Medical Diagnosis
Case 132
【Progress】He hesitated to get surgery but two months later, he decided to receive the resection of the mass. The tumor mass was resected under local anesthesia. The tumor was present in the subcutaneous region like mounting on the muscle fascia. The cutting surface of the tumor was solid and yellow-whitish.
Microscopic examination revealed undifferentiated-unclassified sarcomas (undifferentiated spindle cell sarcoma or undifferentiated pleomorphic sarcoma) according to WHO classification. This tumor corresponded to be previously called “malignant fibrous tumor” whose name and concept come to unused.
【Discussion】
World Health Organization (WHO) updated a revised classification of sarcoma in 2013 (1). One of the new concepts includes that gastrointestinal stromal tumor (GIST) was newly incorporated in sarcoma classification (2). Another concept includes that undifferentiated-unclassified tumors were incorporated in sarcoma classification, taking place of pleomorphic undifferentiated sarcoma or pleomorphic malignant fibrous tumors (MFH) (1, 2). Namely, the term of MFH previously called for long time is no more used but undifferentiated-unclassified tumor is used from now on. In our case, the pathologist reported that the specimen from the resected tumor showed undifferentiated-unclassified sarcoma with the notes that this tumor is corresponded to MFH in the past.
Soft tissue composes of lipid, fibrin, muscle, nerve and vessels. Each component generates neoplasm, irrespective of benign and malignant. Undifferentiated-unclassified sarcomas probably indicate that the origin of this neoplasm cannot be identified. In short, this tumor contains several components of viable soft tissue density, hemorrhage, necrosis and calcification (3– 6). There exists a case report with this tumor with metastatic pulmonary calcified tumor (3). Meanwhile, liposarcoma originated from lipid is subclassified into types of well differentiated liposarcoma, dedifferentiated liposarcoma (components of lipid, soft tissue and mixed density) (2) and myxoid liposarcoma (components of lipid and myxoid). Fibrosarcoma originated from fibrin is dermatofibrosarcoma protuberance (component of fibrin and marked expansion) and extra-pleural solitary fibrous tumor (component of fibrin and dilated feeding artery)(2). Malignant neurinoma is classified into nerve sheath tumor.
There are more than 50 different types of soft tissue sarcomas. Some are quite rare and difficult to make an exact diagnosis. As an imaging diagnosis on soft tissue tumor, CT is useful to find out the component of calcification and lipid in the tumor, while MRI is superior to CT in detecting components of fibrosis, necrosis, hematoma, myxoid, melanin, and subtle lipid using several sequences of T1WI (in phase and out of phase), T2WI, fat suppression T2WI. Further, MRI with diffusion weighted imaging (DWI) is used whether malignant or benign. Especially, it is reported that median ADC values (× 10-3 mm2/sec) of benign and malignant tumors were 1.7 - 2.3 and 0.9 - 1.0, respectively (7, 8). In our case, MRI with DWI showed high signal intensity corresponded to the tumor, implying malignant tumor, although ADC values were not calculated.
【Summary】
We present a fifty five-year-old male with subcutaneous mass sized 2.5 cm in the left upper arm. MRI with T1WI and fat suppression T2WI showed low signal intensity and high signal intensity, respectively. MRI with DWIb1000 showed high signal intensity. Although ADC values were not calculated, malignant-potential tumor was implied. Microscopic examination of the resected tumor revealed undifferentiated-unclassified sarcomas. We should keep in mind that median ADC values (× 10-3 mm2/sec) of benign and malignant soft tissue tumors were approximately 2.0 and less than 1, respectively. In WHO classification for soft tissue sarcoma, MFH that has been used clinically for long time, is no more used. Instead, undifferentiated-unclassified sarcomas are replaced probably because this tumor origin is not clarified. Further, GIST was newly incorporated in sarcoma classification.
Soft tissue composes of lipid, fibrin, muscle, nerve and vessels. Liposarcoma originated from lipid is subclassified into types of well differentiated liposarcoma, dedifferentiated liposarcoma (components of lipid, soft tissue and mixed density) and myxoid liposarcoma (components of lipid and myxoid). Fibrosarcoma originated from fibrin is dermatofibrosarcoma protuberance (component of fibrin and marked expansion) and extra-pleural solitary fibrous tumor (component of fibrin and dilated feeding artery). Malignant neurinoma is classified into nerve sheath tumor.
【References】
1.Fletcher C, et al. World Health Organization classification of tumours of soft tissue and bone: pathology and genetics of tumours of soft tissue and bone, 4th ed. Lyon, France: IARC Press, 2013 [Google Scholar]
2.Akshay D, et al. Soft-Tissue Sarcomas: An Update for Radiologists Based on the Revised 2013 World Health Organization Classification. American Journal of Roentgenology. 2016;206: 924-932. 10.2214/AJR.15.15498
3.Mylarappa, P et al. Pleomorphic undifferentiated sarcoma of urinary bladder with calcified pulmonary metastasis: A rare entity. Indian J Urol. 2013 Jul-Sep; 29(3): 253–256.
4.Karki B, Xu YK, Wu YK, Zhang WW. Primary malignant fibrous histiocytoma of the abdominal cavity: CT findings and pathological correlation. World J Radiol 2012; 4:151–158
5.Dong A, et al. MRI and FDG PET/CT findings of malignant fibrous histiocytoma of the prostate. Clin Nucl Med 2014; 39:889–891
6.Park SW, et al. Malignant fibrous histiocytoma of the head and neck: CT and MR imaging findings. AJNR 2009; 30:71–76
7.Pekcevik, Y, et al. Characterization of Soft Tissue Tumors by Diffusion-Weighted Imaging. Iran J Radiol. 2015 Jul; 12(3): e15478. doi: 10.4103/0970-1591.117263
8.van Rijswijk CS, et al. Diffusion-weighted MRI in the characterization of soft-tissue tumors. J Magn Reson Imaging. 2002 Mar;15(3):302-7.
2018.12.5