Monochorionic (MC) twin and triplet pregnancies pose complex clinical problems and high risks of types that are not seen in dichorionic (DC) twin pregnancies. Fetal growth discordance (FGD) and twin-to-twin transfusion syndrome (TTTS) are the most common problems. The MC twin placenta is usually a truly single, not fused, placenta that is produced by a single zygote and intended for the metabolic support of a singleton fetus. There are three vascular consequences of the insertion of two or more umbilical cords into an MC placenta: cord insertions, single umbilical artery, and interfetal vascular connections. TTTS is usually caused by a relatively low number of small diameter arteriovenous connections (AVCs) in combinations that result in net chronic blood seepage into the recipient twin. All types of vascular connections are involved in major complications in MC twins, including TTTS, donor/recipient role reversal after treatment, and neurological damage of a single surviving fetus.

Noninvasive imaging techniques are playing an ever-increasing role in the diagnosis and management of patients with lesions of the vascular structures of the head and neck. Stroke is the most important clinical indications for which patients undergo emergent imaging. Computed tomography angiography (CTA) is accurate, more rapid, less expensive, and requires less staffing than surgical exploration or conventional angiography. Initial noncontrast CT followed immediately by CTA and CTP provides a rapid yet thorough assessment of potential intracranial hemorrhage, stroke mimics, large evolved infarct, arterial clot and stenosis, infarct size and location, and penumbra. Many patients who present with signs of trauma to the head, neck, or great vessels receive noncontrast CT imaging as part of the initial diagnostic workup. Technical factors such as slice thickness, length of coverage, kilovolt and milliampere settings, and bolus delay time can influence the accuracy and speed with which a CTA is obtained.