MRI Semiotics Features and Difficulties of Differential Diagnosis of Hepatic Metastases from Neuroendocrine Tumours

Abstract

Relevance: Isolated bilobar multifocal hepatic lesion is consider to be the most common metastatic neuroendocrine tumor(NET) growth pattern. Underestimation of the metastatic burden in the NET patients at the initial diagnosis frequently occurs, thus leading to a high postoperative recurrence rate (more than 60 % of cases within 5 years).Purpose: To identify the MRI-hallmarks of liver metastatic NETs and to present the most difficult diagnostic cases.Material and methods: 103 patients with histology confirmed liver metastatic NET were enrolled in the study. All patients underwent abdominal contrast-enhanced (CE) MRI. A total of 241 lesions were assessed. Quantitative indicators of signal intensity (SI) on native and post-contrast T1-weighted images (WI) were measured in metastases. Additionally, the shape, contours, surface of metastases, SI on native images, characteristics of CE, the presence of hemoglobin degradation products and the boundary levels in the structure of metastases were qualitatively assessed.Results: Metastatic liver disease in NET is mostly multifocal: 78 (75.7 %) patients had 5 or more lesions. Metastases were round in 53.5 % of cases, oval in 17.5 % of cases, irregular in 29 % of cases. In 61 % of cases, the contours of the lesions were clear, in 39 % — indistinct. Smooth and bumpy surface of metastases was determined in 31.5 % and 68.5 % of cases, respectively. The presence of hemoglobin degradation products in the structure of metastases was determined in 26.2 % of patients, the formation of the boundary levels — in 8.1 % of patients. Most of the lesions had a hyperintense signal on T2-WI with and without FS and a hypointense signal on native T1-WI. The proportions of actively, moderately and poorly MR contrast agent (MRCA) enhanced lesions were 30.8, 32.6 and 36.6 %, in the arterial phase and 16.3, 55.4 and 28.3 % in the venous phase, respectively. The apparent diffusion coefficient (ADC) values varied significantly. In some cases, small metastatic NET were visualized only in the arterial phase of CE and were not detected on other MRI sequences, thus requiring differentiation from other hepatic hypervascular lesions.Conclusion. The MRI semiotics features of hepatic metastases from NETs is described. Small flesions of active accumulation of MRCA in the arterial phase in the presence of primary NET must be differentiated from metastatic lesions.