Hepatic GIST metastases: an illustrative case series

Gastrointestinal stromal tumours (GISTs) are uncommon mesenchymal tumours affecting the gastrointestinal tract. The liver is one of the most common sites for metastatic disease from GISTs and may exhibit a variety of CT and MR imaging appearances. These imaging features can vary prior to and following treatment with tyrosine kinase inhibitors. We report on the spectrum of imaging appearances of hepatic GIST metastases on multiphase contrast CT imaging and hepatocyte-specific contrast enhanced MR. To our knowledge, there are no published series specifically focusing on the appearances of liver metastases from GISTs.

An awareness of the protean appearances and pitfalls on CT and MRI of hepatic GIST metastases, prior to and at different times along the treatment pathway, will assist in early diagnosis of liver metastases, accurate assessment of tumour response and detection of recurrent metastatic disease.

Assessment of arterially hyper-enhancing liver lesions using virtual monoenergetic images from spectral detector CT: phantom and patient experience

PURPOSE

To investigate a benefit from virtual monoenergetic reconstructions (VMIs) for assessment of arterially hyper-enhancing liver lesions in phantom and patients and to compare hybrid-iterative and spectral image reconstructions of conventional images (CI-IR and CI-SR).

METHODS

All imaging was performed on a SDCT (Philips Healthcare, Best, The Netherlands). Images of a non-anthropomorphic phantom with a lesion-mimicking insert (containing iodine in water solution) and arterial-phase images from contrast-enhanced patient examinations were evaluated. VMIs (40-200 keV, 10 keV increment), CI-IR, and CI-SR were reconstructed using different strengths of image denoising. ROIs were placed in lesions, liver/matrix, muscle; signal-to-noise, contrast-to-noise, and lesion-to-liver ratios (SNR, CNR, and LLR) were calculated. Qualitatively, 40, 70, and 110 keV and CI images were assessed by two radiologists on five-point Likert scales regarding overall image quality, lesion assessment, and noise.

RESULTS

In phantoms, SNR was increased threefold by VMI_40keV compared with CI-IR/SR (5.8 ± 1.1 vs. 18.8 ± 2.2, p ≤ 0.001), while no difference was found between CI-IR and CI-SR (p = 1). Denoising was capable of noise reduction by 40%. In total, 20 patients exhibiting 51 liver lesions were assessed. Attenuation was the highest in VMI_40keV, while image noise was comparable to CI-IR resulting in a threefold increase of CNR/LLR (CI-IR 1.3 ± 0.8/4.4 ± 2.0, VMI_40keV: 3.8 ± 2.7/14.2 ± 7.5, p ≤ 0.001). Subjective lesion delineation was the best in VMI_40keV image (p ≤ 0.01), which also provided the lowest perceptible noise and the best overall image quality.

CONCLUSIONS

VMIs improve assessment of arterially hyper-enhancing liver lesions since they increase lesion contrast while maintaining low image noise throughout the entire keV spectrum. These data suggest that to consider VMI screening after arterially hyper-enhancing liver lesions.

High-flow haemangiomas versus hypervascular hepatocellular carcinoma showing "pseudo-washout" on gadoxetic acid-enhanced hepatic MRI: value of diffusion-weighted imaging in the differential diagnosis of small lesions

AIM

To validate the usefulness of diffusion-weighted imaging (DWI) in the differentiation of high-flow haemangiomas showing pseudo-washout appearance on gadoxetic acid-enhanced hepatic MRI from small hypervascular hepatocellular carcinomas (HCCs).

MATERIALS AND METHODS

DWI (b=50, 800 s/mm²) with apparent diffusion coefficient (ADC) maps for 50 haemangiomas (6.4±2.9 mm) showing intense enhancement on arterial dominant phase imaging and hypointensity on transitional and/or hepatobiliary phase imaging during gadoxetic acid-enhanced MRI were retrospectively analysed and compared with that of 113 hypervascular HCCs (12.8±3.7 mm). In addition to measurement of mean ADC values on DWI and contrast-to-noise ratio (CNR) on corresponding T2-weighted imaging, qualitative analysis of DWI was performed for each lesion by two independent observers using a five-point scale.

RESULTS

Both of mean ADC value (1.902 versus 0.997×10^-3 mm²/s) and mean CNR (119.2 versus 36.9) for haemangioma were significantly larger than for HCC (p<0.001). On receiver operating characteristic (ROC) analysis, an area under the curve (AUC) of 0.995 for ADC values was significantly larger than 0.915 for CNRs (p=0.002). When the ADC value of 1.327×10^-3 mm²/s was used as the threshold for the diagnosis of haemangioma, the sensitivity and specificity were 98% and 97.3%, respectively. The mean sensitivity and specificity of qualitative analysis for the differentiation of haemangioma from HCC were 92% and 99.1%, respectively.

CONCLUSION

For high-flow small haemangiomas showing pseudo-washout appearance during gadoxetic acid-enhanced hepatic MRI, high b-factor DWI including an ADC map may provide additional information to enhance the confidence to exclude small hypervascular HCCs.

Magnetic Resonance Imaging of Liver Metastasis

Liver magnetic resonance imaging (MRI) is becoming the gold standard in liver metastasis detection and treatment response assessment. The most sensitive magnetic resonance sequences are diffusion-weighted images and hepatobiliary phase images after Gd-EOB-DTPA. Peripheral ring enhancement, diffusion restriction, and hypointensity on hepatobiliary phase images are hallmarks of liver metastases. In patients with normal ultrasonography, computed tomography (CT), and positron emission tomography (PET)-CT findings and high clinical suspicion of metastasis, MRI should be performed for diagnosis of unseen metastasis. In melanoma, colon cancer, and neuroendocrine tumor metastases, MRI allows confident diagnosis of treatment-related changes in liver and enables differential diagnosis from primary liver tumors. Focal nodular hyperplasia-like nodules in patients who received platinum-based chemotherapy, hypersteatosis, and focal fat can mimic metastasis. In cancer patients with fatty liver, MRI should be preferred to CT. Although the first-line imaging for metastases is CT, MRI can be used as a problem-solving method. MRI may be used as the first-line method in patients who would undergo curative surgery or metastatectomy. Current limitation of MRI is low sensitivity for metastasis smaller than 3mm. MRI fingerprinting, glucoCEST MRI, and PET-MRI may allow simpler and more sensitive diagnosis of liver metastasis.

Vascular anomalies: hemangiomas and beyond--part 2, Slow-flow lesions

OBJECTIVE

The purpose of this article is to review the medical literature and the current classification of the vascular anomalies to clarify common misconceptions and provide guidance for imaging and treatment. In this second article of a two-part series, we focus on slow-flow vascular anomalies.

CONCLUSION

Nonuniformity of terminology across the medical literature hampers understanding of vascular anomalies. A familiarity with the classification and biology on which it is based are essential for accurate and precise diagnosis.

"Pseudo washout" sign in high-flow hepatic hemangioma on gadoxetic acid contrast-enhanced MRI mimicking hypervascular tumor

OBJECTIVE

The purpose of this article is to describe the "pseudo washout" sign of high-flow hepatic hemangioma that mimics hypervascular tumor on gadoxetic acid-enhanced MRI.

CONCLUSION

High-flow hemangiomas might show relatively low signal intensity because of gadoxetic acid contrast uptake in the surrounding normal liver parenchyma during the equilibrium (3-minute delay) phase. Such findings are called pseudo washout and can mimic hypervascular hepatic tumors. However, high-flow hemangioma can be diagnosed by observing bright signal intensity on T2-weighted imaging, arterial phase-dominant enhancement, pseudo washout sign during the equilibrium phase, and isointense or slightly increased signal intensity on subtraction images.