Introduction: Accessory liver lobe (ALL), an autonomous island of normal liver parenchyma, is a rare congenital anomaly that is difficult for preoperative diagnosis and often identified incidentally. It can also be accompanied with benign or malignant diseases, which is extremely rare. There are only 3 cases of focal nodular hyperplasia (FNH) detected on ALL reported by previous literature.
Patient concerns: A 33-year-old woman was incidentally diagnosed with a mass in left upper quadrant abdomen by a routine ultrasound examination. Doppler ultrasound revealed that the mass was attached to left liver lobe with a vascular pedicle. A spoke-wheel artery with diffuse enhancement during hepatic arterial phase was visualized on contrast-enhanced ultrasound, and the mass was continuously hyper-enhanced with a hypo-enhanced intralesional scar during the portal and delayed phase. And contrast-enhanced computed tomography showed a similar enhancement mode of the mass.
Diagnosis: The mass was resected and postoperative histopathologic result of the lesion revealed a nodular hyperplastic parenchyma with a central fibrous scar, without tumor cells. And a final diagnosis of FNH on ALL was determined accordingly.
Interventions: Mass resection was conducted according to patient's demand.
Outcome: After general postoperative administration, the patient was discharged. Then, she had been undergoing regular serological tests and imaging examinations in our hospital for 24 months.
Conclusion: The finding of a mass connecting with liver by a stalk should alert the clinician of the possibility of ALL, as well as benign or malignancies on an ALL. This is the first case of FNH on ALL preoperatively confirmed by contrast-enhanced ultrasound. We suggest that an integrated radiologic approach is crucial to evaluate an incidentally detected, asymptomatic abdominal focal mass.