**Region:** Chest and Shoulders # Internal Mammary Artery Perforator Flap ## Anatomy - Pedicle: internal mammary artery perforator(s) (branching from the internal mammary/internal thoracic artery which arises from the first part of the subclavian artery and continues inferiorly as the superior epigastric artery). Typical perforator size measured in cadaver/clinical series: - 1st intercostal space mean diameter 1.50 mm (range 1.0–2.2 mm). (Hanasono) - 2nd intercostal space mean diameter 1.83 mm (range 1.3–2.4 mm); clinically commonly 1.0–1.5 mm. (Hanasono; Neligan) - 3rd intercostal space mean diameter 1.47 mm (range 1.3–1.7 mm). (Hanasono) - Perforator veins at second interspace clinically ~1.5–2.0 mm. (Hanasono) - Course: internal mammary artery runs along the sternal border (~1.5 cm lateral to the sternum on average) giving perforators through each intercostal space. Perforators travel through/adjacent to pectoralis major (musculocutaneous route) and send oblique cutaneous branches to the overlying skin; perforators demonstrate distal collateralization/choke connections to adjacent intercostal perforators. (Hanasono; Neligan; Gillis 3D) - Perforator pattern: - Dominant perforators typically located in the first four intercostal spaces; the second intercostal perforator is most commonly dominant. (Neligan; Hanasono) - Number: clinical designs usually rely on 1–2 perforators; flaps can be based on a single perforator or include multiple neighboring IMAPs. - Type: predominantly musculocutaneous/indirect (pierce pectoralis major near its insertion) with accompanying venae comitantes; small lateral perforators from lateral thoracic or intercostal arteries may enter the lateral flap and can be divided safely. (Taylor; Hanasono) - Territory / angiosomes: - First-interspace IMAP: perfuses to clavicle and lateral mammary fold in all injected cases; reaches inferiorly to xiphisternum ~1/3 of cases. (Hanasono) - Second-interspace IMAP: reached clavicle and xiphisternum in 4/6 injection cases; lateral mammary fold in all cases. (Hanasono) - Third-interspace IMAP: reached clavicle in 40%, xiphisternum in 60%, lateral mammary fold in 80%. (Hanasono) - Superior IMAPs (1st–2nd) tend to have more horizontal territory; inferior IMAPs take a more inferolateral orientation. (Hanasono; Taylor angiosome concepts) - Nerves: - Cutaneous nerves commonly run with perforator territories; perforator-based flaps may incorporate cutaneous nerves when harvested centrally and therefore can be fashioned as sensate flaps if deliberately included. (Taylor; Blondeel) - No specific named sensory nerve consistently included with IMAP in the sources; planning for sensate reconstruction requires deliberate capture of identified cutaneous nerve branches where present. - Included tissues: - Usual harvest: skin and subcutaneous tissue with preservation of pectoralis fascia; flap elevated in a suprafascial/subfascial plane over pectoralis major. Muscle is not routinely included unless conversion to musculocutaneous required. (Hanasono; Neligan) - Thickness: similar to upper chest skin; thickness variable with patient habitus (Blondeel general trunk principles). IMAP flaps are relatively thin compared with many donor sites and can be suitable for head/neck resurfacing. - Arc of rotation/length: as a pedicled flap, second-intercostal IMAP can support a narrow (6 cm) and long (20 cm from perforator) flap that may extend 2–3 cm beyond the anterior axillary fold into the axilla; flap orientation horizontal (parallel to ribs) for second interspace based designs gives inconspicuous donor scar. (Hanasono; Neligan) - Common variants/anomalies: - Perforator size/venous caliber variable; second intercostal usually largest but occasional dominance of other levels occurs. (Hanasono; Neligan) - IMAP may be harvested across the midline based on a contralateral perforator in select cases, increasing reach. (Neligan; Angrigiani) - Prior internal mammary artery harvest (e.g., coronary bypass) commonly precludes reliable use on that side. (Hanasono; Taylor) ## Dissection Steps 1. Positioning, markings, landmarks. - Patient supine. Identify sternal border and palpate/mark the second and third ribs; mark intercostal spaces. (Hanasono; Neligan) - Use a handheld Doppler to map IMAP signals at the second and third interspaces lateral to the sternal border; choose target perforator(s) (usually second interspace unless Doppler stronger elsewhere). (Hanasono; Neligan) - Flap design: elliptical/horizontal axis parallel to ribs for second-interspace IMAP; medial limit anterior midline, lateral limit midaxillary line; superior border just above the second rib curved toward axilla. Width typically planned to allow primary closure: 5–8 cm (commonly 6–8 cm). Distal tip may extend 2–3 cm beyond anterior axillary fold. (Hanasono) - Verify reach: intraoperative “sponge/towel” rehearsal with point-of-rotation to confirm flap can reach defect and to decide ipsilateral vs contralateral pedicle. (Neligan) 2. Plane (suprafascial/subfascial), perforator identification (handheld/IO Doppler). - Incise superior (medial half first) border down to fascia. Proceed with subfascial dissection inferiorly (or suprafascial just above pectoralis fascia per surgeon preference) using scissors/monopolar while preserving fascia until perforators encountered. (Hanasono) - Identify perforator(s) as they emerge through pectoralis muscle/fascia; handheld Doppler and visual confirmation guide selection. (Hanasono; Neligan) - Do not routinely skeletonize perforator(s) unless planning free flap transfer; maintain small cuff of tissue around perforator for pedicled island flap unless pedicle length must be increased. (Hanasono) 3. Pedicle dissection: exposure, control, division; transfer/inset; perfusion checks. - For routine pedicled IMAP: once perforator identified, complete remaining skin incisions and elevate flap in plane just above pectoralis fascia toward perforator. If needed, divide pectoralis major attachments cephalad to perforator(s) to increase pedicle mobility. (Hanasono) - For propeller transfer: dissect perforator toward its source to gain length and prevent acute torsion; check Doppler prior to rotation and immediately after inset. Rotate both directions to assess perfusion — flaps may perfuse asymmetrically depending on twist. (Neligan) - If greater pedicle length and vessel caliber required (e.g., free flap or to reach high neck), dissect down to internal mammary artery and vein: remove costal cartilage above perforator if necessary, include a segment of internal mammary artery/vein and divide distal to perforator run-off. This converts the flap to a longer pedicle (pedicled on internal mammary trunk or harvested as free flap). (Hanasono; Neligan) - Lateral intercostal or lateral thoracic perforators encountered in the lateral flap may be divided if they impede dissection — these do not typically contribute critically to IMAP perfusion. (Hanasono) - Perfusion checks: clinical (bright red bleeding from cut skin edge), handheld Doppler signal on perforator(s), and ICG angiography if available (ICG is more accurate than clinical judgment for marginal areas). (Neligan; Hanasono) - Inset: transfer through subcutaneous tunnel or after dividing narrow skin bridge; check that pedicle is not kinked, and that Doppler signal persists. Secure flap with minimal tension. (Hanasono; Neligan) 4. Donor-site closure techniques. - Donor site commonly closed primarily when flap width ≤ ~6–8 cm; wide elliptical design and horizontal orientation facilitate primary closure with an inconspicuous scar. (Hanasono) - If donor cannot be closed primarily, coverage options: thoracodorsal artery perforator (TDAP) flap as pedicled island to cover donor site, lateral split latissimus myocutaneous flap, or skin graft. (Hanasono) - Subcutaneous drains per surgeon preference for larger defects; standard layered closure of fascia and skin. ## Indications and Contraindications - Indications: - Regional pedicled reconstruction of lower neck and upper chest cutaneous defects (tracheostoma, neck resurfacing). (Hanasono; Neligan) - Closure of chest wall defects, small–moderate-sized anterior chest skin defects. (Neligan; Blondeel) - Head & neck reconstruction when free tissue transfer is high-risk or not available; tracheostoma and pharyngoesophageal/ circumferential pharyngo-esophageal reconstruction (including bilateral IMAP tube creation). (Hanasono; Neligan) - As a free flap for facial resurfacing, pharyngoesophageal reconstruction, or breast/volume replacement when pedicle length and vessel caliber permit. (Neligan; Hanasono) - Salvage/coverage of exposed prosthetic material or native structures in medically fragile patients. (Neligan case examples) - Size limits and tissue character: - Best for thin-to-moderate-sized cutaneous paddles; single IMAP can carry narrow 6 cm × up to 20 cm length flap clinically reported. Flap width typically limited to permit primary closure (5–8 cm). (Hanasono) - Not suitable when large bulk is required unless combined or converted to other flaps (e.g., TDAP, latissimus). (Blondeel) - Sensate needs: - Sensory nerve branches may be included when identified to produce sensate reconstruction; deliberate inclusion required. (Taylor; Blondeel) - Contraindications: - Prior ipsilateral internal mammary artery harvest (e.g., LIMA coronary bypass) generally precludes reliable use on that side. (Hanasono; Taylor) - Prior extensive anterior chest wall surgery or radiation: requires preoperative CTA to confirm vessel patency and perforator anatomy; prior scarring may interrupt midline crossover and affect flap viability. (Hanasono; Taylor) - Severe peripheral vascular disease or small-caliber perforator/vein on Doppler/CTA that will not support flap or free transfer. (Neligan; Hanasono) ## Postoperative Care - Monitoring schedule/method: - Immediate postoperative checks: clinical inspection of flap color, turgor, capillary bleeding; handheld Doppler over perforator before and after inset and at regular bedside checks. (Neligan; Hanasono) - Indocyanine green (ICG) angiography may be used intraoperatively to confirm perfusion of marginal tissue and guide trimming. (Neligan) - No special continuous implantable probe protocol documented in the source chapters for IMAP; standard flap observation intervals apply (hourly early postoperative checks subject to institutional protocol). (Neligan/Hanasono implied) - Warming/positioning: - Avoid external compression or tight dressings over pedicle; position and dressings to prevent kinking of pedicle through tunnel. (Neligan; Hanasono) - Antithrombotic practice: - Sources describe intraoperative heparin injection as a chemical leech salvage in marginal territories in other angiosome contexts (Taylor case), and Neligan references ICG rather than routine antithrombotics; no standardized antithrombotic regimen for IMAP specified in the attached texts. Use institutional microvascular/thromboprophylaxis protocols when free-transfer or as indicated. (Taylor; Neligan) - Drains, mobilization, diet, analgesia: - Standard layered closure care: consider drains for larger donor sites; early mobilization as tolerated; diet/analgesia per usual head/neck or chest reconstruction protocols. (Blondeel/Hanasono general principles) - Return-to-OR thresholds and time windows: - Immediate re-exploration indicated for loss of Doppler signal or sudden arterial/venous compromise after rotation/inset. (Neligan) - For distal cyanosis or progressive demarcation of distal territory, consider early interventions (re-exploration, chemical leech/heparin irrigation in selected cases as salvage described in angiosome experience). Time-sensitive re-exploration within hours if arterial inflow likely lost; manage venous congestion urgently (institutional protocol). (Neligan; Taylor) ## Complications (rates & management) - Reported frequencies: no incidence percentages for IMAP-specific complications are provided in the attached IMAP chapters. Avoid numeric incidence statements not present in sources. - Common complications and management described in sources: - Venous congestion / arterial insufficiency: - Immediate check of pedicle for kinking; confirm Doppler; if absent/weak signal → further dissection of pedicle or immediate re-exploration. (Neligan) - ICG can identify poorly perfused zones intraoperatively to guide trimming. (Neligan) - Taylor describes “chemical leech” (local heparin injection into marginal zone) as a salvage technique for marginal distal territory in multiterritory flaps (used to rescue borderline zone); this is an available adjunct in select cases. (Taylor) - Partial flap loss / distal necrosis: - Clinical confirmation (bleeding, color); small distal necrosis may be debrided and allowed to heal secondarily or skin-grafted depending on size; prevention via ICG/perforator selection and preservation of venous outflow. (Neligan; Hanasono) - Total flap loss: - Rare in documented case series described qualitatively; immediate re-exploration for vascular compromise recommended. (Neligan) - Infection: standard wound care and antibiotics as indicated. - Fat necrosis / contour irregularity: limited with thin IMAP skin paddles; donor-site contour deformity minimal if primary closure possible. (Hanasono; Blondel general trunk notes) - Donor-site issues: - Seroma/hematoma: routine drain use and layered closure as indicated. - Contour deformity/scar: minimized with horizontal design and widths permitting primary closure (5–8 cm recommended). (Hanasono) - Management algorithms (from attached sources): - Absent/weak Doppler after rotation → check for external compression/kinking → further pedicle dissection toward source vessel → re-explore immediately if no improvement. (Neligan) - Marginal distal ischemia in multiterritory flaps → consider chemical leech (local heparin injection) and close monitoring (Taylor case). (Taylor) - If free-transfer with internal mammary trunk included: standard microvascular thrombosis algorithms apply (not detailed in IMAP chapters; follow institutional microsurgical protocols). ## Key Clinical Pearls - Perforator anatomy and sizing: - The internal mammary artery lies on average ~1.5 cm lateral to the sternal border; target perforators in the second intercostal space are most commonly dominant. (Hanasono) - Expect perforator arterial diameters at second interspace ~1.3–2.4 mm (mean ~1.8 mm) and accompanying veins ~1.5–2.0 mm clinically. (Hanasono; Neligan) - Flap design & donor closure: - Design horizontal/elliptical flap parallel to ribs when based on the second interspace to facilitate inconspicuous donor scar and primary closure; plan width ≤ ~6–8 cm if primary closure is desired. (Hanasono) - A single IMAP (second interspace) can clinically carry a narrow 6 cm × up to 20 cm length flap and reach 2–3 cm beyond the anterior axillary fold. (Hanasono) - Harvest technique: - Incise medial half of superior border first and dissect subfascially to identify perforator(s) before committing to full flap elevation — rapid harvest is possible (often ≤ ~30 minutes to elevate as reported clinically). (Hanasono; Neligan) - For propeller rotation, dissect the perforator toward its source to gain length and avoid acute torsion; always confirm Doppler signal before and after rotation. (Neligan) - When more reach needed: - To lengthen/larger pedicle or convert to free flap, remove costal cartilage above perforator and dissect to the internal mammary artery and vein; divide the internal mammary distal to perforator run-off to advance/pedicle the flap. (Hanasono; Neligan) - Preoperative planning: - Use handheld Doppler routinely; obtain CTA only when prior anterior chest surgery or radiotherapy or when detailed mapping is required (e.g., contralateral IMAP harvest or free flap planning). (Hanasono; Neligan) - Contraindications: - Prior ipsilateral LIMA harvest for CABG is a contraindication to ipsilateral IMAP use; always ask cardiac surgery history and consider CTA if doubt. (Hanasono; Taylor) - Salvage: - If marginal distal ischemia develops in extended or multiterritory flaps, consider local heparin (chemical leech) and close monitoring as a salvage adjunct (documented in angiosome experience). (Taylor)