Gastrointestinal Stromal Tumors (GISTs) are a rare cancer originating in the digestive tract, specifically from interstitial cells of Cajal or their precursors. They are the most common mesenchymal tumors of the gastrointestinal tract. Understanding imaging techniques is valuable for managing and assessing these tumors.
Understanding GIST Tumor Imaging
Healthcare professionals employ several imaging techniques to visualize GIST tumors. Computed Tomography (CT) scans use X-rays to create detailed cross-sectional images, revealing the tumor’s size, location, and relationship to surrounding organs. Magnetic Resonance Imaging (MRI) uses strong magnetic fields and radio waves to produce detailed images, helpful for assessing soft tissues and detecting smaller lesions, especially in the liver or rectum.
Positron Emission Tomography (PET) scans show the metabolic activity of cells. A small amount of radioactive tracer, often a sugar molecule, is injected; highly active tumor cells absorb more tracer, appearing as “hot spots.” Endoscopic procedures, such as an upper endoscopy or colonoscopy, involve inserting a thin, flexible tube with a camera into the digestive tract to directly visualize the tumor’s surface and obtain tissue samples. Biopsies provide microscopic views, allowing pathologists to examine the tumor’s cellular characteristics.
Visual Characteristics of GIST Tumors
GIST tumors exhibit distinct visual features across imaging modalities. On CT and MRI scans, GISTs appear as rounded or lobulated soft tissue masses originating from the digestive tract wall, most commonly the stomach or small intestine. They vary in size, from small “tumorlets” less than 1 cm to large masses over 10 cm.
Small GISTs appear as homogeneous masses with sharp borders and show strong enhancement after contrast material is administered. Larger tumors are more heterogeneous, displaying areas of necrosis (dead tissue), hemorrhage (bleeding), or cystic change. Mucosal ulceration on the tumor’s surface is observed in about half of cases, and larger tumors may have cavities communicating with the lumen. PET scans highlight the metabolic activity of GISTs, with untreated tumors showing intense tracer uptake. Under a microscope, pathologists examine biopsy samples for specific cellular features, such as spindle cells (elongated) or epithelioid cells (round or polygonal), the two main cell types found in GISTs, with spindle cells being more common. The presence of proteins like KIT (CD117) and DOG1 is also a diagnostic marker for GISTs.
The Importance of Imaging in GIST Care
Imaging plays a role throughout the GIST patient journey. Initially, imaging is used for diagnosis, to identify the presence of a tumor and distinguish it from other gastrointestinal masses. CT scans are the primary modality for initial diagnosis and localization.
Imaging also assists in staging the tumor, determining its size, precise location, and whether it has spread to other areas, such as the liver or peritoneum. This information guides treatment decisions, including whether surgery is feasible or if targeted therapies, like imatinib, are appropriate. During treatment, imaging monitors the tumor’s response to therapy; for instance, a decrease in tumor density on CT scans or a reduction in metabolic activity on PET scans can indicate a positive response, even if tumor size does not change significantly. Regular imaging surveillance is conducted after treatment to detect any tumor recurrence, ensuring timely and informed decisions for ongoing patient care.