Imaging in gastrointestinal stromal tumours: current status and future directions

Primary GIST with dumbbell-type morphology. Axial, contrast-enhanced CT demonstrates a large, solid, lobulate mass with both intraluminal and exophytic components related to the stomach with central low attenuation (arrow), consistent with a typical morphology for gastric GIST.

Metastatic GIST with complicated hepatic metastases. Axial, contrast-enhanced CT demonstrates multiple hepatic metastases in both lobes of the liver, several of these demonstrate a fluid–fluid level (arrow heads) likely due to internal haemorrhage, a known complication of GISTs. Note also the primary gastric GIST (arrow) showing internal calcific areas likely secondary to treatment.

Postoperative assessment of risk of relapse. M, mitotic figures; hpf, high power field; int, intermediate; V, very.

Follow-up schedule in organ-confined operable GISTs.

Histopathologic appearances (haematoxylin and eosin stain, ×400) of primary and post-treatment GISTs. A pre-treatment biopsy specimen (a) reveals a cellular lesion with frequent mitotic figures. After 6 weeks of imatinib treatment histopathological examination now demonstrates large areas of predominant myxoid degeneration (b).

Pitfalls of response assessment showing increase in size but with cystic change. Axial, contrast-enhanced CT (a) demonstrates an exophytic gastric GIST with soft-tissue elements (short arrow) and multiple hepatic metastases. The largest hepatic lesion demonstrates a fluid–fluid level (long arrow). (b) Follow-up CT 3 months post-treatment with imatinib demonstrates that both the primary GIST (short arrow) and the hepatic metastases (long arrow) have increased in size suggesting disease progression on conventional RECIST criteria. The lesions, however, now show predominant cystic attenuation and this is in keeping with treatment response despite the slight increase in size. (c) Follow-up CT at 6 months post-treatment demonstrates that the cystic change is maintained and now there is a decrease in size of both the gastric GIST (short arrow) and the hepatic metastases (long arrow) in keeping with continued response to treatment. Decrease in size can occur several months after cystic change limiting early response assessment by standard RECIST criteria.

Pitfalls of response assessment with development of spurious new liver lesions. Axial, contrast-enhanced CT (a) in the portal venous phase demonstrates an exophytic gastric GIST and unremarkable appearances of the liver. Follow-up post-imatinib treatment CT at 3 months (b) demonstrates multiple apparently new hypodense hepatic lesions (arrow heads) and a decrease in size of the primary gastric GIST (arrow). Findings are in keeping with a partial response to treatment despite the spurious new hepatic lesions. This should not be misinterpreted as disease progression as these appearances are due to post-treatment cystic change, which makes the hepatic lesions visible on the portal venous phase images; the lesions were previously isodense and apparently not seen.

Limited disease progression in GISTs with a nodule-within-a mass pattern. Axial, contrast-enhanced CT (a) demonstrates a predominantly low-density mass in the left supracolic omental region (arrow) with focal calcific areas in a patient taking imatinib for metastatic GIST. Follow-up CT (b) after 3 months demonstrates the development of a new, enhancing, solid nodule in the inferior portion of the previously noted supracolic omental mass (arrow), which otherwise has shown no significant change in size, in keeping with limited disease progression.

Response assessment on PET/CT. Baseline PET/CT image (a) performed in a patient with a metastatic GIST to assess response to a clinical trial drug after second-line treatment failed to show response. High-grade FDG uptake is seen in a primary small bowel GIST (short arrows) and also in the hepatic metastases. Four-week follow-up PET/CT (b) demonstrates persistent high-grade uptake in the primary tumour (short arrows) and in several new hepatic lesions (long arrows). Findings are in keeping with progressive disease.