Preoperative simulation for microvascular decompression in patients with idiopathic trigeminal neuralgia: visualization with three-dimensional magnetic resonance cisternogram and angiogram fusion imaging.

OBJECTIVE Precise assessment of the complex nerve-vessel relationship at the root entry zone of the trigeminal nerve is useful for planning microvascular decompression in patients with idiopathic trigeminal neuralgia. We have applied a fusion imaging technique of three-dimensional (3-D) magnetic resonance cisternography and co-registered 3-D magnetic resonance angiography (MRA) that allows virtual reality for the preoperative simulation of the neurovascular conflict at the trigeminal nerve root entry zone. METHODS Fusion images of 3-D magnetic resonance cisternograms and angiograms were reconstructed by a perspective volume-rendering algorithm from the volumetric data sets of magnetic resonance cisternography, obtained by a T2-weighted 3-D fast spin echo sequence, and co-registered MRA, by a 3-D time-of-flight sequence. Consecutive series of 12 patients with idiopathic trigeminal neuralgia were studied with fusion 3-D magnetic resonance cisternogram and MRA in the preoperative assessment for the microvascular decompression of the affected trigeminal nerve. RESULTS The complex anatomical relationship of the offending vessels to the trigeminal nerve root entry zone was depicted on the fusion 3-D magnetic resonance cisternogram and MRA. The presence of offending vessels and compressive site of neurovascular conflict was assessed from the various viewpoints within the cistern and was presumed by the preoperative simulation through the surgical access (surgeon's-eye view). The blinded surgical trajectory was discerned by the virtual image through the opposite direction projected from above (bird's-eye view). The 3-D visualization of the nerve-vessel relationship with fusion images was consistent with the intraoperative trajectory and findings. CONCLUSION Fusion imaging of 3-D magnetic resonance cisternogram and MRA may prove a useful adjunct for the diagnosis and decision-making process to execute the microvascular decompression in patients with idiopathic trigeminal neuralgia.