Which sign is characterized by an egg on a string appearance?

The sign characterized by an "egg on a string" appearance is most commonly associated with transposition of the great arteries (TGA). In TGA, the aorta and pulmonary artery are switched, leading to two separate circulatory systems. The chest X-ray in this condition typically shows a narrow appearance of the mediastinum and the heart resembling an "egg" rather than the usual shape, hence the term "egg on a string." This finding provides a crucial visual diagnosis in pediatric patients and indicates the need for immediate medical intervention.

The other conditions listed have distinct imaging characteristics that do not resemble the "egg on a string" appearance. For instance, coarctation of the aorta may present with differential blood pressures and a characteristic "figure 3" sign on imaging, while persistent pulmonary hypertension usually shows enlarged pulmonary arteries and right ventricular hypertrophy on chest X-rays. Heart failure might reflect cardiomegaly and pulmonary venous congestion but would not present with the specific morphology indicative of TGA. Understanding these imaging characteristics helps in diagnosing the conditions accurately and determining appropriate management strategies.