GIST should always be among the differential diagnosis of an intra-abdominal non-epithelial malignancy. CT is essential for evaluating the primary tumor and for accurate staging. Magnetic resonance imaging (MRI) has a comparable diagnostic yield [
16] and lacks radiation exposure. However, CT is preferred initially for screening and staging. CT is better at global evaluation of the abdomen, especially the hollow viscera, than MRI. MRI may be preferred for GISTs at specific sites, such as rectum or liver. Tumors that are greater than 5 cm, lobulated, enhance heterogeneously, and have mesenteric fat infiltration, ulceration, regional lymphadenopathy, or an exophytic growth pattern on CT are more likely to metastasize [
17‐
21]. In contrast, GISTs with less metastatic potential tend to enhance in a homogeneous pattern, and often show an endoluminal growth pattern. CT or MRI scanning can assess the decrease in lesion density which can be an early marker of beneficial response in GIST patients treated with TKI drugs [
22]. Routine clinical practice rarely requires Positron Emission Tomography (PET) imaging of GIST for clinical care [
23]. PET imaging may have the advantage of detecting small lesions at least 1 cm in size because neither the normal bowel nor omentum takes up the fluorodeoxyglucose (FDG) tracer with excess avidity. The reported sensitivity of PET for GIST is 86 to 100% [
24,
25]. PET can be useful for detecting an unknown primary site or resolving ambiguities from CT [
26]. On upper GI endoscopy, a smooth, mucosa-lined protrusion of the bowel wall, with or without signs of bleeding and ulceration may be seen [
27]. However, endoscopic biopsies using standard techniques usually do not obtain sufficient tissue for a definite diagnosis [
28]. Endoscopic ultrasound (EUS) -guided fine-needle biopsy forceps also may not yield enough tissue, but might exclude other lesions that arise sub-mucosally. Snare biopsies can result in perforation and generally should be avoided except in carefully selected cases [
28]. A preoperative biopsy is not generally recommended for a resectable lesion in which there is a high suspicion for GIST, and the patient is otherwise operable. However, a biopsy should be done to confirm the diagnosis particularly when metastatic disease is present or suspected. If preoperative imatinib is considered in a patient who has a large locally advanced lesion thought to represent GIST, a biopsy should be done. An EUS-guided biopsy (in carefully selected patients and preferably of the primary lesions) is more desirable than a percutaneous biopsy [
29].