Gastrointestinal stromal tumour

Gastrointestinal stromal tumours (GIST) are the most common mesenchymal tumours of the gastrointestinal tract. They account for ~5% of all sarcomas. They respond remarkably well to chemotherapy. 

Previously these tumours have been variably referred to as leiomyomas, leiomyosarcomas, leiomyoblastomas.

GISTs usually occurs after the age of 40, with most seen in older patients 1 except when associated with tumour syndromes when they may present earlier and are often multiple (see below). It is equal in both male and female with possible slight male predilection.

Clinical presentation is variable and reflects the variability of radiographic appearances, location (see below) and biological behaviour. Many tumours are incidentally identified on imaging for other indications but mostly present with dysphagia. Some tumours, on the other hand, are aggressive and present with metastases or symptoms relating to local disease 1. Ulceration is seen in 50% of tumours although it is commoner in large tumours 1. Haemorrhage may occur, with presentation relating to gastrointestinal bleeding.

GISTs are believed to arise from the interstitial cells of Cajal 2-3, with 95% staining positive for CD117 (c-KIT) and 70% for CD34 2. The former is a tyrosine kinase growth factor receptor and the target of ST-571 (imatinib/Gleevec/GlivecTM1.

As the tumours are intramural but submucosal, the overlying mucosa often appears intact on pathological and imaging assessment.

Grading GISTs requires assessment of both tumour size and mitotic index 3. Smaller lesions have less aggressive biological behaviour, as do stomach GISTs when compared to tumours elsewhere along the gastrointestinal tract 3.

Macroscopic appearance

They are rounded with frequent haemorrhage. Larger tumours may also demonstrate necrosis and cystic change 1-2. Size is variable, ranging from 1 to 30 cm 1.

Histology

Histology demonstrates a relatively cellular tumour composed of spindle cells (70-80%) and plump epithelioid cells (20-30%) 1-2. They appear to arise from the muscularis propria layer.

Associations

The vast majority of GISTs are sporadic. However, they occasionally occur in the setting of a recognised syndrome, including 2:

Location and classification

Common sites of involvement include 8:

GISTs occur not only anywhere along the gastrointestinal tract, but also in the mesenteryomentum and retroperitoneum, these are then called extra-gastrointestinal GISTs 1,4.

Metastatic lesions may also be seen in cases of malignant extra-gastrointestinal GISTs 7.

Specific appearances will vary according to location (see above), but in general, these tumours appear as rounded soft tissue masses, arising from the wall of a hollow viscus (most commonly the stomach) and projecting into the lumen, or less commonly outwards from the serosa. Mucosal ulceration is present in 50% of cases 1 with large necrotic cavities communicating with the lumen also seen.

Plain radiograph

When large, soft tissue density displacing bowel loops may be seen, which is, of course, non-specific.

Fluoroscopy

On upper abdominal studies, filling defect projecting from the wall of the stomach may be seen, with overlying ulceration or cavitation. The tumour margins are normally seen as smooth and may form right or obtuse angles with the adjacent mucosa due to its intramural origin.

CT

Appearances vary with size and location. Typically the mass is of soft tissue density with central areas of lower density when necrosis is present (usually in larger tumours) that occasionally appear as fluid-fluid levels.

As the tumours are often exophytic, it can be difficult to delineate them on CT if the stomach is distended with barium, though the non-enhancing central necrotic area may be helpful. A deep crescent-shaped ulceration demonstrating an internal air-fluid level may be referred to as the Torricelli-Bernoulli sign 9.

Enhancement is typically peripheral (due to central necrosis) 1. Calcification is uncommon (3%) 1.

Metastases (distant, peritoneal, omental) or direct invasion into adjacent organs may be seen in more aggressive lesions. Lymph node enlargement is not a feature 1.

MRI

The presence of necrosis, haemorrhagic and cystic change make appearances variable:

  • T1:
    • low signal intensity solid component
    • enhancement is usually present, and predominantly peripheral in larger lesions
  • T2: high signal intensity solid component

Surgical en-bloc resection is the primary mode of therapy for GISTs 4. Up to 50% of all GISTs will have evidence of metastatic disease at the time of presentation 3, which significantly impacts prognosis.

Adjuvant chemotherapy with ST-571 (imatinib) is effective in the majority of cases and has had a dramatic impact on prognosis even with only one year of therapy, reducing recurrence at one year from 17% to 3% 4. Longer treatment regimes (2-3 years of imatinib) are currently under investigation 4. Other second-line agents (e.g. sunitinib) are also being studied and used for patients with imatinib-resistant tumours.

Historically, before ST-571 (imatinib) up to 85% of tumours would locally recur or develop subsequent distal metastases despite treatment 3,4 and had proven to be resistant to standard chemotherapy 4.

FDG-PET may be used in monitoring treatment response and is considered superior to CT in monitoring treatment response in the initial phases of treatment10.

General imaging differential considerations include:

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Article information

rID: 6758
Section: Pathology
Tag: stomach
Synonyms or Alternate Spellings:
  • GIST
  • Gastrointestinal stromal tumours
  • Gastrointestinal stromal tumor
  • Gastrointestinal stromal tumour (GIST)
  • Gastrointestinal stromal tumors
  • GIST's

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Cases and figures

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    Macro (distal gas...
    Figure 1: gross pathology - gastric GIST
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    Case 1
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    GIST stomach
    Case 2
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    Case 3: GIST
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    Case 4: jejunal GIST
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    Case 5: H & E stain
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    Case 7
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    Case 8
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    Case 9: on ultrasound
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    GIST - Coronal re...
    Case 10
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    Case 11
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    Case 12: small omental lesion
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    Case 13: large intra-abdominal GIST
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    Case 14: oesophageal GIST - arrowed
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    Case 15: duodenal GIST
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    Case 16: with hepatic metastases
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    Case 17
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    Case 18: on ultrasound
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