Relevant Imaging Modalities to Distinguish Gastrointestinal Stromal Tumours from Their Mimics

Abstract

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract. GISTs arise in the smooth muscle pacemaker interstitial cell of Cajal (ICC). They are defined as tumors whose behavior is driven by mutations in the KIT gene (85%), PDGFRA gene (10%), or BRAF kinase (rare). 95% of GISTs stain positively for KIT (CD117). GISTs primarily occur in middle-aged and older persons, with a median age of approximately 60 years. They are more common in males than females. The majority of GISTs are sporadic, but they have been identified in association with Carney triad and Neurofibromatosis type 1 (NF1). Common sites of GIST involvement include: stomach (70%), small intestine (20-25%), anorectum (7%), oesophagus (rare). They occur not only anywhere along the gastrointestinal tract, but also in the mesentery, omentum and retroperitoneum, which is called extra-gastrointestinal GISTs. Macroscopically they are well-circumscribed lesions, exhibit a tan-white fleshy cut-surface with foci of cystic degeneration, hemorrhage, or necrosis. Large tumors may show ulceration of the overlying mucosa. Microscopically they demonstrate 3 main histologic subtypes: spindle cell type (70%), epithelioid type (20%), and mixed spindle and epithelioid type (10%). The majority of GISTs (70%) present with non-specific clinical symptoms, which vary depending on the size and site of involvement. The symptoms can include bleeding, perforations, and less commonly, obstruction. Approximately 20% of cases are asymptomatic and are found during endoscopy, surgery, or radiologic studies for other reasons.