Urethral diverticulum

Urethral diverticulum (or, or urethrocoele) is, is a focal outpouching of the urethra. It should not be confused with a ureterocoele of the distal ureter. 

Epidemiology

Urethral diverticula occur far more frequently in women than in men, and are estimated to occur in 1-6% of women, especially those with stress incontinence. 

Usually, patients present between the 3^rd and 5^th decades but can affect all age groups ¹.

Clinical presentation

The clinical diagnosis of structural abnormalities of the female urethra can be challenging because they are often associated with a widebroad range of non-specific clinical symptoms, and often are not detectable at physical examination ¹. Classically, the presenting symptoms are summarizedsummarised as the "3Ds" ⁴:

• dysuria: 30-70%
• post-void dribbling: 10-30%
• dyspareunia: 10-25%

Usually, an array of non-specific genitourinary symptoms predominatepredominates ^1,4.:

• frequency/urgency: 40-100% 
• recurrent urinary tract infection (UTI): 30-50% 
• haematuria: occurs in 10-25%
• stress incontinence

The symptoms often occur in combination with those of pelvic floor weakness ^1-2. 

In additionAlso, up to 10% of patients eventually develop stones within the diverticulum. Repeated infection and irritation also predisposespredispose to malignant transformation of the lining urothelium ⁴. 

Pathology

Urethral diverticula usually communicate with the urethral lumen and protrude through and stretch the periurethral smooth muscle. Occasionally, they extend proximally beneath the bladder neck and trigonal area. Complicated anatomical patterns, however, may exist with multiple ostia, in some cases, the urethral diverticula may extend partially (‘saddlebag’, ‘horseshoe’) or circumferentially around the urethra ¹.

At histologic examination, a urethral diverticulum demonstrates marked inflammation of the transitional epithelial mucosa, which overlies a thinned circumferential diverticular wall. This wall consists of fibromuscular tissue with or without an inner epithelial lining ³. 

The aetiology of urethral diverticula remains largely unknown. It has been suggested that they are congenital in origin due to the persistent embryological remnants, yet they are rarely found in children. The current prevailing view is that repeated infection and obstruction of the periurethral and urethral glands (Skene’s glands) results in cyst / abscess formation, these eventually rupture into the urethral lumen and remain as an outpouching, which epithelializes to become a true diverticulum as opposed to a urethrocoele or pseudo-diverticulum ¹.

Radiographic features

A uretheral diverticulum is a cystic lesion that typically arises from the posterolateral mid or distal urethra. It often wraps around the urethra. It can be multilocular.

Fluoroscopy

• voiding cystourethrography (VCUG)
  • an examination in which fluoroscopy of the bladder and urethra is performed during voiding 
  • the bladder needs to be filled with contrast through catheterisation of the bladder with a 14 French Foley catheter
  • was traditionally considered as the investigation of choice ³
  • images are obtained during filling and voiding as well as after voiding
  • nowadays many feel that the technique is equivocal  andand often additional imaging studies are necessary ^1,3
• double-balloon catheter urethrography (DBU)
  • a double-balloon 14 French Foley catheter is inserted into the urethra and contrast medium is injected at high pressure within the "isolated" urethra, allowing filling of any urethral communications
  • used to be considered as the gold standard investigation ^1-3
  • there are an increasing number of studies showing greater urethral diverticula detectondetection with MRI ¹

Ultrasound 

Transabdominal, transvaginal, transperineal and endourethralendo-urethral techniques have been described. Ultrasound may be of particular benefit in differentiating a septated urethral diverticulum from multiple urethral diverticula, when compared with MRI. The principal drawback is that these techniques are operator dependent ^1,3.

CT 

• conventional contrast-enhanced CT can help characterizecharacterise female urethral abnormalities to a limited extent. A urethral diverticulum may be visualizedvisualised at CT as a cystic mass with wall thickening and enhancement at the level of the pubic symphysis ³
• CT voiding urethrography (virtual urethroscopy) 
  • consists of a CT during VCUG
  • reformatted images are viewed interactively on a workstation
  • the technique is however still experimental ^1,3

MRI

MRI has become the imaging study of choice in many centres and is strongly advocated prior tobefore performing any surgery ^1,2.

MR imaging may be performed with a torso phased-array array coil or an endoluminal (endorectal, endovaginal, or endourethral) coil. Phased-array endoluminal MR imaging is the most accurate method for identifying and characterizingcharacterising female urethral diverticula ³. 

The suggested protocol consists of axial, coronal, and sagittal fast spin-echo T2-weighted sequences. Axial 2D fat-saturated fast spoiled gradient-echo T1-weighted sequences can be performed before and after the intravenous administration of gadolinium-based contrast material. 

• T1
  • T1 sequences before IV administration are not considered very useful 
  • a diverticulum or urethrocoele is T1 hypo intensehypointense
• T2: preferred pulse sequence
  • often shows the presence of hyperintense fluid in a diverticulum
  • diverticulum with circumferential involvement is described as "saddle bag diverticulum"
• T1 C+ (Gd) 
  • IV gadolinium can be administered for detection of inflammation or infection
  • it can also aid in the diagnosis of the rare diverticular adenocarcinoma
  • malignancy can be visualizedvisualised as enhancing soft tissue within the diverticulum

Treatment and prognosis

Patients with no or minimal symptoms are usually followed up and treated symptomatically with antibiotics and anticholinergics as needed ¹.

Those with ongoing/severe symptoms are treated operatively ¹; the common surgical treatment for urethral diverticulum is transvaginal diverticulectomy ^3-4. Excellent surgical results can be obtained, and complications are minimal ¹. Voiding cystourethrography is performed 2two weeks after surgery to evaluate for urethral healing and presence postoperative complications ³.

Differential diagnosis

General imaging differential considerations include:

• vaginal wall cyst
• Skene gland abscess
• Skene duct cyst
• ectopic ureterocoele
• uretheralurethral diverticular adenocarcinoma