Hypothesis That Urethral Bulb (Corpus Spongiosum) Plays an Active Role in Male Urinary Continence

Abstract

The proximal urethral bulb in men is enlarged, surrounds the bulbous urethra, and extends dorsally towards the perineum. During intercourse engorgement takes place due to increased blood flow through the corpus spongiosum. Antegrade ejaculation is facilitated by contraction of the bulbospongiosus muscles during climax. Micturition during sexual stimulation is functionally inhibited. Supporting the bulb may indirectly facilitate continence in a certain subset of patients with postprostatectomy incontinence. During physical activity with increased abdominal pressure, reflex contraction of the pelvic floor muscles as well as the bulbospongiosus muscles occurs to support sphincter function and limit urinary incontinence. Operations to the prostate may weaken urinary sphincter function. It is hypothesized that the distal urinary sphincter may be supported indirectly by placing a hammock underneath the urethral bulb. During moments of physical stress the "cushion" of blood within the supported corpus spongiosum helps to increase the zone of coaptation within the sphincteric (membranous) urethra. This may lead to urinary continence in patients treated by a transobturator repositioning sling in patients with postprostatectomy incontinence. This paper describes the possible role of the urethral bulb in male urinary continence, including its function after retroluminal sling placement (AdVance, AdVance XP® Male Sling System, Minnetonka, USA).

Figure 1

Anatomy corpora cavernosa and spongiosum: note the rather large urethral bulb. Red arrow shows direction and position of transobturator retroluminal repositioning sling (AdVance Male Sling System, American Medical Systems (Minnetonka, USA)). Adapted from Public Domain: Wikipedia, 15.4.2015 at 12h00, available from http://en.wikipedia.org/wiki/Corpus_spongiosum#/media/File:Grant_1962_198.png.

Figure 2

Bulbospongiosus muscle (red). Adapted from Public Domain: Wikipedia, 15.4.2015 at 12h00, available from https://en.wikipedia.org/wiki/Bulbospongiosus_muscle#/media/File:Bulbospongiosus-Male.png.

Figure 3

Midperineal elevation demonstrating prompt narrowing of the lumen within the sphincteric urethra. This test shows healthy sphincter reactivity. This test does not give an indication of length of sphincteric urethral coaptation. Images ^©Peter Rehder.

Figure 4

Correct placement of helical needle trocar from “outside-in.” The tip of the helical needle trocar enters the perineal wound underneath the lumen of the urethra in a distal position and underneath the membranous (sphincteric) urethra. The entrance of the introducer needle tip into the perineal wound should be in the uppermost corner between inferior pubic ramus and urethral bulb. The corpora cavernosa (not shown) lie “on top” of the inferior pubic rami and are not in the line of the needle trocar passage-measured safety margin of sling to dorsal penile nerve 5 mm. Note that the level of the tip of the trocar is and should be below the lumen of the membranous urethra. When the sling is tensioned, it is pulled into a straight line well underneath the level of the caudal membranous urethral wall. Only the distalmost portion of the membranous urethra is thus supported from the dorsal side. Correct sling placement should therefore have a very low risk of urethral erosion. The main risk for urethral damage is intraoperative perforation of the urethra during trocar passage. It is imperative to protect the urethra, noticed by a transurethral catheter in situ, with the surgeons' index finger, during needle trocar passage.

Figure 5

Cadaver dissection demonstrating helical trocar for transobturator route in relation to the sphincteric urethral lumen with bulb-headed probe in situ. Image, ^©Peter Rehder [15].

Figure 6

The dotted double circle is showing the extent of the urethral sphincter outer circumference. Note that the tip of the helical trocar is well below the sphincteric urethral lumen. Image, ^©Peter Rehder [15].

Figure 7

Positioning of sling at proximal urethral bulb before tensioning. Note relative short zone of coaptation, blue area within sphincteric urethra. Image, ^©Peter Rehder [15, 16].

Figure 8

Indentation of the proximal corpus spongiosum by sling, distal and dorsal to the sphincteric urethra. Note longer zone of urethral coaptation marked in blue. Note the “cushion” of healthy spongeous tissue between the sling and the distal sphincteric urethra (yellow ellipse). Image, ^©Peter Rehder [15, 16].

Figure 9

Placement of the AdVance sling [15]: (a) marking the point of entrance for the needle trocar just laterally and below the insertion of the adductor longus tendon (red star). (b) Protecting the urethra with the index finger. (c) The thumb is used to push the helical trocar, in order to deliver the needle tip straight into obturator fossa. (d) The index finger is used to protect the urethra, while rotating the handle of the introducer needle to deliver the needle tip into the perineal wound. (e) The tip of the introducer needle is guided into the perineal wound. (f) The connector attached on the plastic sheath that covers the sling and is clicked into position onto the tip of the introducer needle. (g) The needle tip is pushed back to the edge of the inferior pubic ramus. (h) The helical part of the needle is gripped and jerked a little towards the tip of the ipsilateral scapula, to dislodge it around the broad male inferior pubic ramus. (i) The sling can now be pulled through the obturator fossa. (j) The sling is held out of the way to prepare delivery on the contralateral side. (k) This image shows the sling connector and the helical needle trocar in situ. (l) The sling is pulled into position loosely flushed onto the bulb before fixating the distal edge of the midportion to the bulb with resorbable sutures (Vicryl 2/0).

Figure 10

Retroluminal position of transobturator sling (long arrow) dorsal to the urethral lumen (short arrow).

Figure 11

Proximal indentation of urethral bulb (outline thin dotted line) by transobturator sling (thick dotted line). (a) = bladder. (b) = pubic symphysis. (c) = transurethral catheter.

Figure 12

Sling in straight line between inferior pubic rami (lines between arrows). (r) = rami (inferior pubic). (b) = bulb (proximal urethral, posterior urethral bulb). (a) = anus.

Figure 13

Sling in retroluminal position in double-folded fashion (fat dotted line). (s) = symphysis and (df) = Denonvilliers' fascia. Tightening of the sling leads to a rotational cranial movement with double folding, supporting the dorsal distal aspect of the sphincteric urethra. This support is indirect as spongiosum tissue is interpositioned between sling and urethral lumen. Spongiosum outline indicated with small dotted line.

Figure 14

Urethral bulb after radical prostatectomy (no prostate) in patient suffering from urinary incontinence. Explanation: images show perineal skin and bulb top and bladder below (deep), ventrally on left and dorsally on right side as it appears on page; ultrasound probe oriented in midsagittal plane.

Figure 15

Urethral bulb and prostate in a patient rendered incontinent after transurethral resection of the prostate. Duplex Doppler showing blood flow within proximal bulb and prostate.

Figure 16

Midperineal elevation test: relaxed state without elevation. Normal blood flow within CS.

Figure 17

Midperineal elevation test: relaxed state with elevation. Increased Doppler activity during elevation within corpus spongiosum (CS).

Figure 18

Sling position indenting the urethral bulb. Dotted line indicates path of urethral lumen, double yellow line represents the sling, and light blue outline indicates the indented urethral bulb.

Figure 19

Duplex Doppler showing blood flow after sling placement. Blood flow within urethral bulb after sling placement is maintained. Note the healthy (>1 cm long) proximal portion of urethral bulb on the right side (white dotted ellipse).