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 (P0.05)

and similar to that of skeletal muscle (48.9±2.28) HU (P0.05). 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.