INTRODUCTION The anatomy of cranial nerves is complex and the use of 3D Constructive interference in steady state (CISS) MR sequences help in demonstrating the fine structure of these nerves. While traditional Magnetic Resonance (MR) imaging sequences offer superior resolution of soft tissues, they lack spatial resolution required to distinguish minute structures like cranial nerves. Cranial nerves can be involved in both inflammatory and non-inflammatory conditions. Non inflammatory conditions include primary cranial nerve tumors, other tumors involving the cranial nerves and neurovascular conflicts. MATERIALS AND METHODS This study, which was both prospective and retrospective, involved 35 patients in total. The study covered all age group patients suspected of having CNS infections involving cranial nerves, traumatic cranial nerve palsies, cranial nerve neoplasms, and clinically diagnosed cranial nerve palsies. The patients having general contraindications for MRI study were excluded. Study was performed using 1.5 T 18 channel MR Scanner (Magnetom Avanto, Siemens, Munich, Germany) in KMC hospital, Ambedkar circle, Mangalore. MR sequences performed were contrast enhanced T2W 3D CISS, contrast enhanced T1W 3D MP-RAGE, plain T2W 2D TSE and contrast enhanced T1W 2D TSE. RESULTS 35 patients with symptoms of cranial nerve symptoms underwent MRI evaluation. 12 patients were found to have inflammatory etiology, 23 patients were found to have non inflammatory pathology which included primary nerve tumors, secondary tumors, other tumors involving cranial nerves and vascular conflicts. Three imaging criteria -lesion picked up, changes in signal intensity, and enhancement following contrast administration-were used to assess inflammatory lesions. Non-inflammatory lesions were evaluated using five imaging criteria which included lesion picked up, signal intensity changes, enhancement after contrast administration, nerve encasement and change in course of nerve with a score of 1 for each parameter. In summary, CISS performed better than other MR sequences when combining both etiologies to detect lesion, evaluate changes in signal intensity, determine nerve encasement, and determine nerve course. In determining the nerve enhancement, only MPRAGE outperformed CISS CONCLUSION MR examination is essential in evaluating cranial nerve lesions. On MR examination not just any sequence but dedicated thin section 3D sequences should be employed for their detection. We have encountered that CISS sequence is superior to other sequences in detecting neurovascular conflict, primary cranial nerve tumors or other extra axial tumors involving the cranial nerves. However, in the case of inflammatory conditions of cranial nerves MPRAGE was superior to CISS in detecting the lesion. On initial evaluation both the CISS and MPRAGE sequence should be included in the MR protocol while for follow up cases the required sequence can just be employed.

Constructive Interference in Steady-State (CISS), Magnetic Resonance Imaging, Neurovascular Conflict, Magnetization Prepared Rapid Gradient Echo (MPRAGE), Cranial Nerves