Due to its increased signal-to-noise ratio, good resolution and multiplanar capability, MRI is known to be the imaging modality of choice for diagnosis and preoperative planning in female patients with urethral and periurethral disease. At our centre, the following MRI sequences are performed through the pelvis on a 1.5-T/3T scanner (Siemens Vida) for evaluation of the female urethra: T1-weighted axial imaging fat saturation, T2-weighted axial, sagittal and coronal, T2-weighted isotropic 3D fast spin echo sequence (‘SPACE’ sequence – Siemens). This SPACE sequence enables acquisition of high resolution 3D datasets [2].

Fig 1: The X14L4 is a high resolution transducer ideal for imaging the anterior and...

Fig 2: Normal anatomy of the urethra. 2D endovaginal US (EVUS) of the urethra in a mid...

The use of high frequency 3D EVUS is well known in the diagnosis of pelvic floor disorders, however more recently is being used to investigate female urethral and periurethral disease [3], as the small, high frequency endoluminal transducer allows a complete evaluation of urethral pathology. In our centre, 3D EVUS is used with a high-frequency (12-16 Mhz X14L4 – BK Medical) endo-cavity transducer that provides automatic 360° image acquisition with built in 3D imaging capabilities. The Smart button allows for easy activation, freezing, printing and storing of images [Figures 1, 2]. Post processing and reformatting is possible with the ability to alter the tilt to achieve the desirable plane, much like the MPR capability with CT [Figure 3].

Fig 3: 3D EVUS of urethra. Green cube represents 3D data obtained with high frequency...

Fig 4: T2 weighted MR pelvis of a normal female patient, demonstrating the multiplanar...

The MR SPACE (isotropic T2-weighted 3D fast spin echo) sequence is directly comparable to 3D EVUS as it mimics the views that are obtained through high frequency 3D EVUS [Figures 3, 4].

Case Review

Fig 5: A 52 year old presented with an anterior vaginal wall swelling – MRI found...

Fig 6: A 76 year old presented with post-menopausal bleeding. Transvaginal (TV) and...

Fig 7: 35 year old with para-urethral lump on examination. T1 weighted (A) and T2...

Fig 8: 35 year old with para-urethral lump on examination – continued. MR Space...

Fig 9: 56 year old female presented with a 3 cm anterior vaginal lump. T2 weighted...

It has been shown that 3D EVUS measurements of sub-urethral masses taken with Pelvic floor US (PFUS) in comparison to MRI do not differ significantly (85% agreement between PFUS and MRI) and can be used interchangeably dependent on availability and expertise [3]. Uniquely 3D EVUS provides demonstration of the coronal plane, perpendicular to the transducer face, facilitating easy identification of surface irregularities [4], [Figure 3].

The advantages of EVUS include reduced scanning time with cost effective use of equipment and sonographer time. Offline analysis and post-processing allows further interrogation of imaging following the US procedure, decreasing time taken during scanning. 3D EVUS enables real time imaging in different orientations negating the consequences of patient movement and enabling an improved assessment of both normal anatomy and complex anatomic anomalies [5].

The average 3D EVUS scan was found to take a maximum of 10 minutes with 360 degree views obtained in 60 seconds by the 3D EVUS probe. In comparison to this, the optimal MRI sequence for assessing the peri-urethral area (SPACE - T2-weighted isotropic 3D fast spin echo) itself takes 6 minutes. Additional to this, the time taken to perform the remaining MR sequences mean that the total on table time frequently exceeds 30-40 minutes. This of course, does not include any acquisitions that have to be repeated due to movement artefact. As the images are not reviewed in real time, at times patients have to be recalled due to movement artefact or inadequate sequences.

The MR SPACE sequence mimics the views that are obtained through high frequency 3D EVUS, and so in centres where 3DUS is not available; MR SPACE (or comparable T2-weighted isotropic 3D fast spin echo sequence) could be used in place of standard MRI techniques in assessing peri-urethral masses.