Imaging pediatric gastrointestinal stromal tumor (GIST)

Pediatric gastrointestinal stromal tumors—a review of diagnostic modalities

“…CT characteristics for GIST vary depending on size and primary vs. metastatic disease. A large (>5 cm) lesion is typically exophytic, hypervascular with heterogeneous enhancement on contrast enhanced CT (17) (Figures 1,2), while the smaller lesions (<5 cm) are typically submucosal or endoluminal polypoid masses that show homogenous contrast enhancement (18). Metastasis on CT will have arterial enhancement (due to its hypervascular nature) and will lack enhancement on portal venous and venous phases (19) ( Table 1).…”

“…It is recommended that the German GIST Imaging Working Group protocol be utilized for these cases (14). According to a paper by Herzberg et al in 2018, it is recommended to utilize MRI, contrast-enhanced ultrasound (CEUS), and positron-emission tomography (PET)-CT/MR (depending on availability) for initial staging with surveillance imaging with MRI and CEUS every 6 months for at least 3 years post-therapy, with the caveat that lifelong annual imaging may be required due to the chronicity of this disease (17). Features of GIST on MRI are also variable depending on size and presence of high-risk tumor features.…”

“…CEUS combines ultrasonography with a contrast agent that acts as a pure blood pool agent, allowing for the evaluation of hypovascular and hypervascular lesions as small as 40 micrometers (21) ( Table 1). As stated previously, the guidelines suggested by Herzberg et al utilize CEUS of the tumor and liver in both the initial staging process and subsequent serial surveillance imaging (17). In addition to its utility in staging/surveillance scenarios, CEUS has also been shown efficacious to assess disease progression and treatment response when tyrosine kinase inhibitors (TKIs) are utilized ( Table 1).…”

“…It is thought that treatment alters tumor structure, causes decreased vascularity and eventual tumor necrosis, which CEUS can detect (22) and has increased sensitivity over PET scan for small hypovascular lesions (23). The characteristics of GIST on CEUS are hypervascular on arterial phase and hypoenhancing on portal venous phase (17). Dietrich describes low-risk GISTs to be homogenously enhancing, while high-risk GISTs tend to show more heterogeneous enhancement with areas of avascularity (24) ( Table 1).…”

“…However with cost-utilization taken into consideration, CEUS has similar sensitivity when anatomy allows its use and should be utilized if possible before PET scan is employed for surveillance (26). As stated previously, it is recommended to use PET-MR (if available, CT if not available) for initial staging in the pediatric population (17,28). Due to its high avidity for brown adipose tissue, and the pediatric population's higher percentage of this type of fat, it is recommended to pre-treat patients with a beta-blocker which can aid reducing the [18] fludeoxyglucose (FDG) avidity for brown adipose tissue and will decrease the false-positive rate.…”