Gastrointestinal Stromal Tumors: Imaging Features Before and After Treatment.

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract, with most occurring in the stomach. GISTs may present with clinical symptoms (eg, gastrointestinal bleeding) or may be found incidentally at surgery, endoscopy, or imaging. At initial staging, GISTs often appear as well-circumscribed, round, solid masses. Small tumors may appear solid, whereas larger tumors may demonstrate central areas of necrosis. At follow-up imaging, decreasing tumor attenuation at computed tomographic indicates treatment response even in the setting of stable tumor size. Localized tumors are treated with resection. Imatinib mesylate, a tyrosine kinase inhibitor, is typically prescribed for metastatic disease and increasingly in a neoadjuvant role before resection. Imaging plays a key role in the identification of GISTs, evaluation of tumor extent and presence or absence of metastatic disease, and in assessing response to therapy.