12.1.6\ Microvascular

Decompression/Jannetta

Procedure

12.1.6.1\ Discussion

Microvascular decompression can be used to effectively treat vascular loop syndromes, such as trigeminal neuralgia and glossopharyngeal neuralgia (Figs. 12.19, 12.20, and 12.21). The technique essentially consists of interposing Teflon between the affected nerve and the offending vessel. The concept behind this procedure is that the Teflon distances and redirects the transmitted pulsation of the adjacent artery away from the nerve. Teflon is hyperattenuating on CT and low signal intensity on all MRI sequences. High-­resolution T2-weighted MRI sequences are particularly useful for analyzing the position of the pledgets and altered anatomy, which often entails distortion of the nerve course. During the

a

early postoperative period, reversible elevated T2 signal and restricted diffusion is often observed in the ipsilateral pons after trigeminal decompression and does not necessarily indicate infarction. Perhaps the most common complication of microvascular decompression is recurrent symptoms related to suboptimal pledget positioning (Fig. 12.22). For example, in patients with persistent hemifacial spasm after microvascular decompression, residual vascular compression is most commonly encountered proximal to the pledget, along the attached segment of the nerve. Hearing loss is a more unusual complication that can result from Teflon migration or the use of excess Teflon that compresses cranial nerve 8 within the internal auditory canal (Fig. 12.23). Granulomas can occasionally form in reaction to the presence of Teflon, which forms a mass that has low T2 signal and enhances (Fig. 12.24).

b

Fig. 12.20  Microvascular decompression for hemifacial spasm. Axial CISS MRI shows Teflon (white arrow) interposed between the left facial nerve (arrowhead) and the enlarged, tortuous basilar artery (black arrow)

Fig. 12.21  Microvascular decompression for glossopharyngeal neuralgia. Axial CT image shows pledgets (arrow) used to isolate the right glossopharyngeal nerve root entry zone from surrounding vessels

Fig. 12.22  Failed microvascular decompression. The patient presented with persistent symptoms of trigeminal neuralgia following attempted decompression. Coronal (a, b) and sagittal (c, d) CISS (thin section) MR images

show that the pledget (black arrows) is positioned superior to the superior cerebellar artery (arrowheads), which directly contacts the left trigeminal nerve (white arrows)

Fig. 12.24  Teflon granuloma. Axial T2-weighted MRI (a) shows a globular hypointense lesion in the right cerebellopontine angle cistern (arrow). Axial pre- (b) and

post-contrast T1-weighted (c) MR images show corresponding mild enhancement of the lesion (arrows)