a 55-year - old man , presented to our hospital , complained of a large pelvic mass , which was found incidentally during a routine ultrasonography .
the patient had no history of abdominal or pelvic discomfort , nor any abdominal or pelvic surgery .
in addition , the patient had no relevant medical or family history except for diabetes mellitus . upon a digital rectal examination , a large mass with a stone - like hardness was palpated at 5 - 6 cm above the anal verge .
a single - phase helical ct ( lightspeed ultra ; ge healthcare , milwaukee , wi ) , spanning the whole abdominopelvic cavity , was performed .
the ct scanning parameters included a beam collimation of 8  1.25 mm , a reconstruction interval of 1.25 mm , a pitch of 1.35 , a rotation time of 0.8 seconds , a table speed of 13.5 mm / rotation , 120 kv and 160 mas .
transverse ct images were obtained 70 seconds after the intravenous injection of non - ionic contrast material ( 120 ml ) at a rate of 3 ml / sec ( ultravist 300 ; bayer schering pharma , berlin , germany ) .
the ct images revealed a large , well - defined mass in the presacral space of the pelvic cavity , which seemed to have a long stalk arising from the left gluteus medius muscle ( fig .
the stalk traversed along the surface of the left iliac bone , and proceeded through the left sciatic foramen , and ended up connecting with the mass .
the ct attenuation generated an easily recognizable mass , which was mainly composed of fatty tissue and calcification , with most of the stalk becoming calcified .
some focal areas of intermediate attenuation were identified as a mixture between fatty tissue and calcification , and occupied only a limited portion of the mass .
mr imaging ( horizon 1.5 t ; ge healthcare , milwaukee , wi ) was also performed with the use of a torso coil . on both the t1-weighted ( 366/8 , echo train length of zero , 5-mm slice thickness , 2-mm gap , 256192 matrix , 24-cm field of view , 2 signal acquired , and sequence duration of 3 - 4 minutes ) and t2-weighted ( 4300/84 , echo train length of ten , 5-mm slice thickness , 2-mm gap , 512256 matrix , 24-cm field of view , 2 signal acquired , and sequence duration of 3 - 4 minutes )
mr images , the mass was revealed to mainly consist of the hyperintense and signal void areas that represent fatty tissue and calcification , respectively ( fig .
1c - e ) . also seen are the focal areas of intermediate signal intensity , as shown on the ct images .
the gadolinium - enhanced t1-weighted mr images obtained 30 seconds , 60 seconds , and 3 minutes after the intravenous injection of contrast material ( gadovist ; bayer schering pharma , berlin , germany ) , and the focal areas of the intermediate signal intensity around the calcifications observed at 30 and 60 seconds post - injection , became isointense as the surrounding fat tissue at 3 minutes post - injection .
the main mass was resected using a transabdominal approach , whereas the stalk was removed through the sciatic foramen .
the surgical specimen consisted of a 13 cm , well - circumscribed , hard mass , with a severely calcified external surface .
the cut surface of the resected specimen revealed a mass mixed with fatty tissue and calcification ( fig .
a histopathological examination revealed that the mass was composed of lipoma with chondroid metaplasia ( fig .
the term mesenchymoma was originally defined by stout ( 7 ) in 1948 to describe tumors containing at least two mesenchymal tissues not normally found together .
the tumors can be classified as benign or malignant , and most of the benign varieties have been called angiomyolipomas , angiolipomas , chondrolipomas , osteolipomas , and other names depending on the predominant tissue form in the tumor .
however , fibrous tissue is found in all mesenchymal tumors , and is not counted as one of the elements ( 6 ) .
conversely , if a mesenchymal tumor is well - defined or encapsulated and composed predominantly of one type of mesenchymal tissue , along with one or more minor element , the diagnosis should reflect the predominant mesenchymal tissue ( 6 ) . in our case ,
the diagnosis of a chondrolipoma was appropriate , since the mass was composed of a sufficiently high proportion of both fatty tissue and extensively calcified chondroid tissue , though it was well - defined and encapsulated .
two possible explanations for the pathogenesis of cartilage and bone formation in benign mesenchymomas have been proposed ( 5 , 6 , 8 , 9 ) .
the first is that cartilage arises from chondro - osseous metaplasias of adipose tissue , presumably as a result of mechanical stress or trophic disturbance .
the close proximity or contact with bone and a large joint , myxoid background , or a lipodystrophy - like change , which are often associated with these tumors , suggest a metaplastic process caused by a trophic disturbance or mechanical stress ( 8 - 10 ) .
a previous immunohistochemical study supported the explanation that the pattern of expression for growth factor- , latent transforming growth factor- binding protein-1 transforming , and bone morphogenetic protein might play an important role in the transformation of multipotential cells into the chondrolipoma ( 11 ) .
considering the proximity of the identified chondrolipoma to the iliac bone of our case study , we agree with the first explanation of chondroid - osseous metaplasia , which states that the mass may be a result of a micro - trauma .
our mass occupied both the inside and outside of the pelvic cavity ; however , we could not clarify whether its primary site was the pelvic cavity or the left buttock . according to previously reported cases
the only reported case of an abdominal chondrolipoma in a human occurred in the small bowel ( 8) , whereas a chondrolipoma was once documented in the pelvic cavity of a dog ( 12 ) . considering these reports , we thought that in our case , a chondrolipoma in the buttock might be extended to the pelvic cavity through the sciatic foramen , though the proportion of the mass in the pelvis was greater than in the buttock .
there are few reports pertaining to the imaging features of chondrolipomas of various organs , with most cases describing their mr features ( 5 , 9 , 13 , 14 ) . for these reports ,
chondroid and fatty tissues were described as intermediate and high signal intensity areas on t1-weighted images , respectively .
both chondroid and fatty tissues were identified as having a higher signal intensity area than the surrounding muscle , whereas chondroid tissue was depicted as having a higher signal intensity area than fatty tissue on t2-weighted images .
signal void areas corresponding to calcifications were only found in a small portion of these reported cases . for the ct images ,
fatty tissue was depicted as a low attenuation area ( less than -30 hounsfield units ) , whereas chondroid tissue was depicted as an intermediate attenuation area . in our case ,
the mass was depicted to be primarily composed of fatty tissue and calcification , which matched the ct attenuation and mr signal intensity .
also , we found that additional focal areas of intermediate attenuation or signal intensity corresponded to chondroid tissue .
these findings were different from those described in previously reported cases whereby , in our case , the calcification was much more extensive , and the signal intensity of chondroid tissue on the t2-weighted images was intermediate
. moreover , we found extensive calcification located peripherally in a linear and rosary pattern .
a previous report also cited the observation of chondroid tissue in a rosary pattern ( 9 ) . despite the very limited number of reported cases , we propose that the rosary pattern of either the chondroid tissue or calcification could be a characteristic finding of chondrolipomas , and in our case , the calcification in a rosary pattern was likely a consequence of the dystrophic change involving the chondroid tissue .
moreover , the signal intensity of chondroid tissue was intermediate on the t2-weighted images , and could be explained by the presence of fibrous tissue within the chondroid tissue ( fig .
1i ) , which reduced the signal intensity of chondroid tissue below the fatty tissue .
it is interesting that the focal areas of intermediate signal intensity around the calcifications showed delayed enhancement on the gadolinium - enhanced mr images .
( 9 ) described the presence of enhancing foci between the fatty tissue and chondroid tissue in a chondrolipoma , without clarifying the histopathological findings .
also , there have been no reports of chondrolipomas with delayed enhancement . in our case ,
however , keeping in mind that the location of these focal areas corresponded to chondroid tissue , and that chondroid tissue is usually not enhanced , even on the delayed phase , the delayed enhancement of these focal areas may be attributed due to sufficient fibrous tissue within the chondroid tissue . despite the characteristic imaging findings of chondrolipomas , fatty tumors such as lipomas or liposarcomas , which contain chondro - osseous differentiation ,
the treatment of choice for chondrolipomas is surgical excision ( 5 , 8 , 14 ) .
conclusively , we experienced the only reported human case of a chondrolipoma in the pelvic cavity , and found that it had characteristic imaging features consistent with fatty tissue and calcification , as well as the areas corresponding to cartilage .
 a chondrolipoma is an extremely rare form of a benign mesenchymal tumor containing mature cartilage and fatty tissue . 
 chondrolipomas may be found in almost any part of the body , particularly in the connective tissue of the breast , head and neck area , as well as in the skeletal muscle . 
 however , to the best of our knowledge , chondrolipomas located in the pelvic cavity have not been reported . in this case report 
 , we describe a case of a chondrolipoma in the pelvis , and show that it has its own characteristic imaging findings , which included the composition of fatty tissue and calcification in most parts , as well as some focal areas of chondroid tissue based on the ct and mr findings . 
CASE REPORT
DISCUSSION