Macrocephaly, defined as a head circumference greater than 2 standard deviations above the mean, is a relatively common presenting symptom in the pediatric population at routine well-child examinations and a common indication for neuroimaging. Multiple imaging modalities are complementary in evaluating macrocephaly, including US, CT, and MRI. The differential diagnosis for macrocephaly is broad, and many disease processes lead to macrocephaly only when the sutures are open. In patients with closed sutures, these entities instead lead to increased intracranial pressure, according to the Monroe-Kellie hypothesis, which states that there is an equilibrium between intracranial constituents due to the fixed intracranial volume. The authors describe a useful paradigm for classifying macrocephaly by identifying which of the four components of the cranium (ie, cerebrospinal fluid, blood and vasculature, brain parenchyma, or calvarium) has an increased volume. Patient age, additional imaging findings, and clinical symptoms are also useful features. Most cases in the pediatric population are due to increased cerebrospinal fluid spaces, such as benign enlargement of the subarachnoid space, which must be carefully distinguished from subdural fluid collections in patients with accidental or nonaccidental trauma. Other common causes of macrocephaly are discussed, including hydrocephalus secondary to an aqueductal web, hemorrhage, or a neoplasm. The authors also provide information on some of the rarer diseases for which imaging may provide the impetus for genetic testing (eg, overgrowth syndromes and metabolic disorders). RSNA, 2023 Quiz questions for this article are available through the Online Learning Center.

Palliative procedures are performed for congenital heart diseases that are not amenable for definitive surgical procedures or as a component of hybrid procedures along with transcatheter interventions. Multimodality imaging plays an important role in the follow-up of these palliative procedures, mainly for the timely detection of complications and for planning any subsequent palliative or definitive procedure. Echocardiography is the first-line imaging modality, with CT and MRI used as complementary techniques in indeterminate cases. MRI provides anatomic, functional, flow, and tissue characterization information. CT is performed for the evaluation of vascular anatomy and when MRI cannot be performed due to contraindications, challenges, or artifacts. The modified Blalock-Taussig shunt procedure is the most common systemic-pulmonary artery (PA) shunt procedure, with thrombus being the most serious complication. Other complications of systemic-PA shunts include shunt stenosis, infection, pulmonary overcirculation, and cardiac failure. The Glenn shunt procedure is the second stage of palliation in single ventricle physiology, with thrombus, stenosis, superior vena cava syndrome, and infection being the common complications. The Fontan shunt procedure is the third stage of palliation in single ventricle physiology. Complications can be cardiovascular (heart failure, valve regurgitation, thromboembolism, shunt stenosis, arteriovenous malformation), venolymphatic (collaterals, protein-losing enteropathy, plastic bronchitis), or hepatic (congestion, cirrhosis, portal hypertension). PA banding is used to decrease pulmonary flow or to train the systemic ventricle. Complications include stenosis, thrombus, erosion, pseudoaneurysm, and subaortic obstruction. Atrial septostomy and atrial switch procedures are performed for increasing intracardiac mixing. Complications of atrial septostomy can be mechanical, traumatic, embolic, or electrical. Complications of the atrial switch procedure include baffle stenosis, baffle leak, and systemic ventricle failure. The authors review the role of multimodality imaging in the evaluation of these palliative procedures. RSNA, 2023 See the invited commentary by Bardo and Popescu in this issue. Quiz questions for this article are available through the Online Learning Center.