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Mirastschijski et al. Plast Aesthet Res 2020;7:45 I http://dx.doi.org/10.20517/2347-9264.2020.44 Page 3 of 13

METHODS
Anatomical studies
Initially, dissection studies were performed on cadavers at Hannover Medical School. Perfusion fixation
was carried out via the femoral artery with a solution containing 2.7% paraformaldehyde (n = 4). Because
the scrotal sac is positioned in the lower, dorsal parts of the supine laying body, a lot of liquid was found
in the tissue which made vessel studies difficult. Furthermore, this fixation technique turned the normally
soft and flexible genital tissue into a stiff matrix with rigid skin such that flap studies were impossible.
Consequently, for flap surgery, fresh cadavers within 24 h of death were chosen. Male pelvic parts of fresh
cadavers including the genitals (n = 4) were instilled with red silicone dye S 10 (KSK02A15.0 BIODUR® S
10; Biodur® Products GmbH, Heidelberg, Germany). Before vessel injection, the dye was mixed with the
hardener S 6 (KSH03A1.0 BIODUR® Härter S 6) in a ratio of 100:5. The abdominal aorta was dissected
and incised above the bifurcation. An anterograde tube was then inserted into the abdominal aorta above
the bifurcation into both common iliac arteries. Using a 500 mL perfusion syringe, the colour suspension
was pressed through the tube into the aorta by hand. The femoral artery was clamped below the exit of the
profunda femoris artery. About 500 mL was injected. The solution was distributed over the internal iliac
artery into the internal pudendal artery and over the external iliac artery into the external pudendal artery.
After one-day of hardening, preparation of the vessels was started. Pictures were taken with a Nikon D5100
and a Nikon D800E camera.

For studies of the genital vasculature, the main vessels were prepared and branches to the scrotal sac
and penis were followed. Of note, the testicular vasculature (funiculus spermaticus) was not dissected
or investigated. First, the external pudendal artery was dissected at its origin in the groin or upper
medial thigh and its course followed until the point of branching at the lateral aspect of the scrotal skin.
Interestingly, there were variations with regard to its origin: directly from the femoral artery (n = 3), from
the profound femoral artery (n = 2) and from the inferior epigastric artery (n = 1). Two donors had femoral
artery surgery previously such that anatomical studies of the thigh vessels were impossible due to severe
scarring and the presence of vascular implants.

For flap anatomy, incision markings were positioned as shown in Figure 1A-C, parallel to the midline
scrotal raphe. After incision, the scrotal fasciae were dissected carefully starting from the most caudal
point of the flap [Figure 1D-F]. The septum was visualized. Due to the prominent visibility of the septal
vessels, with the terminal branch running from the dorsal aspect of the septum like an arch to the ventral
plane of the scrotum, a second vessel was noticed with the same course but in a different plane. After
further dissection, it became clear that the scrotal midline is separated beneath the raphe by two septa each
containing one terminal branch of the internal pudendal artery on each side. Considering the embryology
and the fact that the scrotal sac is formed by the fusion of two embryonal swellings, this observation is
not the least surprising but rather, a logical consequence of embryological development. We could also
demonstrate a dual septum with separate vessels which were communicating with each other. Next, the
flap was pedicled on both septa and septal arteries, and lateral branches communicating with the central
branches were dissected, retaining those branches that inserted directly into the flap. The septa at the dorsal
aspect of the scrotum were released up to its cranial root and until sufficient mobility of the flap for penile
shaft coverage was achieved. The flap was wrapped around the penile shaft and closed at its dorsal aspect
[Figure 1G-I]. Because scrotal tissue is highly elastic, and due to pre-existing excessive cutaneous tissue,
the donor site was closed primarily after orchidopexy [Figure 1H and I]. Because the flap and its vascular
pedicle were designed around the scrotal midline, which is also called raphe, the flap was named the MiRA
flap.

The novel finding of the scrotal anatomy with presence of two scrotal septa including an arch forming
terminal branch of the internal pudendal artery is shown in detail in Figure 2. Since the scrotum is