echinococcosis in an important parasitic infection that is still a common health problem in undeveloped and developing countries ( 1 ) . the right atrium , right ventricle , and liver have been reported as embolic origins of such cysts ( 4 ) . here , we present a case of embolism of a hydatid cyst inside the left main pulmonary artery . the cyst was in the upper segmental branch of the lingular artery , and segmental and sub segmental branches of the lower lobe artery . however , no hydatid cysts were found in other organs . this case is interesting because there are only a few cases in which isolated pulmonary artery hydatid cyst without other organ involvement has been reported in the literature . we believe that this case is the first example of pulmonary artery hydatid cyst diagnosed by ebus . she had no complaints of sputum , chest pain , or dyspnea , but she had a suspicious history of hemoptysis she had a dog in her childhood and she also lived in the rural area . no abnormal signs were observed on her chest radiograph . pulmonary function tests and laboratory test results were within normal limits except for eosinophilia and minimally elevated d - dimer in the blood test . d - dimer level of the patient was 600 ng / ml , while normal limits are 0 - 500 . a negative d - dimer result may exclude pulmonary embolism , but there are many reasons that cause d - dimer elevation such as infection , trauma , deep venous thrombosis , and disseminated intravascular coagulation . in this case , the reason of elevated d - dimer was parasitic infection . the patient was treated with 250-mg fluticasone dry powder twice daily in an inhaler and montelukast once daily under a suspicious diagnosis of allergic asthma ; she asked for a control examination 2 weeks later . at the control examination thoracic computed tomography ( ct ) was performed to investigate the etiology of cough and her minimally elevated d - dimer level . filling defects were observed inside the left main pulmonary artery , upper segmental branch of the lingular artery , and segmental and subsegmental branches of the lower lobe artery on her thoracic ct angiogram ( figure 1 a - d ) . this finding at the main and superior branch of the lingular artery showed continuity with an 18  16 mm nodular opacity considered likely to be a cystic embolism . the right pulmonary artery and its branches were clear . subcutaneous low - molecular - weight heparin anticoagulant therapy was administered on the basis of the suspicious diagnosis of pulmonary thromboembolism . left and right ventricular parameters on echocardiographic evaluation were normal . no intracardiac thrombi , or any thrombosis in the deep veins of the lower extremities were observed . clinical and radiological findings were not completely compatible with thromboemboli . because pulmonary artery filling defects appeared more well - circumscribed and smooth , and they showed continuity with an 1816 mm nodular cystic opacity different from usual features of emboli , the other reasons such as pulmonary artery sarcoma and hydatid cyst causing filling defects in the pulmonary artery on ct were investigated . so for assessment of the other differential diagnoses , the patient underwent endobronchial ultrasound ( olympus evisexera ii cv180 ) . an anechoic cystic area was visualized inside the left pulmonary artery ( figure 2 ) . we performed endobronchial doppler ultrasound to investigate whether it was a cystic lesion that was causing the filling defects inside the pulmonary artery . doppler ultrasonography revealed a cystic formation that made the vascular filling defect inside the left pulmonary artery . thoracic magnetic resonance angiography was performed to investigate the cyst in more detail and it revealed cystic formations in the left pulmonary artery ( figure 3 a - d ) . the lesions were hyperintense both on t1-w and t2-w mri images that showed the liquid within the cyst was rich of protein . on mri examination , either distal branches of the pulmonary artery were not filled with contrast and showed cystic lesions in them . the nature was the same in the lesions on the proximal branches of the pulmonary artery . indirect hemagglutination and specific ige tests were performed to confirm the diagnosis of hydatid cyst ; both results were positive . the patient was scanned for frequent locations of organ involvement of hydatid cysts , but no other cysts were observed . the diagnosis of pulmonary artery hydatid cyst was decided by the patient s history of living in an endemic area , thoracic ct , mri and ebus findings and also positive serology tests . the size of the cyst in the left pulmonary artery on control thoracic ct scans shrunk 7.9 mm in diameter after one year of albendazole treatment ( figure 4 a and b ) . the liver ( 70% ) and lungs ( 25% ) are the organs most often affected . although cardiac involvement is observed in only 0.2 - 3% of cases , early diagnosis and treatment are important ( 5 ) . in primary cardiac hydatidosis , larvae usually reach the myocardium via the coronary circulation , the pulmonary circulation , or a patent foramen ovale . intestinal lymphatic vessels , thoracic duct , superior and inferior vena cava , and hemorrhoidal and pulmonary veins may be involved ( 6 ) . a variety of cardiac sequelae including sudden cardiac death , massive pulmonary embolism , and pulmonary hypertension may be encountered clinically . echocardiography , ct , and magnetic resonance imaging ( mri ) can be used to identify cardiac hydatidosis ( 7 ) . hydatid cysts located in the pulmonary arteries are frequently the consequence of embolisms from primary cardiac locations ( 8) . in the present case , a hydatid cyst was located inside the left pulmonary artery and its branches , without any cyst in the heart or other organs . intra - arterial hydatid cysts grow slowly into the lumen , ultimately occluding it . in the pulmonary arteries , this process may occur over a long period . because pulmonary arteries have adequate pulmonary perfusion through the bronchial arteries symptoms can be observed when the cysts compress a vital structure or interrupt blood circulation , which may also lead to anaphylactic shock ( 9 ) . , the cough might be the result of compression of the left lower bronchus by the cyst . hydatid cysts usually have a characteristic appearance on mri ; an oval lesion hypo intense and hyper intense on t1-and t2-weighted images , respectively . in this case , the lesions were hyper intense both on t1-w and t2-w mri images that shows the liquid within the cyst was rich of protein ( 10 ) . in the differential diagnosis of pulmonary artery hydatid cyst , pulmonary thromboembolism ( fat , amniotic fluid , septic emboli , particulate material ) and primary arterial tumors such as sarcoma should be considered since they also make intraluminal defects ( 11 ) . radiological findings and the patients clinical features help to make the differential diagnosis since patients with disseminated pulmonary artery thrombosis show a more aggressive clinical manifestation . hydatid disease may involve the heart , including the left ventricle ( 60% ) , right ventricle ( 10% ) , pericardium ( 7% ) , pulmonary artery ( 6% ) , and interventricular septum ( 4% ) ( 12 ) . because of the significant risk of cyst rupture and anaphylactic shock , surgery should be performed promptly after diagnosis . echocardiography , spiral ct , mri , ct angiography , magnetic resonance imaging angiography , and conventional pulmonary angiography can be used for the diagnostic investigation of patients suspected of hydatid pulmonary embolism . if there is no history of hydatid disease , its existence can be suspected based on the presence of anti - echinococcal antibodies and eosinophilia in blood tests ( 14 ) . the present case had eosinophilia and positive indirect hem agglutination and specific ige test results . imaging methods are sometimes limited by the small size of the lesion and the atypical images that are difficult to distinguish from abscesses or neoplasms . routine laboratory diagnosis of hydatid cysts depends on detection of specific antibody response . according to who manual for hydatid cysts , ct findings alone allow a correct diagnosis of 61% hydatid cysts of the liver , lung , kidney , spleen and some other sites and the correct diagnosis rate is 94% if ct is combined with serology ( 15 ) . according to a comma , the sensitivity and specificity of iha was 100% and 83.3 - 99% , respectively ( 16 ) . however , it should be kept in mind that embolectomy of the hydatid cyst from the main pulmonary truncus increases morbidity and mortality ( 16 ) . symptoms are usually absent or nonspecific and include chest pain , dyspnea on exercise , and fever . eosinophilia occurs in 20% of the cases and may be associated with recent rupture ( 18 ) . hydatid cysts can be solitary or multiple and vary in size ( 16 ) . in the present case , a cystic filling defect was found inside the main pulmonary artery and a solid defect was found inside the left lower intermediate artery . rupture into the cardiac chambers occurs most often in the right ventricle and can cause anaphylaxis , or pulmonary or systemic embolism of the daughter cysts ( 19 ) . repeated pulmonary emboli may produce pulmonary arterial hypertension and multiple lung cysts ( 20 ) . in the present case , left ventricular systolic function , the right atrium , and the systolic pulmonary artery pressure were normal and no intracardiac thrombus was found . ebus is increasingly used for lung cancer staging and the assessment of sarcoidosis ( 21 ) . it is useful for producing real - time images of both lymph nodes and pulmonary arteries ( 22 ) . after one year of treatment with albendazole , in the follow - up thoracic ct scan , there was a decrease in the size of the cystic lesion in the left pulmonary artery . as a result , albendazole treatment can be an alternative therapy for surgery especially for patients who reject operation .