mediastinal and b parenchymal windows shows diffuse numerous dense micronodules with calcified thickening of interlobular septa and subpleural cysts

insightsimaging.springeropen.com • CC-by-2.0

Metabolic and

storage lung diseases: spectrum of imaging appearances. A man with pulmonary alveolar microlithiasis. Contrast-enhanced HRCT image shows diffuse high attenuation ground-glass opacity with superimposed septal lines (crazy-paving) (arrowheads) as well as foci of calcified lung consolidation (arrows). Courtesy of Gerald F. Abbott, M.D. (Boston, MA)

insightsimaging.springeropen.com • Open Access

Radiopaedia • CC-by-nc-sa 3.0 • de

Pulmonary alveolar microlithiasis (PAM) is a rare idiopathic condition characterized by widespread intra-alveolar deposition of spherical calcium phosphate microliths (calcospherites).

Epidemiology

A slight female predilection may be present in the familial form . Most cases are reported in Asia and Europe .

Associations

testicular microlithiasis

Clinical presentation

Often discovered incidentally on a chest radiograph. The radiographic features are frequently disproportionate to the clinical symptoms .

Pathology

Pulmonary alveolar microlithiasis is believed to be due to a mutation in the SLC34A2 gene that causes inactivation of a sodium-dependent phosphate cotransporter, which is found mainly in alveolar type II cells. This cotransporter normally clears phosphate from degraded surfactant, and when inactivated there is accumulation of phosphate in the alveolus, and calcium phosphate microliths are then thought to form .

An autosomal recessive inheritance pattern has been proposed given familial occurrence in a majority of cases . Usually, there is no abnormal calciummetabolism.

Location

The distribution of pulmonary alveolar microlithiasis is bilateral with a middle and lower zone predilection .

Radiographic features

The pattern in children differs from that in adults .

Plain radiograph

Chest x-ray typically demonstrates:

sand-like calcification distributed throughout the lungs
black pleura sign

CT

HRCT better shows numerous sand-like calcifications throughout the lungs with subpleural and peribronchial distribution (typically ~1 mm) . Additional accompanying HRCT features include

crazy paving pattern
calcified interlobular septa (virtually pathognomonic)
small subpleural cysts/emphysema
black pleura sign
ground glass opacities: tends to be more common in children

PET-CT

On occasion, PET may show high FDG uptake, but primarily in the lung regions that spare calcification .

Treatment and prognosis

No known treatment is available. Overall prognosis is good, but occasionally slow progression can result in an end-stage lung fibrosis requiring lung transplantation.

Differential diagnosis

Some consider the radiographic appearance to be pathognomonic .

Differential for fine granular densities includes

silicosis
healed varicella pneumonia
idiopathic pulmonary hemosiderosis: tend to be large nodular opacities; no calcification
pulmonary stannosis: deposition of tin dust
pulmonary baritosis: deposition of barium particles
talcosis
mitral stenosis: may produce small foci of pulmonary ossification