Diffuse alveolar haemorrhage (DAH) is a subset of diffuse pulmonary haemorrhage 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.
Aetiology
Causes include:
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pulmonary vasculitides (particularly small vessel vasculitides): a pulmonary capillaritis is considered the most common underlying lesion associated with diffuse alveolar haemorrhage
- ANCA associated pulmonary vasculitides
- non-ANCA associated pulmonary vasculitides: Goodpasture syndrome
- certain connective tissue disorders
- systemic lupus erythematosus 2,3: considered commonest associated connective tissue disorder to result in diffuse alveolar haemorrhage
- mixed connective tissue disease 8
- coagulative disorders
- medications: excessive antiplatelet therapy 9
- inhaled toxins
- conditions causing back pressure
- pulmonary haemorrhage complicating multifocal infection
- pulmonary haemorrhage complicating diffuse alveolar damage
- pulmonary haemorrhage complicating widespread pulmonary malignancy
- post bone marrow transplantation 1
- pulmonary haemosiderosis
- antiphospholipid syndrome 6
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 haemorrhage 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 haemorrhage 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
-
between chronic recurrent bleeding events
- ill-defined centrilobular nodules
- reflecting an intra-alveolar accumulation of pulmonary macrophages
- usually uniform in size (1-3 mm)
- diffusely distributed
- no zonal predominance
- ill-defined centrilobular nodules
- with severe repeated haemorrhage: may progress with features of interstitial fibrosis
Treatment and prognosis
Complications
Repeated episodes can lead to organising pneumonia, collagen deposition in small airways and ultimately pulmonary fibrosis 7,8.