Parenchymal Opacifications on HRCT

Parenchymal opacities can be subdivided into two categories, ground glass and consolidation. A third category, super- dense opacification, is included for completeness.

Ground Glass Opacities (GOO)

A parenchymal opacity is said to be "ground glass" in attenuation if underlying vessels remain visible. It is often said that ground-glass suggests the presence of a reversible abnormality. Diseases which may have ground glass opacities as the predominant lesion include:

• NSIP -- Non-Specific Interstitial Pneumonia. Clinically similar to IPF but generally with better outcomes.
• DIP -- Desquamative Interstitial Pneumonia. Rare, associated with smoking.
• PAP -- Pulmonary Alveolar Proteinosis. Usually also has smooth septal thickening (the combination of ground glass opacities with smoth septal thickening has been termed "crazy paving").
• Hypersensitivity Pneumonitis -- May also have nodules and/or air trapping

Consolidation

A parenchymal opacity is said to be consolidation if the underlying vessels are obscured. While many acute diseases such as pneumonia and pulmonary edema may present with consolidation, only the classic chronic diseases (those likely to get a HRCT) are considered here.

• Chronic Eosinophilic Pneumonia -- Peripheral areas of consolidation.
• BOOP -- Bronchiolitis Obliterans with Organizing Pneumonia, may appear identical to chronic eosinophilic pneumonia.
• Bronchioloalveolarcell Carcinoma
• Parenchymal Lymphoma

Superdense Opacities

A superdense opacity is more attenuating than soft tissue. The things listed here don't really look like each other.

• Metastatic Calcification -- Patchy or nodular areas of calcium deposition within lung parenchyma, usually in patients with abnormal calcium/phosphate metabolism (e.g. renal patients).
• Alveolar Microlithiasis -- Minutely-small but numerous dots of calcification within the alveoli.
• Amiodarone Toxicity -- Classically gives a very dense parenchymal consolidation