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Bilobed Flap

The bilobed flap is a double transposition flap consisting of two lobes that share a common pivot point, designed to recruit tissue from an area of greater laxity through a sequential relay mechanism — the primary lobe fills the defect, the secondary lobe fills the primary lobe's donor site, and the secondary donor site is closed primarily.[1][2] Best known as a workhorse for nasal reconstruction, the bilobed principle has been adapted to urologic and urogynecologic reconstruction through innovative regional-flap modifications — particularly the bilobed pudendal artery perforator (PAP) flap and the bilobed gracilis myocutaneous flap.

This page is the foundations-level deep dive on the bilobed principle in GU reconstruction. Site-specific technique pages link back here.

Geometric Principle​

The bilobed flap was originally described by Esser (1918) with two equal-sized lobes at 90° and 180° from the defect. Zitelli's modification (1989) — now the standard design — reduced the total arc of rotation to approximately 90–100°, with each lobe pivoting ~45° from the preceding one, which significantly decreased the standing cutaneous deformity (SCD, or "dog ear") and pincushioning.[3][4]

Key design elements​

ElementDetail
Pivot pointGeometric center around which both lobes rotate. Its precise placement is the single most critical determinant of flap mechanics — altering the SCD size or orientation shifts the pivot point and changes the effective arc of rotation[5]
Primary lobeWidth equal to the defect diameter; length extends from the pivot to the far edge of the defect; fills the defect[2][6]
Secondary lobeTypically 50–75% the width of the primary lobe; fills the primary-lobe donor site; smaller size allows primary closure of the secondary donor site[2][6]
Standing cutaneous deformity (SCD)Triangle of redundant tissue excised at the base to allow rotation. Mathematical modeling shows that altering SCD length or orientation changes the pivot location, requiring compensatory adjustment of the rest of the design[5]
Total arc of rotation~90–100° (Zitelli) vs. 180° (Esser) — reduces tissue distortion and secondary motion[3][4]

A simple triangle template method facilitates accurate flap design: an equilateral triangle is constructed with one vertex at the center of the defect and the opposite side serving as the base of the secondary lobe, ensuring correct pivot placement.[7]

Why bilobed differs from single-flap transpositions​

The bilobed flap distributes the tension of closure across two sequential transpositions rather than concentrating it in a single flap (as in the rhomboid / Limberg flap). This is particularly suited to areas where tissue laxity is asymmetrically distributed — the secondary lobe can be oriented toward the zone of greatest laxity while the primary lobe is directed toward the defect.[1]

Urologic Applications​

Bilobed gracilis myocutaneous flap — perineal and genital reconstruction​

The most significant urologic adaptation of the bilobed principle is the bilobed gracilis flap, developed by Vyas and Pomahac (2010) and refined by Weinstein et al. (2020).[8][9]

Rationale. The traditional gracilis myocutaneous flap has a well-known limitation — when harvested with a vertical skin paddle, distal-tip necrosis is common because of inconsistent perforator anatomy beyond the proximal angiosome. Orienting the paddle transversely improves reliability but shortens the rotational arc and limits skin-paddle size. The bilobed design solves both problems:[8]

  • A larger transverse primary lobe (with a shorter, more reliable arc of rotation) is transposed into the perineal / genital defect
  • A shorter vertical secondary lobe is inset into the transverse donor site (rather than into the critical wound bed), maximizing incorporation of the gracilis muscle's nearly circular angiosome
  • This design harvests a larger total skin paddle while maintaining reliable perfusion throughout

Clinical experience.

  • Weinstein et al. (2020) reported 6 bilobed gracilis flaps (5 oncologic perineal defects, 1 Fournier's gangrene) in patients with compromised abdominal donor sites (prior surgery, radiation). All patients had received adjuvant chemoradiation. The bilobed gracilis provided ample soft-tissue bulk for deep, irregularly contoured defects where the VRAM flap was unavailable.[9]
  • Recommended indications: moderate-to-large perineal / genital defects, defects requiring substantial soft-tissue bulk, and patients with limited abdominal donor sites (prior laparotomy, ostomy, prior VRAM harvest).[9]

This flap is particularly relevant in urologic practice for reconstruction after abdominoperineal resection, pelvic exenteration, and Fournier's gangrene — settings where the VRAM workhorse may be unavailable.

Penile and scrotal reconstruction — bilateral flap designs​

While the term "bilobed" is not always explicitly used, the geometric principle of bilateral pedicled flaps with sequential tissue relay is applied in penile-skin reconstruction. Modified bilateral scrotal flaps — described as "butterfly" configurations — use bilateral pedicled flaps from each side of the scrotal midline to cover circumferential penile-skin defects:[10][11]

  • 7-patient series: bilateral scrotal flaps achieved significant increases in flaccid and erectile penile length, with only 2 cases of minor partial necrosis managed conservatively[10]
  • 22-patient series (buried penis, foreign-body injection, trauma): bilateral pedicled scrotal flaps achieved median global satisfaction 8/10 and erection-hardness 3.5/4, though 27.3% required late surgical revision for skin retraction[11]

These bilateral designs share the bilobed flap's fundamental principle of distributing closure tension across two tissue sources rather than relying on a single flap.

Urogynecologic Applications​

Bilobed pudendal artery perforator (PAP) flap — vulvar and perineal reconstruction​

Yun et al. (2010) described the bilobed PAP flap specifically designed for the unique anatomy of the perineum.[12]

Anatomic rationale. The perineum consists of two functionally distinct triangles — the urogenital triangle (anterior) and the anal triangle (posterior) — which differ in tissue characteristics and function. A single unilobed flap often cannot adequately reconstruct defects spanning both triangles while preserving the distinct properties of each. The bilobed design addresses this by:[12]

  • Improving the arc of rotation — the two lobes can be independently oriented to cover wide, irregularly shaped defects
  • Increasing flap mobility — enabling coverage of deep defects
  • Preserving the functional characteristics of each triangle — each lobe can be tailored to match its recipient tissue

Clinical results (15 female patients):[12]

  • Indications: 7 vulvar cancer, 7 extramammary Paget's disease, 1 rectovaginal fistula
  • 9 bilobed flaps and 6 unilobed flaps — selected based on defect location and shape
  • Flap sizes ranged from 3 × 4 cm to 13 × 12 cm
  • 100% flap survival during the entire follow-up period (mean 4.6 months)
  • All reconstructed areas achieved good functional and aesthetic conditions

The bilobed PAP flap is positioned within the vulvoperineal reconstruction algorithm as an option for medium-to-large defects spanning the urogenital and anal triangles, where a single unilobed flap would be insufficient or would distort adjacent anatomy.[12][13]

Perineal body reconstruction after obstetric injury​

Jandali et al. (2010) described bilateral pedicled bilobed flaps for reconstruction of cloacal-like defects after fourth-degree obstetric lacerations:[14]

  • Fourth-degree lacerations can destroy the anterior anal sphincter and thin the perineum / rectovaginal septum, causing fecal incontinence and sexual dysfunction
  • The technique combines anterior anal-sphincter repair with perineal body reconstruction using bilateral bilobed flaps
  • The bilobed design provides sufficient bulk to reconstruct the perineal body while simultaneously restoring rectovaginal-septum thickness
  • Each bilobed flap contributes two tissue components: one lobe reconstructs the perineal body, the other closes the donor site

This is particularly relevant in urogynecology, where complex perineal-body deficiency after failed primary obstetric repair may require tissue augmentation beyond what simple layered closure can achieve.

Vulvar reconstruction algorithms​

Modern vulvar reconstruction algorithms incorporate the bilobed principle within the broader framework of perforator-based reconstruction. The Toulouse Algorithm (Ricotta et al., 2025) proposes a location-based approach to vulvar cancer reconstruction with perforator flaps as the first-line option:[13]

  • For defects spanning multiple vulvar subunits, multiple perforator flaps (which may include bilobed configurations) are preferred over single large musculocutaneous flaps
  • Perforator flaps reduce donor-site morbidity vs. traditional musculocutaneous options (VRAM, gracilis) while providing equivalent coverage[13]

Hong et al. (2017) demonstrated the feasibility of multiple pedicled perforator flaps for extensive perineal defects, using a mean of 2.31 flaps per patient with 100% flap survival and no donor-site complications in 16 patients.[15] While not all were bilobed configurations, the principle of combining multiple tissue sources to cover complex multi-compartment defects is conceptually aligned with the bilobed approach.

Comparison with Other Geometric Flap Techniques​

FeatureBilobedRhomboid (Limberg)Z-plastyV-Y advancement
MechanismDouble transposition via two sequential lobesSingle transposition into a rhomboid defectTransposition of two triangular flapsAdvancement into a defect
Arc of rotation90–100° (Zitelli)~60°VariableNone (linear advancement)
Key advantageRecruits tissue from zone of maximal laxity via relaySimple, predictable geometryScar reorientation up to 90°No transposition; perforator-based
Tension distributionAcross two transpositionsConcentrated at single closureRedistributed along new axisAlong advancement vector
Best forAsymmetric tissue laxity; multi-compartment defectsSmall–moderate defects with adequate adjacent tissueCircumferential contracturesTissue advancement into a defect
Urologic nichePerineal / genital reconstruction (bilobed gracilis)Epispadias-exstrophy, scrotal reconstructionHypospadias revision, phimosisPenile lengthening, Fournier's
Urogynecologic nicheVulvoperineal defects spanning both triangles; perineal-body reconstructionSmall posterior vulvar defectsTransverse vaginal septum, vaginal constrictionVulvovaginal oncologic defects

When to Reach for the Bilobed Flap in GU Reconstruction​

  • Defects that are irregularly shaped or span multiple anatomic compartments (urogenital + anal triangle), or where tissue laxity is asymmetrically distributed.[9][12]
  • When the primary workhorse flap is unavailable (prior VRAM harvest, hostile abdomen, ostomy adjacent to the planned skin paddle).[9]
  • Preferred bilobed configurations:
    • Bilobed PAP flap — vulvoperineal defects spanning both triangles[12]
    • Bilobed gracilis — deep pelvic / perineal defects requiring bulk after APR / exenteration / Fournier's[8][9]
    • Bilateral bilobed perineal flaps — perineal-body reconstruction after fourth-degree obstetric injury[14]

Limitations: more complex design and execution than single-lobed transposition flaps; requires careful pivot-point planning; the secondary lobe must be oriented toward adequate tissue laxity for primary closure.[1][5]

Technical Pearls​

  • Plan the pivot point first, then design both lobes outward from it. Most bilobed-flap problems trace back to a misplaced pivot rather than to lobe sizing.[5]
  • Make the secondary lobe smaller than the primary (typically 50–75% width). Equal-sized lobes recreate the original Esser geometry and produce more pincushioning.[2][6]
  • Orient the secondary lobe toward the zone of greatest tissue laxity, not toward an aesthetic axis — the secondary donor site is what closes primarily, so its laxity determines whether the design works.
  • Use the triangle-template method for design discipline, especially when learning the flap.[7]
  • In bilobed gracilis, harvest the transverse paddle as the primary lobe and the vertical paddle as the secondary lobe — this preserves the reliable proximal angiosome for the recipient site.[8][9]
  • In bilobed PAP, map perforators with handheld Doppler before incision to confirm the bilobed configuration the perforator anatomy will support.[12]

See Also​

References​

1. Miller CJ. "Design Principles for Transposition Flaps: The Rhombic (Single-Lobed), Bilobed, and Trilobed Flaps." Dermatol Surg. 2014;40(Suppl 9):S43–S52. doi:10.1097/DSS.0000000000000115

2. Mehta JS, Olver JM. "Infraglabellar Transnasal Bilobed Flap in the Reconstruction of Medial Canthal Defects." Arch Ophthalmol. 2006;124(1):111–115. doi:10.1001/archopht.124.1.111

3. Yong JS, Christophel JJ, Park SS. "Repair of Intermediate-Size Nasal Defects: A Working Algorithm." JAMA Otolaryngol Head Neck Surg. 2014;140(11):1027–1033. doi:10.1001/jamaoto.2014.2258

4. Bennett A, Peters V, Meade A, Thornton J. "A Comprehensive Review of Bilobed Flaps in Nasal Reconstruction: Technique, Outcomes, and Considerations." J Craniofac Surg. 2024;35(7):2146–2149. doi:10.1097/SCS.0000000000010466

5. Pelster MW, Maher IA. "One-Sized Bilobed Flap Does Not Fit All Standing Cones: A Mathematical Analysis of the Standing Cone in Bilobed Flap Dynamics." Arch Dermatol Res. 2023;315(3):401–407. doi:10.1007/s00403-022-02361-z

6. Xue CY, Li L, Guo LL, Li JH, Xing X. "The Bilobed Flap for Reconstruction of Distal Nasal Defect in Asians." Aesthetic Plast Surg. 2009;33(4):600–604. doi:10.1007/s00266-009-9336-x

7. Man LX, Chang B. "A Simple Method of Designing a Bilobed Flap Using a Triangle Template." Dermatol Surg. 2004;30(10):1345–1348. doi:10.1111/j.1524-4725.2004.30408.x

8. Vyas RM, Pomahac B. "Use of a Bilobed Gracilis Myocutaneous Flap in Perineal and Genital Reconstruction." Ann Plast Surg. 2010;65(2):225–227. doi:10.1097/SAP.0b013e3181c9c434

9. Weinstein B, King KS, Triggs W, Harrington MA, Pribaz J. "Bilobed Gracilis Flap: A Novel Alternative for Pelvic and Perineal Reconstruction." Plast Reconstr Surg. 2020;145(1):231–234. doi:10.1097/PRS.0000000000006341

10. Yao H, Zheng D, Xie M, et al. "A Modified Bilateral Scrotal Flap for Penile Skin Defect Repair." J Vis Exp. 2022;(189). doi:10.3791/64017

11. Mendel L, Neuville P, Allepot K, et al. "Bilateral Pedicled Scrotal Flaps as an Alternative to Skin Graft in Penile Shaft Defects Repair." Urology. 2023;176:206–212. doi:10.1016/j.urology.2023.03.025

12. Yun IS, Lee JH, Rah DK, Lee WJ. "Perineal Reconstruction Using a Bilobed Pudendal Artery Perforator Flap." Gynecol Oncol. 2010;118(3):313–316. doi:10.1016/j.ygyno.2010.05.007

13. Ricotta G, Russo SA, Ferron G, Meresse T, Martinez A. "The Toulouse Algorithm: Vulvar Cancer Location-Based Reconstruction." Int J Gynecol Cancer. 2025;35(4):100065. doi:10.1016/j.ijgc.2024.100065

14. Jandali S, Noone RB, Pearson PY, Noone RB. "Perineal Reconstruction With Bilateral Bilobed Flap for Cloacal-Like Defect After Childbirth." Ann Plast Surg. 2010;64(1):62–64. doi:10.1097/SAP.0b013e31819ae0a6

15. Hong JP, Kim CG, Suh HS, et al. "Perineal Reconstruction With Multiple Perforator Flaps Based on Anatomical Divisions." Microsurgery. 2017;37(5):394–401. doi:10.1002/micr.30152