This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
Contrast media of choice for myelogram is 
Select and explain. 
A. Urografin 75%, B. Conray 470, C. lohexol, D. Biligrafin
C: lohexol
Answer: C: lohexol 
Explanation: C i.e. lohexol - Dianosil is used in oesophageal atresiaQ, as in most cases it is frequently associated with tracheooesophageal fistula; so on instillation of contrast media, there is risk of flooding in the lungs. Water soluble-nonionic LOCM are licenced for intrathecal use eg Iohexol (omnipaque) and Iopamidol (neopam)Q and are contrast agents of choice for myelographyQ. These are non neurotoxic, donot cause epileptic fits, can be used without withdrawing other drugs & are devoid of arachioid toxicity and anticonvulsant cover is unnecessary. Whereas ionic contrast media (both HOCM & LOCM) are very very toxic & often fatal when injected into subarachnoid space.