Crazy Paving

Crazy paving of the lungs refers to scattered or diffuse ground-glass attenuation with superimposed interlobular septal thickening and intralobular lines. While initially thought to be specific for pulmonary alveolar proteinosis, it has since been reported in so many conditions that it is essentially a nonspecific finding. The oculoglossal reflex of PAP persists, however. Clinical presentation can help narrow the differential diagnosis.

Chronic presentation

• Pulmonary alveolar proteinosis (shown above): Rare, classic condition associated with Crazy paving. Radiographs reveal bilateral, symmetric alveolar consolidation or ground-glass opacity in a perihilar or hilar distribution resembling pulmonary edema. CT reveals diffuse ground-glass attenuation with superimposed intra- and interlobular septal thickening. Patients present with chronic (months to years) progressive dyspnea and dry or minimally productive cough.
• Nonspecific interstitial pneumonitis: Symmetric, subpleural and basal-predominant ground-glass attenuation is the most common CT finding. Superimposed consolidation and irregular reticular lines can be seen. Patients present with gradually worsening dyspnea over several months, and they often experience fatigue and weight loss.

Subacute presentation

• Cryptogenic organizing pneumonia (COP): Associated with collagen-vascular diseases, infection, and drugs. Scattered and asymmetric consolidation bilaterally, and classically peripherally. The crazy paving pattern is uncommon. Patients present with mild dyspnea, cough, and fever that have been developing over a few weeks.

Immunocompromised

• Infection: Pneumocystis jirovecii pneumonia in immunocompromised patients. Ground-glass areas represent foamy alveolar exudates, while the lines represent thickening of the alveolar walls by edema and cellular infiltrates.

Laxative ingestion, use of oil-based nose drops, or fire-breathing

• Lipoid pneumonia: Due to inhalation of lipid. Consolidation is characteristically fat attenuation. Crazy paving can also be seen, reflecting intraalveolar and interstitial accumulation of lipid-laden macrophages and thickening of alveolar walls.

ICU patient

• Diffuse alveolar damage:
• Pulmonary edema:

Miscellaneous

• Brochoalveolar carcinoma: Ground-glass areas reflect intra-alveolar glycoprotein and the superimposed reticular attenuation is caused by interstitial infiltration by inflammatory or tumor cells.
• Pulmonary hemorrhage: Multiple causes, including idiopathic pulmonary hemosiderosis, Wegener granulomatosis, Churg-Strauss syndrome, Goodpasture syndrome, collagen-vascular diseases (systemic lupus erythematosus, rheumatoid arthritis, systemic sclerosis, polymyositis, and mixed connective-tissue disease), drug-induced coagulopathy, and hemorrhage associated with malignancy.
• Inflammatory: Sarcoidosis
• Pulmonary alveolar microlithiasis (mimic): When extensive, the calcifications can result in interlobular septal thickening. Microliths smaller than 1 mm can produce a ground-glass appearance. Together, these can give an appearance similar to crazy paving.

References

• Frazier AA, Franks TJ, Cooke EO, Mohammed TL, Pugatch RD, Galvin JR. From the archives of the AFIP: pulmonary alveolar proteinosis. Radiographics. 2008 May-Jun;28(3):883-99.
• Gasparetto EL, Tazoniero P, Escuissato DL, Marchiori E, Frare E Silva RL, Sakamoto D. Pulmonary alveolar microlithiasis presenting with crazy-paving pattern on high resolution CT. Br J Radiol. 2004 Nov;77(923):974-6.
• Mueller-Mang C, Grosse C, Schmid K, Stiebellehner L, Bankier AA. What every radiologist should know about idiopathic interstitial pneumonias. Radiographics. 2007 May-Jun;27(3):595-615.
• Patsios D, Roberts HC, Paul NS, Chung T, Herman SJ, Pereira A, Weisbrod G. Pictorial review of the many faces of bronchioloalveolar cell carcinoma. Br J Radiol. 2007 Dec;80(960):1015-23.
• Rossi SE, Erasmus JJ, Volpacchio M, Franquet T, Castiglioni T, McAdams HP. "Crazy-paving" pattern at thin-section CT of the lungs: radiologic-pathologic overview. Radiographics. 2003 Nov-Dec;23(6):1509-19.