Hypospadias is one of the most common congenital defects in pediatric urology. It is caused by anterior urethral maldevelopment, so the ectopic urethral meatus may be located anywhere from the tip of glans to perineum. The penile shaft is often accompanied by ventral curvature and the prepuce accumulate at the dorsum of the glans. Urethroplasty is the only method to treat hypospadias. Today, there are more than 300 surgical techniques to treat this disease, but every technique has some corresponding surgical complications, which is most likely in urethral fistula. So far, there are no common standard surgical techniques has been approved by all pediatric urologists [19-21].
In our center, tubularized preputial island flaps are the most commonly used technique of single-stage urethroplasty for hypospadias accompanied by penile curvature. The most common short-term complications are urethral fistula and stricture. It is reported that preputial vascular pedicle flap ischemia and necrosis are the reason for fistula. The exact relationship between the postoperative complications and the structure of the patients’ preputial blood vessels is unclear [10]. To figure out this problem, we utilized micro-CT for 3D analysis of morphologic characteristic on the rat model of hypospadias.
Preputial skin is the ideal molding materials for urethroplasty. In order to get a preputial pedicle flap with an adequate blood supply, we need to understand the distribution of preputial vessels. The prepuce vessels are the terminal branch, the capillaries are extremely narrow, thus knowledge about the vessels is limited. Much work has been done to study prepuce vessels, such as transillumination with endoscopic cold light source, microscopic observation of gelation and India ink perfusion, 3D reconstruction of histological sections [10-12]. In this study, an advanced technology, micro-CT scanning, is used to analysis the distribution of preputial vessels.
Micro-CT is an innovative non-invasive and high-resolution imaging technology. O’Neill et al found the results of virtual sectioning at micro-CT and conventional histologic sectioning are highly correlated [18]. The CTvox(Bruker)software can be used to observe the samples by transverse, sagittal, and coronal section image, and established 2- or 3-dimensional reconstruction on interesting parts. The highest resolution has reached 0.5μm, while the mean diameter of capillary vessels is 6 to 9μm, so micro-CT can be used to micro vessels scanning[22] .
There are a variety of choices for preputial vessel pedicle flap in hypospadias surgery. Although all flaps are reasonably designed to preserve sufficient blood supply for a better survival, the complication did not reduce significantly. Today, blood supply of the penis is divided into three systems:1. the dorsal penile vessels which provides the blood supply to glans, urethra and inner prepuce; 2.the cavernosa artery supply the blood to the deep soft tissues, especially to the corpora cavernosa and corpus spongiosum; 3. the superficial fascia vessels originated from the descending branch of the external pudendal arteries which provide the blood supply to the penile skin and prepuce. The superficial and deep layers of the superficial fascia are easy to dissociate. The junction of the inner and outer prepuce where has abundant blood supply and is suitable to make a preputial vessel pedicle. Four main types of deep layer vessels have been described: single branch predominant type (41%), two branches predominant type (25%), arching H-type (12.5%), or net-like type (21%). The qualities of the vascular pedicle and the urethral plate are the two important surgical variables [23].
Tubularized preputial island flaps are the ideal single-stage repairs for the proximal hypospadias. For the patients with severe hypospadias and severe ventral curvature, two-stage operation is still meaningful [24]. Clinical data indicates that penile curvature corrected in the first phase, urethroplasty is done in second phase to reduce the incidence of complications. Two-stage surgery reduce the difficulty of operation somewhat, on the other hand it increases surgical operation times and prolonged treatment time [25]. This experiment confirmed that in the normal group and the mild hypospadias group, the blood vessels at the junction of the inner and outer prepuce had a wider caliber and formed a vascular ring. While in the group with severe hypospadias, the blood vessels at the junction of the inner and outer prepuce had a relatively smaller caliber displayed a net-like distribution and could not form a clear and complete vascular ring. These results may explain patients with severe hypospadias are more likely to suffer from postoperative complications than the ones with mild hypospadias.
We divided the severe hypospadias group into two types based on their vascular morphology: The first type has a sufficient blood supply, although the blood vessels at the junction of the inner and outer prepuce could not form a vascular ring completely due to the ventral prepuce defect, there is a semi-circular vessel structure, and the semi-vascular ring diverge small branches into the inner preputial skin to ensure an efficient supply of blood; For the second type, there is no semi-vascular ring to support the efficient blood circulation, the vessels are netlike distributed and contains mainly capillaries so there is no sufficient supply of blood to the preputial vessel pedicle flap.
This result may explain that patients with severe hypospadias achieved satisfactory results without postoperative complications after one stage surgery because their blood vessels at the junction of inner and outer prepuce provide a sufficient amount of blood for a better survival of the flap. At the same time, we conclude that patients of severe hypospadias with poor vessels structures are highly recommended to underwent two-stage surgery to reduce postoperative complications.
The limitation of this study is that the human penile anatomy is different from penile anatomy of rats. This study may not represent the anatomy of the humans. The next step, the clinical experiment will be used to detect the exact relationship between the postoperative complication and the anatomy of the preputial vessels.