IMAGE FINDINGS Figure 1: Sagittal T1 MRI demonstrates a large soft tissue mass centered in the heel pad measuring approximately 4.8 cm AP x 4.5 cm TR by 3.3 cm CC. Mass is intimate with the plantar aponeurosis with extension through the plantar aponeurosis, and involvement of the abductor digiti minimi and flexor digitorum brevis muscles. Mass is well circumscribed inferiorly and ill-defined at interface with muscle. Figure 2: Sagittal T2 FS MRI demonstrates a large soft tissue mass centered in the heel pad intimate with the plantar aponeurosis with extension through the plantar aponeurosis, and involvement of the abductor digiti minimi and flexor digitorum brevis muscles. Mass is well circumscribed inferiorly and ill-defined at interface with muscle. No signal abnormality adjacent calcaneus. Figure 3. Coronal T1 MRI demonstrates a large soft tissue mass centered in the heel pad. Mass is intimate with the plantar aponeurosis with extension through the plantar aponeurosis, and involvement of the abductor digiti minimi and flexor digitorum brevis muscles. Mass is well circumscribed inferiorly and ill-defined at interface with muscle. Figure 4. Coronal T2 FS MRI demonstrates a large soft tissue mass centered in the heel pad intimate with the plantar aponeurosis with extension through the plantar aponeurosis, and involvement of the abductor digiti minimi and flexor digitorum brevis muscles. Mass is well circumscribed inferiorly and ill-defined at interface with muscle. No signal abnormality adjacent calcaneus. Figure 5: Color Doppler ultrasound demonstrates a heterogeneous mass with mixed hypo-and hyperechoic components utilizing a high frequency probe in a longitudinal projection. Small amount of internal vascularity on color doppler interrogation.
Fibrosarcoma Malignant Melanoma Malignant peripheral nerve sheath tumor Melanotic schwannoma Synovial sarcoma Alveolar soft part sarcoma Epithelioid sarcoma PEComa (perivascular epithelioid cell neoplasms) FINAL DIAGNOSIS Clear Cell Sarcoma of Soft Tissue DISCUSSION
Figure 5. Color Doppler Ultrasound Right Foot Figure 6a. Ultrasound guided biopsy right foot mass
Figure 6b. Color Doppler Ultrasound Right Groin
Clear cell sarcoma of the soft tissue is a rare malignant mesenchymal tumor with characteristic intracellular glycogen accumulation that most commonly involves the tendons, fascia, and aponeuroses of the lower extremities and feet. Clear cell carcinoma has been identified less commonly in various regions, including the upper extremities, the retroperitoneum, genitourinary organs, and the gastrointestinal system. The incidence of clear cell sarcoma is exceedingly rare, constituting only about 1% of soft tissue sarcomas, and most commonly affects young adults between the second and fourth decade of life. These tumors share histological, immunohistochemical, and clinical characteristics with malignant melanoma of the soft tissue. Both are known to arise from neural crest cell lines. Prognosis depends on factors including tumor size, tumor location, presence of necrosis, and the presence of metastasis1,2,3,4. Clear cell sarcoma and malignant melanoma share a wide variety of features which ultimately resulted in the prior classification of clear cell carcinoma as “malignant melanoma of soft parts”; however, this term has fallen out of favor due to the cytogenetic differences that exist between the tumor subtypes regardless of their similarities. Both tumor types will generally demonstrate positivity for specific melanocyte markers, including HMB-45, S-100, and melanin-A. Clear cell sarcoma is distinguished through cytogenetic testing, which most commonly reveals a t(12;22)(q13- 14;q12) translocation resulting in an EWSR1/ATF1 gene fusion2,3,4. Though possessing a generally benign appearance on MR imaging, an appropriate diagnosis is imperative given the malignant characteristics of the tumor, tendency for local recurrence, and potential for distant metastasis and lymph node involvement. Radiological findings of clear cell sarcoma are primarily nonspecific. However, some of the most common findings include homogenous appearance on both T1 and T2 weighted images, often well-defined, and rarely bone involvement1. As the signal intensity on T2-weighted images correlates with intra- and extracellular water content, the paramagnetic effects of melanin on T2 shortening, in conjunction with high cellularity and a nucleocytoplasmic index greater than 1, are believed to contribute to the intermediate to low signal intensity of clear cell sarcoma on T2-weighted images. High T1 weighted signal intensity pattern may be attributed to the melanocytic composition of the tumor. Histological and radiological overlap between clear cell sarcoma and many other soft tissue pathologies reveals the important role of cytogenetic testing in accurate diagnosis2.
Figure 7. Coronal CT scan with Contrast
Figure 8. Axial CT scan with Contrast
REFERENCES 1.
Al-Nakshabandi NA, Munk PL. Radiology for the surgeon. Musculoskeletal case 38. Diagnosis: clear cell sarcoma of the foot. Can J Surg. 2007 Feb;50(1):58-9. PMID: 17391618; PMCID: PMC2384241. 2. De Beuckeleer LH, De Schepper AM, Vandevenne JE, Bloem JL, Davies AM, Oudkerk M, Hauben E, Van Marck E, Somville J, Vanel D, Steinbach LS, Guinebretière JM, Hogendoorn PC, Mooi WJ, Verstraete K, Zaloudek C, Jones H. MR imaging of clear cell sarcoma (malignant melanoma of the soft parts): a multicenter correlative MRI-pathology study of 21 cases and literature review. Skeletal Radiol. 2000 Apr;29(4):187-95. doi: 10.1007/s002560050592. PMID: 10855466. 3. Frichie KJ, van Rijn M. 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, Bianchi G, Stavropoulos N, Papagelopoulos P, Ruggieri P. Clinicopathological features, diagnosis and treatment of clear cell sarcoma/ melanoma of soft parts. Hippokratia. 2013 Oct;17(4):298-302. PMID: 25031505; PMCID: PMC4097407. ACKNOWLEDGEMENTS Magdalena Palac MD and Michael Chen MD are currently interns and will start their radiology residency in 2025. Neel Dewan Gupta, MD is a clinical and academic musculoskeletal radiologist in New Orleans and serves as a clinical assistant professor within the Department of Radiology at the Tulane University Medical Center. Patrick Valente, MD is a fourth year Tulane University radiology resident. Jeremy Nguyen MD, FACR is a clinical radiology professor within the Department of Radiology at the Tulane University Medical Center. Donald Olivares, Digital Imaging Specialist and Graphic Designer.
Figure 6a. Three passes were made with a 14-gauge biopsy needle using a 2-cm throw and lateral approach.
Figure 6b. Color Doppler ultrasound demonstrated abnormal right groin lymph node that is hypoechoic, demonstrates eccentric cortical thickening, and is mildly hypervascular. Figure 7: Coronal contrast enhanced CT demonstrates enlargement and abnormal attenuation of a right inguinal lymph node concerning for metastatic disease. Figure 8. Axial contrast enhanced CT demonstrates enlargement and abnormal attenuation of multiple right iliac chain lymph nodes concerning for metastatic disease. Figure 9 and 10. FDG-PET demonstrates intense FDG uptake in the right popliteal lymph nodes, right inguinal lymph nodes, right external and common iliac nodes highly suspicious for nodal metastatic involvement. Intense FDG noted in the right hindfoot, primary concern most suggestive of soft tissue neoplasm. DIFFERENTIAL DIAGNOSIS Clear Cell Sarcoma of Soft Tissue Desmoid Tumor
Figure 9. FDG-PET scan
Figure 10. FDG-PET scan
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J LA MED SOC | VOL 177 | SPRING 2025
J LA MED SOC | VOL 177 | SPRING 2025
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