DOI:10.2214/AJR.04.1950
AJR 2007; 188:268-274
© American Roentgen Ray Society
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 and
Ruth C. Carlos1
1 Department of Radiology, University of Michigan, University of Michigan
Hospitals, B1 132 H Taubman Center, 1500 East Medical Center Drive, Ann Arbor,
MI 48109-0030.
2 Department of Surgery, University of Michigan, Ann Arbor, MI.
Received December 22, 2004;
accepted after revision September 5, 2005.
Address correspondence to A. M. Kelly
(ainekell{at}umich.edu).
Abstract
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.
Keywords: head and neck cancer • fibular free flap • mandibular reconstruction • MR angiography
Introduction
Most 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.
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 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.
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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%).
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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.
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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 x 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 vascular 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].
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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.
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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.
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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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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 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.
9A,
9B,
10A,
10B,
10C,
10D,
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).
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Fig. 9A —45-year-old man with stenosis of right external iliac artery
(arrow, A) as measured on 3D MR angiography
maximum-intensity-projection image. This stenosis is approximately 50%,
indicating 75% reduction in cross-sectional area, which is significant.
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Fig. 9B —45-year-old man with stenosis of right external iliac artery
(arrow, A) as measured on 3D MR angiography
maximum-intensity-projection image. Opposite side was used for fibular flap
harvest.
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Fig. 10D —MR angiogram of 75-year-old woman. 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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Fig. 12A —MR angiography of 72-year-old man. Nonsignificant diffuse
arteriosclerotic disease in superficial femoral artery bilaterally
(arrows) and significant stenosis in right popliteal artery
(arrowhead).
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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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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.
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)
Acknowledgments
We acknowledge the assistance of David Williams and Theodoros Teknos in
preparing and drafting this article.
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Abstract
Introduction
