Hepatocellular carcinoma (HCC) is the fifth most common malignant tumor, and its mortality ranks third among all malignancies. HCC affects 620,000 new patients and causes 600,000 deaths every year posing a serious threat to people's health (1). Nearly half of patients with primary hepatocellular carcinoma (PHC) die due to lymph node metastasis (2). At present, 90% of PHC is developed from hepatitis and liver cirrhosis, and the risk of PHC is even greater after infection with hepatitis B and C (3). Cirrhosis also has a 35% risk of malignant transformation (4). Other causes of chronic liver injury include alcoholism, cholestasis, metabolic disorders, autoimmune and steatohepatitis (5,6). Due to the lack of obvious clinical features in early stage of HCC, most patients miss the best treatment time by the time of diagnosis, leading to a poor prognosis because of the high degree of malignancy and metastasis caused by HCC (7).

In recent years, imaging techniques have been continuously developed, and it is very important to be familiar with the characteristics and advantages of different imaging methods. It is of great significance to select appropriate imaging examination methods according to patient's pathological conditions to improve the early diagnosis of HCC and improve patients' survival. Therefore, the diagnosis of small HCC has become a hot topic in recent years (8–11). Small HCC is defined as a single tumor nodule with a diameter ≤3 cm (12,13). The most commonly used imaging methods for diagnosing HCC in clinical practice are computed tomography (CT) and magnetic resonance imaging (MRI) (14). Compared with CT, MRI is more complex. Each sequence has a different organization-contrast mechanism, and each sequence is irreplaceable. MRI can provide liver anatomy images and information about patients' physiological and metabolic function (15,16). However, MRI examinations are expensive, scan time is long and there are contraindications for patients. Therefore, MRI examinations are often used as supplementary means for CT examinations. The purpose of this study was to analyze the diagnostic value of CT and MRI examinations for small HCC in patients, and to analyze the prognostic factors of PHC patients.

The main functions of liver are metabolism and blood supply. Occurrence and development of primary HCC are complex, and its early diagnosis has important significance in improving the prognosis and quality of life of patients (17). MRI and CT scans are clinically important screening methods for diagnosing liver cancer, and can provide detailed parameters for specific tumor conditions. It has been reported that an important factor in the diagnosis and evaluation of postoperative clinical efficacy is the detection rate of small HCC (18). Because of the high cost, combination of MRI and CT has not been popularized in clinical application. MRI and CT have their own advantages and disadvantages in clinical applications, and application of single technique may cause misdiagnosis or diagnostic errors. For screening of small HCC, diagnostic accuracy of MRI is higher than that of CT scan (19–21). Therefore, in the actual clinical application, patient's condition should be combined to improve diagnostic efficiency. Patients who are at risk but do not have obvious symptoms should be checked regularly to increase the early diagnosis rate and improve therapeutic effects.

This study showed that MRI reached screening sensitivity of 78.82%, specificity of 78.46%, accuracy of 78.67%, positive predictive value of 82.72% and negative predictive value of 73.91%. CT screening showed a sensitivity of 62.35%, a specificity of 73.85%, an accuracy of 67.33%, a positive predictive value of 75.71%, and a negative predictive value of 60.00%. Differences in sensitivity, accuracy, and negative predictive value between MRI and CT screening were statistically significant (P<0.05). There was no statistically significant difference between two methods in specificity and positive predictive value (P>0.05). The diagnostic performance of MRI is better than that of CT. Consistent findings were found in the study reported by Hwang et al (22). Although CT scan technology has high temporal and spatial resolution, it has limitations in the screening of small HCC. Differences in tumor lesions and uneven liver density, CT may not be active in the diagnosis of small HCC (23). Univariate analysis showed that factors affects the prognosis of patients with HCC included age, background of hepatitis B cirrhosis, tumor stage, and portal thrombosis. Cox multivariate regression analysis showed that background of liver cirrhosis, tumor staging, and portal vein embolization were risk factors for the prognosis of HCC and the differences were statistically significant (P<0.05). McNally et al (24) also reported that cirrhosis, tumor staging, and portal thrombosis were independent risk factors for poor prognosis of HCC. Liver cirrhosis causes changes in the microenvironment of the liver, resulting in circulation of hepatoma cells and the emergence of new lesions. The number, size, degree of infiltration, and metastasis of tumors are all related to tumor stage, and have an impact on the survival of patients. If portal embolism affects normal blood supply to the liver, tumor may spread via the portal route (25).

In conclusion, the diagnostic efficacy of MRI in the diagnosis of small HCC is better than that of CT scan screening. When CT screening is not sufficient to accurately determine liver tumor lesions, MRI can provide a more precise imaging basis. Univariate and Cox multivariate regression analysis showed that the background of hepatitis B liver cirrhosis, tumor staging, and portal vein embolization were independent risk factors for poor prognosis of HCC. Therefore, developing individualized comprehensive treatment programs based on different situations of patients, regularly reviewing and timely taking measures for complications may effectively prolong the survival of patients. Thus, within the affordable scope of medical expenses, MRI diagnosis can provide important basis and screening method for appropriate treatment of HCC.