SYNOPSIS Pseudomembranous trigonitis presents in females with the urethral syndrome and a characteristic lesion restricted to the trigone of the bladder. The histology shows 'vaginal metaplasia' of the epithelium together with underlying oedema and vascular dilatation, but no significant inflammation. Thirty-one such cases are included in the study. The possible role of oestrogen stimulation is discussed, together with a suggestion that the trigone has an embryological derivation distinct from the remainder of the bladder, allowing the trigonal epithelium to respond to oestrogenic stimulation in a manner denied to the vesical transitional epithelium.The 'urethral syndrome' is one of the causes of urgency and frequency of micturition in the female, which may be distressing at times. While this may be due to a number of factors, a certain proportion of these women have a normal urine, which is sterile on culture, and a characteristic lesion of the trigone on cystoscopy. Biopsy reveals a metaplasia of the trigonal epithelium which comes to resemble that of the vagina. This condition was first described by Heymann (1905) as 'trigonal cystitis' and has since passed under a variety of names, including pseudomembranous trigonitis, urethrotrigonitis, granular trigonitis, and vaginal or squamous metaplasia of the trigonal epithelium. In a survey of this condition endoscopic biopsy has been performed in 31 cases and the histological findings are described here. Three male patients are also included, two with a papillary transitional-cell carcinoma of bladder and one on oestrogen therapy for carcinoma of the prostate. Clinical FindingsThe 31 patients were all women with urgency and frequency of micturition. Their ages ranged from 15 to 73 with a mean of 38 years. Nine patients were postmenopausal. The urine was normal on routine testing and sterile on culture. Clinical examination was negative. Cystoscopic FindingsOn endoscopy, the changes are confined to the

SUMMARY Fourteen formalin fixed and paraffin wax embedded biopsy specimens from 10 women (age range 34-68) presenting with pseudomembranous trigonitis were studied using a combination of anti-oestrogen receptor monoclonal antibodies in an avidin-biotin immunoperoxidase technique. All epithelial areas showing vaginal metaplasia exhibited staining confined to the nucleus in the basal and parabasal layers of the squamous epithelium while no staining was encountered in adjacent trigonal transitional epithelium included in nine of the biopsy specimens.The selective expression of nuclear oestrogen receptor in trigonal epithelium affected by vaginal metaplasia in a distribution similar to that reported in vaginal epithelium by other workers lends further support to oestrogen mediated aetiology in this condition and is consistent with an embryological derivation of the trigone, distinct from that of the rest of the bladder.Pseudomembranous trigonitis, a recognised cause of the "urethral syndrome", is characterised by urgency and frequency of micturation. A characteristic lesion of the bladder trigone is seen on cytoscopy. Biopsy specimens show squamous metaplasia of the trigonal epithelium closely resembling vaginal squamous epithelium. The epithelial cells are vacuolated and contain abundant glycogen, while the lamina propria shows noticeable venous dilatation associated with oedema. ' Originally described by Heymann as "trigonal cystitis",2 the lesion has since been termed pseudomembranous trigonitis, granular trigonitis, urethrotrigonitis, and squamous or vaginal metaplasia of the trigonal epithelium. The lesion is almost exclusively found in women, although in one study of 31 cases' three were in men, one ofwhom was receiving oestrogen for carcinoma of the prostate.While some reports have considered vaginal metaplasia of the trigone to be an adaptive response to inflammation of the bladder,315 other studies have suggested that it develops under the hormonal influence of oestrogens.6' In particular, Tyler correlated variations in the histological appearance of the vaginal metaplasia with phases of the menstrual cycle.8 Although no study ofthe presence of oestrogen receptor has been reported in pseudomembranous

The clinical features in 14 female patients with chronic urinary retention unassociated with extrinsic or obvious intrinsic obstruction or neurological disease are described. Management, results and histological findings are presented and discussed in relation to the clinical findings.