Abstract: Background and purpose: Since the detection of renal neoplasm is increasing, it's important to distinguish myomatous angiomyolipoma (mAML) from malignant tumors. This study aimed to investigate the imaging features of renal mAML on computer tomography (CT) and improve the accuracy of diagnosis and differential diagnosis. Methods: Ten patients were diagnosed with mAML. The cases were composed of 4 men and 6 women, with a mean age of 53.2 years (range 38-64). Among all of the cases, the percentage of spindle cell is more than 70%. Two radiologists reviewed all of the images to evaluate general characteristics, imaging features on unenhanced CT and enhanced CT. The mean attenuation on the unenhanced CT of mAML, normal renal parenchyma and skeletal muscle was compared by the paired-sample t test. Results: Among all of the tumors, nine lesions were solitary, and the other one was accompanied with typical AML. Six lesions were at the left kidney while four lesions were at the right side. Five lesions located intracapsularly. All the lesions were well-defined, nine of them were regular. The tumor sizes ranged from 15 to 80 mm with mean (43±19) cm. Intratumoral macroscopic fat, cystic degeneration and vessels were found in two lesions, two lesions and three lesions, respectively. Calcification or hemorrhage was not detected in any cases. On unenhanced CT, 70% cases were hyperattenuating. Eight cases were homogeneous or slightly heterogeneous. The mean attenuation of the tumor lesions on unenhanced CT was (48.60±5.50) HU, which was higher than that of normal renal parenchyma (39.70±6.67) HU (P<0.05), and similar to that of skeletal muscle (48.9±2.28) HU (P>0.05). After intravenous injection of contrast media, seven cases were categorized as the slightly heterogeneous or heterogeneous enhancement type. Four cases showed a weak enhancement whereas five cases were with a moderate enhancement. The gradual, prolonged and early washout enhancement patterns were observed in 40%, 40%, and 20% of the cases, respectively. Conclusion: The radiological appearance of mAML had a tendency to be hyperattenuating on unenhanced CT images without macroscopic fat; it could be homogeneous or slightly heterogeneous on unenhanced scans. After the injection of contrast agent, mAML tended to have a weak or moderate, lightly heterogeneous to heterogeneous enhancement, and it could demonstrate gradual and prolonged enhancement patterns.

Key words: Renal, Myomatous angiomyolipoma, Computed tomography