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An anterolateral thigh flap is very useful in head and neck reconstruction because of its long and large-caliber vascular pedicle, large skin territory and elevation simultaneous with tumour resection. However, the number and locations of cutaneous perforators vary individually, and thus, it is not widely used because flap elevation is often complicated and time-consuming owing to unexpected anatomical variations. To overcome this disadvantage, we assessed the number and locations of cutaneous perforators preoperatively by colour Doppler flowmetry. These data were compared with the intraoperative anatomical findings and their reliability evaluated. A total of 48 cutaneous perforators were found by preoperative colour Doppler flowmetry scanning of 17 anterolateral thigh flaps. All the perforators except two were found intraoperatively. Doppler scanning failed to detect four perforators. Colour Doppler flowmetry assessment therefore has a 92% true-positive rate and a 95.8% positive predictive value. All the flaps except one included multiple perforators, and sufficient blood circulation was observed in all cases. No flaps were unexpectedly changed to anteromedial thigh flaps or contralateral anterolateral thigh flaps because of inappropriate cutaneous perforators or the absence of perforators. Though this investigation is relatively time-consuming (30–40 min) and requires skill, it is very useful for preoperative flap planning and increases the reliability and safety of elevating an anterolateral thigh flap.
The anterolateral thigh flap, first reported by Song et al in 1984, has many advantages, such as a long and large-calibre vascular pedicle, a large pliable skin paddle, the possibility of a flow-through flap and a sensate flap, its combination with other flaps and minimum morbidity at the donor site.
It can be harvested in the supine position; thus elevation simultaneous with tumour resection is often possible using two surgical teams. However, the anterolateral thigh flap is not as popular as the rectus abdominis myocutaneous flap or the radial forearm flap in spite of these advantages. This may be because the number and locations of cutaneous perforators vary individually, meaning that flap dissection is often more complicated than in these standard flaps.
To overcome these anatomical variations and make flap harvesting simpler and safer, we assessed the number and locations of cutaneous perforators preoperatively by colour Doppler flowmetry. These data were compared with the intraoperative data and their reliability was evaluated.
1. Patients and methods
Between February 2000 and May 2002, 21 anterolateral thigh flaps were elevated. The number and locations of cutaneous perforators were evaluated preoperatively by colour Doppler flowmetry in 17 flaps. The patients were ten men and seven women; their ages ranged from 19 years to 71 years, with an average of 53.4 years.
A digital ultrasound system, LOGIC 700 (General Electric Medical Systems), with a broad-spectrum 6–13 MHz linear transducer, was used to assess the number and locations of cutaneous perforators. In the supine position, the patient's thigh length was measured from the anterior superior iliac spine to the centre of the lateral part of the patella. This line corresponds to the lateral intermuscular septum between the vastus lateralis muscle and the rectus femoris muscle. First, the vastus lateralis muscle, rectus femoris muscle and lateral intermuscular septum were identified in B-mode. The femoral artery, profunda femoris artery and lateral circumflex femoral artery (LCFA) were identified in the colour flow mode. The descending branch of the LCFA was also identified between the rectus femoris muscle and the vastus intermedius muscle, and its course and anatomical relation to neighbouring muscles were determined. Then, the cutaneous perforators of the descending branch of the LCFA were located by sliding the introducer very slowly along the line between the anterior superior iliac spine and the centre of the lateral part of the patella, which corresponds to the lateral intermuscular septum. When a cutaneous perforator was found as a blinking narrow line running vertically in the vastus lateralis muscle and entering the subcutaneous fat, the location of the transducer was marked, and the distance from the centre of the lateral part of the patella was measured. The arterial waveform of the cutaneous perforator was also recorded in the pulse wave Doppler mode, and the peak velocity was measured.
During surgery, a longitudinal incision was made in the middle of the anterior thigh and extended down through the fascia of the rectus femoris muscle. The cut end of the deep fascia was grasped with several mosquito clamps and retracted laterally. The loose areolar tissue between the deep fascia and the underlying muscle was dissected carefully, and the cutaneous perforator was found and isolated along the lateral intermuscular septum. The distance from the centre of the lateral part of the patella to the cutaneous perforator was measured. The type of perforator, whether septocutaneous or myocutaneous, and its diameter were also recorded.
The locations of the cutaneous perforators identified by preoperative colour Doppler scanning were compared with the intraoperative anatomical findings, and the true positive rate and the positive predictive value were evaluated.
2. Results
A total of 48 cutaneous perforators were found preoperatively by colour Doppler scanning in 17 anterolateral thigh flaps (mean: 2.8 perforators per flap). The median location was 44.3% of the thigh from the distal end, and about 83% of cutaneous perforators were located in the middle third of the thigh (Fig. 1) . All perforators except two were found intraoperatively, and four perforators were not detected by preoperative Doppler scanning. Colour Doppler flowmetry assessment therefore has a 92.0% true positive rate and a 95.8% positive predictive value.
Figure 1Locations of cutaneous perforators identified by preoperative colour Doppler scanning; 48 perforators were found in 17 anterolateral thigh flaps (mean: 2.8 perforators per flap), and 83% were located in the middle third of the thigh.
Of the four perforators not detected by preoperative Doppler scanning, one had a very small diameter, less than 0.5 mm, and no pulse was found on visual inspection. We ligated the perforator because there was insufficient blood flow for flap nutrition. The other three undetected perforators had a median diameter of about 0.5–1 mm. They were pulsating, and we included them in the flap. The colour signals of the two false-positive perforators were small dots in the subcutaneous fat and the vastus lateralis muscle. They were thought to be a branch of the suprafascial plexus and a branch of the descending artery running through the superficial layer of the vastus lateralis muscle, respectively.
The flow velocity of the small cutaneous perforators was difficult to measure because the LOGIC 700 could not measure the flow velocity during the colour flow imaging, and arterial waveforms could be recorded in six perforators. The peak systolic flow velocity ranged from 7.4 to 19.1 cm s−1 (mean: 12.5 cm s−1). These six perforators were found in almost the same locations as marked preoperatively. Their diameter averaged about 1 mm and they all had vigorous pulses.
The number of cutaneous perforators included in the flap ranged from one to five, and all flaps except one included multiple cutaneous perforators. No flap was changed to a tensor-fascia-latae myocutaneous flap, anteromedial flap or contralateral anterolateral thigh flap because of a lack of appropriate cutaneous perforators for flap circulation.
3. Case report
A 65-year-old woman was referred to our hospital with a painful swelling in her left cheek. A biopsy and CT scan revealed squamous cell carcinoma of the left maxillary sinus (T4N0), and reconstruction of the maxillectomy defect with a titanium plate and an anterolateral thigh flap was planned. Prior to surgery, the locations of the cutaneous perforators were assessed by colour Doppler flowmetry. The blood flow in the descending branch of the LCFA was also measured because she had diabetes and severe atherosclerotic change in her major vessels. Sufficient blood flow in the descending branch of the left LCFA was confirmed by pulse wave Doppler mode (19.1 cm s−1). In the colour flow mode, three cutaneous perforators were found, at 24, 17 and 14 cm from the distal end of the thigh. The cutaneous perforator at 24 cm was considered to be septocutaneous because a colour signal was running through the lateral intermuscular septum (Fig. 2) . The other two perforators were thought to be myocutaneous because the descending branch of the LCFA was running in the vastus lateralis muscle and the colour signals of the perforators were running vertically in the vastus lateralis muscle, entering the subcutaneous fat (Fig. 3) . The peak velocity of the cutaneous perforator at 24 cm was 17.6 cm s−1.
Figure 2Colour signal of septocutaneous perforator located 24 cm from the distal end of the thigh. It was running through the lateral intermuscular septum between the rectus femoris muscle and the vastus lateralis muscle. VL, vastus lateralis muscle; VI, vastus intermedius muscle; RF, rectus femoris muscle; F, fatty tissue.
Figure 3Colour signal of myocutaneous perforator located 17 cm from the distal end of the thigh. The descending branch of the LCFA and the cutaneous perforator were running in the vastus lateralis muscle. VL, vastus lateralis muscle; VI, vastus intermedius muscle; F, fatty tissue.
Three cutaneous perforators were found intraoperatively, almost exactly at the sites marked preoperatively (Fig. 4) . The perforator at 24 cm was a septocutaneous perforator, and the other two perforators were myocutaneous perforators, as assessed by colour Doppler scanning. They all had vigorous pulses and were included in a 7 cm×18 cm anterolateral thigh flap (Fig. 5) . This was used to line the maxillary defect, and titanium mesh was used to reconstruct the orbital floor. The vascular pedicle was anastomosed to the facial artery and the common facial vein. There were no postoperative complications, and no flap necrosis except for a small subcutaneous abscess.
Figure 4Intraoperative view of isolated cutaneous perforators in the left thigh. Three perforators were found at almost exactly the locations marked by preoperative colour Doppler scanning (arrows). VL, vastus lateralis muscle; RF, rectus femoris muscle.
Figure 5Anterolateral thigh flap combined with the vastus lateralis muscle. All three cutaneous perforators were included in the flap, as planned preoperatively.
Identifying suitable perforators during flap dissection is the key to the successful elevation of an anterolateral thigh flap. Several authors have recommended preoperative mapping of the perforators by a conventional hand-held Doppler probe.
However, they did not demonstrate the reliability of this method, and the inability to distinguish cutaneous perforators and the vascular pedicle was pointed out.
Though conventional Doppler study is non-invasive and inexpensive, it is not practical for the preoperative mapping of cutaneous perforators owing to its unreliability.
Colour Doppler flowmetry with a high-frequency transducer enables the anatomical analysis of superficial structures and vascular flow. Small vessels can be seen as either red or blue streaks, depending on the flow direction relative to the transducer. In pulse wave Doppler mode, the arterial waveforms and flow velocities can be displayed by pointing the cursor at the objective vessel on the display. Hallock
first used this tool for the preoperative detection of fasciocutaneous perforators and reported its high reliability, despite individual perforator variation. Since then, it has been used for the preoperative assessment of perforators in various flaps, including posterior tibial fasciocutaneous flaps,
In preoperative cutaneous-perforator mapping of DIEP flaps, high reliability was reported, with a true-positive rate of 96.2% and a positive predictive value of 100%.
In our study of 17 anterolateral thigh flaps, 48 cutaneous perforators were found preoperatively. Of these, 83% were located in the middle third of the thigh, and the median location of the perforator was 44.3% of the way along the thigh from the distal end, which is similar to other anatomical studies.
In comparison with the intraoperative findings, colour Doppler scanning failed to detect four perforators. One perforator was very small and not suitable for flap nutrition, but the other three perforators were relatively large (0.5–1.0 mm) and carried sufficient flow. Of the three, one occurred in our first case, and we suspect that a technical error, such as an insufficient scan area, caused the failure. The other two false-negative perforators were found in the same patient. He had very thin muscles and subcutaneous fat in his thigh, and one cutaneous perforator was found with difficulty after extended Doppler scanning. Colour Doppler scanning of thin and atrophic thighs is very difficult because the excessive pressure exerted by the transducer can interrupt the blood flow to the cutaneous perforator and make the colour signal invisible.
Turning to the two false-positive perforators, a branch of the suprafascial plexus and a branch of the descending artery running along the superficial layer of the vastus lateralis muscle were misidentified as cutaneous perforators. This could have been avoided by confirming continuity of the colour signal between the suprafascial and the subfascial layers. In our study, the true-positive rate was 92% and the positive predicative value was 95.8%. This suggests that almost all perforators can be identified by preoperative Doppler assessment and that almost all the perforators identified preoperatively are located accurately. Though care must be taken to avoid excess pressure during scanning, especially in thin patients, this assessment proved very reliable for the preoperative mapping of anterolateral thigh flap cutaneous perforators.
Determining the number and locations of cutaneous perforators offers numerous benefits for preoperative flap planning. The greatest benefit is that unplanned alterations to the flap in the operating theatre due to the absence of suitable perforators can be avoided. Many authors have described the anatomy of cutaneous perforators in detail, and most have reported that there is at least one cutaneous perforator.
have been reported. Kimata et al reported that no perforators were found in 5.4% of cases, and a tensor fasciae latae myocutaneous flap or an anteromedial flap had to be used instead.
Celik et al reported that, in their series of 672 cases, no suitable perforator was found in six cases (0.89%) and a contralateral anterolateral thigh flap was harvested.
When suitable perforators or the lateral descending branch of the LCFA cannot be found by preoperative Doppler scanning, a contralateral anterolateral thigh flap can be harvested safely after confirming its vascular anatomy by Doppler scanning.
Another merit of this assessment is that, depending on the locations of the cutaneous perforators, the flap design can be customised preoperatively to meet the reconstructive requirements. When there are no suitable recipient vessels near the tissue defect, a long vascular pedicle can be obtained by including the most distal perforator in the flap. Planning an anterolateral thigh flap with multiple skin sections is also easy. Comparing the multiple skin flap with an anteromedial thigh flap,
the operating procedure is simplified because dissection of the medial descending branch of the LCFA is unnecessary. When a large flap is required, sufficient blood circulation can be achieved by including multiple perforators. This also reduces the risk of total necrosis due to venous thrombus.
Small cutaneous perforators easily thrombose soon after congestion develops, and salvage is difficult if the flap is based on a single perforator.
It is possible to distinguish between myocutaneous and septocutaneous perforators, as illustrated by the case report. The complexity of the dissection is quite different for the two types.
If the two types of perforator are identified by preoperative assessment, including the septocutaneous perforator in the flap shortens the operating time and avoids the tedious procedure of intramuscular dissection. The measurement of peak systolic velocity in pulse wave Doppler mode is imperative to evaluate patency if the patient has a general blood-vessel disorder, such as atherosclerosis. The condition and thickness of the vascular pedicle can also be established in B-mode, and the difficulty of vascular anastomosis can be estimated.
Though colour Doppler assessment of the cutaneous perforators provides accurate and valuable information for flap planning, it has some disadvantages. Compared with the conventional hand-held Doppler probe, the investment cost is high, and the apparatus is too large for portable use. Another disadvantage is that it requires both scanning skill and a detailed knowledge of the operative procedure. To make an accurate and practical flap plan, the surgeon harvesting the anterolateral thigh flap is the best person to perform this assessment. There are two keys to obtaining a precise assessment: apply the transducer with appropriate pressure to avoid interrupting the blood flow to the cutaneous perforator, and slide the transducer slowly so as not to miss the small perforators. Thus, it is relatively time-consuming (30–40 min) to complete the precise mapping of one thigh.
Preoperative assessment by colour Doppler flowmetry offers precise information about the number and locations of cutaneous perforators, and flap harvesting can be achieved more safely and reliably than with other methods. We believe that this non-invasive, repetitive and accurate assessment will promote the widespread use of anterolateral thigh flaps for various kinds of reconstruction by overcoming the difficulties of anatomical variation of the cutaneous perforators.
References
Kimata Y.
Uchiyama K.
Ebihara S.
et al.
Versatility of free anterolateral thigh flap for reconstruction of head and neck defects.
Arch Otolaryngol Head Neck Surg.1997; 123: 1325-1331
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