‘Stop going off on a tangent’: a novel method for discriminating pathological from tangential fluorescence during photodynamic diagnosis cystoscopy

BACKGROUND Fluorescence photodynamic diagnosis (PDD) cystoscopy is gaining credence in the diagnosis and surveillance of bladder cancer. It combines normal white light cystoscopy with periodic blue light examination of the bladder pre-instilled with a tumour selective porphyrin, hexa-aminolevulinic acid (hexa-ALA).1 This method detects areas of fluorescent tissue suggestive of tumour or carcinoma in situ, and has been shown to decrease recurrence rates and improve outcomes when compared with white light cystoscopy.2 The mucosa of the bladder neck and lateral bladder wall is viewed at an angle on blue light cystoscopy and displays tangential fluorescence following hexa-ALA instillation. Although a useful observation, by acting as a positive control,3 a common conundrum remains the discrimination between pathological and tangential fluorescence. We describe a simple technique to aid in discriminating between the two.