Biopsy histology revealed
Case 306
【Progress】
Although she was introduced to University Hospital, multiple metastasis was found there. She did not hope further treatment of either surgical resection or chemotherapy and was transported to other hospital for palliative care.
【Discussion】
It is sometimes difficult to make an approach to imaging diagnosis for soft tissue tumor in case of containing no fat tissue. Although the pattern of signal intensity of T1WI and T2WI is useful to check a lesion containg in edema, hemosiderin, lipid or melanin. The combination of Diffusion WI and ADC values is also useful to check a lesion with or without malignant potential components of the tumor. However, this combination has several pitfalls for judging malignancy because abscess, keratin, mucin and hematoma cause repression of water molecule motion, inducing high signal intensity on DWI and lowering values on ADC values.
For example, infarction and abscess in fresh stage cause marked decrease of ADC values (0.2 to 0.3) (1), gradually increase in reparative stage and finally similar ADC values in absorption stage as surrounding intact tissue. Further, dermal cyst including keratin can cause decrease of ADC values below 1.0 (1).
Although there is a report that an ADC value of 1.38 can be a cutoff point of soft tissue tumors between benign and malignancy, the cutoff of 1.38 might be too high but should be less than 1.2 for judging malignancy from my opinion (2). Based on my data whose says that ADC values of neurinoma are 1.2 or greater and those of cholangiocarcinoma is around 1.1 (1).
In present case, mean ADC value was 0.774 indicative of abscess, epidermal cyst or malignant tumor. This lesion is difficult to make this mass abscess because of painless, no redness and no thermal. There are several soft tissue tumors of lowering ADC values of around 1.0: dermatofibrosarcoma protuberans, giant cell tumor of the tendon and clear cell sarcoma (melanoma of soft part) (1). I thought ADC values are too low for listing these tumors for differential diagnosis, falling a pitfall of making misdiagnosis of epidermal cyst.
Clear cell sarcoma predominantly induces melanocytic differentiation whose histologic findings are the same as melanoma, then called melanoma of soft parts (4, 5). Although histologic findings show least difference from skin melanoma, gene abnormality between them is reported to be different (4). Clear cell sarcoma includes melanoma component. Tumor cells of clear cell sarcoma contain much glycogen which microscopically induce tumor cytoplasm clear on Hematoxylin eosin stain. MRI images of melanoma are characteristic of high signal intensity on T1WI and low signal intensity on T2WI. In case of clear cell sarcoma, this pattern does not always match to this MRI image pattern because of minimum component of melanin (4-7).
Clear cell sarcoma is reported to occur in approximately 1% of soft tissue tumors and found in foot, wrist and extremities rather than trunk neck and head (4). Clear cell sarcoma arises from fascia (connect muscle to muscle), aponeurosis and tendon (connect muscle to bone), and ligament (connect bone to bone). In our case, clear cell sarcoma arose from trunk. Ten years before, she experienced melanoma on foot. We are not sure whether the present tumor was metastatic melanoma of ten years before or the second original melanoma.
【Summary】
We presented an eighty-one -year-old female for lumbar skin mass sized 4cm that was found three months before. The lesion with low signal intensity on T1WI, high signal intensity on T2WI, high signal intensity on DWI and mean ADC values of 0.774. Histologic findings revealed clear cell sarcoma (melanoma of soft parts). It is borne in mind that when skin mass is encountered in interpret of MRIDWI and ADC values of 1.1 or less, tumors with malignant potentials of dermatofibroma protuberance, tendon giant cell tumor and clear cell sarcoma (melanoma of soft parts) plus epidermal cyst plus abscess.
【References】
1.Case 221, Case 259, Case 266 in home page of Hannan Municipal Hospital.
2.Razek A, et al. Assessment of soft tissue tumours of the extremities with diffusion echoplanar MR imaging. Radiol Med 2012;117:96-101
3.Frichie KJ, et al. Clear cell sarcoma of soft tissue. In: WHO Classification of Tumours Editorial Board. Soft tissue and bone tumours. Lyon (France): International Agency for Research on Cancer; 2020. (WHO classification of tumours series, 5th ed.; vol. 3).
4.Mavrogenis A, et al. Clinicopathological Features, Diagnosis and Treatment of Clear Cell Sarcoma/Melanoma of Soft Parts. Hippokratia. 2013;17(4):298-302.
5.Ibrahim R, et al. Clear Cell Sarcoma-A Review. Journal of Orthopaedics. 2018;15(4):963-6.
6.Choi JA, et al. Clear Cell Sarcoma of the Wrist: MRI Findings with Diffusion-Weighted Image and Histopathologic Correlation. Korean Society of Magnetic Resonance in Medicine (KSMRM) iMRI 2016;20:136-139
7.Ashikiyan O, et al. Evaluation of giant cell tumors by diffusion weighted imaging-fractional ADC analysis. Skeletal Radiol. 2019 Nov;48(11):1765-1773.
2023.8.1