A 17-year-old girl presented with a slow-growing soft tissue mass of the left thenar for a couple of months (Fig. 1). The mass was tender and felt warm at clinical examination. There was no recent trauma. A magnetic resonance imaging (MRI) of the left hand was performed.
A MRI was performed and showed a tumour in the thenar muscle with hypointense margin (fibrous tissue) and hyperintense (myxoid tissue) centre (Fig. 2a, 2b, 3a). The lateral part of the tumour had a gyriform to lobulated shape. After contrast administration, there was no enhancement in the central myxoid and peripheral fibrous component of the tumour (Fig. 2c, 3b).
After bolus injection, the time intensity curve showed no enhancement in the myxoid and fibrous component of the tumour (Fig. 4).
A subsequent plain radiography was performed to exclude myositis ossificans (Fig. 5). A mass of the thenar was seen. There were no calcifications or ossifications.
After histopathological examination of the biopsy and the resected mass the final diagnosis of low-grade fibromyxoid sarcoma (LGFMS) was made.
Distant staging with CT of the lungs showed one aspecific flattened pulmonary nodule not suspect for metastasis. The next follow-up CT was scheduled to take place in 6 months.
Low-grade fibromyxoid sarcoma (LGFMS) was first described by Evans in 1987 and is also known as Evans tumour [1]. It occurs most commonly in young adults and in deep tissues of the lower extremities and trunk.
LGFMS is a rare subtype of fibrosarcoma with a benign histological appearance but with a propensity for local recurrence (in 64 %) and metastasis (in 45 %). Long-term clinical follow-up and imaging surveillance is important because of the long latency periods between diagnosis and recurrence (ranging up to 15 years) and slow tumour growth. The most common distant metastatic site is the lung with the interval period to metastases ranging up to 45 years [2]. Treatment for patients with LGFMS is surgical resection, but even with successful resection, recurrence or metastases are possible. Up to now, there is no dedicated protocol regarding follow-up recommendations. In this case, clinical follow-up with CT of the chest for an extensive, if not lifelong period was planned. However, it is still unclear how regularly imaging of the chest should be repeated [3]. In our case, the interval was 6 months.
In 2012, Hwang et al. described the imaging features of LGFMS. Calcifications and bone erosions are uncommon on radiographs. On ultrasound, LGFMS was solid with heterogeneous echogenicity. On CT, LGFMS tends to be hypodense to muscle with focal isodensity. LGFMS displays heterogeneous signal intensity on fluid-sensitive MR sequences, reflecting the histology of the tumour, which consists of fibrous (hypointense) and myxoid (hyperintense) tissue. Two patterns of signal distribution were observed: intralesional nodules with hyperintense signal and gyriform patterns [4].
Desmoid tumour is an important differential diagnosis of LGFMS. On MRI desmoid tumour typically shows linear extension along fascial planes (fascial tail sign) and hypointense bands across all sequences representing collagenized hypocellular bands. After contrast administration these collagen bands stand out in relation to the enhancing cellular areas of the tumour [5]. These MRI features of desmoid tumour are not present in our case.
Histologically, the tumour contained striking bland fibroblasts in a fibromyxoid matrix. In many areas, the tumour had a swirling, whorled pattern (Fig. 6). MUC4, a highly sensitive and specific immunohistochemical marker for LGFMS, showed diffuse strong positive staining (Fig. 7) [6].
In conclusion, radiologic imaging plays an important role in the clinical management of LGFMS, from tumour detection to treatment follow-up. Certain specific patterns (intralesional nodules and gyriform pattern) on MRI can help differentiate LGFMS from other fibrous and myxoid tumours.
Low-grade fibromyxoid sarcoma (LGFMS).
Based on the imaging examinations (including X-ray and MRI) of the thenar region (the thumb muscle area) of the patient’s left hand, the following characteristics are observed:
Considering the patient is a 17-year-old female, presenting with a gradually enlarging soft tissue mass in the left thenar region, and based on the imaging findings, the following differential diagnoses are primarily taken into account:
Characteristics: Commonly occurs in young adults, often in deep soft tissues. The imaging may show a mix of fibrous and myxoid components, and histopathologically, MUC4 staining is usually positive. It grows slowly but has the potential for local recurrence and distant metastases (mainly pulmonary).
Characteristics: Frequently seen in younger individuals, and the tumor can extend along the fascia (“fascial tail”). On MRI, linear low-signal bands (collagen-rich) may be seen, and heterogeneous enhancement appears after contrast injection. However, this case lacks the typical fascial tail sign and low-signal bands.
Characteristics: Commonly found near the joints in the fingers or proximal palm, showing local growth. MRI often demonstrates low T2 signals with scattered hemosiderin deposition. However, in this case, the T2 sequence shows significant fibrous-myxoid features, making GCT-TS less likely.
Combining clinical presentation, patient age, MRI features (mixed fibrous and myxoid signals), and pathological immunohistochemical results (MUC4 positive), the most likely diagnosis is Low-grade Fibromyxoid Sarcoma (LGFMS).
1. Treatment Strategy
2. Rehabilitation and Exercise Prescription
Disclaimer: This report is a reference-based analysis drawn from the provided medical history and imaging data, and cannot replace an in-person consultation or professional physician’s diagnosis and treatment advice. If you have any questions or notice any changes in your condition, please seek prompt medical attention.
Low-grade fibromyxoid sarcoma (LGFMS).
