B i.e. MRI Vascular Rings Vascular rings is a condition in which an anomalous configuration of the arch and /or its associated vessels completely or incompletely surrounds the trachea & oesophagus causing compression of these structures. Neonates present with respiratory distress and older children present with stridor or dysphagia. Fouh developmental arch is most impoant. The two most common types of complete vascular rings, which account for 85-95% of cases are double aoic arch and right aoic arch with left ligamentum aeriosum Chest x-ray is the first & most commonly performed investigation. The identification of right aoic arch or ill defined arch location and compression of trachea in symptomatic child indicate the diagnosis. Many authorities consider barium oesophagoscopy to be the most impoant study in patients with suspected vascular ring and it is diagnostic in vast majority of cases. - A double aoic arch produce bilateral & posterior compression of oesophagus, which remain constant regardless of peristalsis. The right indentation is usually slightly higher than left and posterior one is usually wide & course in a downward direction from right to left. Right subclan aery takes a retrooesophageal course, there is a posterior defect slanting upward from left to right. The posterior defect is less broad than in double aoic arch. Echocardiography can be used but structures without lumen such as ligamentum aeriosum or an atretic arch are difficult to be identified. Plain x-ray & barium swallow can not reliably distinguish among the types of vascular rings. Cross section images by CT, MRI and digital substraction angiography (DSA) can be useful diagnostic tool in delineating the anatomy and aiding in presurgical planning & post surgical assessment. MR angiography (MRA) is an excellent substitute for DSA but young patients may require general anesthesia & where there is already airway compromise, this should be avoided. MRI is preferred as it is non invasive and avoids radiation riskQ. Multidetector CT is rarely used b/o radiation implication. Angiography (an invasive method) is rarely required unless cardiac catheterization is necessary for investigation of associated cardiac anomalies and if MRI is equivocal (same protocol applies for coarctation of aoa i.e. MRI > CT > Angiography).