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Clinical Meetings at RH Year 2012

2012 - Out of the Blue

Drs Kin-Keung KWONG and Yiu-Cheong YEUNG; Department of Medicine and Geriatrics, Princess Margaret Hospital
Case history

A 66 year-old lady presented to our department with 1 week history of productive cough and shortness of breath in Dec 2010. She was a non-smoker and non-drinker. She had known history of suspected scleroderma, having regular follow-up in our rheumatology clinic since 2003. Esophageo-gastro-duodenoscopy (OGD) showed reflux esophagitis and she was therefore put on pantoprazole.

High resolution computer tomography (HRCT) scan of the thorax that time had no evidence of interstitial lung disease. Physical examination on admission revealed multiple telangiectasia over her forehead. Lung auscultations had no added sounds. Chest X-ray had no definite consolidative changes over lung fields. However, she was found to have persistent desaturation despite given high flow oxygen via non-rebreathing mask. White cell count was normal. Augmentin was empirically started. Arterial blood gas (ABG) showed type 1 respiratory failure with increased A-a gradient. She was eventually given Bi-level Positive Airway Pressure (BIPAP) support and intubated on day 2. Urgent contrast computer tomography scan of the thorax was performed, which incidentally found multiple PAVMs over bilateral lower zones of her lungs. There were no evidence of pulmonary embolism and no significant consolidative changes over both lungs. She was then transferred intensive care unit for further management and was successfully weaned from mechanial ventilation. Significant intra-pulmonary shunt was confirmed by contrast echocardiography. However, despite stabilization, she had persistent hypoxemia requiring oxygen supplement of 4L/min on discharge from acute medical ward. Detailed history confirmed that she had personal history of epistaxis since 25 year old. She was therefore diagnosed to have hereditary hemorrhagic telangiectasia by Cucao Criteria. Radionuclide scan by 99m Tc was arranged and shunt fraction was estimated to be 24.6% after calculation. Lung function test showed isolated decreased DLCO of 58% predicted after adjusted with alveolar volume.

Four sessions of embolization therapy were performed by radiologist in Princess Margaret Hospital from May 2011 to Nov 2011. Antibiotic prophylaxis was given before each session to prevent cerebral abscess. Echocardiogram was also arranged after each session of embolization therapy. So far, findings were quite similar to her pre-procedure ones and no pulmonary hypertension was demonstrated. With successful embolization therapy, she was able to gradually tail down and eventually wean off oxygen supplement with room air SpO2 93-95% afterwards. Follow-up computer tomography scan was arranged 6-12 months after the last embolization for monitoring in addition to regular outpatient visit.

Discussion

Pulmonary arteriovenous malformation (PAVM) is a rare disease but well-known to associate with hereditary hemorrhagic telangiectasia (also known as Olser-Weber-Rendu syndrome). It is defined as presence of abnormal vascular communications between pulmonary arteries and veins that lead to right-to-left (veno-arterial) shunting. According to the number of feeding arteries, it can also be divided into simple and complex type. Simple PAVM comprises only one feeding artery and accounts for 80-90% of all cases while complex AVMs that are supplied by two or more segmental arteries only account for the remaining 10-20%.

The estimated prevalence is around 1 in 50000 in US (Mayo clinic) but it is 2 times more common in women. PAVM typically affects lower zone of the lungs and tends to be multiple, bilateral with complex structure especially when it occurs in context of hereditary hemorrhagic telangictasia (HHT). The size of PAVM can be variable and sometimes can exceed 10 cm.

PAVM is mostly congenital and rarely can be due to previous thoracic surgery, trauma and infections like tuberculosis, actinomycosis and schistosomiasis etc. Majority of patients are diagnosed in 4th to 6th decade of life either incidentally found pulmonary nodule(s) in chest X-rays or presenting with exertional dynspnea. Other clinical features include hypoxemia, clubbing, hemoptysis, murmurs, bruits and so on. One should also raise the suspicion of the diagnosis if neurological complications, in particular, unexplained brain abscess, stroke and transient ischemic attacks (TIAs) happen in an otherwise healthy patient, as the occurrence rates are as high as 18– 33% in the literature1.

To diagnose PAVM, several methods can be used to demonstrate intra-pulmonary shunt2. 100% oxygen method, which requires measuring partial pressure of alveolar oxygen (PaO2) and arterial oxygen saturation (SaO2) after breathing with 100% oxygen for 20 minutes, is sensitive but the accuracy is operator-dependent. Shunt fraction is then calculated by equations. Further investigations are recommended if shunt fraction is more than 5%. Contrast echocardiography is the next option. By injecting agitated saline into a peripheral vein of the patient, echocardiogram is performed to demonstrate any abnormal bubbles in the left heart chambers so as to confirm presence and severity of shunting. Contrast echocardiography is again very sensitive to diagnose shunt but alone is difficult to quantify shunt fraction. Therefore, a scoring system (from Grade 0-4) is advocated in the literature3. Though not universally recognized, study showed that it had good correlation with radiological detection of PAVM by computer tomography and even size of the feeding artery. Radionuclide imaging by technetium-99m (99m Tc) is another alternative method to diagnose PAVM but it is expensive and not widely available. It is less operator dependent than 100% oxygen method. Shunt fraction can be calculated by Gates’ semi-quantitative equation.

Radiologically, contrast enhanced computer tomography scan is now widely used for diagnosing PAVM. With reconstruction techniques, it enables interventional radiologists to delineate the architecture of PAVM precisely. Conventional pulmonary angiography remains the gold standard but it is an invasive procedure.

Nowadays, embolization therapy is the first line treatment for PAVM. It has replaced invasive surgery since 1980s. The aim of treatment is mainly to prevent neurological complications secondary to paradoxic embolism and improve hypoxemia. By deploying detachable ballons, coils or amplatzers to the aneurysmal part of PAVM, right-to-left shunting is disrupted. The efficacy of embolization therapy had been repeatedly demonstrated by clinical trials with success rate up to 80-97%1,4,5,6,7,8. It is a safe procedure. Self-limiting pleuritic chest pain and fever are the most common complications. Rarely, it can cause air embolism, stroke, migration of coils etc9. Pulmonary hypertension after embolization therapy was reported but study suggested most patients, in fact, had a fall instead of raised pulmonary artery pressure afterwards10. So far, there is no international consensus regarding the absolute contra-indications of performing embolization therapy. But investigators believe that in those patients with pre-existing moderate to severe pulmonary hypertension and positive balloon occlusion test (defined as rise more than 5 mmHg in mean pulmonary arterial pressure), risks outweigh potential benefits11,12,13.

Finally, screening of PAVM is mandatory in all HHT patients according to international guideline 200914. Chest X-rays and contrast echocardiography were recommended to be the initial investigation of choice with sensitivity up to 100% combining the two15. Computer tomography is important in delineating the architecture of PAVM before embolization therapy, follow-up to detect growth of untreated PAVM and reperfusion of treated lesions.












Figure 2: Tc-99m lung perfusion scan showed abnormal uptakes in brain, thyroid, kidneys and bowel

Figure 3: embolization therapy and patient’s latest chest X-rays after total 4 sessions of procedures

Figure 4: Screening strategy of PAVM in patients with HHT (abstracted from HHT international guideline 2009)

References
  1. Pollak JS. Saluja S. Thabet A. Henderson KJ. Denbow N. White RI Jr. Clinical and anatomic outcomes after embolotherapy of pulmonary arteriovenous malformations. Journal of Vascular & Interventional Radiology. 17(1):35-44; quiz 45, 2006 Jan
  2. Iqbal M. Rossoff LJ. Steinberg HN. Marzouk KA. Siegel DN. Pulmonary arteriovenous malformations: a clinical review. Postgraduate Medical Journal. 76(897):390-4, 2000 Jul.
  3. Parra JA. Bueno J. Zarauza J. Farinas-Alvarez C. Cuesta JM. Ortiz P. Zarrabeitia R. Perez del Molino A. Bustamante M. Botella LM. Delgado MT. Graded contrast echocardiography in pulmonary arteriovenous malformations. European Respiratory Journal. 35(6):1279-85, 2010 Jun.
  4. Mager JJ. Overtoom TT. Blauw H. Lammers JW. Westermann CJ. Embolotherapy of pulmonary arteriovenous malformations: long-term results in 112 patients. Journal of Vascular & Interventional Radiology. 15(5):451-6, 2004 May.
  5. Prasad V. Chan RP. Faughnan ME. Embolotherapy of pulmonary arteriovenous malformations: efficacy of platinum versus stainless steel coils. Journal of Vascular & Interventional Radiology. 15(2 Pt 1):153-60, 2004 Feb
  6. La combe P. Lagrange C. Beauchet A. El Hajjam M. Chinet T. Pelage JP. Diffuse pulmonary arteriovenous malformations in hereditary hemorrhagic telangiectasia: long-term results of embolization according to the extent of lung involvement. Chest. 135(4):1031-7, 2009 Apr.
  7. Shin JH. Park SJ. Ko GY. Yoon HK. Gwon DI. Kim JH. Sung KB. Embolotherapy for pulmonary arteriovenous malformations in patients without hereditary hemorrhagic telangiectasia. Korean Journal of Radiology. 11(3):312-9, 2010 May-Jun.
  8. Hsu CC. Kwan GN. Thompson SA. van Driel ML. Embolisation therapy for pulmonary arteriovenous malformations. Cochrane Database of Systematic Reviews. (5):CD008017, 2010
  9. Ha tjema T. ten Berg JM. Overtoom TT. Ernst JM. Westermann CJ. Unusual complications after embolization of a pulmonary arteriovenous malformation. Chest. 109(5):1401-4, 1996 May.
  10. Shovlin CL. Tighe HC. Davies RJ. Gibbs JS. Jackson JE. Embolisation of pulmonary arteriovenous malformations: no consistent effect on pulmonary artery pressure. European Respiratory Journal. 32(1):162-9, 2008 Jul.
  11. Sho vlin CL. Gibbs JS. Jackson JE. Management of pulmonary arteriovenous malformations in pulmonary hypertensive patients: a pressure to embolise?. European Respiratory Review. 18(111):4-6, 2009 Mar.
  12. Dinkel HP. Triller J. Pulmonary arteriovenous malformations: embolotherapy with superselective coaxial catheter placement and filling of venous sac with Guglielmi detachable coils. Radiology. 223(3):709-14, 2002 Jun.
  13. Pelage JP. Lagrange C. Chinet T. El Hajjam M. Roume J. Lacombe P. Embolization of localized pulmonary arteriovenous malformations in adults. Consultation Pluridisciplinaire Maladie de Rendu-Osler. Journal de Radiologie. 88(3 Pt 1):367-76, 2007 Mar
  14. International Guidelines for hereditary hemorrhagic telangiectasia 2009. http://jmg.bmj.com/content/early/2009/06/29/jmg.2009.069013.full.pdf+html
  15. Cottin V. Plauchu H. Bayle JY. Barthelet M. Revel D. Cordier JF. Pulmonary arteriovenous malformations in patients with hereditary hemorrhagic telangiectasia. American Journal of Respiratory & Critical Care Medicine. 169(9):994-1000, 2004 May 1
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