DIFFERENTIATING INTRATHECAL CATHETER TIP GRANULOMAS FROM NORMAL MAGNETIC RESONANCE IMAGE DISTORTION CAUSED BY METALLIC CATHETER TIPS

OBJECTIVETo characterize the normal image distortion produced by metallic intrathecal catheter tips and define features that differentiate them from a catheter tip granuloma. METHODSThree Medtronic Inc. (Minneapolis, MN) intrathecal catheter models (M8709, M8711, and M8731) were placed in a water-filled phantom, which was secured with a spinal coil and scanned with a 1.5-T magnetic resonance imaging (MRI) scanner. MRI scans from two patients receiving intrathecal opiate therapy without a granuloma and one patient with a granuloma were analyzed for comparison. RESULTSAll three catheter models produced a metallic susceptibility artifact, which distorted the local tissue image. The tip appeared as a round, dark void sandwiched between two bright bands in the sagittal plane. Axial views produced an oval-shaped, dark central void completely surrounded by a bright rim. On MRI scans, catheter tip diameter varied from 2.3 to 6.7 mm and tip length varied from 4.0 to 7.5 mm, which is a 74 to 480% increase over their actual size. The catheter tip appearance in the phantom correlated with the tip appearance in MRI scans from patients with intrathecal catheters. Images from a tip granuloma show a bright rim surrounding the catheter tip in the sagittal plane with or without contrast as well as postcontrast enhancement of the whole granuloma, and the catheter tip appeared greater than 5 mm in diameter and length. CONCLUSIONWhen evaluating possible granuloma development around an intrathecal catheter tip, it is important to take into account the characteristic metallic susceptibility artifact and increased size of normal metallic catheter tips on MRI scans.

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