The internal mammary perforator flap
The internal mammary perforator (IMAP) flap is a relatively new flap for the reconstruction of head and neck defects. It was first described by Kalender and colleagues for the reconstruction of breast defect.1 Subsequently, the flap was described as an island flap for the treatment of chest wall radionecrosis.2 One of the first descriptions of the IMAP in the repair of head and neck defects was by Yu for the repair of a tracheostoma reconstruction.3 Later, Neligan described the IMAP in a case where the flap was used to resurface a large neck defect.4
Since the first description of the IMAP, several publications have further clarified the vascular distribution to the flap and the extent of perfusion from the arterial perforators to the anterior chest wall.5,6 This improved understanding has made the use of the IMAP predictable and reliable for the reconstruction of various head neck defects.
The IMAP flap has several advantages for the reconstruction of head neck defects. This flap is often used in cases of previously radiated necks with unstable skin and in patients with laryngectomies who have developed pharyngocutaneous fistulas. In these cases, the primary goal is the closure of the fistula. The guiding principle in these reconstructions is to repair the fistula while minimizing obstruction to the stoma.
The IMAP serves as a good flap option because it has the advantage of being distant from the previously radiated field, while also being a thin and pliable fasciocutaneous flap. Another obvious advantage of this flap is that it enables the repair of the fistula and the overlying skin while minimizing the need to enter the previously operated and radiated neck. This makes the reconstruction becomes more predictable and easier to execute. The location of the donor site is also favorable for most donors as it is easily concealed.
One of the disadvantage of this flap is that its use can be limited to the anterior neck and the arc of rotation.
The IMAP flap is an easy flap to harvest. When the reach will be adequate without the need for intramuscular perforator dissection, the flap may be raised rapidly with careful dissection along the medial aspect where the perforators emerge from the muscle.
The arterial supply to this flap is from the perforating branches of the internal thoracic artery (also known as the internal mammary artery). This is a paired artery arising from the subclavian artery near its origin, it travels downward approximately 1 cm lateral to the sternum and terminates as the superior epigastric and musculophrenic arteries. Cutaneous perforators arise from the internal thoracic artery in the first 5 to 6 intercostal spaces. They pierce through the intercostal muscles and medial fibers of the pectoralis major, travel in the subcutaneous tissue in a laterocaudal direction supplying the overlying skin.7 In their course, the perforators are accompanied by their venae comitantes. The anterior cutaneous branch of the intercostal nerves can provide sensory innervation to the flap.8 The perforators segmentally supply the skin of the anterior chest from the clavicle to below the submammary fold and from the midline to the anterior axillary line. From cadaveric studies, a reliable anatomy has been determined and the mean size of the skin area perfused by a single perforator is 13 × 7 cm, with the second perforator having the largest area of skin supplied measuring 16 × 9 cm.9 This allows a flap harvest size ranging from 13 × 7 cm up to 20 × 13 cm when based on adjacent perforators. The mean diameter of the perforators is 1.3 ± 0.5 mm with the second perforator consistently having the largest diameter with a mean of 1.6 ± 0.5 mm.10 Flaps based on the first and second internal mammary artery perforators are routinely used for anterior neck reconstruction.
Flap harvest is depicted in Figures 20.1 to 20.8.
- The patient is positioned in the supine position. Before making the flap design, a Doppler should be used to confirm the most prominent perforator and its intercostal location. Another option for confirming the location and best caliber of the perforator is to use a color flow ultrasound to inspect the size of the perforator as well as the path it takes towards the skin.
- The location and size of the defect is inspected and measured. Using a cord from the lap sponge or any other measuring string, the pivot point is placed directly over the main perforator. The opposite end of the string is then placed at the distal end of the defect. Care should be made to insure that the string is passive and not tented as this would result in a deficiency of the length and a potential problem with the reach of the flap.
- The string is then rotated to the thorax and the distal end is marked. This point represents the most distal end of the flap. The markings are then transferred to the chest wall. The design of the flap may be placed in several positions, either horizontally, vertically, or obliquely. It is most important to insure that the width and length of the flap will be sufficient to cover the defect and that flap placement is such that it will be perfused by the perforator.
- The flap may be elevated from either the distal end and dissected toward the midline where the location of the perforators are expected or by beginning at the medial aspect, directly inferior to the expected location of the perforator flap.
- If the elevation is begun inferior to the perforator, the dissection is extended to the subfascial plane and then the direction is changed to a superior or cephalad direction towards the expected perforator. Once the dissection nears the perforator, attention should be taken to not injure it. At this time, the use of monopolar electrocautery should be limited and bipolar electrocautery should be used more liberally.
- Once the location and adequacy of the caliber of the perforator is confirmed, the design of the flap is once again confirmed and, if needed, a new design made so that the perforator is better placed.
- With the flap design confirmed and the perforator dissected, the remainder of the flap is elevated in a subfascial plane.
- At this point, the rotation and reach of the flap is tested. If the flap is able to reach the defect without any tension then no further dissection of the pedicle is needed.
- If there is tension on the flap in order for it to reach the defect site, intramuscular dissection of the perforator is performed towards the axial vessel, i.e., the internal mammary artery.
- Once the vessels are reached, the portion of the vessel inferior to the takeoff of the perforator is then mobilized, ligated, and divided.
- Dissection of the vascular pedicle is then carried out in a cephalad direction; the next site of obstruction will be the costal cartilage of the rib. If the flap is still unable to reach the desired/>