Mohs Micrographic Surgery: Design and Execution of Tunneled Flaps

Indications

Skin flaps are indicated to repair large surgical defects or to minimize distortion of anatomically or cosmetically sensitive areas of the head and neck, such as eyelids, nose, lips, or mouth. Surgical defect repairs on the face can be particularly challenging due to this area's dynamic nature, function, mobility, and cosmetic importance. Surgeons often find it useful to conceptualize the face in terms of cosmetic units, dividing it into distinct regions based on location, fixed anatomical features, and functional considerations. This approach helps guide surgical planning to ensure repairs blend seamlessly with the face's natural contours and aesthetic characteristics. A surgical defect involving more than half of a cosmetic unit or important structures, such as cartilage, muscle, mucosa, and fat, may be classified as a more challenging or complex defect requiring a more complicated repair.[11]

When selecting a repair method, surgeons must carefully evaluate the defect's width, depth, and location; the presence of fixed anatomic structures; patient comorbidities; skin texture characteristics; and the availability of tissue reservoirs for movement. These factors ensure optimal functional and aesthetic outcomes. A tunneled island flap may be a good option for repairing large defects, minimizing distortion of fixed structures, or for patients wanting to limit the number of procedures. Tunneled flaps may be particularly useful for one-stage repairs in the central face where anatomical structures converge and on the ears with minimal distortion of facial architecture. In particular, they have been used to repair defects in the medial canthus, paranasal, and auricular areas.[10][12][13][14]

Tunneled flaps can minimize wound healing time compared to large defects left for secondary healing, thereby limiting the number of surgical repair procedures required. Compared to a standard island pedicle flap, the tunneled flap has a longer pedicle. The longer pedicle offers greater mobility and larger movement, allowing coverage of larger defects. In addition, preserving the integrity of the tunnel of normal skin helps enhance and maintain facial symmetry.[5]

Technique or Treatment

In a tunneled flap procedure, a subcutaneous tunnel is created adjacent to the defect, allowing a nearby stalk of skin to be moved through the tunnel to cover the defect left by tumor excision.

The procedure begins with tumor excision and confirmation of complete tumor clearance, either through Mohs micrographic surgery or permanent histological evaluation. A donor skin area of size and shape similar to the defect is selected nearby, and the pedicle is marked using a skin marker. To ensure flap survival, the pedicle must be designed with a width sufficient to maintain adequate blood supply (approximately 10-20 mm) and a length long enough to reach the defect without tension.

A full-thickness vertical incision is made, preserving underlying subcutaneous tissue and, in some cases, a portion of the muscle in the central pedicle. A tunnel is then created by lifting the subcutaneous plane with forceps and dissecting it with scissors to form a passage for the flap. The portion of the pedicle beneath the tunnel is typically de-epithelialized. The donor flap is passed through the tunnel and positioned into the recipient site with forceps. The flap is sutured into place, and the donor site is closed (see Image. Supraclavicular Artery Island Flap for Facial Reconstruction). Care is taken to avoid compressing, twisting, or overstretching the flap, as these factors can impede vascular perfusion and lead to necrosis or flap failure.[5]

Tunneled transposition flaps for auricular conchal bowl defects have demonstrated favorable aesthetic outcomes.[13] Common reconstruction options for conchal bowl defects include secondary healing, skin grafts, and flaps. Two-stage procedures, such as the flip-flop flap or cartilage-sacrificing flaps, are also frequently used for repair in this region. Tunneled flaps are particularly advantageous when tumor removal results in perichondrium loss. In such cases, secondary healing may be prolonged, and full-thickness skin grafts carry a high risk of failure unless the area is allowed to granulate or cartilage is removed to ensure adequate vascular perfusion. The tunnel often passes through the cartilage rather than subcutaneous tissue for auricular repair. The flap pedicle is typically harvested from the preauricular or postauricular region, depending on the defect's location, size, surrounding skin quality, and degree of sun damage.

A tunneled flap technique for conchal bowl reconstruction involves creating a subcutaneous tunnel between the tragus and antitragus and using a preauricular transposition flap with a caudal base. The segment of skin passed through the tunnel is de-epithelialized, allowing it to integrate with the recipient site. The preauricular donor site is closed linearly, and the distal end of the flap is sutured into the conchal bowl defect. This single-stage approach demonstrated excellent cosmetic outcomes, with a remarkable result observed 3 months postoperatively.[13]

Another option for conchal bowl reconstruction is a posterior-inferior-based postauricular donor pedicle tunneled through a subcutaneous channel at the defect's inferior edge. This technique offers the advantage of sun-protected donor skin, providing a good cosmetic texture and matching the conchal bowl. Another postauricular transcartilage tunneled flap, called the flip-flop flap, involves raising an island of skin from the mastoid and posterior ear surface.[15][5] These approaches provide effective aesthetic and functional repair options for conchal bowl defects.

For defects on the nasal root or medial canthus, a tunneled flap pedicle can be used to repair medially based surgical wounds. A lateral tissue reservoir supported by the superficial temporal artery may be tunneled medially for reconstruction. The glabellar region, supplied by the supratrochlear artery, serves as a viable tissue reservoir for nasal root defects.[16] A tunneled paramedian forehead flap using the supratrochlear artery minimizes the need for multiple procedures compared to the classic paramedian flap.[5][17] However, care must be taken to preserve the supraorbital nerve that runs superiorly from above the eyebrows to the scalp. Damage to this nerve during forehead surgery can lead to paresthesias, a risk that should be discussed with patients.

Tunneled flap pedicles have also been successfully taken laterally from the nasolabial fold to repair defects on the nasal tip, dorsum, or ala. This approach allows for a sebaceous tissue match to enhance cosmesis and discreetly places the donor site scar within the nasolabial groove. Unlike classic nasolabial cheek-to-nose flaps, tunneled paranasal flaps avoid complications such as blunting or fold elevation.[4] Tunneled flaps may rely on random vascularization, provided their length is less than 3 times their width. In cases like paramedian flaps, a named vessel, such as the supratrochlear artery, can be used for perfusion.[5][18]

Complications

Tunneled pedicle flaps are limited by the distance they can cover and the elevation they may cause above the pedicle. As with many skin flaps, tunnel flaps can also result in a trap door effect.[5] In some cases, this can be prominent and cosmetically unappealing. Oversizing the flap can result in bulkiness, tightness, or protrusion of the tissue tunnel. The trapdoor effect, or protrusion of the flap above the surrounding skin, can be minimized by designing a flap with a small base, undercutting the edges of the surrounding skin, undersize the flap by 20% to 25%, massaging the flap, and use of intralesional steroids. Primarily due to the flap causing elevation along the tunnel affecting the final cosmetic result, this flap is rarely used by plastic and dermatologic surgeons in favor of other more cosmetically pleasing closure techniques.[5][10][19] 

Periorbital flaps carry the risk of ectropion, and perioral flaps have the risk of eclabium. Perinasal or auricular flaps with cartilage removal carry the risk of inadequate functional support, contracture, or collapse. Other possible complications of tunneled flap procedures include flap failure or necrosis, most commonly at the distal edge of the flap. General surgical risks such as bleeding, hematoma, infection, bruising, contracture, and scarring also apply. The risk of flap failure or poor blood supply increases with a longer pedicle length, an overly narrow pedicle base limiting blood flow, or patient-specific risk factors, such as smoking or diabetes mellitus. Smoking, in particular, poses the highest risk to flap viability by impairing blood perfusion. Patients should be strongly encouraged to cease smoking before surgery to minimize this risk and optimize outcomes.

Clinical Significance

Tunneled flaps hold significant clinical value because they can achieve functional and cosmetic reconstruction of surgical defects while preserving nearby tissue integrity. These flaps are particularly beneficial in areas where tissue conservation is crucial, such as the face, ears, or other anatomically complex regions. By creating a subcutaneous or transcartilage tunnel to transfer a vascularized flap to the defect, this technique ensures a reliable blood supply and promotes optimal healing with minimal risk of wound dehiscence or necrosis.

Clinically, tunneled flaps are used to repair defects in cosmetically sensitive areas such as the nasal root, medial canthus, conchal bowl, and nasal tip. These flaps allow surgeons to use tissue reservoirs with similar texture, color, and sebaceous quality, enhancing overall aesthetic outcomes. In addition, tunneled flaps reduce donor site morbidity and often hide scar lines in natural anatomic concavities, such as the nasolabial fold or postauricular region.

This technique is particularly advantageous for managing complex defects caused by tumor excision, trauma, or congenital anomalies. The versatility of tunneled flaps allows for tailored repair in cases where secondary healing, skin grafts, or other flaps may not provide satisfactory results. Furthermore, using vascularized pedicles minimizes the risk of infection and enhances wound healing, making tunneled pedicle flaps a cornerstone in reconstructive surgery for challenging defects.

Enhancing Healthcare Team Outcomes

Effective execution of Mohs micrographic surgery with tunneled flap reconstruction requires a multidisciplinary approach to optimize patient-centered care, outcomes, and safety. Clinicians and surgeons must possess advanced skills in defect mapping, flap design, and tunneling techniques to ensure vascular integrity and achieve functional and cosmetic success. Nurses are critical in preoperative education, assisting during surgery, and monitoring for postoperative complications such as infection or flap necrosis. Pharmacists contribute by managing perioperative medications, including antibiotics and analgesics, and advising on anticoagulation management for patients at risk of bleeding. Advanced practitioners assist with patient evaluations, counseling, and setting realistic expectations. Collaborative interprofessional communication ensures thorough surgical planning, tailored patient care, and adherence to postoperative regimens, ultimately enhancing safety, outcomes, and team performance.

Although many Mohs micrographic surgical repairs can be completed in an outpatient setting under local anesthesia, some cases require referral to specialists for operating room-based procedures under general anesthesia. For example, extensive eyelid involvement affecting the tarsal plate, lacrimal apparatus, or levator muscle warrants referral to an oculoplastic surgeon. Large or complex nasal defects, particularly those involving the upper nose, may require an otolaryngologist, whereas oral involvement often necessitates oral maxillofacial or otolaryngology expertise. Total ear defects may need plastic surgery for rib grafting.[20][16] Recognizing when to involve specialists ensures optimal outcomes, especially for tumors in anatomically or functionally critical areas, underscoring the importance of a coordinated, multidisciplinary approach to care.