Delayed contrast-enhanced MRI to localize Botox after cystoscopic intravesical injection

There is a lack of studies to show localization of botulinum toxins (BoNT) within bladder wall and/or absorption rates. Our study examined the later distribution of BoNTA/gadolinium within the bladder wall by performing a delayed MRI scan after intravesical injection. This potentially may help to explain the level and mechanism at which BoNT may be producing its effect.

A prospective study enrolled 20 consecutive patients with neuropathic or idiopathic overactive bladders. The Aim of the study was to perform MRI 3 h post procedure. Botox 100-200 IU was reconstituted with 19 ml saline and 1 ml of gadolinium contrast. Intradetrusor injections were administered using a rigid 21F cystoscope with a total of 20 injections into bladder wall, including two into the trigone. The depth of injection was approximately 2 mm, without raising a bleb. One radiologist reviewed films and reported on the number of bladder walls with contrast, location, the presence of extravesical extravasation, contrast in distal ureter(s), and bladder wall thickness.

Ninety percentage of patients had contrast within bladder wall. There was a variation in the number of bladder walls involved; 85 % had contrast seen in at least two walls. Also, a variation was noted in the extent of extravasation; 80 % showed some evidence.

Diffusion of BoNT after intravesical injection is very common once bladder wall is breeched. Precise injection localization into muscle layer may not be as relevant to outcome as previously assumed. The assumption in our study that localization and diffusion of contrast also represents the localization of BoNT is open to critique as BoNT diffusion is potentially slower (Mehnert et al. in World J Urol 27(3):397-403, 2009). The absence of systemic symptoms after the injection in our series supports guidelines concerning the safety of procedure.