Urethral Strictures

4. CLASSIFICATIONS

4.1. According to stricture location

Classification according to stricture location is important as this will affect further management.

4.1.1. In males

4.1.1.1. Anterior urethra

The anterior urethra runs from the meatus to the urogenital diaphragm and is surrounded in its entire length by the corpus spongiosum [11,140]. Further subdivision is made in three different areas (from distal to proximal) [12]:

Meatal strictures: these strictures are located at the external urethral meatus and may extend into the fossa navicularis of the glans.

Penile strictures: these are located in the segment between the fossa navicularis and the bulbar urethra. Externally, the penile urethra begins approximately at the balanopreputial sulcus and continues to the penoscrotal junction. The whole penile urethral segment lies in the groove ventral to corpora cavernosa and is surrounded by a thin layer of corpus spongiosum.

Bulbar strictures: the bulbar urethra starts at the penoscrotal junction and is surrounded by the bulbospongious muscle. It ends in the membranous urethra proximally at the level of the urogenital diaphragm. The bulbar urethra can be subdivided into a proximal and distal part. The proximal bulbar urethra is defined as the segment within 5 cm of the membranous urethra; the urethra lies eccentrically in this part with abundant ventral spongious tissue. The distal bulbar urethra is defined as the adjoining segment extending to the penoscrotal junction [141]. Strictures extending towards the membranous urethra are termed bulbomembranous strictures (BMS).

Penobulbar strictures: these extend from the penile urethra into the bulbar segment, compromising long segments of urethra.

The difference between penobulbar strictures and multifocal strictures should be noted. The latter are defined by two or more narrowed segments, either in the same or different subdivision of the urethra but preserving healthy lengths of urethra between them (e.g., iatrogenic strictures related to TUR procedures which typically affect the fossa navicularis and the penoscrotal junction with healthy urethra in between).

4.1.1.2. Posterior urethra

The posterior urethra is approximately 5 cm long, with three different segments [12]:

• The membranous urethra is the area of the urethra traversing the urogenital diaphragm, between the proximal bulbar and the distal verumontanum.
• The prostatic urethra runs through the prostatic gland, starting at the proximal membranous urethra and extending to the bladder neck.
• The bladder neck is surrounded by the internal urinary sphincter and is the junction between the prostatic urethra and the bladder. Stenosis (or contracture) of the bladder neck implies a prostate in situ (i.e., after TURP or simple prostatectomies). If the narrowing or obliteration appears at this level but after a RP, the correct term is VUAS [12].

4.1.2. In females

The female urethra is approximately 4 cm long and arbitrarily divided in an upper, mid, and lower part [15,125,127,128,130-132,137,139].

4.2. According to stricture tightness

Several classifications systems have been proposed over the years [142]. The definition of low- vs. high-grade strictures remains debatable [143-145]. A urethral plate less than 3 mm is considered a high-grade or tight stricture [146]. It has been demonstrated with a normally functioning bladder that flow rate will not diminish until the urethral lumen has a diameter below 10 Fr [144].

Table 4.1 presents a suggested classification for male patients with a normal functioning bladder. This classification was developed by the EAU Urethral Stricture Panel based on a consensus process.

Table 4.1: EAU classification according to the degree of urethral narrowing

4.3. Strictures in transgender men and woman

4.3.1. Trans women

After MtF gender confirming surgery, the penile urethra has been resected. Meatal strictures are defined as strictures occurring at the neomeatus, which is formed between the junction of the distal bulbar urethra and the neovagina. The other segments (bulbar and posterior) are the same as in a biological man.

4.3.2. Trans men

Four different areas can be identified in the urethra after FtM gender confirming surgeries [147]:

• The native urethra is the female urethral segment which remains preserved during surgery. It goes from the bladder neck to the original external meatus.
• The fixed part (pars fixa) or perineal urethra follows the native urethra, starting at the original external meatus. This segment is reconstructed using local tissues, typically vestibular mucosa, or anterior vaginal mucosa. Its course is similar to the bulbar urethral segment in males, but without being covered by spongiosal tissue.
• The anastomotic part is the area where the pars fixa joins the neophallus.
• The phallic urethra is the segment located within the neophallus or the metoidioplasty and is usually made of skin tube. Its course is similar to the penile urethra in males, but without being covered by spongiosal tissue.