Preoperative MR Angiography in Free Fibula Flap Transfer for Head

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Kelly et al. MR Angiography for Head and Neck Cancer

Va s c u l a r I m a g i n g • P i c t o r i a l E s s a y

Preoperative MR Angiography in Free Fibula Flap Transfer for Head and Neck Cancer: Clinical Application and Influence on Surgical Decision Making Aine M. Kelly1 Paul Cronin1 Hero K. Hussain1 Frank J. Londy1 Douglas B. Chepeha2 Ruth C. Carlos1 Kelly AM, Cronin P, Hussain HK, Londy FJ, Chepeha DB, Carlos RC

Keywords: head and neck cancer, fibular free flap, mandibular reconstruction, MR angiography DOI:10.2214/AJR.04.1950 Received December 22, 2004; accepted after revision September 5, 2005.

OBJECTIVE. We review the fibular free flap surgical procedure to illustrate the usefulness of preoperative lower limb MR angiography and to show how calf vascular anatomy on MR angiography affects patient surgical management. CONCLUSION. With its high positive predictive value and sensitivity, preoperative MR angiography can improve the chances of a successful outcome at the recipient mandibular site. It provides the reconstructive surgeon with a road map, revealing vascular anomalies or disease that could alter or contraindicate surgery. ost head and neck cancers involving the mandible are treated by surgical excision. Surgical excision can leave a cosmetic defect with loss of function. Osteocutaneous free tissue transfer involves harvesting the patient’s own soft tissue and bone from another site in the body. Today, many of these grafts are vascularized, using microsurgical technique to anastomose the donor and recipient arteries and veins. The use of vascularized grafts speeds recovery and return of function, when compared with nonvascularized grafts. Various donor sites in the body have been used as grafts, including the rib, radius, scapula, ilium, and metatarsals. Currently, the fibular free flap is the workhorse of free tissue transfer in mandibular reconstruction for head and neck cancer. We review the fibular free flap surgical procedure to illustrate the usefulness of preoperative lower limb MR angiography, and to show how calf vascular anatomy on MR angiography can affect patient surgical management.

M

1Department

of Radiology, University of Michigan, University of Michigan Hospitals, B1 132 H Taubman Center, 1500 East Medical Center Drive, Ann Arbor, MI 48109-0030. Address correspondence to A. M. Kelly ([email protected]).

2Department

of Surgery, University of Michigan, Ann Arbor, MI.

AJR 2007; 188:268–274 0361–803X/07/1881–268 © American Roentgen Ray Society

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Surgical Approach and Technique The fibula has been used as a long bone donor in cases of trauma and cancer since 1989 [1]. It has the advantages of being long, straight, and strong, and of being composed of mainly dense cortical bone with a small medulla. The peroneal artery parallels the length of the bone and remains sizable, allowing for postoperative monitoring with Doppler sonography. The fibular flap can

conveniently be dissected in the supine patient by using a lateral approach. Donor and recipient sites are far enough apart to allow two surgical teams to operate. The side opposite the mandibular defect is most commonly chosen [2]. A flap is considered viable when it remains well perfused 1 month after the date of surgery. Justification for Preoperative Evaluation It is essential that patients be safely and comprehensively evaluated for vascular disease or significant anatomic variants before surgery. Defining the length and branching pattern of the peroneal artery preoperatively provides the surgeon with a road map that aids and shortens the time required for peroneal artery dissection. The most feared donor-site complication in fibula flap harvest is foot ischemia secondary to sacrifice of the peroneal artery. In most people, the peroneal artery does not supply a significant amount of the pedal circulation. However, in persons with peripheral arterial disease, and in some congenital variants of it, the peroneal artery becomes the main supply to the foot. The three situations when the peroneal artery becomes the main vessel supplying the foot are when there is significant arteriosclerotic disease, when the tibial artery is either hypoplastic or absent, and in the case of peroneal artery magna. Preoperative imaging is recommended in patients with arteriosclerotic disease, in patients with abnormal pedal

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MR Angiography for Head and Neck Cancer

Fig. 1—Normal calf artery anatomy (88%) and the more commonly seen significant anatomic variants with their incidence. a. = artery, AT = anterior tibial artery, Per = peroneal artery magna, PT = posterior tibia artery. Reprinted with permission from [20]. A, Absent anterior tibial artery (3.8%). B, Absent posterior tibial artery (1.6%). C, Peroneal artery magna (0.2%). D, Absent peroneal artery (< 0.1%). E, Abnormally long tibioperoneal trunk (0.1%).

Fig. 3—MR angiography of 32-year-old woman with short tibioperoneal trunks (trifurcations) bilaterally (arrows). Posterior tibial arteries are also hypoplastic bilaterally (arrowheads), more so on left side. Consequently, right calf was judged more suitable for fibular flap harvest. Fig. 2—MR angiography of 39-year-old man shows normal lower limbs.


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Kelly et al. pulses, and in patients with a history of significant lower leg trauma to assess vessel anatomy and for vessel disease. Many head and neck cancer patients are elderly and have a history of smoking, as well as a higher incidence of peripheral vascular disease than is found in the general population. Preoperative imaging should also be performed in patients with congenital abnormalities; however, these patients often have normal physical examinations. We routinely perform preoperative imaging on all patients, although only in patients with congenital anomalies or atherosclerotic disease is the imaging likely to be abnormal. Our justification for imaging all patients is the increased prevalence of atherosclerosis in this patient population and because congenital anomalies may go undetected on physical examination. MR Angiography Imaging Evaluation with Doppler sonography, conventional angiography, or CT angiography has been performed [3–5]. MR angiography is being increasingly used and there are now several reports in the surgical literature about its use. The advantages of MR angiography include multiplanar capability, safer contrast agents, and lack of invasiveness. We have been using lower limb MR angiography at our institution since 1996 and have imaged more than 100 cases before performing fibular flap reconstruction. Our protocol uses a 1.5-T system with a 12-element phased-array coil. Sequences include a 2D vascular time of flight and 3D spoiled gradient-recalled echo with IV contrast material (60 mL gadolinium total) and automated contrast bolus detection (SmartPrep, General Electric Medical Systems). Coverage extends from the lower abdominal aorta to the foot using automated table motion (SmartStep). The lower aorta and pelvic arteries are included to evaluate for proximal stenoses. We use 30 mL of contrast medium for the calves, and 30 mL for the thighs and pelvis, injected at a rate of 2 mL/s. Scanning parameters include slice thickness for the pelvis of 2.8 mm, 2.6 mm for the thighs, and 1.6 mm for the calves; a field of view of 48 cm; a matrix of 320–512 × 192; bandwidths of 62.5 for the pelvis and thighs, and 31.25 for the calves; TR < 6 ms; TE minimum; and zero filling for all three stations. MR angiography requires approximately 30–45 minutes for acquisition and 20–30 minutes to interpret, including time after processing. MR angiography studies at our institution are reviewed by both an MR radiologist and a vascu-

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lar interventional radiologist simultaneously. The few contraindications to these MR angiography studies include general MRI contraindications and metallic hardware in the lower limbs, which cause susceptibility artifact, especially on spoiled gradient-recalled echo imaging. Subsystolic thigh compression [6, 7] and parallel imaging [8, 9] can improve resolution when imaging the calf arteries. Contrast-enhanced MR angiography of the lower limb vessels has sensitivities in the range of 77–100%, and is reported to detect significant stenosis (moderate stenosis to occlusion) when using conventional angiography as the standard of reference, with specificities of 87.6–99.7% [10–13]. Interreader agreement is very good to excellent for detection of both occlusion and significant stenosis [12, 13]. Normal Calf Vessel Anatomy In the most common anatomic situation, the popliteal artery bifurcates to become the tibioperoneal trunk and the anterior tibial artery. The tibioperoneal trunk then bifurcates and gives rise to the posterior tibial artery and the peroneal artery (Fig. 1). The peroneal artery terminates just above the ankle, dividing into an anterior perforating branch, which joins the anterior tibial artery, and a posterior communicating branch, which joins the posterior tibial artery. The anterior tibial artery supplies the dorsum of the foot via the dorsalis pedis artery, and contributes to the plantar foot arch via the deep plantar artery. The posterior tibial artery supplies the plantar aspect of the foot via the medial and lateral plantar arteries and the deep plantar arch. Thus the blood supply of the foot is provided by the anterior and posterior tibial arteries. This pattern is seen in approximately 88% of individuals [14]. In patients with atherosclerosis of the tibial arteries, collaterals from the peroneal artery may provide a significant contribution to the pedal circulation. History and physical examination may not identify all of these patients. Calf Vessel Variants In one large angiographic series, a normal branching pattern was observed in 92% of patients (Figs. 1 and 2) [15, 16]. However, normal variants occur in 5–7% of the population [15–17]. Many of these variants are insignificant and of no consequence. In some patients, however, congenital anomalies exist whereby the peroneal artery supplies a significant contribution to the pedal circulation. In 3.8% of patients, the posterior tibial artery is absent or hypoplastic (Figs. 1B, 3, and 4)

or ends at the lower leg with the plantar arteries branching from the peroneal artery [15]. In 1.6% of patients, the anterior tibial vessel is absent or hypoplastic (Fig. 1A) or terminates in the lower leg with the dorsalis pedis artery then originating from the anterior perforating branch of the peroneal artery [15]. In 1% of patients, the dorsalis pedis arises from two roots of equal size from the peroneal and anterior tibial arteries (Fig. 4) [15]. In 0.2–7% of patients, both the anterior tibial and posterior tibial arteries are hypoplastic with the entire pedal circulation supplied by the peroneal artery, also known as the peroneal artery magna [15, 16] (Figs. 1C, 5, and 6). The peroneal artery may be absent or hypoplastic (Figs. 1D and 7). In fewer than 0.1% of patients, the peroneal artery is absent [18]. Rarely, the tibioperoneal trunk is abnormally long with a resultant short peroneal artery (Fig. 1E). The calf vessels may arise above the knee joint (Fig. 8). The peroneal artery origin above the knee joint occurs in 0.16% of patients [14]. When aberrant arterial anatomy is found in one leg, the opposite side is also aberrant in 28–50% of cases [16, 17]. Any of these variants may require modification of the surgical approach taken. The physical examination of the peripheral pulses is often normal in these individuals [19, 20]. Reporting Lower Extremity MR Angiography Examinations At our institution, surgeons want to know whether significant proximal arteriosclerotic disease is present, whether three-vessel runoff to the calf on at least one side is present, and the distal extent of the peroneal artery from its origin at the trifurcation. The radiologist needs to ensure that two vessels, other than the peroneal artery, supply the foot. The anterior and posterior tibial arteries must reach the ankle joint and our surgeons request that we indicate whether the peroneal artery extends to within 8 cm of the distal aspect of the fibula. Any abnormality in the point of origin of the peroneal artery should also be indicated preoperatively because assessment for congenital variation is difficult to perform at the time of surgery. The presence of some congenital variants is a contraindication to fibular flap harvest (Appendix 1). Contraindications to Free Fibula Flap Transfer At our institution, contraindications to free fibula flap transfer include significant atherosclerotic disease in the abdominal




Fig. 4—MR angiography of 54-year-old man shows hypoplastic posterior tibial arteries bilaterally (arrows). This variant was not sufficient to cancel free fibula flap harvest.

Fig. 5—MR angiography of 54-year-old man shows hypoplastic right posterior tibial artery (arrowhead), with right peroneal artery (arrow) reconstituting posterior tibial artery/plantar arch.

Fig. 7—MR angiography of 51-year-old man shows hypoplastic peroneal arteries bilaterally (arrows). This variant thought to be nonsignificant. Venous contamination is seen on right side. Fibular flap was performed using right side.


Fig. 6—MR angiography of 48-year-old woman shows dominant peroneal artery on right side (arrow), which predominantly supplies plantar arch (arrowhead). Consequently, left fibula was used for free tissue transfer.

Fig. 8—MR angiography of 59-year-old man with high take-off of right posterior tibial artery (arrow). This variant is thought to be nonsignificant. Patient has normal arterial anatomy on left. Right fibular flap was performed.

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A

B

Fig. 9—45-year-old man with stenosis of right external iliac artery (arrow, A) as measured on 3D MR angiography maximum-intensity-projection image. A, This stenosis is approximately 50%, indicating 75% reduction in cross-sectional area, which is significant. B, Opposite side was used for fibular flap harvest.

A

B

Fig. 10—MR angiogram of 75-year-old woman. A, Diffuse arteriosclerotic disease of superficial femoral arteries bilaterally with significant stenosis in right superficial femoral artery (arrow). B, Significant stenosis of both anterior tibial arteries (arrows). C, Significant stenosis of right anterior tibial artery (arrow). D, Significant stenosis of left anterior tibial artery (arrow) and left peroneal artery (arrowhead). Alternate flaps were used due to her bilateral calf arterial disease.

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B

Fig. 11—MR angiography of 79-year-old woman. A, Diffuse disease of both superficial femoral artery (arrowheads) and total occlusion of left superficial femoral artery (arrow). B, Bilateral occlusions of posterior tibial arteries (arrows). Patient had alternate site (scapula) used for free tissue transfer.

A

B

C

Fig. 12—MR angiography of 72-year-old man. A, Nonsignificant diffuse arteriosclerotic disease in superficial femoral artery bilaterally (arrows) and significant stenosis in right popliteal artery (arrowhead). B, Significant stenosis of left tibioperoneal trunk (arrow). Alternate flap transfer was performed because of his bilateral disease.

Fig. 13—MR angiography of 58-year-old man shows diffuse, nonsignificant disease of right posterior tibial artery (arrows) and hypoplastic left posterior tibial artery (arrowheads). Alternate flap was performed (rectus) because of large size of his mandibular defect.


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Kelly et al. aorta, iliac or femoral arteries, or popliteal artery; prior major trauma to the limb; and the congenital variants listed in Appendix 1. Arteriosclerotic disease is considered significant when 2D MR angiography shows greater than 50% diameter narrowing of the vessel (Figs. 9, 10, 11B, and 12B). If significant stenosis is present in the iliac, femoral, or calf arteries, the opposite calf is used. Mild proximal arteriosclerotic disease (i.e., stenosis that is less than half the 2D diameter of the vessel) is not considered a contraindication to the procedure (Figs. 11A, 12A, and 13). Conclusion Free fibular flap transfer for mandibular defects in head and neck cancer patients is widely performed. It is essential that patients be safely and comprehensively evaluated for disease or significant anatomic variants before surgery. MR angiography can provide a minimally invasive and accurate tool for the preoperative evaluation of the fibular donor vessels without exposing the patient to an iodinated contrast agent or ionizing irradiation. Because of its high positive predictive value and sensitivity, preoperative MR angiography can improve the chances of a successful outcome at the recipient mandibular site. It provides the reconstructive surgeon with a road map, revealing the vascular anomalies or disease that could alter or contraindicate surgery. Acknowledgments We acknowledge the assistance of David Williams and Theodoros Teknos in preparing and drafting this article.

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APPENDIX 1: Contraindications to Fibular Flap Harvest Surgery • Significant atherosclerotic disease in the abdominal aorta, external iliac arteries, superficial femoral arteries, or popliteal arteries: Moderate stenosis (50% reduction in 2D vessel diameter) Severe stenosis (75% reduction in 2D vessel diameter) Complete occlusion of the vessel (100% reduction in 2D vessel diameter) • Trauma • Congenital variants: Absent or hypoplastic anterior tibial artery (1.6% incidence) Absent or hypoplastic posterior tibial artery (3.8% incidence) Peroneal artery magna (0.2% incidence) Absent or hypoplastic peroneal artery (< 0.1% incidence) Abnormally long tibioperoneal trunk (< 0.1% incidence)

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