Imaging of gastrointestinal stromal tumours with contrast enhanced ultrasound

Gastrointestinal stromal tumors (GIST) are rare tumors of the gastrointestinal tract. Dealing with these tumors requires a profound knowledge of the nature of the lesions and their malignant potential. Modern ultrasound techniques provide the necessary tools to give the clinician the information he needs to diagnose and treat the patient.

The review, summarizing the current literature and our own clinical data, discusses the application of ultrasound contrast agents in the imaging of patients with gastrointestinal stromal tumors, including contrast enhanced ultrasound (CEUS), contrast enhanced low mechanical endoscopic ultrasound (CELMI-EUS) and dynamic contrast enhanced ultrasound (DCE-US).

Contrast enhanced ultrasound as well as contrast enhanced endoscopic ultrasound are promising imaging techniques which may help to assess the malignant potential of subepithelial gastrointestinal tumours by analyzing their microvascularisation patterns. The presence of irregular vessels and of avascular areas within these tumours should amend the traditional sonographic criteria of malignancy (size, heterogeneity, echogenic or cystic internal structures, irregular outline). Prospective studies using these techniques in larger patient populations with GIST and other hypoechoic subepithelial gastrointestinal tumours are warranted to confirm the high accuracy of CELMI-EUS in predicting malignant behaviour especially of GIST with a diameter below 3 centimeters.

Moreover, CEUS is a highly valuable tool allowing very early diagnosis and functional evaluation of liver metastases of GIST, as typical GIST-metastases are hyperenhancing in the arterial phase and hypoenhancing in the portal venous and late phases. Prediction of treatment response is possible very early after initiation of treatment by analyzing decrease of vascularity before any volume reduction can be observed. Therefore contrast enhanced ultrasound in future may become a safe, highly accurate and cost-effective alternative to CT and PET-CT in monitoring efficacy of imatinib and other anti-angiogenetic drugs and to optimize dose and type of this treatment. The specific patterns of tumour response to inhibitors of tyrosin kinase in GIST and of recurrence during treatment should be described through new criteria differing from those traditionally used for cytotoxic chemotherapy. Prospective studies are required to compare contrast enhanced ultrasound with cross sectional imaging and functional imaging using FDG-PET for follow-up of patients after surgical treatment and for monitoring patients with metastatic GIST treated with tyrosin kinase inhibitors.