Findings: The chest CT examination shows diffuse ground glass with some septal lines and a spiculated fat-attenuation mass in the left lower lobe.
A. Pulmonary alveolar proteinosis refers to the deposition of lipo proteinaceous material in the alveolar spaces. For this reason, some refer to it as endogenous lipoid pneumonia. Chest radiography shows bilateral diffuse alveolar opacities, often with a superimposed fine reticular pattern. CT scanning demonstrates diffuse ground glass opacity with smooth septal lines (crazy-paving appearance). Although the ground glass appearance and the septal lines are consistent with alveolar proteinosis, the diagnosis is not the best because it would not explain the fat-attenuation in the left base. Macroscopic fat, however, is never seen with this entity.
B. Lipoid pneumonia results from aspiration of vegetable, animal, or mineral oil, and usually occurs in debilitated patients with swallowing abnormalities or patients taking mineral oil for treatment of constipation. Most patients are relatively asymptomatic. Plain chest radiographs show areas of lung opacification or mass lesions that remain stable or slowly increase over a period of months. On CT, these areas have a low attenuation because of their lipid contents.
C. The most common radiographic findings of pulmonary edema include interstitial and alveolar edema, pulmonary vascular redistribution and pleural effusions. The edema is usually gravity dependent and therefore more severe at the lung bases. CT findings include ground-glass opacity and septal lines. In the test case, the ground glass opacity and septal lines are not gravity dependent, and therefore not consistent with pulmonary edema. Moreover, this diagnosis would not explain the fat-attenuation.
D. Usual interstitial pneumonia (UIP) is a type of chronic interstitial pneumonia. Radiographic findings include ground-glass opacities and reticular interstitial opacities, including thickened septal lines and honeycombing. The abnormality has a predilection for the subpleural aspects of the lung bases. Symmetric bilateral ground glass opacity with superimposed septal lines forming a crazy paving pattern is not a feature of UIP. A fat attenuation mass also is not a characteristic of UIP. It should be noted that spiculated lesions may be seen with UIP and are concerning given the increased incidence of bronchogenic cancer with this condition.
E. Wegenerâ€™s granulomatosis is characterized by necrotizing granulomatous vasculitis of the respiratory tract. The disease involves both arteries and veins. Upper airway involvement manifesting as sinusitis, rhinitis, and otitis is common. The typical imaging features are nodules, either single or multiple, which may cavitate, and areas of lung opacity, which may have a ground glass appearance, representing hemorrhage. The fat attenuation within the mass lesion of this patient is not characteristic of Wegenerâ€™s Granulomatosis and makes this diagnosis very unlikely.