Is Magnetic Resonance Imaging Able to Provide Specific Diagnoses? A Case Report of Clear Cell Sarcoma of Soft Tissue in the First Metacarpal of the Hand

Clear cell sarcoma (CCS) is classified as a tumor of uncertain differentiation in the 2020 Classification of Soft Tissue Tumors by the World Health Organization [1]. It has a low incidence and usually presents as a slow-growing painless mass [2]. This can easily lead to its misdiagnosis as benign. CCS has low chemotherapy sensitivity, so surgical resection is the first-choice treatment. However, the condition has a poor prognosis, with half of those affected suffering local recurrence or distant metastasis [3, 4]. This makes early diagnosis crucial. Such diagnosis is dependent on preoperative imaging, as the clinical symptoms and histopathological features of CCS lack the specificity required. However, its identification in imaging results necessitates knowledge of the characteristic imaging features. CCS most commonly affects the distal lower extremities and trunk. In this report, we describe a case of CCS of soft tissue in the first metacarpal of the hand, with a description of its features on computed tomography (CT) and magnetic resonance imaging (MRI).

This study was approved by the Medical Ethics Committee of Beijing Jishuitan Hospital, Capital Medical University, Beijing (Approval No. k2023-212-00). Written informed consent was obtained from the patient for publication of this case report and conducted in accordance with the tenets of the 2013 revision of the Declaration of Helsinki.

A 43-year-old male presented with swelling of the left hand, which had begun 5 months earlier and worsened over the last month. When the swelling began 5 months ago, the first metacarpal bone of the left hand was found to be enlarged and deformed. Although painless, the swelling had gradually increased. One month ago, the affected area was injured, which caused the swelling to worsen and increase.

An X-ray showed bone destruction of the first metacarpal bone of the left hand and swelling of the surrounding soft tissue (Fig. 1a, b). CT imaging confirmed bone destruction and identified a soft tissue mass with uneven density and an unclear boundary around the left first metacarpal bone. A contrast-enhanced scan showed obvious heterogeneous enhancement and local necrosis (Fig. 1c–e).

T1-weighted MRI showed a slightly hyperintense signal in the affected area, while T2-weighted images showed signals with mixed hyperintensity. On both T1-weighted and T2-weighted sequences, hypointense strips were apparent within the mass, with osteolytic destruction of the metacarpal bone. On enhanced imaging, the mass also showed obvious heterogeneous enhancement (Fig. 2). The treatment was left forearm amputation.

The postoperative pathological results identified the mass as a spindle cell malignant tumor, with clear cytoplasm and some cells arranged in nests (Fig. 3a, b). The immunohistochemical results found that the tumor cells tested positive for the melanoma markers S100 protein, HMB-45, and Melan-A (X200) (Fig. 3c–e). The gene result showed EWS-AFT1 gene rearrangement: positive (Fig. 3f). These findings, together with the other immunohistochemical features and tumor morphology, confirmed the diagnosis of CCS.

CCS was first reported by Enzinger [5] in 1965. It typically involves the lower extremities, especially the tendons and aponeuroses of the foot and ankle. The exact histogenesis for the CT findings of CCS is unknown.

Studies of CCS CT findings have found that CCS is characterized by soft tissue mass, surrounding osteolytic bone destruction, and uneven internal density. However, these CT findings are not diagnostically specific.

It has been pointed out that the MRI manifestations of CCS differ depending on the internal melanin content of the individual tumor. When the melanin content is high, the signal intensity increases on T1-weighted images and decreases on T2-weighted images [6]. Since few other soft tissue tumors have this characteristic, a slightly higher signal on T1-weighted sequences is believed to be an important indicator of possible CCS. In the case presented herein, the T1-weighted images showed slightly high signals, while the T2-weighted images showed mixed high signals. This is consistent with the signal performances suggested by De Beuckeleer et al. [7] to be indicative of CCS. However, some scholars argue that intratumoral melanin levels cannot fully explain the MRI signal changes seen in these carcinomas [8, 9], and even some scholars pointed out that CCS showed a hypointensity signal or a hyperintensity signal on both T1-weighted and T2-weighted MRI images [10]. On both T1 and T2-weighted sequences, we observed some hypointense strips. These were not significantly enhanced. We speculate that these strips may be a thin or dense fibrous connective tissue septum, but further study is required to verify this. On our patient’s enhanced MRI scan, there was obvious heterogeneous enhancement, with some patches of nonenhancement. The enhanced areas were suggestive of dense tumor cells and an abundance of blood vessels in the pathological tissue. It was speculated that the tumor body may be accompanied by cystic degeneration and necrosis [11]. Based on MRI findings, it can be used to differentiate CCS from malignant melanoma [12], malignant peripheral nerve sheath tumor [13], and perivascular epithelioid cell tumor [14].

CCS is a rare, highly malignant soft tissue tumor. It most commonly affects the distal lower extremities and trunk and is rarely seen in the bones of the hand. Nevertheless, we suggest that the imaging features described in this case, in particular, the hypointense strips on MRI, should indicate the need to include CCS in differential diagnoses. The CARE Checklist has been completed by the authors for this case report, attached as online supplementary material (for all online suppl. material, see https://doi.org/10.1159/000540745).

The authors would like to thank Enago (www.enago.com) for the English language review. The authors would like to thank the editor and the reviewers for their helpful, constructive comments, which were a great help in producing this improved version of the paper.

Written informed consent was obtained from the patient for publication of this case report and any accompanying images. This study was approved by the Medical Ethics Committee of Beijing Jishuitan Hospital, Capital Medical University, Beijing (approval No. k2023-212-00).

The authors have no conflicts of interest to declare.

This study was not supported by any sponsor or funder.

All authors have made substantial contributions to the conception of the work and acquisition, analysis, and interpretation of data for the work. All authors approved the final version of the manuscript. Yunxin Li: data collection and writing of the initial draft of the manuscript; Ranran Huang, Aijie Wang, and Guowei Zhang: interpretation of the data and writing of the manuscript; and Yongbin Su: revision of the manuscript.

All data generated or analyzed during this study are included in this article and its online supplementary material. Further inquiries can be directed to the corresponding author.