MRI of the Urethra in Women with Lower Urinary Tract Symptoms: Spectrum of Findings at Static and Dynamic Imaging

Genevieve L. Bennett; Elizabeth M. Hecht; Teerath Peter Tanpitukpongse; James S. Babb; Bachir Taouli; Samson Wong; Nirit Rosenblum; Jamie A. Kanofsky; Vivian S. Lee

Disclosures

Am J Roentgenol. 2009;193(6):1708-1715. 

In This Article

Materials and Methods

The institutional review board at our institution approved this HIPAA-compliant retrospective study and waived informed consent.

Patients

A search of the MRI database at our hospital from March 16, 2001, to December 24, 2007, was performed to identify women who were referred for MRI evaluation of the urethra and who underwent both dynamic and static imaging. Patients with a history of lower urinary tract malignancy were excluded. A dynamic sequence was added to the protocol for MRI of the female urethra at our institution in 2001 when we began to perform dynamic pelvic floor imaging. This search yielded a total of 122 patients. For 84 patients, clinical charts were also available for review; therefore, the study population was limited to these 84 patients. The age range was 18–81 years (mean, 40.1 years). Indications for the MRI examinations were suspected urethral diverticulum (n = 45), recurrent urinary tract infection (n = 16), urinary symptoms including pain or urinary frequency (n = 16), other suspected periurethral mass (n = 5), and incontinence (n = 2). Two patients had undergone prior pelvic floor surgery: one colporrhaphy and one urethral sling. Six patients had undergone hysterectomy.

MRI Protocol

Patients were imaged using one of three 1.5-T clinical systems (Vision, Symphony, or Avanto; Siemens Healthcare) and a torso phased-array coil. In accordance with the routine protocol at our hospital, patients did not undergo bowel preparation, and no intraluminal contrast agent was administered. Each patient was asked to empty her bladder 1 hour before entering the magnet, which typically resulted in the bladder being half full at the time of image acquisition. All studies included sagittal, axial, and coronal high-resolution T2-weighted turbo spin-echo (TSE) images through the urethra with the following parameters: TR/effective TE, 6,000/116; refocusing flip angle, 180°; turbo factor, 31; rectangular field of view, 150–206 x 200–275 mm, depending on the imaging plane; matrix, 192 x 512; slice thickness, 3–4 mm with an interslice gap of 0.2–0.6 mm, depending on imaging plane; bandwidth, 195 Hz/pixel; no parallel imaging; 35 slices through the urethra and bladder; 2–3 signal averages; average time of acquisition, 4 minutes 40 seconds. Axial and coronal imaging planes were prescribed with respect to the urethra. Contrast-enhanced 3D fat-suppressed volumetric interpolated breath-hold examination (VIBE) data sets were also acquired before and after administration of a standard weight-based dose (0.1 mmol/kg, with a maximum of 20 mL) of IV gadopentetate dimeglumine (Magnevist, Bayer HealthCare Pharmaceuticals), at 45 and 180 seconds after injection.

To evaluate for prolapse, a dynamic true fast imaging with steady-state free precession (trueFISP) sequence was performed before contrast injection. This was a continuous acquisition of a single sagittal slice while the patient alternated every 5 seconds between rest and maximal strain (Valsalva maneuver) with the following parameters: 3.9/1.9; refocusing flip angle, 70°; matrix, 256; a rectangular field of view optimized to the patient's body habitus (300–350 mm); slice thickness, 8 mm; bandwidth, 673 Hz/pixel; acquisition time per measure, 0.6 second; 90 consecutive measures; acquisition time, 54 seconds. The dynamic sequence was performed at a midline sagittal slice position that best depicted the anatomy of all three pelvic compartments, as prescribed by the technologist on the basis of the multiplanar T2-weighted TSE sequences. If inadequate strain was observed, the dynamic sequence was repeated after additional patient instruction. The dynamic sequence was performed once in 60 patients, twice in 19 patients, three times in four patients, and five times in one patient. In four patients, including the patient in whom it was repeated five times, the acquisition was repeated for technical reasons, including wrap and other artifacts. For the remainder with more than one acquisition, the sequence was repeated because of poor strain effort during the initial image acquisition.

Image Analysis

All studies were reviewed retrospectively on a PACS workstation (Sienet, Siemens Healthcare) by two radiologists with 10 and 6 years of experience in interpreting abdominal MRI. The readers had no knowledge of clinical symptoms but did know that the patients were referred for and had undergone urethral imaging, presumably for urinary symptoms. The MRI examinations were reviewed in random order and in consensus. For each study, static images were initially evaluated, followed by review of the dynamic sequence, which is how these studies are interpreted in our clinical practice.

Urethral abnormalities were classified according to previously published criteria.[3–6] Using accepted criteria, the presence and degree of pelvic organ prolapse at rest and with strain were also determined. Prolapse was diagnosed when the pelvic organs descended more than 1 cm below the pubococcygeal line, a line extending from the inferior margin of the pubic symphysis to the last joint of the coccyx and representing the level of the pelvic floor.[10–14,19,20] Grading of prolapse was based on the distance of a perpendicular line drawn from the pubococcygeal line to the inferior margin of the organ of interest as follows: negative, < 1 cm; mild, < 2 cm; moderate, 2–4 cm; and severe, > 4 cm. A cystocele was diagnosed when the bladder neck descended to more than 1 cm below the pubococcygeal line, and urethrocele was diagnosed when the urethra descended to more than 1 cm below the pubococcygeal line. Hypermobility of the urethra refers to inferior descent of the urethra below the pubococcygeal line and rotation from its resting axis resulting from laxity of the urethral supporting structures.[12,24,25] Hypermobility of the urethra was defined as horizontal translation of the urethra away from the normal vertical axis, with strain at an angle greater than 30°, as defined in the literature.[25] No MR grading system exists for severity of urethral hypermobility. For this study, hypermobility was graded as mild (> 30° and < 45° from the vertical) or (severe > 45°). A rectocele was defined as anterior bulging of the rectal wall greater than 2 cm from a line drawn parallel to the center of the anal canal.

Clinical Correlation

Clinical charts were available for retrospective review in all 84 patients. Because these 84 patients were all referred by urologists, clinical symptoms and physical examination findings related to the anterior compartment were specifically examined. Physical examinations were performed by three urologists who perform most urethral and pelvic floor surgery at our medical center. The findings were classified according to Baden and Walker.[26] The presence of the following urinary tract symptoms in each patient was recorded: dysuria, urinary frequency, nocturia, recurrent urinary tract infection, stress urinary incontinence, urge incontinence, urgency, and voiding difficulty. The total number of pregnancies, vaginal deliveries, and cesarean sections for each patient was also recorded.

Statistical Analysis

SAS version 9.0 (SAS Institute) was used for all statistical computations. The Fisher's exact test was used to evaluate the association of each anterior compartment finding at MRI (cystocele, urethrocele, urethral hypermobility) with each clinical symptom, the number of pregnancies, and type of delivery. An exact Mann-Whitney test was used to compare MRI findings and patient age. An exact Mann-Whitney test also was used to compare women with and without a specific symptom in terms of cystocele, urethrocele, and urethral hypermobility severity. All reported p values are two-sided and were not subjected to multiple comparison correction. Results were declared significant when associated with a p value less than 0.05. Comparison was also made between physical examination findings and MRI findings. Patients with cystoceles and urethral hypermobility detected only on MRI or physical examination, on both MRI and physical examination, or on neither MRI nor physical examination were identified. Charts were also reviewed for patient management and findings at pathology.

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