18F-FDG PET/CT and MR imaging features of liver metastases in gastrointestinal stromal tumors: a cross-sectional analysis

Abstract

Background: Early detection of gastrointestinal stromal tumor (GIST) liver metastases is crucial for the management and prognosis. In our experience, GIST liver metastases can display hypermetabolism on ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) and marked enhancement on magnetic resonance imaging (MRI), which are uncommon in other tumors before treatment. Most literature focus on the imaging evaluation, prognosis after treatment and less is known about imaging features on both imaging methods before treatment. This study analyzes the imaging features of newly diagnosed GIST liver metastases on ¹⁸F-FDG PET/CT and MRI, with goal of improving diagnostic accuracy.

Methods: This retrospective study included 55 patients with pathological or radiographical confirmed GIST liver metastases who underwent PET/CT (n=29), MRI (n=22), or both methods (n=4). PET/CT and MRI interpretation including lesion's morphologic features, number, density or signal intensity, hemorrhage, cystic changes or necrosis, maximum standardized uptake value (SUV_max) of liver metastases and liver background on PET imaging, degree and pattern of enhancement on MRI were obtained by two experienced nuclear medicine physicians and two radiologists respectively. Data are presented as numbers, percentages, means ± standard deviations or median (interquartile range). The correlation between diameter and SUV_max of metastases, and primary tumor SUV_max and synchronous liver metastases SUV_max were analyzed by Spearman's rank test.

Results: On PET/CT visual analysis, 38.9%, 23.9%, and 37.2% of lesions showed significant hypermetabolism, slightly higher metabolism, and equal or lower metabolism than liver, respectively. There was a weak correlation between the diameter and SUV_max of liver metastases (r_s =0.370, P<0.001), and a moderate correlation between SUV_max of synchronous liver metastases and the primary tumors (r_s =0.492, P<0.001). On contrast-enhanced MRI, 90.8% of lesions showed heterogeneous enhancement in the arterial phase with the variable presentation, and 74.3% had different enhancement patterns between margins and intratumoral parenchyma.

Conclusions: Liver lesions in GIST displaying significant, slight hypermetabolism on ¹⁸F-FDG PET/CT, marked or heterogeneous gradual enhancement within the intratumoral parenchyma with ring-like enhancement on MRI may denote the diagnosis of liver metastasis. However, GIST liver metastases may also display equal or lower metabolism than liver parenchyma on PET, making small lesions more difficult to diagnose.

Keywords: Gastrointestinal stromal tumor (GIST); imaging features; liver metastases; magnetic resonance imaging (MRI); positron emission tomography (PET).

Figure 1

Imaging findings of 3 GIST patients with liver metastases without treatment who underwent both ¹⁸F-FDG-PET/CT and MRI. (A) Imaging data of a 45-year-old man with solitary liver metastasis from gastric stromal tumor. CT image shows a hypodense nodule (red arrow) in the right lobe of the liver with unclear margins. PET image shows that the metabolism was significantly higher than the liver parenchyma, even higher than the primary tumor (white arrow), which was considered to be a type A lesion on visual analysis (hypermetabolism). Ring-like hyper-enhancement can be seen in the arterial and portal venous, and delayed phases and the intratumoral parenchyma showed gradual mild to moderate enhancement on MRI. (B) Imaging data of a 50-year-old female patient with multiple liver metastases from small intestinal stromal tumor. CT image shows multiple round masses in the liver with clear margins and slightly heterogeneous density. PET image of the largest lesion (red arrow) shows slightly higher metabolism in some areas of the mass, which was slightly higher than the liver parenchyma. Visual analysis showed a type B lesion (slightly hypermetabolism). The MR image showed rim enhancement and inner heterogeneous gradual enhancement, even partial areas was equal to or slightly higher than liver parenchymal in delayed phase. The other two lesions (white arrows) showed no hypermetabolism compared to the liver background, and no radioactive defect. These were type C lesions on visual analysis (iso- or hypo-metabolism). MRI shows marginal enhancement with inner heterogeneous gradual enhancement which was higher than liver parenchyma in the delayed phase. (C) Imaging data of a 53-year-old female patient with multiple liver metastases from colonic stromal tumor. The lesion in the left lobe of the liver (white arrow) showed significantly hypermetabolism on PET (type A lesion) with gradual enhancement on MRI. Another lesion in the right lobe (red arrow) was a missed diagnosis on PET/CT because of the presence of fatty liver disease, which showed no definite abnormal density on unenhanced CT and no hypermetabolism on PET. Ring-like enhancement of the margin and mild enhancement of the intratumoral parenchyma can be seen on MRI. GIST, gastrointestinal stromal tumor; ¹⁸F-FDG, ¹⁸F-fluorodeoxyglucose; PET, positron emission tomography; CT, computed tomography; MRI, magnetic resonance imaging.

Figure 2

Magnetic resonance imaging of a 68-year-old female patient with postoperative haptic recurrence 4 years after primary tumor resection shows different enhancement patterns. From left to right: arterial phase, portal venous phase, and delayed phase imaging at the same cross-sectional level. The first row of lesions (black arrows) shows obvious enhancement in the arterial phase, and decreased enhancement in the portal venous phase and delayed phase with marginal ring-like enhancement. The second row of lesions (white arrow) show obvious enhancement in all three phases. The third row of lesions (red arrow) show heterogeneous gradual enhancement in the arterial and portal venous phases, and obvious enhancement in the delayed phase.