Hyperattenuating lung parenchyma: A rare diagnostic consideration

Pulmonary alveolar microlithiasis is a rare idiopathic, autosomal recessive pulmonary parenchymal disorder that may result from mutations in the SLC34A2 gene, which is highly expressed in type II alveolar cells and is involved in phosphate metabolism. Pulmonary alveolar microlithiasis is characterized by the intra-alveolar and interstitial deposition of microliths composed of calcium and phosphate in the absence of calcium and phosphorus metabolic abnormalities. The disorder is often detected asymptomatically at thoracic imaging studies obtained for incidental reasons. When symptoms are present, progressive dyspnea, chest pain, and cough are most commonly encountered. Late in the disease course, cor pulmonale and respiratory failure develop leading to death. The chest radiographic appearance of pulmonary alveolar microlithiasis is frequently suggestive of the disorder, showing multifocal or diffuse, bilateral small circumscribed dense opacities with a mid and lower lung predominance, creating a "sandstorm" appearance. Linear and reticular opacities are often present as well. High-resolution thoracic computed tomography typically shows very dense, small pulmonary parenchymal nodules associated with areas of ground-glass opacity and consolidation. Linear opacities consistent with perilobular accumulation of calcipherites or the accumulation of microliths within the alveolar septae are often observed. The radiographic and clinical presentations are frequently markedly discordant, which is an important clue to the correct diagnosis. Most therapies for pulmonary alveolar microlithiasis have proven ineffective, with lung transplantation reserved for advanced cases.