Acute mediastinitis is uncommon. When it occurs, it usually follows an esophageal perforation or thoracic surgery. We report on a case of a 2-year-old girl with non traumatic mediastinitis secondary to a pharyngitis, due to Staphylococcus aureus. The anatomic pathways that connect the cervical region with the mediastinum explains how the infection can spread within the cervicothoracic spaces. Knowledge of this anatomy is also important in evaluating the possible causes of symptoms and signs in this area, and the possible complications of infections in these regions. The treatment associates antibiotics and drainage of the abscess by either surgical procedure or computed tomography guided selective needle aspirations.