DOI:10.2214/AJR.05.0484
AJR 2006; 187:800-806
© American Roentgen Ray Society
MRI Appearance of Myocutaneous Flaps Commonly Used in Orthopedic Reconstructive Surgery
Michael G. Fox1,
Laura W. Bancroft2,
Jeffrey J. Peterson2,
Mark J. Kransdorf2,3,
Sarvam P. TerKonda4 and
Mary I. O'Connor5
1 Department of Radiology, University of Virginia, Charlottesville, VA
22908.
2 Radiology Department, Mayo Clinic, 4500 San Pablo Rd., Jacksonville, FL
32224.
3 Department of Radiologic Pathology, Armed Forces Institute of Pathology,
Washington, DC 20306-6000.
4 Department of Plastic and Reconstructive Surgery, Mayo Clinic, Jacksonville,
FL 23224.
5 Department of Orthopedic Surgery, Mayo Clinic, Jacksonville, FL 23224.
Received March 18, 2005;
accepted after revision August 1, 2005.
Address correspondence to M. J. Kransdorf
(kransdorf.mark{at}mayo.edu).
Abstract
OBJECTIVE. Our aim was to describe the MRI appearance of
myocutaneous flaps and to determine whether postoperative radiation therapy
affects imaging.
MATERIALS AND METHODS. We retrospectively reviewed 30 myocutaneous
flaps in 27 patients (n = 165 examinations; mean, 6.1 examinations
per patient). Examinations were analyzed for flap type, location, degree of
atrophy, signal intensity, and enhancement.
RESULTS. Sixty-three percent (19/30) of the flaps developed high
T1-weighted signal (mean, 15 months); 83% (25/30) developed high T2-weighted
signal (mean, 10 months). This occurred sooner in those patients with
postoperative radiation therapy (9 vs 12 months). T2-weighted signal returned
to baseline in 32% (8/25) of the flaps (mean, 21 months); this occurred sooner
in flaps not exposed to postoperative radiation (10 months vs 38 months).
Seventy-one percent (20/28) of the flaps enhanced greater than the background
musculature. Enhancement was seen more frequently in patients treated with
postoperative radiation therapy than those not treated with radiation (83% vs
63%). All flaps atrophied; however, the two functional latissimus dorsi flaps
atrophied less. Although increased T2-weighted signal and enhancement were
seen in flaps after postoperative radiation therapy as compared with those
without, this was not significant (p = 0.35 and p = 0.40,
respectively).
CONCLUSION. Myocutaneous flaps used in orthopedic reconstructive
surgery typically show increased signal intensity on T2-weighted images and
contrast enhancement initially, followed by some degree of atrophy and
increased signal intensity on T1-weighted images. Postoperative radiation
therapy may increase the likelihood that the flap will exhibit increased
T2-weighted signal and enhancement.
Keywords: MRI • musculoskeletal imaging • myocutaneous flap • orthopedic surgery • radiation therapy
Introduction
Myocutaneous flaps are often used in orthopedic reconstructive surgery,
with up to 69% of reconstructions occurring after surgical treatment for
extremity sarcoma [1]. They are
used most frequently for soft-tissue coverage, particularly after tumor
resection, but they may also be used after extensive debridement for
osteomyelitis or trauma. The selection of the type of flap depends on many
factors but is primarily based on the size and location of the soft-tissue
defect. Occasionally a flap is selected to provide a degree of function in
addition to soft-tissue coverage
[2-6].
Patients receiving flaps for aggressive malignancies may also receive external
radiation therapy, which can further complicate the imaging appearance
[7-12].
Consequently, those unfamiliar with the normal time-related changes in
myocutaneous flaps may confuse them for recurrent tumor.
We reviewed our experience with flaps commonly used in orthopedic
reconstructive surgery to describe the normal postoperative imaging appearance
and establish the time-related changes in signal intensity, morphology, and
enhancement. We also evaluated the effect of postoperative radiation therapy
on the imaging appearance.
Materials and Methods
This investigational protocol was conducted with the approval of the Mayo
Clinic institutional review board. In accordance with the requirements of a
retrospective review, informed consent was not required.
The cases, followed by a single orthopedic surgeon specializing in
reconstructive and tumor surgery, were selected from a review of 45 patients
who had undergone myocutaneous flap reconstruction between 1995 and 2001. The
study group consisted of 27 patients (13 men and 14 women) with a mean age of
59 years (range, 27-88 years) who had postoperative MRI available. A total of
30 myocutaneous flaps were used for soft-tissue coverage after either
orthopedic tumor resection (26 flaps, 25 patients) or osteomyelitis (four
flaps, two patients). A total of 165 MRI examinations were retrospectively
reviewed (average, 6.1 examinations per patient; range, 1-13) by four
radiologists with experience in musculoskeletal imaging. More than one
postoperative examination was available to evaluate 28 of the flaps.
Contrast-enhanced imaging was available in all but two cases.
Thirteen of 26 (50%) flaps in patients undergoing tumor resection received
concomitant postoperative radiation therapy. The average dose was 1,972 cGy
(range, 800-5,040). In two patients, radiation dose was unknown.
Of the 26 flaps used for orthopedic oncology, 11 were placed during
reconstructive surgery after resection of grade 3 or 4 malignant fibrous
histiocytoma. The other tumors included liposarcoma (four cases); grade 3 or 4
leiomyosarcoma (two cases); poorly differentiated or grade 4 sarcoma (two
cases); synovial sarcoma (two cases); desmoid, alveolar soft-part sarcoma;
extraskeletal osteosarcoma; dermatofibrosarcoma protuberans; and chordoma (one
flap case).
The MRI examinations were reviewed to determine the type of muscle used and
location of the flap. All flaps were myocutaneous, containing both muscle and
overlying skin. A flap was designated as a rotational flap if the native
neurovascular supply was preserved via a pedicle and the flap was rotated into
position (Figs. 1A and
1B). A free flap was defined as
one that was completely detached and required microvascular reanastomosis of
the pedicle (Figs. 2A,
2B,
2C,
2D,
2E,
2F, and
2G). Flaps were also
characterized as coverage-only or coverage-and-functional flaps, depending on
their purposes.
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Fig. 1A —41-year-old woman with rotational medial gastrocnemius flap
used for coverage after debridement for osteomyelitis. Axial proton-density
(TR/TE, 4,000/15; echo-train length, 8) image obtained 35 months after surgery
shows preserved vascular pedicle (arrows) and flap signal
characteristics similar to background muscles.
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Fig. 2A —39-year-old woman with rectus abdominus free flap to ankle
after resection of dermatofibrosarcoma protuberans. Coronal T1-weighted
(TR/TE, 683/17) spin-echo MR image at 4 months after placement of free flap
(asterisk).
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Fig. 2C —39-year-old woman with rectus abdominus free flap to ankle
after resection of dermatofibrosarcoma protuberans. Progressive fatty atrophy
of rectus abdominus free flap to ankle is seen. Patient did not receive
radiation therapy. Coronal T1-weighted image obtained at 5 months (C),
at 15 months (D), at 28 months (E), and at 41 months
(F).
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Fig. 2D —39-year-old woman with rectus abdominus free flap to ankle
after resection of dermatofibrosarcoma protuberans. Progressive fatty atrophy
of rectus abdominus free flap to ankle is seen. Patient did not receive
radiation therapy. Coronal T1-weighted image obtained at 5 months (C),
at 15 months (D), at 28 months (E), and at 41 months
(F).
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Fig. 2E —39-year-old woman with rectus abdominus free flap to ankle
after resection of dermatofibrosarcoma protuberans. Progressive fatty atrophy
of rectus abdominus free flap to ankle is seen. Patient did not receive
radiation therapy. Coronal T1-weighted image obtained at 5 months (C),
at 15 months (D), at 28 months (E), and at 41 months
(F).
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Fig. 2F —39-year-old woman with rectus abdominus free flap to ankle
after resection of dermatofibrosarcoma protuberans. Progressive fatty atrophy
of rectus abdominus free flap to ankle is seen. Patient did not receive
radiation therapy. Coronal T1-weighted image obtained at 5 months (C),
at 15 months (D), at 28 months (E), and at 41 months
(F).
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Fig. 2G —39-year-old woman with rectus abdominus free flap to ankle
after resection of dermatofibrosarcoma protuberans. Coronal fast spin-echo
T2-weighted (TR/TE, 3,000/95) image shows markedly increased T2-weighted
signal at 4 months after flap placement.
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Most of the flaps were rotational (n = 28) using the rectus
abdominis (n = 11), gastrocnemius (n = 5), rectus femoris
(n = 5), latissimus dorsi (n = 4), gracilis (n =
1), pectoralis major (n = 1), and lateral hamstring (n = 1).
Free flaps were used in two cases, with the rectus abdominis providing the
coverage in both instances. The flaps were used primarily for coverage
(n = 28; 93%) of the following areas: thigh (n = 12),
pelvis/groin (n = 7), upper arm/shoulder (n = 3), proximal
lower leg (n = 3), ankle (n = 2), and lower abdomen
(n = 1). Both coverage and function (n = 2; 7%) were
provided to the upper arm with latissimus dorsi flaps after triceps
(n = 1) and biceps (n = 1) resection.
MR images were assessed for evidence of flap atrophy and for changes in the
flap signal intensity and enhancement characteristics. Flap signal intensity
was compared with that of normal muscle on all pulse sequences. Muscle atrophy
was evaluated subjectively on T1-weighted images and determined by the maximum
decrease in size of the flap compared with the first postoperative
examination. Atrophy was graded as minimal (0-25%), mild (26-50%), moderate
(51-75%), and marked (76% or more). The fat content within the flap was
compared with that of normal muscle. Enhancement was characterized as present
or absent. If present, enhancement was subjectively graded as mild, moderate,
or marked compared with that of normal background muscle, which was used as a
baseline for enhancement.
All MRI examinations were performed on a 1.5-T magnet, with the majority
being performed on a 1.5-T Symphony (Siemens Medical Solutions). All
examinations included T1-weighted, T2-weighted, and enhanced T1-weighted
spin-echo images.
Atrophy, signal intensity, and enhancement results for flaps treated with
postoperative radiation therapy and those not treated were compared using
Fisher's exact test or Wilcoxon's rank sum test depending on the variable
type. A p value of 0.05 was considered statistically significant.
Results
Atrophy was evaluated in 28 flaps. Two cases were not assessed (one with
and one without postoperative radiation therapy) in which there was only a
single postoperative examination. All flaps showed some degree of muscle
atrophy. Atrophy was minimal in 32% of the flaps (9/28), mild in 36% (10/28),
moderate in 14% (4/28), and marked in 18% (5/28). The degree of atrophy was
most pronounced in the rectus abdominis flaps with 31% (4/13) showing greater
than 75% atrophy (Figs. 2A,
2B,
2C,
2D,
2E,
2F, and
2G). The degree of atrophy was
greater in patients receiving postoperative radiation therapy but not
statistically significant (Table
1).
Increased T1-weighted signal was shown in 63% (19/30) of flaps (mean, 15
months; range, 2-54 months). This occurred in 62% (8/13) of flaps with
postoperative radiation therapy (mean, 14 months; range, 4-26 months) and in
65% (11/17) of flaps with no postoperative radiation therapy (mean, 16 months;
range, 2-54 months). Increased T2-weighted signal was present in 83% (25/30)
of flaps (mean, 11 months; range, 3-58 months) (Figs.
2A,
2B,
2C,
2D,
2E,
2F, and
2G). This was observed in 92%
of flaps with postoperative radiation therapy (12/13; mean, 11 months; range,
3-31 months) and in 76% of flaps with no postoperative radiation therapy
(13/17; mean, 12 months; range, 3-58 months). The increased T2-weighted signal
returned to baseline (similar to that of the surrounding muscle) in 32% of the
flaps (8/25) (mean, 21 months; range, 5-31 months) (Figs.
3A and
3B). This occurred in 38% of
the flaps not receiving postoperative radiation therapy (5/13; mean, 10
months; range, 7-21 months) and in 25% of those treated with postoperative
radiation therapy (3/12; mean, 38 months; range, 20-56 months)
(Table 2).
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Fig. 3A —42-year-old man with rectus abdominus rotational flap.
Resolution of hyperintense T2-weighted flap signal for high-grade malignant
fibrous histiocytoma is seen. Axial conventional T2-weighted (TR/TE 2,930/80)
spin-echo MR image obtained 2 months postoperatively displays hyperintense
signal in flap (large asterisk) relative to background musculature.
Patient had received postoperative radiation, and increased signal is also
seen in native muscle of anterior compartment (small asterisk).
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Fig. 3B —42-year-old man with rectus abdominus rotational flap.
Resolution of hyperintense T2-weighted flap signal for high-grade malignant
fibrous histiocytoma is seen. Axial conventional T2-weighted (TR/TE, 2,250/80)
spin-echo MR image obtained during follow-up at 27 months shows marked atrophy
of flap (large asterisk) with near reversion of flap signal to that
of adjacent muscles. Slight increased signal is seen within flap because of
fatty infiltration. Note slight residual increased signal in radiated muscle
(small asterisk).
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Gadolinium-enhanced imaging was performed at least once in 28 of the flaps.
Seventy-one percent of the flaps showed enhancement greater than that of the
surrounding tissue (20/28; mean, 9 months; range, 3-35 months) (Figs.
4A,
4B,
4C, and
4D). This occurred in 83% of
flaps with postoperative radiation therapy (10/12; mean, 10 months; range,
4-32 months) and in 63% of the flaps with no postoperative radiation therapy
(10/16; mean, 8 months; range, 3-35 months). Enhancement returned to baseline
(similar to that of the surrounding muscle) in 30% of the flaps (6/20; mean,
18 months; range, 12-27 months). This was observed in 30% of flaps with
postoperative radiation therapy (3/10; mean, 20 months; range, 15-27 months)
and in 30% of those without radiation therapy (3/10; mean, 16 months; range,
12-21 months) (Table 3).
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Fig. 4A —72-year-old woman with rectus abdominus flap. Resolution of
flap enhancement is seen after resection of well-differentiated liposarcoma.
Patient received postoperative radiation. Axial T1-weighted image (A)
and enhanced fat-suppressed image (B) obtained 6 months after flap
placement shows diffuse enhancement of this rotational flap. Margins of flap
are well delineated (arrows) in A.
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Fig. 4B —72-year-old woman with rectus abdominus flap. Resolution of
flap enhancement is seen after resection of well-differentiated liposarcoma.
Patient received postoperative radiation. Axial T1-weighted image (A)
and enhanced fat-suppressed image (B) obtained 6 months after flap
placement shows diffuse enhancement of this rotational flap. Margins of flap
are well delineated (arrows) in A.
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Fig. 4C —72-year-old woman with rectus abdominus flap. Resolution of
flap enhancement is seen after resection of well-differentiated liposarcoma.
Patient received postoperative radiation. Axial T1-weighted image (C)
and enhanced fat-suppressed image (D) obtained at 19 months. Signal
intensity of flap now equals that of background muscle. Margins of flap are
well delineated (arrows) in C.
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Fig. 4D —72-year-old woman with rectus abdominus flap. Resolution of
flap enhancement is seen after resection of well-differentiated liposarcoma.
Patient received postoperative radiation. Axial T1-weighted image (C)
and enhanced fat-suppressed image (D) obtained at 19 months. Signal
intensity of flap now equals that of background muscle. Margins of flap are
well delineated (arrows) in C.
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Discussion
Soft-tissue reconstructive flaps show characteristic MRI appearances with
respect to time-related changes in signal intensity and morphology. In our
study, all flaps showed some degree of atrophy; 63% showed increased
T1-weighted signal intensity (mean, 15 months), 83% showed increased
T2-weighted signal (mean, 10 months), and 71% showed enhancement after
contrast administration (mean, 9 months).
Atrophy on MRI is seen as decreased flap size. This is associated with
fatty infiltration of the muscle within the myocutaneous flap, which will show
increased signal intensity of T1-weighted MR images. Previous studies have
attributed the fatty atrophy to denervation from transection of the nerves
during elevation of the flap, before rotation of the rotational flap
[13]. In addition to fatty
atrophy from denervation, disuse and radiation therapy also predisposes a flap
to fatty atrophy [10,
14]. Our findings are similar
to previous reports in the literature
[15-21];
however, Chong et al. [22]
found no evidence of atrophy of the flaps used for coverage after head and
neck tumor resection. Most flaps in the study by Chong et al. were free flaps,
and the authors acknowledged the discordance of findings with previous reports
in the literature.
Less atrophy was observed in the latissimus dorsi rotational flaps, which
were used for both coverage and upper arm function
[2]. With continuing use,
muscle would not be expected to atrophy to the same degree as a muscle used
strictly for coverage in free and rotational flaps. Unfortunately, only two
functional flaps were included in our study, and the sample size is too small
to analyze.
The cause of the increased signal within flaps on T2-weighted images is
likely multifactorial. Increased extracellular water and edema in subacute
denervated muscle have been suggested as the cause
[15,
16,
23]. Varnell et al.
[24] reported increased
T2-weighted signal in myocutaneous flaps in piglets that were vascularized and
those with vascular occlusion, theorizing that the increased signal could be
related to numerous causes, including ischemia, inflammation, edema,
hemorrhage, and infection. Increased T2-weighted signal in muscle after
radiation therapy has also been noted
[7-12],
likely related to radiation-induced inflammation and edema caused by damage to
the microcirculation [7,
9]. We theorize that a flap is
likely more susceptible to the effects of radiation therapy because of a more
tenuous blood supply, partial denervation, or both. Fatty infiltration with
replacement of muscle with higher signal intensity fat also contributes to the
increased muscle signal intensity.
After gadolinium administration, 71% of the flaps enhanced greater than the
background musculature. This increased to 83% the flaps that received
postoperative radiation. These results are similar to previous reports that
have described enhancement in approximately 90% of radiated flaps
[8,
10]. Chong et al.
[22] noted enhancement in 89%
of flaps but did not indicate whether they had been irradiated. Varnell et al.
[24] theorized that
enhancement of flaps was related to either venous congestion because of
postoperative edema or hyperemia, perhaps from revascularization. Denervated
muscle has been reported to show increased blood flow, increased extracellular
space, and a relative increase in the number of capillaries
[10,
25-28].
Because gadolinium accumulates in the extracellular space
[29], enhancement in
denervated muscle would be expected
[16].
Our study was limited by several factors, including the retrospective
fashion in which the data were collected. As a result, baseline and follow-up
MRI examinations were not performed at the same time intervals. This may
distort the calculation of the mean time of onset of the imaging findings just
described. Because the patients in our study did not all have the same tumor
type, they did not receive the same radiation dose over the same time interval
or fractionated in the same number of treatments. However, most patients did
receive a similar dose. We cannot make a definitive conclusion regarding the
MRI differences between coverage-only flaps and coverage-and-function flaps
because only two functional flaps were included in the study.
In summary, myocutaneous flaps used in orthopedic reconstructive surgery
show some degree of atrophy over time. Increased signal intensity on
T1-weighted and T2-weighted images is seen, as is contrast enhancement. These
imaging findings are present regardless of concomitant radiation therapy.
However, postoperative radiation therapy increased the likelihood that the
flap would exhibit increased T2-weighted signal and enhancement.
Acknowledgments
We thank Julia E. Crook, Department of Biostatistics, Mayo Clinic,
Jacksonville, Florida, for her assistance in the statistical analysis, and
John V. Hagen, medical illustrator, Mayo Clinic, Rochester, Minnesota, for his
assistance in the design of the illustrations.
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Abstract
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