Infections originating in the submandibular and submental spaces commonly spread downward into the anterior mediastinum via the fascial planes of the neck. This occurs because the deep cervical fascia and investing layers create a continuous pathway from these spaces to the anterior mediastinum. Such spread can rapidly lead to mediastinitis, a life-threatening condition requiring prompt surgical drainage and broad-spectrum antibiotics. Understanding this anatomical relationship is vital in managing deep neck infections and preventing fatal complications.

Reference: Gray's Anatomy, Standring S., 42nd Edition.