Diffuse alveolar hemorrhage (DAH) is a subset of diffuse pulmonary hemorrhage when bleeding is diffuse and directly into the alveolar spaces. It can occur in a vast number of clinical situations and can be life-threatening.
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Pathology
Blood tends to fill alveolar spaces at multiple sites.
Etiology
Causes include:
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pulmonary vasculitides (particularly small vessel vasculitides): pulmonary capillaritis is considered the most common underlying lesion associated with diffuse alveolar hemorrhage
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ANCA-associated pulmonary vasculitides
non-ANCA associated pulmonary vasculitides: Goodpasture syndrome
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certain connective tissue disorders
systemic lupus erythematosus 2,3: considered the commonest associated connective tissue disorder to result in diffuse alveolar hemorrhage
medications: excessive antiplatelet therapy 9
inhaled toxins
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conditions causing back pressure
pulmonary hemorrhage complicating diffuse alveolar damage
pulmonary hemorrhage complicating widespread pulmonary malignancy
post bone marrow transplantation 1
Radiographic features
Plain radiograph
The clinical context is crucial in image interpretation. The exact pattern may differ depending on the underlying cause. In general, the typical feature on plain film during an acute diffuse alveolar hemorrhage is a diffuse infiltrative opacification pattern 5. At times there may a slight predilection towards the mid zones 5 with some apical sparing 8.
CT
The HRCT pattern can vary with time of onset of the hemorrhage and the clinical context is crucial in image interpretation:
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acute phase
can range from lobular or lobar areas of ground-glass opacities to predominant consolidation
ground-glass opacity is generated by subtotal alveolar filling with blood and is accompanied by the apparent prominence of segmental and subsegmental bronchi, which has been referred to as the “dark bronchus sign"
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2–3 days
intralobular lines and smooth interlobular septal thickening superimpose on areas of ground-glass opacity
may sometimes give rise to a crazy-paving pattern 10
these can often resolve
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between chronic recurrent bleeding events
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ill-defined centrilobular nodules
reflecting an intra-alveolar accumulation of pulmonary macrophages
usually uniform in size (1-3 mm)
diffusely distributed
no zonal predominance
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with severe repeated hemorrhage: may progress with features of interstitial fibrosis
Treatment and prognosis
Complications
Repeated episodes can lead to organizing pneumonia, collagen deposition in small airways and ultimately pulmonary fibrosis 7,8.
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