Imaging of perforasome territories: the evolution of techniques

Background: Perforator flaps are widely used in reconstructive plastic surgery and technological advances in preoperative imaging have facilitated improvements in flap perfusion and clinical outcomes. The ‘perforasome’ concept describes the vascular territory supplied by a single arterial perforator and the imaging of these zones of perfusion has become increasingly advanced. Methods: This paper presents a qualitative analysis of the current literature on perforasome imaging. A review of the literature was performed using PubMed and Medline. Historical and background studies were also included for completeness. Results: The review identified an initial 858 records for assessment, with 52 studies formally reviewed. To date, there is largely level III and IV evidence for the available imaging techniques, although level II studies are emerging. There is currently no level I evidence for any imaging technique. Conclusion: There have been significant developments in imaging techniques since the introduction of the perforasome concept nearly a decade ago. In this review we have described the evolution of these methods over time, from simple perforator location to advanced threeand four-dimensional imaging and real-time dynamic perfusion imaging. With this progression and ongoing innovation, we believe perforasome imaging has the potential to improve outcomes in perforator flap surgery.

The perforasome concept describes the vascular territory supplied by a single arterial perforator and is an evolution of the angiosome concept described and imaged in 1987 by Taylor and Palmer. 1 Since those initial descriptions of the perforasomes by Saint-Cyr et al 2  Articles were excluded if they did not specifically describe or focus on a perforator or perforasome imaging technique. Studies that did not meet inclusion criteria but were relevant for historical reasons were included in the discussion but not in the formal review.

Results
After exclusions, 51 studies met criteria for inclusion in this review (Figure 1). Six imaging techniques were discussed within these studies ( Table 1).

Doppler sonography
While not strictly an imaging technique, handheld Doppler ultrasound has long been used to locate perforators in flap planning. 4 This use of sonography has significant limitations, such as both high false-positive 5, 6 and false-negative rates, 6,7 lack of information regarding calibre, flow volume 6 and perforator course, 8 and operator dependence. 9 However, the method is cheap, simple to use, noninvasive and risk-free for the patient and can be used in conjunction with preoperative imaging.

Colour duplex ultrasonography
Colour duplex ultrasonography holds many of the benefits of hand-held Doppler while providing more information on the flow volume, calibre and course 6 of perforator vessels. Its accuracy is superior to hand-held Doppler, 5, 6, 10 given its added ability to visualise vessels. Other studies show CDU to be inferior to CTA for identifying perforators in the abdomen, 11,12 though Zhang et al describe CDU as having higher accuracy than CTA in mapping of perforators in the lower extremities. 13 Notably, contrast-enhanced ultrasonography plus threedimensional reconstruction has been reported to increase accuracy and precision 14 when compared with regular CDU and hand-held Doppler.
While CDU involves no radiation exposure and is negligibly invasive, it only gives two-dimensional Rozen, Leung, Chae, Hunter-Smith: Imaging of perforasome territories: the evolution of techniques

Computerised tomographic angiography
Computerised tomographic angiography is generally accepted as state-of-the-art for perforator visualisation. 16,17 Its high accuracy 11,[18][19][20][21][22] and excellent image quality mapping of location, calibre, course and branching of a perforator, 11,23 have led to reduced operation times and fewer postoperative complications. 23,24 As the first technique to produce highly detailed perforator images, 16 CTA is well-studied as a preoperative perforator visualisation technique in multiple types of perforator flaps. While CTA requires radiation exposure and an iodinated contrast injection, there are many benefits. It is affordable, accessible and operator-independent, gives significant detail on perforator anatomy and can visualise small vessels to 0.3mm in diameter. 25 Additionally, CTA has better fat-to-vessel contrast than MRA, allowing easier mapping of a perforator's subcutaneous course, though intramuscular course is clearer on MRA. 26,27 Another feature of CTA is its potential for threedimensional image processing, 28  Given CTA's main and significant disadvantage is its use of contrast and radiation, 23,24,26 there has been investigation into using lower doses of both. 29 Several studies have found that low-dose techniques achieve high-quality vascular imaging similar to conventional CTA. 29,30 Overall, CTA is an excellent resource for preoperative perforator imaging with continuing developments to mitigate the risks of iodinatedcontrast and radiation exposure.

Magnetic resonance angiography
Magnetic resonance angiography provides a threedimensional image of perforator vessels but often using safer, non-iodinated contrast-enhancement.

AJOPS | ORIGINAL ARTICLE
More research is required to ascertain parameters of hypo-perfusion, but ICG angiography shows promise in dynamically assessing perforasomes intra-operatively.

DIRT
As a perforasome mapping technique, DIRT can be used preoperatively in flap planning and intraoperatively to assess flap viability.
On a thermogram, the perfusion territory of a perforator is indicated by the 're-warming' areas surrounding the hotspot 41

Disclosure
The authors have no financial or commercial conflicts of interest to disclose.