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clinical and radiologic findings of three patients are summarized in table 1 . a 32-year - old woman presented with chest discomfort .
it had been diagnosed as alveolar soft - part sarcoma and the patient had undergone radiotheraphy .
chest radiography at that time had revealed a small , well - defined nodule in the left lower lung zone , but biopsy was not performed .
enhanced ct scan demonstrated a clearly enhanced nodule containing focal low attenuation , and clearly enhanced tubular structures , thought to be dilated vessels , were seen in the left lower lobe ( fig .
the attenuation of the focal low - attenuated area and the tubular structures was 1812 h and 928 h , respectively , while the attenuation of back muscle was 4213 h. wedge resection of the lung was performed , and gross examination showed that tumor size was 2.01.51.5 cm ( fig .
microscopic examination revealed dilated vessels corresponding to the enhanced tubular structures demonstrated by ct scan ( fig .
the pathologic diagnosis was alveolar soft - part sarcoma . a 24-year - old man presented with neck stiffness and headache .
eight years previously a chest wall mass originating from the right second and third ribs had been removed .
a chest radiograph obtained on admission showed a mass in the right paratracheal area and multiple nodules in both lungs .
ct scan demonstrated a 55-cm - sized , well - circumscribed , enhanced mass compressing the superior vena cava in the right paratracheal area .
high - attenuated tubular structures within the mass , suggesting dilated vessels , were noted , and multiple enlarged hilar lymph nodes and nodules were observed in both lungs .
brain mr images showed clearly enhanced nodules in the right cerebellar hemisphere and at the right occipital pole .
resection of the cerebellar lesion and biopsy of the pulmonary nodule were performed , and pathologic examination revealed metastatic alveolar soft - part sarcoma of the brain and lung .
a 31-year - old woman was admitted with left lower leg mass and pain , and she also complained of coughing and blood tinged sputum .
enhanced ct scan revealed multiple enhanced masses of various sizes and intratumoral dilated vessels ( fig .
it had been diagnosed as alveolar soft - part sarcoma and the patient had undergone radiotheraphy .
chest radiography at that time had revealed a small , well - defined nodule in the left lower lung zone , but biopsy was not performed .
enhanced ct scan demonstrated a clearly enhanced nodule containing focal low attenuation , and clearly enhanced tubular structures , thought to be dilated vessels , were seen in the left lower lobe ( fig .
the attenuation of the focal low - attenuated area and the tubular structures was 1812 h and 928 h , respectively , while the attenuation of back muscle was 4213 h. wedge resection of the lung was performed , and gross examination showed that tumor size was 2.01.51.5 cm ( fig .
microscopic examination revealed dilated vessels corresponding to the enhanced tubular structures demonstrated by ct scan ( fig .
eight years previously a chest wall mass originating from the right second and third ribs had been removed .
a chest radiograph obtained on admission showed a mass in the right paratracheal area and multiple nodules in both lungs .
ct scan demonstrated a 55-cm - sized , well - circumscribed , enhanced mass compressing the superior vena cava in the right paratracheal area .
high - attenuated tubular structures within the mass , suggesting dilated vessels , were noted , and multiple enlarged hilar lymph nodes and nodules were observed in both lungs .
brain mr images showed clearly enhanced nodules in the right cerebellar hemisphere and at the right occipital pole .
resection of the cerebellar lesion and biopsy of the pulmonary nodule were performed , and pathologic examination revealed metastatic alveolar soft - part sarcoma of the brain and lung .
a 31-year - old woman was admitted with left lower leg mass and pain , and she also complained of coughing and blood tinged sputum . enhanced
ct scan revealed multiple enhanced masses of various sizes and intratumoral dilated vessels ( fig .
alveolar soft - part sarcoma was initially defined in 1952 by christopherson et al . ( 6 ) and was described as ' characterized by pseudoalveolar or organoid arrangement of cells in relation to numerous delicate endothelial - lined vascular sinuses and septa ' .
they described twelve cases of rare soft tissue tumor that showed remarkable uniformity and an alveolar pattern . because of the uncertain origin of the cells , they were forced to use the descriptive term ' alveolar soft - part sarcoma ' .
gross pathology shows the tumors to be firm , often bulging slightly , variegated in color , and frequently hemorrhagic and necrotic ; a tumor may clearly extend into blood vessels .
the mass often appears to be well encapsulated but almost always there is histologically proven infiltration .
microscopically , the granular cells are arranged in nests ( ' alveoli ' ) separated by connective septae that have a rich vascular networks ( 3 ) .
the tumor usually involves patients between the second and fourth decade of life , and involves the lower extremities , the head and neck , the upper extremities , and the trunk , in decreasing order of incidence .
there is female predominance and the median age at diagnosis is 22 years for females and 27 years for males ( 3 ) .
alveolar soft - part sarcoma is of particular clinical significance because of the high prevalence of metastases ; at original diagnosis this involves 24 percent of patients . of those without metastases at original diagnosis , 40%
develop these within five years , 62% within 10 years , and 85% within 20 years ( 3 ) .
pulmonary metastases are found in 42 - 65% of patients ( 2 ) , and the lung is the most commonly involved site by metastatic tumor the brain and skeleton are the next most commonly invowed sites .
the median survival term in patients in whom metastases do not develop is 11 years , but with metastases , this period is reduced to three years ( 7 ) . in cases of extrapulmonary disease that can be controlled , complete resection of pulmonary metastases of soft tissue sarcoma , including alveolar soft - part sarcoma ,
can prolong survival even if multiple pulmonary metastases are present ( 8) . because of the high prevalence of pulmonary metastasis and good clinical results of pulmonary metastasectomy , annual screening of chest ct for an indefinite period might be beneficial for patients with alveolar soft - part sarcoma .
the conventional radiographic and sonographic findings of this condition at the primary site are nonspecific ( 2 ) . when unenhanced ct is used , the soft - tissue tumor is of lower attenuation than muscle ( 2 ) .
enhanced ct scans show significant tumor enhancement and tortuous , dilated , and early draining veins ( 1 , 2 , 5 )
angiography of primary site lesions revealed hypervascularity of the tumor , with multiple enlarged tortuous vessels , prolonged tumor staining and early draining veins ( 1 , 2 , 5 ) . on mr imaging ,
the mass showed high signal intensity on t1-weighted image and very high signal intensity on t2-weighted image .
tubular areas of signal void within the tumor , as seen on both t1-weighted image and t2-weighted image , are typical of rapid blood flow in enlarged vessels ( 2 , 5 ) .
on ct , our cases typically showed dilated , tortuous and tubular structures within the pulmonary metastatic masses , and these represent engorged vessels .
these ct findings are the same as those for primary masses of alveolar soft - part sarcoma and may reflect the characteristic pathologic findings of this rare malignant tumor .
these findings are , therefore , even if not specific , helpful for differential diagnosis of pulmonary masses .
they are , however , present only in cases involving masses larger than 2 cm .
because enhanced ct is not generally accepted in work up for pulmonary metastasis , our observation is in addition , limited . in conclusion
, we have described the ct findings of pulmonary metastatic alveolar soft - part sarcoma of the lung which on enhanced scans manifested as clearly enhanced pulmonary nodules or masses with dilated and tortuous intratumoral vessels , similar to those of the primary lesion .
alveolar soft - part sarcoma is rare , but in cases involving a clearly enhanced pulmonary mass with tortuous and dilated vessels in young adult patients , the possibility of metastatic alveolar soft - part sarcoma should be included in the differential diagnosis .
alveolar soft - part sarcoma is a rare soft tissue sarcoma of young adults with unknown histogenesis , and the organ most frequently involved in metastasis is the lung . 
 we report the ct findings of three patients of pulmonary metastases of alveolar soft - part sarcoma , which manifested as clearly enhanced pulmonary nodules or masses . on enhanced scans , 
 some of the masses were seen to contain dilated and tortuous intratumoral vessels .