Magnetic Resonance Angiography and Computed Tomographic Angiography for Free Fibular Flap Transfer

We read with interest the article by Fukaya et al, “Magnetic Resonance Angiography for Free Fibula Flap Transfer,” in which a significant advancement in imaging technologies prior to perforator flap surgery is described—namely, the identification and analysis of the course of perforating arteries as a tool for preoperative planning.[1] Although magnetic resonance angiography (MRA),[2] computed tomographic angiography (CTA),[3] [4] and conventional angiography have each been used prior to free fibular flap surgery as a tool for mapping the vascular pedicles,[5] Fukaya et al have described advancements in MRA that permit analysis of individual perforators as small as 1 mm in diameter.

Although Fukaya et al have neatly compared their MRA findings to Doppler ultrasound and conventional angiography, we would like to share our experience with advancements in CTA that similarly identify and map the course of perforators prior to free fibula flap surgery. We have used both MRA and CTA and found CTA to display higher-resolution images and have a greater sensitivity at identifying the location, size, and course of perforators. Although perforators as small as 1 mm were described as being identified by Fukaya et al on MRA, we have been able to localize perforators as small as 0.3 mm on CTA. Achieving this has required modifications to traditional CTA scanning protocols, with our protocol described in Table [1].

Table 1 CT Scan Parameters Scanner: Siemens SOMATOM Sensation 64 Scan type: dynamically timed helical multidetector row computed tomographic angiography Slice thickness: 64 detector row × 0.6-mm collimator width Helical detector pitch: 0.9 Gantry rotation speed: 0.37 s Tube potential: 120 kV Tube current: 180 mA Intravenous contrast: Omnipaque 350 100 mL IVI 4 mL per second Contrast bolus tracking: from the popliteal artery (100 HU, minimum delay) Automatic dose modulation (Siemens CareDose4D) disabled Image reconstruction: 1-mm/0.7-mm overlapping axial images

As demonstrated in Fig. [1], perforator features that are able to be identified on CTA include the location of perforators at both skin and fascial levels, the diameter of perforators, the course through muscle and septa, and the subcutaneous course. Perforator localization is aided by the application of a grid to the image reformats, enabling localization from anatomic landmarks. The benefits of this information preoperatively include:

A guide to flap design and incision planning, improving confidence in the perfusion of the flap. The identification of the most suitable perforator (largest diameter, septocutaneous) to guide selection of the limb of choice. Preoperative awareness of the situation where no suitable perforators exist, permitting a change in procedure to a more suitable reconstructive option.

Figure 1 Computed tomographic angiogram with volume-rendered technique image of a large (2.5 mm) septocutaneous perforator. The perforator (blue arrow) is seen to perforate the lateral intermuscular septum (LIS) of the left leg to enter the subcutaneous tissues in supply of a fibular flap. Using multiplanar, three-dimensional reconstructions, the course from source artery (peroneal artery) is determined.

Fukaya et al compare diagnostic tests in Table 2 of their article, with the notable omission of CTA. A suitably updated table can now be produced, as shown in our Table [2]. Although CTA and MRA appear comparable, the notable exceptions include the faster scanning time but radiation exposure associated with CTA. We have found CTA to be highly beneficial for preoperative planning prior to free fibular flap reconstruction, and it is certainly a useful addition to the modalities available for preoperative imaging prior to perforator flaps.

Table 2 Comparison of Diagnostic Tests Feature CTA MRA Conventional Angiography Doppler Ultrasound Images perforators (in subcutaneous tissue) Yes Yes No Yes Images perforators (entire course from peroneal artery to skin) Yes Yes No No Distinguishes types of perforator Yes Yes No No Images trifurcation vessels Yes Yes Yes No Three-dimensional imaging Yes Yes No Yes Invasive No* No* Yes No Uses radiation Yes No Yes No Operator-dependent No No No Yes Speed Fastest Fast Varies Varies CTA, computed tomographic angiography; MRA, magnetic resonance angiography. Intravenous injection of contrast.

REFERENCES

• 1 Fukaya E, Grossman R F, Saloner D, Leon P, Nozaki M, Mathes S J. Magnetic resonance angiography for free fibula flap transfer.  J Reconstr Microsurg. 2007;  23 205-211
• 2 Lorenz R R, Esclamado R. Preoperative magnetic resonance angiography in fibular-free flap reconstruction of head and neck defects.  Head Neck. 2001;  23 844-850
• 3 Leon B R, Carrillo F J, Gonzalez H M, Franco J L. Mandibular reconstruction with the free vascularized fibular flap: utility of three-dimensional computerized tomography.  J Reconstr Microsurg. 1999;  15 91-97
• 4 Chow L C, Napoli A, Klein M B, Chang J, Rubin G D. Vascular mapping of the leg with multi-detector row CT angiography prior to free-flap transplantation.  Radiology. 2005;  237 353-360
• 5 Young D M, Trabulsy P P, Anthony J P. The need for preoperative leg angiography in fibula free flaps.  J Reconstr Microsurg. 1994;  10 283-287