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.
Blood tends to fill alveolar spaces as multiple sites.
- pulmonary vasculitides (particularly small vessel vasculitides): a pulmonary capillaritis is considered the most common underlying lesion associated with diffuse alveolar haemorrhage
- certain connective tissue disorders
- 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
The clinical context is crucial in image interpretation. The exact pattern may differ dependent 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.
The HRCT pattern can vary with time of onset of the haemorrhage and the clinical context is crucial in image interpretation:
- 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 apparent prominence of segmental and subsegmental bronchi, which has been referred to as the “dark bronchus sign"
- 2–3 days
between chronic recurrent bleeding events
- ill-defined centrilobular nodules
- reflecting 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
Repeated episodes can lead to an organising pneumonia, collagen deposition in small airways and ultimately pulmonary fibrosis 7-8.
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