The aim of our study was to assess the use of transvaginal ultrasound for the diagnosis of infection and inflammation in the bladder.  This is the first study to our knowledge with this aim. Ultrasound of the bladder wall thickness has been shown previously to be useful in the diagnosis of detrusor overactivity or bladder outlet obstruction as both have increased bladder wall thickness (1) . At present bladder inflammation can only be diagnosed by cystoscopy with or without hydrodistension which is an invasive procedure (2). This diagnostic method is controversial, as studies have shown that it lacks specificity and correlates poorly with the symptoms of Bladder Pain Syndrome.
The aim of this study is to assess whether transvaginal ultrasound could be used as a non-invasive method of diagnosing bladder inflammation or infection. We hypothesize that there would be a positive association between trigone thickness on ultrasound and an infected or inflamed bladder seen on cystoscopy or bladder biopsy sample.

We conducted a retrospective study of women attending for cystoscopy. These patients had been experiencing lower urinary tract symptoms including frequency, urgency and bladder pain. The cystoscopy was carried out under general anaesthetic involved the use of a rigid cystoscope Ch20, the bladder was initially visualised using a 30 degree cystoscope and the bladder was filled to 400 to 600ml with a pressure between 70 to 140 cmH2O.  The fluid was left in the bladder for 3 to 5 minutes and the bladder was drained and refilled. Again the bladder wall was inspected and the appearance recorded. Areas of the bladder which appeared inflamed were biopsied and sent for histological staining including CD117 immunohistochemical staining. The MAST cell count was carried out and reported as MAST cells per mm2.  A second bladder biopsy was taken and put into saline.  The bladder biopsy was homogenised before being cultured in a broth culture. The cultured organisms were then recorded.  
The transvaginal ultrasound involves the woman voiding and then an ultrasound of the bladder was carried out.  The woman was supine with her knees a hips distance apart. A cover was placed over the transvaginal probe which emits a frequency of 6 to 8 MHz  was used to image the bladder initially in the sagittal plane and then maintaining the probes cranial orientation it is moved laterally to view the bladder in the parasagittal plane approximately 1 cm form the midline.  The bladder image was frozen at the maximum magnification and three measurements were taken of the base of the bladder, dome and anterior  The measurements were taken perpendicular to the urothelial surface of the bladder.  These data were entered onto a database. SPSS v 24, IBM, USA software was used. If the data was non continuous then the Chi Square test was used and for continuous data the independent t test was used and a level of significance p< 0.05.

Three hundred and twenty seven women were studied. The mean measurements for the trigone thickness on ultrasound was mean 5.8mm (95%CI 3.8 to 7.9) and the bladder dome measurement on ultrasound was mean 5.2mm (95%CI 3.3 to 7.7).  The number of women with a MAST cell count in excess of 28 per mm2 were 154 (47%) which has been suggested as abnormal in the ICI committee on bladder pain syndrome.  Two hundred and thirty two biopsies (71%) were cultured and grew an organism.
Using a cut off above 6mm for an abnormal bladder wall thickness then 63% of women had a positive culture on biopsy (Chi Sq p<0.05).  Squamous metaplasia was associated with the positive cultures for bladder biopsy (74%, Chi Sq p<0.05).
The thickened bladder dome was significantly associated with urinary frequency only (independent t test, p<0.05).

Transvaginal ultrasound of the trigone over the 6mm appears to be associated with infection in the bladder, whereas thickened bladder dome is associated with urinary frequency.

Transvaginal ultrasound shows promise of a method to have a non-invasive test for bladder infection or inflammation.

Review on ultrasound measurement of bladder or detrusor wall thickness in women: techniques, diagnostic utility, and use in clinical trials. World journal of urology. 2013; 31 (5): 1093-1104.