Bilgiustam

Use of Oral Mucosa Grafts in the Treatment of Urethral Stricture


Surgical options for urethral stenosis are primarily based on the location of the stricture and the technique used. These include excision and primary anastomosis, recumbent repairs, stenosis excision and augmented anastomosis, flap-based repairs, and staged repairs. In cases where simple excision and primary anastomosis are not suitable to maintain urethral continuity, some form of substitution urethroplasty is required. Replacement urethroplasty is the gold standard in the treatment of male urethral strictures that are unsuitable for excision and primary anastomosis.
Use of Oral Mucosa Grafts in the Treatment of Urethral StrictureThis involves dilation or replacement of the urethra circumference using a patch or tube of suitable material, which may be genital or extra-genital tissues, respectively. This is the transfer of tissues in the form of a free graft or flap. The term graft means that the tissue has been excised and transferred to a graft host bed where a new blood supply develops with a harvest. This process requires about 96 hours and takes place in two stages. The first stage is absorption and at this stage, the vaccine survives by absorbing nutrients from the host bed. The second stage is called vaccination, and this is the time when microcirculation occurs in the vaccine.
On the other hand, a flap means excising and transferring a tissue with either a preserved or surgically reconstructed blood supply at the recipient site. Until recently, flaps have been preferred over grafts for replacement urethroplasty because of their theoretical benefits of carrying blood flow and therefore their viability is safer. Flap construction is time consuming, with extensive dissection and repositioning of the dartos fascia, tending to cause penile deformity and scarring. There has been a recent increase in the use of grafts for urethral reconstruction in the last decade due to the extraordinary success of free grafts that are technically more efficient. There are the following types of graft used for urethral reconstruction:
• Full thickness skin graft,
• Scrotum and,
Skin graft in the thickness of the penis and extra genital areas,
Bladder epithelial grafts
Oral mucosal grafts,
Used for replacement urethroplasty and includes tunica vaginalis, tunica albuginea, colonic mucosa, small intestine submucosa, and human dura matter. Scrotal skin is used for two-stage urethroplasty as it provides a large number of easily accessible grafts. However, keratinized epithelium and split thickness depth postoperative contracture, hyperkeratosis cause graft failure in the wet environment of the urethra and an increased risk of diverticulum formation. In addition, scrotal skin is often hair-retaining and can form hairballs in the urethra.
Non-hairy full-thickness grafts made from the penis initially provided satisfactory results in urethral reconstruction for stricture. However, donor site problems such as penile scar formation, torsion of the penis, recurrence of stenosis and high probability of failure in the presence of balanitis have been found. Bladder mucous grafts may theoretically be well suited for contact with urine, but their use is associated with many complications such as meatal stenosis, prolapse, and granulomatous reaction in the urethral meatus. In addition, removal of the bladder mucosa is difficult, especially in patients who have had previous bladder surgery, exstrophy, chronic cystitis or neurogenic dysfunction, poorly managed and prone to shrinkage.
Unlike the bladder mucosa and skin, the oral mucosa has a thick, non-keratinized epithelial layer and a well vascularized thin lamina propria that supports early vaccination. Among reconstructive urologists, the oral mucosa emerges as the ideal substitute for the urethra with medium-term results comparable to penile skin flaps.

Single Stage Oral Mucosal Graft Meatoplasty

This technique is used in patients with hypospadias or ischemic urethral stenosis within the glans. The external urethral meatus and fossa navicularis are opened completely. The oral mucosa graft is sutured to the left side of the opened urethra. The graft is rotated over the urethral plate and stitched to the right of the urethra. The glans is covered over the graft and the Foley silicone catheter remains in place for a week.

Dorsal Oral Mucosal Graft Urethroplasty

Dorsal oral mucosal grafts are recommended for the repair of penile urethral strictures only in patients with normal corpus spongiosis. A foreskin incision is made by dissolving the penis completely, the penis urethra is exposed and the narrow channel is opened completely through a ventral midline incision. The oral mucosa graft is stitched and quilted by cutting 6/0 sutures to the dorsal urethral incision bed. The urethra is closed and tubular and a dartos facial flap is obtained to close the urethral repair.

Progressive Oral Mucosal Graft Urethroplasty

Staged oral mucosal graft urethroplasty is recommended for patients with complex penile or bulbar strictures associated with a long stenosis, such as fistula, periurethral inflammation, perineal abscess, and extensive local scar, balanitis xerotica obliterans (BXO), or previous failed urethroplasties. Such adverse local tissue conditions do not support graft harvest and therefore require staging of the operation. In the first stage, the urethral plate is removed, the glans is fully opened and the oral mucosa graft is laid over the tunica albuginea and quilted. After six months, the graft is completely removed, and the urethra becomes tubular.

Augmented Anastomotic Urethroplasty

Augmented anstomotic urehroplasty combines stenosis excision and urethral floor (or roof) strip reanastomosis with augmentation of the anastomotic area using a penile skin flap or a full thickness graft (oral mucosa). The urethra is cut at the distal border of the stricture and approached like a standard anastomotic repair, and the narrow part of the urethra is opened proximally on the dorsal surface. Augmentation is strictures susceptible to anastomotic repair, long bulbar strictures (> 2 cm) where excision and primary anastomosis can result in short urethra and cord formation.

Onlay Graft Orientation

There is controversy about placing oral mucosa grafts dorsal, ventral or lateral to the urethra. Traditionally, grafts were placed on the ventral side of the urethra because it allows easier access to the urethra and better visualization of the stricture. Some authors have argued that the use of oral mucosa grafts as ventral onlay grafts gives good results.
Use of Oral Mucosa Grafts in the Treatment of Urethral StrictureAdding that the dorsal approach to bulbar urethral strictures is anatomically superior to the ventral, requires less wide opening of the spongy tissue, and significantly reduces bleeding from the corpus spongiosum and mechanical weakening of the graft, supported dorsal placement of buccal mucosa grafts with better results. Dorsal placement of the graft on the urethra is simpler and safer in the distal portion of the bulbar urethra, while ventral placement of the graft is more effective in the proximal bulbar urethra, where the spongy tissue is thicker and has better vascularization. In addition, a dorsally placed graft is more stable than a ventral graft and is mechanically supported (by the body body).

Combined Tissue Transfer

Widespread, focally dense or panurethral strictures involving multiple segments of the anterior urethra present a very difficult situation as there may not be enough oral mucosa to complete the repair. One of the reconstructive options in this case is the use of a combination of oral mucosa and genital skin island flaps to reconstruct the long urethral defect. Therefore, dorsally placed oral mucosa grafts can be combined with various replacement materials such as preputial skin, pedicle flaps, labial mucosa, and human urethral mucosa of the corpse. This enables one-stage reconstruction of urethral strictures, avoiding the problems associated with hair-bearing flaps and two-stage procedures.

Oral Mucosa as Tube Graft

Tubularized grafts in urethral reconstruction have failed, mainly due to insufficient graft harvest, as they are surrounded by peripheral vascularized tissue. The use of oral mucosa onlay grafts is superior to tubularized grafts.

References:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3193738/
https://www.hindawi.com/journals/au/2015/979868/

Author: Ozlem Guvenc Agaoglu


Leave a Reply

Your email address will not be published. Required fields are marked *