3 DISCUSSION
At present, it is believed that the risk factors for cerebral ischemic stroke in patients with PAVF are: (1) feeding artery diameter > 3 mm; (2) existence of multiple PAVFs.7 Whether patients with PAVF present with clinical manifestations depends on the right-to-left shunt quantity. There are intrapulmonary and extrapulmonary manifestations in patients with pulmonary arteriovenous fistula. The intrapulmonary manifestations are as follows: dyspnea after the activity, dizziness, easy to fatigue, etc.8-10 Physical examination may reveal cyanosis, clubbing fingers(toes), and chest continous murmur, etc. Some patients may only present with abnormal arterial blood gas analysis.The extrapulmonary manifestations are as follows: migraine, TIA, ischemic stroke, brain abscess, epilepsy, etc. 8-10
Espejo-Herrero et al 1 reported a patient with TIA presenting with a short-term (30 min) right limb paralysis, and subsequent pulmonary arteriography showing a PAVF. Pulmonary DSA is the gold standard for the diagnosis of PAVF, which can observe the fistula size, feeding artery, draining vein and other conditions.8 However, DSA is an invasive examination. As a non-invasive examination, CTA can not only show the lesions (even the mild lesions) and the responsible blood vessels of PVAFs, but also accurately judge the peripheral and complex PVAFs, which is more suitable for the diagnosis of PAVF. 8 At present, c-TCD has been widely used for right-to-left shunt screening, which can dynamically observe the emboli entering into the intracranial arteries and the changes of cerebral blood flow in real time.11,12 In our report of this case, c-TCD revealed a positive result with a big right-to-left shunt, which was in line with the diagnosis of PAVF.
Most of the PAVFs will gradually enlarge and rarely atrophy spontaneously, which may cause serious complications. The mortality rate of untreated patients with PAVF was as high as 50%, which can be reduced to 3% after treatment. At present, it is advocated that active treatments should be adopted for patients with symptomatic or asymptomatic PAVFs, if their lesions diameter exceed 3mm. The PAVF treatments mainly include surgery and interventional embolization, which can improve the symptoms of hypoxia and prevent the occurrence of central nervous system complications. 8,9 Todo et al13 reported a patient with recurrent ischemic stroke induced by PAVF with a feeding artery diameter of 1.80 mm, who was successfully prevented from the recurrence of embolic events after embolic treatment. In our report, this case was treated with interventional embolization of PAVF in our hospital, and there was no recurrent seizure of TIA symptoms for 2 years, which further confirmed that the recurrent TIA symptoms were associated with PAVF.
In conclusion, although pulmonary arteriovenous fistula is a rare cause of abnormal embolism, it can not be ignored as the main extracardiac shunt pathway. Most patients with PAVF have atypical clinical presentations, and even present with cerebral ischemic stroke or TIA as the only clinical symptom. Therefore, for the patients with cryptogenic stroke , especially for the children with cryptogenic stroke, the corresponding examinations should be conducted to judge whether they may suffer from PAVF, then active treatments and follow-up should be offered.