Viral Hepatitis: This is a common cause of liver inflammation in children, which can lead to periportal edema. The age of the patient and the isolated nature of the edema make viral hepatitis a plausible diagnosis.

Autoimmune Hepatitis: Although less common, autoimmune hepatitis can present with similar findings and should be considered, especially if there are other systemic symptoms or a family history of autoimmune diseases.
Wilson's Disease: This genetic disorder leads to copper accumulation in the liver and can cause liver inflammation and edema. It's more likely in younger patients and should be considered if there are neurological symptoms or a family history.
Drug-induced Liver Injury: Certain medications can cause liver inflammation and edema. Given the patient's age, this might be less likely but should be considered if the patient is on any medications.

Budd-Chiari Syndrome: This rare condition involves hepatic vein thrombosis, which can lead to liver congestion and edema. It's crucial to consider this diagnosis due to its potential severity and need for prompt intervention.
Veno-occlusive Disease: Also known as sinusoidal obstruction syndrome, this condition can cause liver edema and is particularly important to recognize in patients who may have undergone chemotherapy or have other risk factors.

Polycystic Liver Disease: While primarily a condition of adults, it can occasionally present in children. The presence of a family history would increase the likelihood of this diagnosis.
Congenital Hepatic Fibrosis: A rare genetic disorder that can cause liver fibrosis and potentially edema. It's usually associated with other systemic manifestations or a family history of similar conditions.
Lymphatic Disorders: Rare conditions affecting the lymphatic system, such as lymphangiomas, could potentially cause periportal edema, although this would be extremely uncommon in the context provided.