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- hereditary haemorrhagic telangiectasia
- pulmonary arteriovenous malformation
- cerebral abscess
A 60-year-old man (figure 1) was referred with an incidental abnormality in the right lower zone of his chest X-ray. He was otherwise well. Forty years previously a segment of his left lower lobe had been removed for a benign lesion. Two siblings had died from intracranial haemorrhage. High-resolution computed tomography (CT) scan of the thorax (figure 2) was performed. Before any treatment was given for the lesion visible in figure 2 he was admitted to hospital with right upper motor neurone facial weakness and expressive dysphasia of 2 days duration. CT scan of the head was carried out (figure3).
- What disorder does this patient have and which feature of this does figure 2 demonstrate?
- What complication has he now developed and how is this related to the lesion in figure 2?
- What are the options for treatment of the pulmonary lesion?
This patient has hereditary haemorrhagic telangiectasia (HHT) and the high-resolution CT images show a pulmonary arteriovenous malformation (AVM) with its feeding vessels in the lateral part of the right lower lobe.
Cerebral abscess. The pulmonary AVM lacks capillaries and as such represents a direct connection between the pulmonary artery and vein providing a right-to-left shunt allowing paradoxical embolisation. Septic emboli or possibly a transient bacteraemia infecting existing cerebral infarcts are thought to result in the formation of a cerebral abscess.
Simple observation, surgical removal, and embolisation. Our patient had his cerebral abscess drained with excellent results and subsequently had his pulmonary AVM embolised.
HHT is characterised by mucocutaneous telangiectases, recurrent epistaxis and a family history of the disorder.1 Vascular abnormalities also occur in the lungs, gastrointestinal tract and central nervous system. It is inherited in an autosomal dominant fashion with variable penetrance. Whilst it has been divided into types I and II on the basis of established linkages to the long arms of chromosomes 9 and 12, respectively,2 this is almost certainly an oversimplification.3 Mutations on chromosome 9 (HHT I) affect endoglin, a protein found on vascular endothelial cells. Endoglin binds transforming growth factor beta, which affects endothelial cell migration, proliferation and adhesion and the composition and organisation of the extracellular matrix. The activin receptor-like kinase (ALK1) affected by mutations on chromosome 12 (HHT II) is also found on vascular endothelial cells although its role is unclear. The mechanism by which these mutations cause the angiodysplastic lesions of HHT has yet to be established.
Approximately 15% of people with HHT will have a pulmonary AVM and, conversely, 60–90% of people with a pulmonary AVM will have HHT. It appears that HHT I carries an increased risk of both pulmonary and cerebral AVMs when compared with HHT II. Two-thirds of AVMs occur in the lower lobes, predominantly basally and often multiple. The risk of hypoxia, polycythaemia and haemorrhage with a pulmonary AVM is perhaps better appreciated than is the risk of cerebral ischaemic events, the incidence of the latter being up to 40% in patients with a pulmonary AVM, with a risk of cerebral abscess of 10–15%. Indeed, cerebral ischaemic events are often the first manifestation of both the pulmonary AVM and HHT.
Plain chest radiography and high-resolution CT will detect the majority of pulmonary AVMs. Other methods of diagnosis include angiography, radionuclide shunt studies, and contrast echocardiography. A fall in oxygen saturations between supine and erect postures (due to redistribution of blood through the predominantly basal pulmonary AVM) may also be seen.
The risk of neurological events suggests that pulmonary AVMs should not be treated conservatively, ie, not simply observed. Embolisation, by coil or balloon, has distinct advantages over surgery with lower morbidity (∼ 15%), lower mortality (< 1%) and shorter hospital stay.4 Embolisation can also be performed on multiple lesions without the loss of substantial lung parenchyma. Closure of larger malformations may lead to enlargement of smaller lesions with time and long-term follow-up is required. Screening families with HHT for pulmonary AVM has been advocated but the best method for doing this is debated.
It has been suggested that cerebral abscess and pulmonary AVM be used as markers for each other, but perhaps pulmonary AVM should also be considered when the young person with a stroke is assessed.
Pulmonary AVMs have a high rate of complications and are best treated with embolisation
Cerebral abscess in a patient with HHT and a pulmonary AVM.