The IMAP and MICAP Flaps for Autologous Breast Reconstruction: An Anatomic, Clinical, and Outcome Study

Abstract

Background

Local flaps for breast reconstruction are becoming recognized as a viable alternative to remote flaps.

Objectives

The purpose of this article was to describe the anatomy and clinical outcomes of internal mammary artery perforators and lateral intercostal artery perforator flaps for breast reconstruction.

Methods

Twelve cadaveric specimens were injected with colored latex and dissected to demonstrate the medial perforators of the fifth intercostal space. Twenty-two patients had partial or total breast reconstruction with internal mammary artery perforator flaps, which were combined with lateral intercostal artery perforator flaps in 4 patients. The study was performed at the Hospital de Clinicas Jose de San Martin, which is affiliated with the Universidad de Buenos Aires in Argentina, between March 2018 and December 2023. Outcomes were based on clinical evaluation and statistical analysis. Patient satisfaction was assessed on a 5-point Likert scale based on whether patients were clothed or unclothed.

Results

All flaps survived without any evidence of partial flap necrosis. There were no major complications (total flap loss, partial necrosis); however, fat necrosis was demonstrated in 2 patients. Minor complications included a small hematoma and a minor wound dehiscence. Patient satisfaction was rated as very good or excellent in 100% of females when clothed and rated as good to very good in 93.3% of females when unclothed.

Conclusions

Submammary perforator flaps can be raised on numerous vascular pedicles. This study has demonstrated that the internal mammary and the lateral intercostal perforators can be successfully utilized for partial or total breast reconstruction in properly selected patients.

Level of Evidence: 4 (Therapeutic)

Traditional pedicle flaps for breast reconstruction have included latissimus dorsi and transverse rectus abdominis musculocutaneous flaps. These flaps typically require sacrifice of the underlying muscle. With the advent of perforator-based flaps in which the underlying muscle is preserved, a variety of flaps have been described with donor sites that include the abdomen and gluteal and thigh regions.^1-3 These remote flaps all require a microvascular anastomosis of the recipient artery and vein to the donor artery and vein.

With our increased understanding of the perforator anatomy around the breast, alternative flaps that do not require a microvascular anastomosis but allow for preservation of the underlying muscle have been described. Medially based submammary flaps originating from the fifth and sixth intercostal spaces are occasionally placed for breast reconstruction when the traditional flaps are not available due to previous abdominal surgery, previous flap failure, or patient preference regarding donor site.^4-7 Internal mammary artery perforator (IMAP) flaps based on the second and third intercostal spaces have also been described.^8-12 IMAP flaps from the fifth intercostal space have been placed for medial thoracic and contralateral chest wall defects.^13,14

Recent studies have reported on the utility of combining the medially based submammary flap and the medial intercostal artery perforator flap (MICAP).^15,16 The anatomical distribution of the medial branch of the fifth anterior intercostal perforator (fifth MICAP) has been previously reported.^17-19 This perforator is differentiated from the internal mammary perforator of the fifth intercostal space (fifth IMAP; Figure 1) which is more medial and is a direct branch of the internal mammary artery (Figure 2). The fifth MICAP originates from the anterior intercostal artery, and it is part of the system of anterior intercostal perforators.²⁰ The fifth IMAP originates as a direct branch of the internal mammary artery and reaches the subcutaneous tissue a few centimeters from the midline.²¹ It has a larger diameter than the medial intercostal perforator and can perfuse a medially based submammary flap that is up to 17 to 18 cm in length and can be rotated toward the breast mound as an island flap.

The purpose of this manuscript is to present the results of an anatomical investigation that compares the diameters of the medial anterior intercostal and the internal mammary perforators of the fifth intercostal space and the clinical results of 22 medially based submammary flaps perfused by the fifth IMAP performed for breast reconstruction.

METHODS

Anatomic Investigation

An anatomic study was performed in twelve preserved cadaveric specimens injected with colored latex were dissected to demonstrate the medial perforators of the fifth intercostal space. Direct observation and measurement of vascular diameter was performed. Measurements of the blood vessel diameter was made with calipers. Dissection of the most medial perforator was carried deep to its origin.

Clinical Investigation

This study was approved by the institutional review board at the Hospital de Clinicas Jose de San Martin, Universidad de Buenos Aires, Argentina. Patient demographics are described in Tables 1 and 2. Twenty-two medially based submammary flaps were performed in 14 patients. This included 8 patients who had bilateral reconstruction (16 flaps) and 6 patients that had unilateral reconstruction (6 flaps). The time interval for this study was between March 2018 and December 2023. Within the bilateral cohort, 4 patients had a medially based submammary flap combined with an ipsilateral lateral intercostal artery perforator (LICAP) flap for additional volume. Of the 22 flaps, 18 were placed for volume restoration as deepithelialized flaps, and 4 were utilized for volume restoration and surface reconstruction. Skin surface reconstruction was needed for the patients in which the nipple-areola complex was excised.

Flap viability was assessed intraoperatively by direct observation before deepithelialization. Flap outcomes were evaluated according to clinical evaluation during the postoperative period. Given that most flaps were buried, direct observation of the skin was not possible. Doppler signals correlating to the surface perforator on the flap were assessed by listening to the overlying skin of the breast with a Doppler. Compromised circulation of a buried flap was detected by a change in the Doppler signal, swelling, fever, erythema, or drainage. The presence of any of these signs was an indication for open surgical exploration and restitution of normal perfusion. If unsuccessful, the flap was removed. Well-perfused buried flaps evolve without any of those signs and symptoms and eventually result in complete normal healing.

Patient satisfaction was assessed based on patients' perceptions of several aesthetic aspects while clothed and unclothed. This included general satisfaction as well as satisfaction with various breast characteristics (shape, size, and symmetry). The patient follow-up period ranged from 6 to 24 months (mean, 14 months). Patients were scheduled for a postoperative follow-up visit every 2 months. The satisfaction questionnaire was sent by email 6 months after surgery (Table 3). Patients were asked to rate their responses to the 4 questions regarding their surgery and satisfaction with their appearance on a scale of 1 (not at all satisfied) to 5, (very satisfied). A Likert scale was employed to quantify outcome with the following rating scores: 5, excellent; 4, very good; 3, good; 2, fair; and 1, bad.

Surgical Technique

A traditional submammary flap was designed with a color Doppler to detect the perforators on which the flap was based. The fifth IMAP and the fifth MICAP were evaluated with a comparison of the diameters on color Doppler. The fifth IMAP was a consistent anatomical finding and was easily detected with either the color or the handheld Doppler. The location of this perforator was delineated on the skin and included within the submammary flap design. The width of the flap was based on the ability to primarily close the defect by reverse abdominoplasty principles. The length of the flap coincided with the inferior footprint of the breast. The flap design could be displaced superiorly if the lower part of the breast envelop was planned to be discarded during the surgical procedure. The fifth IMAP was usually a larger-caliber perforator than the MICAP, and was located more medially. Therefore the amount of submammary tissue based on the fifth IMAP perforator was larger, had a better angle of rotation, and was preferred.

The LICAP was also located and marked and usually remained within the flap design. With our early procedures, the LICAP was preserved until the entire flap was elevated. With experience however, a vascular clamp was placed on the LICAP to assess perfusion based solely on the fifth IMAP. In the event of diminished flap perfusion with the LICAP clamped, the orientation of the flap could be changed and elevated as a reverse LICAP flap. However, in this series of patients, the fifth IMAP was sufficient to perfuse the entire submammary flap.

The submammary flap was raised from distal to proximal on the suprafascial plane. Once the pulsating fifth IMAP was observed, flap rotation was gradually performed. In most cases, flap rotation was less than 90° toward the breast mound; therefore it was not necessary to completely dissect and isolate the perforator. The dissection of the perforator was usually performed under loupe magnification to liberate the pedicle from the cartilage. When the IMAP flap was successfully raised, the MICAP might or might not be preserved because it was providing a minor contribution to perfusion. At the proximal part, the superficial internal mammary artery that appeared under the rib cartilaginous cage was observed and ligated to allow better rotation and distal reach of the flap. The donor site was closed directly with upper abdominal wall advancement according to the technique of reverse abdominoplasty. Buried flaps were completely deepithelialized, whereas submammary flaps with a skin paddle were only partially deepithelialized. Flap monitoring was with a handheld Doppler that was applied to the skin paddle of the partially deepithelialized flaps and over the breast skin that correlated to the location of the Doppler on the completely deepithelialized flaps. This technique has been routinely employed in the authors’ practice and found to be reliable.

When additional volume or skin was necessary, the conventional LICAP was harvested. The patient was placed in the contralateral decubitus position. The LICAP flap was elevated from distal to proximal. When the perforator was observed, the skin incision continued toward the submammary area. The donor area of the LICAP was closed directly after complete hemostasis was achieved. The operative area was properly dressed, and the patient was repositioned. In cases of bilateral reconstruction, the patient was placed in the contralateral decubitus position, and the same procedure was performed for the contralateral LICAP. The patient was then placed in dorsal decubitus position and the medially based fifth IMAP flap was elevated in continuity with the LICAP. The complete IMAP–LICAP flap usually measured between 35 and 38 cm in length and was sectioned medial to the piercing point of the LICAP pedicle. The resultant 2 flaps were independently placed in the breast mound as stacked units, with the fifth IMAP flap on the chest wall and the LICAP flap on top.

RESULTS

Anatomic Investigation

In all the cadavers, the most medial perforator at the fifth intercostal space was larger in diameter (Table 4). The diameter of the IMAP perforator ranged from 0.7 to 1.2 mm, whereas the diameter of the MICAP perforator ranged from 0.1 to 0.4 mm. These measurements were obtained at the origin of the perforator as it pierced through the fascia. The length of the IMAP perforator in the cadaver specimens from its origin to the point of entry into the subcutaneous tissue ranged from 4 to 6 mm. It was also observed that the most medial perforator always originated from the internal mammary artery (as the fifth internal mammary artery perforator). This finding coincided with that reported by Morris et al.²⁰ The fifth IMAP coursed around the cartilaginous portion of the rib. It was surrounded by cartilage. The fifth MICAP was near the fifth AICAP and was not surrounded by cartilage. The diameter of the medial fifth anterior intercostal was usually less than 0.3 mm (Figures 3, 4).

Clinical Investigation

Fourteen patients had 22 flaps. All flaps survived without any evidence of partial flap necrosis. There were no major complications (total flap loss, partial necrosis); however, fat necrosis was demonstrated in 2 patients, which was determined by clinical examination and not by imaging. Both patients with fat necrosis were previously radiated, and it was determined that preoperative signs of radiofibrosis were not completely resected during the reconstructive procedure with the MICAP flap. In the first patient, this manifested as inflammation and induration of the breast after 7 days. Ultrasound demonstrated a fluid collection; therefore, it was decided to reexplore in the operating room. Intraoperative findings showed complete flap survival, with the areas of fat necrosis being due to incomplete resection. Following complete resection, the wound healed uneventfully. In the second patient, spontaneous drainage occurred through the wound on postoperative day 8. It was decided to manage this conservatively with antibiotic therapy. The drainage stopped several days later, and the wound healed. Our current practice is to aggressively excise the radiated tissue at the index operation because partial excision may produce additional devascularization of the remaining radiated tissues resulting in inflammation, delayed healing, and drainage. Patient satisfaction was rated as very good or excellent in 100% of females when clothed and rated as good to very good in 93.3% of females when unclothed. Regarding specific breast features, patients reported excellent or very good results regarding shape (100%), size (100%), and symmetry (100%). Minor complications are listed in Table 5. These included a small hematoma that was successfully drained in the office as well as a minor wound dehiscence in the back in the donor area of LICAP flap.

Clinical Cases

Case #1

A 27-year-old female requested explantation of 350-cc breast implants (Figure 5A). Before these implants, she had direct injection of silicone gel into the breast. Due to the silicone gel within the breast parenchyma, she had concerns about losing breast volume with removal of the implants and the interstitial silicone gel. Her goal was to maintain as much of her breast volume as possible. The surgical plan was to remove the implants and perform a partial mastectomy, preserving the parenchyma that was free of silicone gel. Local parenchymal rearrangement alone would be insufficient to maintain her desired volume, therefore a submammary flap was planned as a means of volume replacement. Preoperative calculations estimated the additional needed volume to be 240 cc, based on a flap thickness of 1 cm after deepithelialization; therefore a 24 × 10 cm submammary flap was designed (Figure 5B). Although a thoracodorsal artery perforator (TDAP) or latissimus dorsi flap could have been placed, the patient preferred fat from the submammary region.

A bilateral reducing mastopexy with an inverted-T pattern and deepithelialized bilateral MICAP flaps was performed to preserve volume. The flap was designed along the submammary and inferior portion of the breast; perforators of the submammary area were detected with color Doppler. Preoperative comparison revealed that the LICAP, AICAP, and fifth IMAP were quite similar in diameter; therefore, the decision was made to harvest the flap based on the fifth IMAP because this would result in the best aesthetic outcome at the donor site.

The salient aspects of the operation were as follows. The inverted-T pattern was delineated and incised. The thickness of the mastectomy flaps was maintained at approximately 2 cm. The implant was visualized and explanted. Partial mastectomy was performed, removing the parenchyma with imbedded silicone gel. The reducing mastectomy was partially closed, leaving the horizontal part open. The submammary flap was raised from lateral to medial on the suprafascial plane (Figure 5C). Once the vascular pedicle was observed, careful dissection under 4× magnification was performed to liberate it from the adherent cartilage and to allow a nice rotation without kinking (Figure 5D-F). This maneuver took longer time than the previous harvesting. The flap was deepithelialized and good bleeding was observed from the distal border (Figure 5G). The thickness of the submammary flap was not equal along the entire length, with the thinnest portion being 1.5 cm. Final flap volume was 360 cc. The flap was placed in the base of the breast mound and sutured to the pectoralis fascia. The wound was closed and closed-suction drainage applied. The postoperative outcome at 1-month and 1-year follow-up is demonstrated in Figure 5H, 5I, and 5J.

Case #2

A 37 year-old female patient presented with a severe retractile capsular contracture on the right breast (Figure 6A). The patient had an initial breast implant at age 24 for aesthetic augmentation. By report, she initially had 245-cc smooth round silicone gel implants and developed capsular contracture. A second surgery was performed at another institution that included capsulectomy and new implants. According to her desire, she received 430-cc smooth implants. She developed recurrent capsular contracture associated with pain and discomfort. Our recommendation was explantation, but the patient requested volume preservation. The possible residual final scar was drawn with broad marker on her body so the patient might have a real idea of the result on the donor area (Figure 6B, C). Although a TDAP or latissimus dorsi flap was an option for partial breast reconstruction, the patient preferred submammary flaps to better conceal the scars. A bilateral combined MICAP–LICAP flap was performed for volume replacement (Figures D-H). Operative time was 2 hours and 45 minutes. The patient was discharged from the hospital on the same day and had no postoperative complications. One-month and 1-year follow-up are demonstrated in Figures 5I, 5J, and 5K).

DISCUSSION

Cutaneous perforators arising from the intercostal system were first described by C. Manchot.²² Hamdi introduced the clinical use of intercostal perforator flaps based on these perforators originating from the lower intercostal spaces.²³ Subsequent work described the anatomy of the anterior cutaneous branches of the intercostal arteries of the fifth and sixth intercostal spaces. These studies were performed with a variety of methods that included radiographic, cadaveric, and clinical cases.

Based on these studies, the possibility of harvesting the submammary adipocutaneous flap perfused by the medial perforators located in the inferior inner corner of the breast provided an interesting tool for reconstruction of medial breast defects. Advantages included a favorable donor site with an inconspicuous scar because it could be directly closed by advancement of the upper abdomen utilizing the principles of reverse abdominoplasty. The amount of soft tissue available for reconstruction could be assessed preoperatively by performing a pinch test that provided an approximation of the possible volume to be harvested. Although there are several reports that mention the MICAP and IMAP flaps, the origin and the piercing point of these vessels relative to one another and to the cartilaginous framework of the thoracic skeleton has not been adequately studied.

The MICAP nomenclature was first described by Macmillan and McCulley in 2016; however, the authors did not describe the anatomical location of the medial perforators.¹⁵ They differentiated 2 flaps that included the MICAP and the anterior intercostal artery perforator (AICAP) flaps based off the intercostal system of vessels; however, they did not differentiate the MICAP from the IMAP. According to Soumian et al, the MICAP perforators were located 2 to 3 cm lateral to the sternal edge and 1 to 2 cm inferior to the inferior mammary fold.¹⁶

Persichetti et al utilized these medial intercostal perforator flaps as submammary flaps.¹⁷ Carrasco-Lopez performed anatomic studies of the anterior intercostal perforators at the fifth intercostal space (AICAP).¹⁸ In accordance with the anatomical findings reported in the literature, Oki demonstrated that the fifth intercostal artery gives off an important anterior perforator at the midline meridian of the breast that was accompanied by smaller branches medially and laterally.¹⁹

In our cadaveric study we found that the fifth IMAP was larger than the medial branches of the intercostal artery (MICAP flap), and similar in diameter to the fifth AICAP. In situations in which additional volume is needed for breast reconstruction, we feel that it is preferrable to raise a submammary flap as an IMAP flap because the fifth perforator is located more medially, the amount of flap that can be raised is usually larger, and it has a more favorable arc of rotation. Typically, the arc of rotation is less than 90 degrees; therefore, kinking of the pedicle has not been a concern. Kinking of the pedicle is usually observed in propeller flaps that have a 180° arc of rotation.

It is important to have a good understanding of the perforators in this submammary area because, depending on the location and dimensions of the breast defect, certain flaps may be more advantageous. The perforators include the medial internal mammary perforator, medial intercostal artery perforator, anterior intercostal artery perforator, and the lateral intercostal artery perforator. The IMAP is typically a larger-caliber vessel than the MICAP, therefore, larger-volume flaps should include the IMAP. If a submammary flap is needed for the central portion of the breast, the best choice would be the fifth AICAP because it can sufficiently perfuse a flap that is 18 to 20 cm long and reach the upper pole of the breast mound. This flap surpasses the submammary area and reaches the posterior axillary line. From the perspective of optimizing aesthetics of the donor site, the best choices are the fifth IMAP or the reverse LICAP. Any of these pedicles can adequately perfuse the entire submammary flap. In a situation in which the breast defect is small and located solely on the lower pole of the breast, a true MICAP flap can be raised based solely on the fifth intercostal perforator. Conversely, if the breast defect is large and involves the entire submammary area, then a true MICAP (intercostal perforator only) should be avoided because the intercostal perforator is smaller than the IMAP and would place the submammary flap at risk of partial necrosis. Therefore the submammary flap should include the IMAP.

The important point to remember is that medially based submammary flaps are usually perfused by both the fifth IMAP and fifth MICAP. It is acknowledged that the accepted nomenclature is to call this a MICAP flap. The authors strongly believe that preservation of the fifth IMAP is of utmost importance to assure sufficient perfusion of medially based submammary flaps. In some patients, it might be desirable to include the sixth internal mammary perforator in the flap design. This usually will not cause a distortion in breast shape or contour following transposition. The seventh internal mammary perforator is usually not included in flap design because this perforator is located outside the footprint of the breast. Inclusion of this perforator would likely cause a distortion of breast shape and contour.

It must be remarked that the intercostal arteries may be considered an anastomosis between the anterior internal mammary artery and the posteriorly located aorta. Therefore, it is a strong vascular axis with powerful skin perforators. This fact is one of the factors that partially explains the reliability of these flaps.

Limitations of this study were that flap viability and perfusion were assessed intraoperatively by direct observation based on skin color, skin turgor, and bleeding from the distal edges. Ideally, fluorescent angiography with indocyanine green (ICG) would have been preferred; however, ICG angiography was not available for all patients.

CONCLUSIONS

In summary, the submammary flap can be raised on different vascular pedicles. The surgeon may choose the one that is the most convenient for each case. The location of the flap pedicle at either the medial or lateral aspect of the submammary area can facilitate flap insetting and provides a more optimal arc of rotation. There are 2 good possibilities: the reverse LICAP or the fifth IMAP. In some cases, when necessary, these 2 flaps can be combined as a stacked local flap for volume replacement. We believe that this combination of flaps is particularly effective for most larger breast defects, such as when large-volume implants must be replaced by autologous tissue after explantation. Raising a submammary flap on the lateral intercostal perforator alone does not provide sufficient perfusion for a full-length flap. Therefore, the stacked LICAP and IMAP flap would be a better choice. As an alternative to the IMAP, the submammary area can be based on the fifth AICAP as described by Persichetti. Indication for this flap would be situations in which the defect was confined to the lower pole and not beyond. We believe that the fifth IMAP allows a better insetting of the flap at the inner part of the breast mound, nicely complementing the LICAP flap.

Disclosures

Dr Nahabedian is the Aesthetic Breast Reconstruction section editor for Aesthetic Surgery Journal. The authors declared no potential conflicts of interest with respect to the research, authorship, and publication of this article.

Funding

The authors received no financial support for the research, authorship, and publication of this article.

REFERENCES

Author notes