ASPS is extremely rare in children, comprising 1–2% of all pediatric soft tissue sarcomas [13]​​. It typically progresses slowly and has a high metastatic rate. Compared with adults, children with ASPS exhibit distinct clinical characteristics. The most significant difference lies in the primary site of onset: in adults, ASPS originating from the head and neck region accounts for only 3.4%, whereas in children, this proportion can reach 32% [14]​​. Among younger children, ASPS predominantly affects the head and neck, whereas in older children, it tends to occur in the trunk and limbs. In our group of ASPS cases, 50% were located in the head and neck area. These findings further underscore that pediatric ASPS patients disproportionately involve the head and neck compared with adults.

Previous studies have shown a female-to-male ratio of 2:1 in the general population, but gender differences in children are less pronounced [15]​. In our case series, the female-to-male ratio was 14:6, indicating a higher proportion of females, although more cases are needed for further validation. ASPS typically presents as a slow-growing, painless soft tissue mass that rarely causes functional impairment, leading to delayed detection [16]. Similarly, the older children in our group presented these characteristics. However, younger children, owing to the prevalence of head and neck lesions, tend to present earlier with related symptoms [17]​​. In our series, 6 patients (75%) with lesions in the oropharyngeal region presented symptoms, primarily related to compression.

The ASPS metastasis rate is high, with studies reporting a rate of 59% in adults [18]​​, whereas in this group of children, the overall rate is 40%, which is lower than that in adults. With respect to the locations of metastasis, in adults, metastases are most commonly found in the lungs, brain, bones, liver, and lymph nodes​​. In this group of children, the primary site of metastasis was the lungs (7/8), with 2 patients showing metastasis to surrounding lymph nodes and one child developing vertebral metastasis two years after onset. There is also a significant disparity in the metastasis rates depending on the location of the primary tumor. Compared with tumors in the trunk and limbs (70%), tumors in the head and neck have a low metastasis rate (10%). Previous reports have also indicated that the rates of ASPS metastasis from head and neck tumors (40%) are lower than those from tumors in the limbs (73%). The reasons for this may be related to the specific characteristics of head and neck lesions, where symptoms appear earlier and more prominently, leading to earlier medical intervention. In this group of patients, there was a significant correlation between tumor size and the metastasis rate, with larger tumors indicating a greater risk of metastasis. This finding aligns with previous research conclusions [19]​​.

Ultrasound is often the initial examination in clinical practice for assessing soft tissue masses. It allows for rapid acquisition of information regarding the internal composition of the mass and accurately identifies the specific layer within the soft tissue tumor (such as fat, muscle, or fascia). This information is crucial in guiding subsequent clinical decisions, including regular follow-up, CT, MRI, or biopsy. Although ASPS is rare and difficult to diagnose, it has distinctive ultrasound characteristics. Despite significant clinical differences between head and neck lesions and those in the trunk and limbs, the ultrasound features of tumors in different locations are generally consistent. The most common ultrasound presentation is a well-defined hypoechoic lesion, which is consistent with previous ultrasound studies [8]​​. Lesions often display heterogeneous internal echogenicity; larger tumors may present areas of hemorrhage and necrosis, whereas smaller tumors tend to be relatively homogeneous. This group exhibited lesions with homogeneous echogenicity, with an average maximum diameter of only 2.4 cm. Most lesions had clear boundaries, although unclear margins were observed only in exceptionally large tumors. Tumors in limb muscles are typically spindle shaped, whereas those in the oral cavity tend to be round, possibly reflecting differences in tumor texture and surrounding tissue compression.

In comparison to the gray-scale ultrasound findings of ASPS, the color Doppler ultrasound characteristics are notably more distinctive. ASPS tumors typically exhibit rich intralesional and perilesional vascularization, characterized by tortuous and dilated vessels. In our series, varying degrees of tortuous and dilated vessels were observed both within and around all 20 lesions, with vessel diameters ranging from 0.1 to 2 cm. Some intralesional vessels show signs of proliferation and fusion, which is consistent with imaging findings [20]​​. However, due to the limitations of retrospective studies, the spectral information in our series was incomplete. In this group of cases, three children exhibited ultrasound findings of arteriovenous fistula. Color Doppler ultrasound showed bright and colorful blood flow signals in the fistula region during systole, while Spectral Doppler demonstrated decreased resistance and increased flow velocity at the fistula inlet, with arterialization of the venous spectral signals at the outlet. Additionally, one child underwent contrast-enhanced ultrasound, which revealed uniform moderate to high enhancement with a “fast in, slow out” pattern. Related studies have also reported similar results of ASPS in angiography [21]

ASPS is characterized by multiple malformed blood vessels and extremely rich blood flow signals, which can help differentiate it from lipomas and most soft tissue sarcomas [22]. However, ASPS is highly likely to be misdiagnosed as a vascular tumor or vascular malformation in deep tissues. Among our cohort of 20 pediatric cases, ultrasound provided diagnostic inclinations in 13 cases preoperatively, with 9 cases misdiagnosed as vascular tumors or malformations, highlighting their similarity. Both ASPSs and vascular tumors or malformations can present with tortuous dilated vessels internally and peripherally. Compared with the rare occurrence of ASPS, diagnosing vascular tumors or malformations is evidently easier. Ultrasound features aiding in differentiation include partly unclear boundaries [23]​​, partially increased internal echoes (related to higher intratumoral fat content), and a significantly greater incidence of venous phleboliths than does the ASPS [24]​​. Peripheral and distant metastasis may indicate a greater possibility of ASPS, particularly pulmonary metastases (7/8), which strongly suggest the disease when it is identified alongside highly vascular soft tissue lesions on examination. Based on the characteristics of our own cases and previous literature, we selected relatively common pediatric soft tissue tumors that need to be differentiated from ASPS in clinical practice, and we organized and compared the main ultrasound features of each tumor (Table 3).

Due to the rarity of ASPS, most cases are often advised to undergo regular follow-up examinations when first discovered [25]. In cases where there is rapid growth or significant changes in the condition, it is recommended that the child undergo further imaging studies, including MRI of the local soft tissues and CT of the lungs, to assist in diagnosis. When there is a high suspicion of ASPS, especially in the presence of metastasis, we still prefer to obtain a definitive diagnosis through biopsy as soon as possible, allowing the child to be quickly referred to our hospital’s oncology center for treatment. Of course, prior to the biopsy, we conduct a thorough assessment, which includes: (a) detailed communication with the child’s parents, explaining the risks and obtaining written consent; (b) ensuring the child’s coagulation function is completely normal; (c) using the thinner possible needle (usually 18-20G) during the procedure and obtaining 2–3 tissue strips based on the integrity of the tissue sample. In this group, 8 cases with lesions in the limbs or retroperitoneum underwent ultrasound-guided percutaneous biopsy, and no significant bleeding or other complications were observed postoperatively. Other studies suggest that fine-needle aspiration can also provide sufficient evidence for disease classification, with potentially less damage. However, we do not have such experience, and further validation is needed [26]. ​​.

Children with localized ASPS generally have a favorable long-term prognosis, with an overall 5-year survival rate of approximately 90% [27]. The current preferred treatment for ASPS involves wide surgical excision aiming for tumor-free margins, typically requiring 1–1.5 cm of tumor-free tissue surrounding the tumor bed [28]. For areas that are difficult to excise completely, such as the base of the tongue or adjacent to the pharynx, postoperative adjuvant therapy may be considered to prevent recurrence and metastasis [29]. Currently, targeted therapy shows great promise for children with unresectable or multiple metastatic disease. Many studies indicate that the prognosis of pediatric ASPS is better than that of adults, and the survival rate is higher in younger patients [30]. In our group, there is only one known case of death. Additionally, three pediatric patients in this group underwent surgical resection after tumor embolization. This method helps to reduce intraoperative bleeding from the tumor, which has been applied in surgeries involving other hypervascular tumors [31].

This study also has several limitations. Firstly, due to the rarity of the disease, the number of patients included is small, and the slow progression of the disease over a long period makes it difficult to track some cases, resulting in challenges in collecting prognosis and survival data. Secondly, the strong capabilities of the head and neck surgery department at our hospital may attract a higher number of pediatric patients with head and neck tumors, leading to selection bias. Furthermore, this study is a retrospective analysis that relies on archived ultrasound images and videos, which limits the acquisition of detailed imaging information. Additionally, the settings for color Doppler parameters cannot be standardized uniformly across cases. Despite these limitations, within the context of ASPS being an ultrarare sarcoma, our study represents one of the largest pediatric ultrasound-related research efforts to date.