a 57-year - old woman visited the thoracic surgery department of the samsung medical center , seoul , for further evaluation of an abnormal finding on lung examination that had been incidentally detected by routine medical check - up . she denied any past medical history , and routine physical exams and laboratory tests were within normal limits . chest computed tomography ( ct ) identified a single 4-mm - sized vascular dilation in the anterior segment of left upper lobe ( fig . there was no abnormality in the rest of lung parenchyma . under the impression of pavf cut section of the specimen revealed a 0.5-cm - sized cystic lesion under the pleura . microscopically , the lesion consisted of irregularly shaped aneurysmal dilation of thick vein ( fig . additionally , elastic stain showed hypertrophic arteriopathy of pulmonary arterioles around the main aneurysmal vein ( fig . the patient was discharged without any post - operative complication . a 54-year - old woman presented with incidental abnormal finding on chest x - ray chest ct revealed a 38-mm - sized large aneurysmal sac in the right middle lobe ( fig . cut section of the specimen showed a thin - walled cyst with smooth whitish inner surface , measuring 38 mm in diameter ( fig . elastic stain revealed the lesion to be consisted of aneurysmal dilation of both artery and vein ( fig . he has had symptoms of cyanosis and clubbing of fingers since he was 4 years old and diagnosed with pavf from chest ct work up . he showed general cyanosis and complained of dizziness and general weakness , low extremities in particular . section of the specimen showed many engorged vessels with blood clots mainly in the posterobasal segment , measuring approximately 9 cm in extent ( fig . he was discharged with no specific postoperative complication . however , diffuse pavfs still remained in other lobes . he constantly suffered from general weakness and spo2 was still checked as 70% on average . a 36-year - old man was admitted to the thoracic surgery department for scheduled operation . although his symptom was relieved , post - treatment chest ct still revealed a multi - cystic lesion in the lateral side of right lung showing plump vascular supply through intercostal arteries or pulmonary arteries ( fig . it showed no segmental or lobar distribution . under the clinical impression of congenital cystic adenomatoid malformation ( ccam ) , cut section of the specimen revealed a multi - lobulated cystic lesion filled with blood , measuring 7 cm in extent ( fig . microscopic examination revealed that the cystic lining consisted of dilated thick vascular structure ( fig . the final pathologic diagnosis was given as fistulous arteriovenous malformation / hemangioma ( avmh ) . a 57-year - old woman visited the thoracic surgery department of the samsung medical center , seoul , for further evaluation of an abnormal finding on lung examination that had been incidentally detected by routine medical check - up . she denied any past medical history , and routine physical exams and laboratory tests were within normal limits . chest computed tomography ( ct ) identified a single 4-mm - sized vascular dilation in the anterior segment of left upper lobe ( fig . there was no abnormality in the rest of lung parenchyma . under the impression of pavf cut section of the specimen revealed a 0.5-cm - sized cystic lesion under the pleura . microscopically , the lesion consisted of irregularly shaped aneurysmal dilation of thick vein ( fig . additionally , elastic stain showed hypertrophic arteriopathy of pulmonary arterioles around the main aneurysmal vein ( fig . a 54-year - old woman presented with incidental abnormal finding on chest x - ray . chest ct revealed a 38-mm - sized large aneurysmal sac in the right middle lobe ( fig . cut section of the specimen showed a thin - walled cyst with smooth whitish inner surface , measuring 38 mm in diameter ( fig . elastic stain revealed the lesion to be consisted of aneurysmal dilation of both artery and vein ( fig . he has had symptoms of cyanosis and clubbing of fingers since he was 4 years old and diagnosed with pavf from chest ct work up . he showed general cyanosis and complained of dizziness and general weakness , low extremities in particular . cut section of the specimen showed many engorged vessels with blood clots mainly in the posterobasal segment , measuring approximately 9 cm in extent ( fig . he constantly suffered from general weakness and spo2 was still checked as 70% on average . a 36-year - old man was admitted to the thoracic surgery department for scheduled operation . although his symptom was relieved , post - treatment chest ct still revealed a multi - cystic lesion in the lateral side of right lung showing plump vascular supply through intercostal arteries or pulmonary arteries ( fig . it showed no segmental or lobar distribution . under the clinical impression of congenital cystic adenomatoid malformation ( ccam ) , cut section of the specimen revealed a multi - lobulated cystic lesion filled with blood , measuring 7 cm in extent ( fig . microscopic examination revealed that the cystic lining consisted of dilated thick vascular structure ( fig . the final pathologic diagnosis was given as fistulous arteriovenous malformation / hemangioma ( avmh ) . pavf is described as abnormally dilated vessels that provide a right - to - left shunt between pulmonary artery and pulmonary vein and is divided into simple and complex type . the literature review showed that abnormal communications between pulmonary arteries and veins have been given various names including pavf , arteriovenous aneurysm , and arteriovenous hemangioma [ 1 - 3 ] . while pavfs have been often described as pulmonary arteriovenous malformation in several reports [ 1 - 5 ] , we suggest that pulmonary avmh should be used preferably to describe tumorous hemangioma lesion and pavf should be used preferably to describe abnormal vascular communication . pavfs are divided into simple and complex type , and the former is more common . simple pavfs are those of a well - defined peripheral nodule and may be rounded or multi - lobulated . histologically , simple type presents as a single aneurysmal sac and contains a single segmental artery feeding the malformation . complex pavfs involve multiple abnormal vessels and consist of one or more lobulated venous sacs of variable size supplied by more than one feeding artery , often arising from adjacent segmental pulmonary artery branches . two patients ( cases 1 and 2 ) presented with solitary aneurysmal vascular lesion , which corresponded to simple pavf . these incidental lesions did not cause any clinical symptom and surgical removal was successfully performed . on the other hand , case 3 presented with diffuse vascular lesion causing arteriovenous shunt and was consistent with the diagnosis of complex pavf . lastly , case 4 showed a localized multi - lobular vascular lesion grossly mimicking pulmonary sequestration or ccam . the histology of case 4 was unusual and also different from cases 1 , 2 , and 3 in that it had no definite aneurysmal sac or shunt formation . while avmh is an acquired tumor - like condition characterized by complex thick - walled vessels , it was not certain whether case 4 was a tumorous condition of avmh or not . however , we concluded that the terminology of avmh would represent the histologic characteristics of case 4 the best in that there was definite localized overgrowth of thick vessels . although it did not cause serious hemodynamic or pulmonary symptoms , his episodes of pneumonia may probably be related to this lesion . while most pavf patients are known to have hht , patients in our series did not . pavfs are not easily diagnosed routinely , due to its rarity and its unspecific findings on routine examinations . ct is generally considered the reference standard investigation for diagnosing pavfs . in terms of treatment , the four rare cases of surgically resected pavfs described herein show various spectrums of clinical and histologic features . they can present as either localized or diffuse , and they can involve either thin or thick blood vessels .