Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the small bowel, arising from interstitial cells of Cajal (gastrointestinal pacemaker cells). 20-30% of all GISTs are located in the small bowel (stomach 60% most common). c-KIT (CD117) or PDGFRA tyrosine kinase receptor mutations play a central role in pathogenesis. Typically shows exophytic (outward from lumen) growth — intraluminal component is small and luminal obstruction is rare. On CT, hypervascular, heterogeneously enhancing mass that may show central necrosis/ulceration. Size and mitotic index determine risk classification. Imatinib (tyrosine kinase inhibitor) targeted therapy has been groundbreaking.
Age Range
40-80
Peak Age
60
Gender
Equal
Prevalence
Uncommon
GIST arises from interstitial cells of Cajal that regulate gastrointestinal motility. Gain-of-function mutation of the c-KIT (CD117) proto-oncogene plays a central role in pathogenesis — c-KIT exon 11 mutation is found in 80-85% of cases. This mutation leads to constitutive activation of the tyrosine kinase receptor → uncontrolled cell proliferation and evasion of apoptosis. PDGFRA mutation is found in 5-8%, 'wild-type' in 10-15%. The tumor arises from the submucosal layer showing exophytic growth — extends outward from the serosal surface into the mesenteric/peritoneal cavity. Intraluminal component is generally small because growth direction is outward. Central necrosis and cavitation develop in large tumors — due to ischemic necrosis in the tumor center where rapid growth continues independent of vascular supply. This cavitation explains the heterogeneous enhancement pattern on CT.
Mass growing outward from the bowel wall — characteristic growth pattern of GIST. Intraluminal component is small and obstruction is rare. Exophytic growth distinguishes from adenocarcinoma (intraluminal/annular) and lymphoma (diffuse wall thickening).
Mass growing exophytically from the small bowel wall on arterial phase, showing prominent hypervascular enhancement. Small tumors (<5 cm) show homogeneous enhancement, while large tumors show heterogeneous enhancement due to central necrosis. Mass extends into the mesenteric/peritoneal cavity and may deform the bowel lumen by external compression. Tumor-bowel wall connection is generally broad-based.
Report Sentence
Mass growing exophytically from the small bowel showing prominent hypervascular arterial phase enhancement is observed, consistent with GIST.
Central necrosis in large tumors (>5 cm) on portal venous phase — low-density, non-enhancing central area with enhancing peripheral viable tumor tissue. Cavitation may communicate with lumen showing air-fluid level. Ulceration may create a crater on the mucosal surface leading to GI bleeding.
Report Sentence
Central necrosis/cavitation and peripheral enhancement in the mass are observed, consistent with large GIST.
Heterogeneous signal on T2-weighted images — solid components show intermediate to high T2 signal, necrotic/cystic areas show very high T2 signal, hemorrhagic areas show T2 hypointense signal. This heterogeneous pattern reflects the complex internal structure of GIST. Solid components show diffusion restriction on DWI.
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Heterogeneous T2 signal pattern in the mass on MRI is observed, consistent with solid, necrotic and hemorrhagic components.
Variable FDG uptake in primary tumor and metastases on FDG PET-CT — high-grade GISTs show high SUVmax while low-grade GISTs may show low uptake. PET-CT's most important role is early evaluation of imatinib treatment response — in tumors responding to treatment, FDG uptake decreases before size reduction (metabolic response).
Report Sentence
FDG uptake in the mass on PET-CT is observed, metabolic activity level recorded as reference value for treatment response follow-up.
Hypervascular liver metastases and/or peritoneal nodules on portal venous phase. Liver metastases show prominent arterial phase enhancement. Peritoneal metastases (sarcomatosis) are seen as nodular structures on mesenteric and peritoneal surfaces. Under imatinib treatment, metastases may show cystic degeneration ('pseudoprogression').
Report Sentence
Hypervascular liver metastases are observed, consistent with metastatic GIST.
Diffusion restriction in solid tumor components on DWI — bright signal on high b-value images, low values on ADC maps. Necrotic/cystic areas do not show diffusion restriction. DWI is valuable in solid-cystic differentiation and treatment response monitoring — ADC of solid component increases with imatinib response.
Report Sentence
Diffusion restriction in solid components on DWI is observed, consistent with cellular tumor tissue.
Criteria
Size ≤5 cm and mitotic index ≤5/50 HPF
Distinct Features
Homogeneous enhancement, minimal necrosis. Well-defined small exophytic mass on CT. Surgical resection curative. Low recurrence risk (5%).
Criteria
Size >10 cm or mitotic index >10/50 HPF or rupture
Distinct Features
Heterogeneous enhancement, prominent central necrosis. High metastasis risk (liver, peritoneum). Adjuvant imatinib 3 years recommended.
Criteria
c-KIT and PDGFRA mutation negative — may be SDH deficiency or NF1 associated
Distinct Features
Limited imatinib response. Multifocal gastric GIST in SDH deficiency (Carney triad). Multifocal small bowel GIST in NF1.
Distinguishing Feature
Adenocarcinoma shows annular/intraluminal growth and obstruction; GIST grows exophytically and obstruction is rare
Distinguishing Feature
In lymphoma, diffuse wall thickening and aneurysmal dilation; in GIST, exophytic mass and cavitation
Distinguishing Feature
In carcinoid, small submucosal primary + large desmoplastic mesenteric mass; in GIST, exophytic large mass and no desmoplasia
Distinguishing Feature
In metastasis, known primary malignancy and multiple lesions; GIST is usually solitary and primary bowel origin
Urgency
urgentManagement
surgicalBiopsy
NeededFollow-up
3-monthGIST treatment is determined by risk classification. Surgical resection is the primary treatment — segmental resection is sufficient and wide lymphadenectomy is not needed (GIST rarely metastasizes to lymph nodes). Adjuvant imatinib (400 mg/day, 3 years) reduces recurrence risk in high-risk GIST. Imatinib is first-line treatment in metastatic/inoperable GIST — response rate >80%. If imatinib resistance develops, sunitinib (2nd line) or regorafenib (3rd line) is used. Treatment response is monitored with CT — Choi criteria (size + density) are superior to RECIST.
GIST responds to targeted therapy with imatinib (tyrosine kinase inhibitor). Size and mitotic index determine malignancy risk. Lesions >5cm are high risk. Surgical resection is the primary treatment. PET-CT is important for treatment response assessment.