Author Jared Johnstun, MD Pulmonary and Critical Care Medicine Fellow University of Utah School of Medicine
Case
A 54 year old woman presented to the emergency department for
shortness of breath after 72 hours of fever, chills and a cough
productive of yellow sputum. She was severely hypoxemic with a PaO2
of 36mmHg on room air. Aside from a serum sodium level of 125mmol/L,
the remainder of her labs were unremarkable. A chest X-ray showed
diffuse alveolar opacities and a subsequent high-resolution CT scan is
shown below.
Clinical Question
What is the radiographic finding, and what disease is this finding specific for?
Answer
Crazy-paving. The differential diagnosis for the “crazy-paving sign”
is actually quite large and goes well beyond Pulmonary Alveolar
Proteinosis (PAP). Although the majority of patients with PAP will have a
CT consistent with the crazy paving pattern, this radiographic pattern
is by no means specific to PAP. Crazy-paving can be seen in a variety of
much more common disease states, thus the overall incidence of the
finding will be seen more frequently in the more common disease
processes.
Discussion
Crazy-paving on CT refers to the findings of ground-glass opacities
(patchy or diffuse) with thickened interlobular septae and intralobular
lines. It gets its name from the similar appearance to a pathway made up
of disorganized paving-stones.1-6
Crazy Paving: Public Domain Image, credit Liam Quin
Originally described in 6 case reports from 19895, the
crazy-paving pattern on chest CT scan was thought to be specific to
alveolar macrophage dysfunction resulting in the pulmonary disease known
as Pulmonary Alveolar Proteinosis, or PAP. The exact causes for the
radiographic findings that make up crazy paving turns out to be as
diverse as the differential diagnosis. This finding is detected more
commonly now with newer multidetector CT scans with better image
resolution.
The linear component may be caused by thickened interlobular septae,
thickened intralobular septae, distal airspace compaction and/or
intralobular interstitial thickening.3 The ground glass
opacities (GGOs) represent partially filled alveoli (edema, inflammatory
cells, blood and/or proteinaceous exudates), thickened alveolar walls
and/or thickening of the surrounding interstitium.3,4 In PAP,
the GGOs reflect alveoli partially filled with periodic acid Schiff
positive lipid rich fluid and the linear component reflects interlobular
and interstitial inflammation. 4,5 In heart failure, the linear component and GGOs reflect hydrostatic edema infiltrating the alveoli, septae and interstitium.6
Although the majority of patients with PAP will have a CT consistent with the crazy-paving pattern it is by no means specific4
and it is actually seen more frequently in disease states other than
PAP (Table 1). It is important to recognize that this image finding is
nonspecific and likely warrants further diagnostic evaluation.
Common causes of crazy paving1-7
Acute Respiratory Distress Syndrome (ARDS)
Bacterial Pneumonia
Acute Interstitial Pneumonia (AIP)
Pneumocystis Jerovecii pneumonia (PJP)
Mucinous Bronchoalveolar Carcinoma
Chronic Aspiration
Lipoid Pneumonia
Viral Pneumonia
Fungal Pneumonia
Pulmonary Alveolar Proteinosis (PAP)
Granulomatosis with Polyangitis
Microscopic Polyangitis
Churg-Strauss Syndrome
Goodpastures Disease
Collagen vascular diseases
Idiopathic hemorrhage
Mycoplasma pneumonia
Non-specific Interstitial Pneumonia (NSIP)
Alveolar Sarcoidosis
Chronic Eosinophilic Pneumonia
Acute Usual Interstitial Pneumonia (UIP)
Cryptogenic Organizing Pneumonia (COP)
Drug induced pneumonitis
Pulmonary Veno-Occlusive Disease (PVOD)
Pulmonary edema
Radiation Pneumonitis
Graft-vs Host Disease
Lymphangitic Carcinomatosis
Hypersensitivity Pneumonitis
The patient received mechanical ventilation and underwent diagnostic
bronchoscopy. Neither gross findings nor lavage (80% neutrophils, 10%
macrophages and 10% respiratory epithelial cells) showed evidence of
proteinosis. Subsequent wedge resection biopsy demonstrated
peribronchial lymphohistiocytic infiltrates, extensive alveolar septal
involvement, immature collagen matrix formation, and pigmented
macrophages in the alveolar spaces. These were deemed most consistent
with cryptogenic organizing pneumonia in an active smoker. The patient
was treated with corticosteroids and demonstrated rapid improvement.
Resources
Maimon N, Heimer D. The crazy-paving pattern on computed tomography. CMAJ. 2010;182:1545
Rossi S, Erasmus J, Volpacchio M, et al. “Crazy-Paving” Pattern at
Thin-Section CT of the Lungs: Radiologic-Pathologic Overview.
Radiographics. 2003; 23:1509-1519
De Wever W, Meersschaert J, Coolen J, et al. The crazy-paving
pattern: a radiological-pathological correlation. Insights Imaging 2011;
2:117–132
