External Pudendal Artery Perforator (EPAP) Hemi-Scrotal Flap
The EPAP hemi-scrotal flap is a sensate perforator-based fasciocutaneous flap harvested from one hemiscrotum, pedicled on a perforator of the external pudendal artery with incorporation of the anterior scrotal nerve for protective sensation. First described by Tsukuura et al. (2025) for circumferential penile-shaft skin defect reconstruction, it represents the pedicled clinical realization of the cadaveric STEPA (Super-Thin External Pudendal Artery) flap described by Phoon 2014 — at a mean flap thickness of 1.1 mm, scrotal skin is the thinnest available flap tissue, making the hemiscrotum an ideal donor for "like-with-like" penile resurfacing.[1][11]
For the operative-level deep-dive in scrotal flap glanuloplasty / penile resurfacing see the EPAP Hemi-Scrotal Flap atlas page (04e).
Vascular Anatomy of the External Pudendal System
External pudendal arteries
The external pudendal arteries arise from the femoral artery (occasionally the deep femoral) and exist as two distinct vessels:[2][3]
- Superficial external pudendal artery (SEPA) — courses superficial to the spermatic cord; supplies suprapubic skin, mons pubis, and upper scrotum. Present in 92% of specimens; diameter 1.2–3.8 mm. Variable — duplicated in 46%, common trunk with the deep branch in 24%, single in 30%. Origin 0.8–8.5 cm below the inguinal ligament.
- Deep external pudendal artery (DEPA) — courses deep to the spermatic cord medially; mean internal diameter 0.60 mm. Gives off the inferior external pudendal artery, the dominant supply to each hemiscrotum.[3][4]
Surgical landmark. 83% of external pudendal arteries arise between the inter-pubic-tubercle horizontal and 3 cm below it, centered on the femoral artery.[5]
Scrotal cutaneous territories (Carrera 2009)
Three richly inter-anastomosed territories:[4]
- Two lateral territories — each supplied by an inferior external pudendal artery entering at the midpoint of the scrotal root, fanning out across the entire hemiscrotum.
- One central territory — perineal-artery branches (internal pudendal system) running deep on both sides of the scrotal septum.
This dual-system supply (external pudendal laterally, internal pudendal centrally / posteriorly) is the anatomical basis for safely harvesting one hemiscrotum while preserving contralateral perfusion.
Perineal perforators
Jin's microdissection of 22 sides identified 4 relatively constant perforating arteries in the perineum (inguinal and perineal perforating branches of the SEPA), forming upper, middle, and lower vascular anastomotic networks within the deep fascia above the adductor wall.[6]
The EPAP Flap — Innovations Over Traditional Scrotal Flaps
Traditional scrotal flaps for penile resurfacing (Zhao 2009, n = 18 over 15 yr) used bilateral or total-anterior scrotal-skin flaps supplied by anterior ± posterior scrotal arteries, with three liabilities:[1][7]
- Required sacrifice of both external pudendal arteries (bilateral designs).
- Tunica vaginalis remained attached to the flap pedicle → pain and stretching during erection.
- Midline raphe donor scar.
The EPAP perforator-based design addresses each:[1]
| Innovation | Effect |
|---|---|
| Isolate the perforator | Wider arc of rotation; only one external pudendal system sacrificed. |
| Free the tunica vaginalis from the flap pedicle | Eliminates erection-related pain and stretching. |
| Incorporate the anterior scrotal nerve | Sensate reconstruction (protective sensation for trauma, temperature, pressure). |
| Unilateral harvest | Primary closure of the donor with a lateral (rather than midline) scar. |
Surgical Technique[1]
Preoperative planning
- Handheld Doppler maps the external pudendal artery perforator at the scrotal root.
- Flap designed on one hemiscrotum, pedicle at the scrotal root.
Flap elevation
- Incise the hemi-scrotal skin paddle and elevate above the external spermatic fascia.
- Identify and isolate the external pudendal artery perforator as the vascular pedicle.
- Identify and preserve the anterior scrotal nerve within the flap.
- Free the tunica vaginalis from the flap pedicle — the critical step that distinguishes EPAP from traditional scrotal flaps and prevents testis–penis tethering.
- Rotate the flap on its perforator pedicle to wrap circumferentially around the penile shaft.
Inset and donor closure
- Wrap the flap around the penile shaft for tension-free circumferential coverage.
- Advance the contralateral hemiscrotum and residual scrotal skin for primary donor closure, leaving a lateral scrotal scar.
Flap Characteristics
| Parameter | Value |
|---|---|
| Blood supply | External pudendal a. perforator (SEPA or DEPA) |
| Sensory nerve | Anterior scrotal nerve |
| Flap thickness | ~1.1 mm (thinnest available flap tissue)[11] |
| Pedicle length | ~10–12 cm |
| Pedicle artery diameter | 2.81 mm at origin |
| Pedicle vein diameter | 4.44 mm |
| Composition | Fasciocutaneous (scrotal skin + dartos) |
| Donor closure | Primary |
| Hair-bearing | Yes |
Advantages
- Sensate. Anterior-scrotal-nerve inclusion delivers protective sensation — important on a penis that must perceive trauma, temperature, and pressure.[1]
- "Like with like." Scrotal skin matches penile skin in thinness, elasticity, pliability, and pigmentation. STEPA confirmed ~1.1 mm thickness, the thinnest of all named flap territories.[11]
- No erection-related pain. Freeing the tunica vaginalis from the pedicle removes the tethering source of erectile pain seen with traditional scrotal flaps.[1]
- Unilateral harvest preserves the contralateral hemiscrotum and allows primary donor closure.[1]
- Wider arc of rotation than random-pattern or axial scrotal flaps because perforator isolation untethers the skin paddle from underlying fascia.[1]
- Lateral, more inconspicuous scar vs midline raphe.[1]
- Single-stage — no flap division required.
The External Pudendal Flap Family
The EPAP sits within a family of flaps using the same vascular system:
| Flap | Pedicle | Use | Reference |
|---|---|---|---|
| STEPA (Super-Thin EPA, Phoon 2014) | Free flap on EPA | Cadaveric; thinnest free flap at 1.1 mm; proposed for hand dorsum, foot, head/neck, joints | Not yet clinical[11] |
| EPAP hemi-scrotal (Tsukuura 2025) | Pedicled perforator + anterior scrotal n. | Circumferential penile-shaft resurfacing | Single case report[1] |
| SEPAP (Kim 2023) | Superficial EPA perforator | Suprapubic / upper scrotum in penoscrotal Paget's reconstruction algorithm | Series[12] |
| DEPAP (Kim 2025) | Deep EPA perforator from upper medial thigh | Perineal reconstruction after Fournier's; preoperative handheld Doppler mapping; 9-mo stable result in case report | Case report[13] |
| Superficial EPA pedicle flap (Mayer 1991) | SEPA-pedicled suprapubic skin | Vulvar reconstruction; pre-perforator-era predecessor | Series[14] |
| Pull-up double-opposing KDPIF on SEPAP (Lee 2020) | SEPAP "hot spots" | Circumferential penile defect; 10 × 13 cm bilateral keystones; full survival at 6 mo, no ED / shortening | Case report[15] |
Indications
| Indication | Detail |
|---|---|
| Circumferential penile-shaft skin defect | Primary indication (Tsukuura 2025).[1] |
| Partial penile skin loss | When scrotal skin offers the best tissue match. |
| Post-paraffinoma / foreign-body excision | E.g., petroleum-jelly injection (Lee 2020 keystone variant).[15] |
| Penile SCC excision | Circumferential resurfacing after wide excision. |
| Penile burns / mechanical trauma | Penile-skin avulsion or thermal injury. |
| Penoscrotal Paget's / Fournier's / vulvar reconstruction | Broader EPA family (SEPAP / DEPAP variants).[12][13][16] |
Comparison With Other Penile Resurfacing Options
| Method | Thickness | Sensate | Erection pain | Donor morbidity | Tissue match |
|---|---|---|---|---|---|
| EPAP hemi-scrotal[1] | 1.1 mm | Yes (anterior scrotal n.) | No (tunica freed) | Low; primary closure | Excellent |
| Traditional bilateral scrotal flap[7] | 1.1 mm | Variable | Yes (tunica tethered) | Moderate | Excellent |
| STSG | Variable | No | No | Moderate (thigh donor) | Poor (color / texture) |
| ALT | 5–10 mm | No (unless LFCN) | No | Moderate | Poor (too thick) |
| SCIP | 2–3 mm | No | No | Low | Moderate |
| Keystone SEPAP[15] | 2–3 mm | Variable | No | Low | Good |
Limitations
- Limited clinical experience — described in a single case report; series and long-term outcomes pending.[1]
- Hair-bearing — scrotal hair on the resurfaced shaft may require depilation.[11]
- Pigment / rugation mismatch — scrotal skin is darker and more rugated than native penile skin.[11]
- Anatomical variability of the EPA system — SEPA duplicated 46%, common trunk 24%, absent 8%; preoperative Doppler mapping recommended.[2]
- Finite flap size — a single hemiscrotum provides limited tissue; very large defects may require additional flaps or grafts.
- Ipsilateral testicular position may be altered by harvest, though primary closure of the donor mitigates this.
See Also
- EPAP Hemi-Scrotal Flap (04e atlas page)
- Scrotal Reconstruction Techniques
- SCIP flap
- Singapore / pudendal-thigh flap
- Lotus petal flap
- Anterolateral thigh flap
References
1. Tsukuura R, Engmann T, Miyazaki T, Yamamoto T. The sensate external pudendal artery perforator (EPAP) hemi-scrotal flap for the circumferential skin defect of the penile shaft: a case report and literature review. Microsurgery. 2025;45(7):e70123. doi:10.1002/micr.70123
2. La Falce OL, Ambrosio JD, Souza RR. The anatomy of the superficial external pudendal artery: a quantitative study. Clinics (Sao Paulo). 2006;61(5):441–444. doi:10.1590/s1807-59322006000500011
3. Giraldo F, Mora MJ, Solano A, González C, Smith-Fernández V. Male perineogenital anatomy and clinical applications in genital reconstructions and male-to-female sex-reassignment surgery. Plast Reconstr Surg. 2002;109(4):1301–1310. doi:10.1097/00006534-200204010-00014
4. Carrera A, Gil-Vernet A, Forcada P, et al. Arteries of the scrotum: a microvascular study and its application to urethral reconstruction with scrotal flaps. BJU Int. 2009;103(6):820–824. doi:10.1111/j.1464-410X.2008.08167.x
5. Allepot K, Morel-Journel N, Boucher F. Microsurgical phalloplasty: anatomical study evaluating the use of the external pudendal vessels as recipients. Clin Anat. 2023;36(3):393–399. doi:10.1002/ca.23958
6. Jin B, Hasi W, Yang C, Song J. A microdissection study of perforating vessels in the perineum: implication in designing perforator flaps. Ann Plast Surg. 2009;63(6):665–669. doi:10.1097/SAP.0b013e3181999de3
7. Zhao YQ, Zhang J, Yu MS, Long DC. Functional restoration of penis with partial defect by scrotal skin flap. J Urol. 2009;182(5):2358–2361. doi:10.1016/j.juro.2009.07.048
11. Phoon AF, Shah AK, Cormack GC, Saint-Cyr M. The super-thin external pudendal artery (STEPA) flap. J Plast Reconstr Aesthet Surg. 2014;67(10):1397–1406. doi:10.1016/j.bjps.2014.05.044
12. Kim WJ, Kim SH, Sung HH, Lee KT, Pyon JK. Penoscrotal defect reconstruction using loco-regional flaps in treatment of extramammary Paget's disease: experience and suggestion of a simplified algorithm. Microsurgery. 2023;43(4):316–324. doi:10.1002/micr.30988
13. Kim DG, Lee KA. The usefulness of DEPAP flaps for reconstructing perineal defects caused by Fournier's gangrene: a case report. J Clin Med. 2025;14(24):8732. doi:10.3390/jcm14248732
14. Mayer AR, Rodriguez RL. Vulvar reconstruction using a pedicle flap based on the superficial external pudendal artery. Obstet Gynecol. 1991;78(5 Pt 2):964–968.
15. Lee HG, Lim SY, Yoon CS, Kim KN. Circumferential penile defect reconstruction with pull-up double-opposing keystone-designed perforator island flaps: a case report. Medicine (Baltimore). 2020;99(3):e18762. doi:10.1097/MD.0000000000018762
16. Huang JJ, Chang NJ, Chou HH, et al. Pedicle perforator flaps for vulvar reconstruction — new generation of less invasive vulvar reconstruction with favorable results. Gynecol Oncol. 2015;137(1):66–72. doi:10.1016/j.ygyno.2015.01.526