Epidemiology and presentation
There is no reported significant sex difference [3].
Grading of malignancy is a continuum based on assessment of tumor size and mitotic index [4].
The median survival with metastatic GIST has been calculated as 20 months but in those patients with locally recurrent tumor is 9–12 months [3].
Small lesions are rarely symptomatic and are usually benign,
often having been detected incidentally.
Larger mass often demonstrate an exophytic pattern of growth,
toward the peritoneal cavity.
In tumors larger than 2 cm,
the overlying mucosa can be focally ulcerated because of pressure necrosis with possible signs and symptoms of gastrointestinal bleeding,
such as hematemesis,
melena,
and iron-deficiency anemia.
When GISTs reach a large dimension may cause bowel obstruction or intussusception.
Growth pattern of lesions
GISTs can grow in an endoluminal,
exophytic,
or mixed (dumbbell-shaped) pattern.
Intramural lesions arise in the wall of the gastroenteric tract,
generally within the submucosa or muscularis propria,
often with intact overlying mucosa.
CT findings
CT is important for diagnosis and staging in the majority of patients,
helping to define endoluminal and exophytic extension.
Intramural tumor mass has smooth margins,
homogeneous density and more or less uniform contrast enhancement.
Sometimes calcifications and necrotic-hemorrhagic areas are appreciable in larger masses.
For a radiologic evaluation of the stomach,
adequate gastric distention is important to differentiate prominent gastric rugae from true masses.
A multiphasic contrast enhanced CT (CECT) study is helpful after unenhanced CT acquisition:
· Arterial phase (30 sec)
· Portal venous phase (70-80 sec)
The unenhanced CT is helpful for assessing the presence of calcifications.
The various layers of the gastric wall cannot be differentiated on CT images,
the mucosa can usually be distinguished from other layers by virtue of its prominent enhancement during the arterial phase and an intramural mass may be seen as a low-attenuation filling defect.
In a later phase of contrast enhancement,
the gastric wall may appear as a single enhancing layer.
Hypervascular liver metastases could be missed on portal venous phase images [5].
Metastases
GISTs rarely give lymph node metastases.
Metastasis mainly occurs in the liver and peritoneum.
Mimics,
differential diagnosis
GISTs may mimic more common such as pancreatic and oesophageal tumours; frequently small bowel GISTs mimic bowel lymphoma.
GISTs treatment
The principal treatment for GIST is surgery,
involving wide local excision to achieve “en bloc” removal of the whole tumour (R0 resection,
with not involved margins).
R0 resection has been shown to be a good prognostic indicator and patients with involved margins have a high incidence of metastases [6].