Imaging Features of Gastrointestinal Stromal Tumour: Diagnosis and Evaluation of Treatment Response

INTRODUCTION Gastrointestinal stromal tumours (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract and more commonly found in middle-aged patients. They arise from the interstitial cells of Cajal in the myenteric plexus and are potential malignancies that can occur anywhere along the gastrointestinal tract, most commonly in the stomach (50-60%), followed by the small intestine (30-35%), colon and rectum (5%), and oesophagus (<1%).1 GISTs can also be extraintestinal and originate in the mesentery, omentum or retroperitoneum. In the Chinese population, the incidence among those aged ≥50 years is higher than in those under 50 years old with a mean age at diagnosis of 55.2 years.2 Most GISTs have a KIT or platelet-derived growth factor receptor alpha (PDGFRA) mutation. Neoadjuvant therapy with imatinib acts by blocking the signalling via KIT and PDGFRA. Nonetheless, 10% to 15% of GISTs do not have a detectable KIT or PDGFRA mutation and have a poor response to imatinib. Some are associated with neurofibromatosis type 1, Carney–Stratakis syndrome and Carney triad.3 Biopsy is preferred to confirm the diagnosis for large resectable tumours or metastatic GISTs. This article evaluates the radiological images of pathologically proven GISTs. RISK STRATIFICATION OF GASTROINTESTINAL STROMAL TUMOURS There are several guidelines for assessing the malignant potential of GISTs; the most common are the modified National Institutes of Health criteria and the Armed Forces Institute of Pathology criteria. In both guidelines, risk of recurrence varies with tumour size and mitotic rate. The presence of tumour rupture is an additional prognostic indicator. Intermediate tumours, i.e., large tumours with a low mitotic rate or small tumours with a high mitotic rate, that arise from the stomach have a more favourable prognosis than those in other parts of the gastrointestinal tract.4