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
). 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
). The second is that the cartilage may originate from multipotential cells in the mesenchymoma. A previous immunohistochemical study supported the explanation that the pattern of expression for growth factor-β, latent transforming growth factor-β 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, chondrolipomas were mostly found in the connective tissue and skeletal muscle. 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
). 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 (), 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. Orui et al. (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, the exact histopathology of the focal areas of delayed enhancement was not substantiated. 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, should be included in the differential diagnosis (9
). The treatment of choice for chondrolipomas is surgical excision (5
). Local recurrence is rare, and may represent incomplete removal (5
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.