With technological advances in magnetic resonance angiography (MRA), spatial resolution of 1-mm perforating vessels can reliably be visualized and accurately located in reference to patients’ anatomic landmarks without exposing patients to ionizing radiation or iodinated contrast, resulting in optimal perforator selection, improved flap design, and increased surgical efficiency. As their experience with MRA in breast reconstruction has increased, the authors have made changes to their MRA protocol that allow imaging of the vasculature in multiple donor sites (buttock, abdomen, and upper thigh) in one study. This article provides details of this experience with multiple donor site contrast-enhanced MRA.
Preoperative anatomic imaging of vasculature markedly enhances the ability of a surgeon to devise a surgical strategy before going to the operating room. Before the era of preoperative perforator imaging, a surgeon had little knowledge of an individual patient’s vascular anatomy until surgery was well under way. As a result, perforator selection could be a tedious decision process that occurred in the operating room at the expense of operating time and general anesthetic requirement.
The authors’ favored modality for preoperative imaging has changed as technology has advanced. Initially only a hand-held Doppler ultrasound was used. A Doppler ultrasound is portable and simple to use, but cannot differentiate perforating vessels from superficial and deep axial vessels or robust perforators from miniscule ones, accurately locate perforators that do not exit perpendicular from the fascia, or provide information on the anatomic course of a vessel. By comparison, color Duplex sonography provides more detailed information about the anatomy of the vessels, but requires highly trained technicians with knowledge of perforator anatomy and is time consuming. The technique’s most crucial drawback is an inability to produce anatomic images in a format that a surgeon can easily and independently view. As a result, the authors do not use this modality for imaging perforator flaps in their patients.
Computed tomographic angiography (CTA) is a modality that can demonstrate vessel anatomy, assess vessel caliber, accurately locate perforators, and produce anatomic images in a format that a surgeon can easily and independently view. Although CTA can be performed quickly in as little as 15 minutes, patients must be exposed to ionizing radiation. Recent articles in the medical literature and lay press warn that physicians may be exposing patients to excessive and potentially unnecessary radiation, and question the long-term effects of such exposure. Patients with breast cancer often have a heightened concern for any factor that can potentially increase the risk of developing a second cancer and may perceive the risks of radiation exposure even more negatively. A subset of patients with breast cancer gene (BRCA) mutations, which confer an increased risk of developing both breast and ovarian cancer, are especially concerned about receiving radiation to the abdomen. Furthermore, iodinated contrast for CTA has been associated with small, but real risks of anaphylaxis and nephrotoxicity.
The dose of radiation from one chest radiograph (0.1 millisieverts [mSv]) is relatively low and is approximately equivalent to the dose of environmental radiation one receives by virtue of living on earth for 10 days. By comparison, a computed tomography (CT) scan of the abdomen delivers 6 to 10 mSv of radiation, which is approximately equivalent to 3 years of environmental radiation. Controversy lies in the amount of radiation needed for cancer induction, but experts agree that unnecessary exposure to ionizing radiation should be avoided. Frequently the diagnostic utility of CT outweighs the uncertain, low risk of cancer induction. However, the authors believe that alternative methods of vascular imaging should be employed whenever possible, and this led them to consider MRA (magnetic resonance angiography) as an imaging modality.
Magnetic resonance imaging (MRI) works by using a magnetic field to uniformly align the spin of hydrogen atoms in tissue. The subsequent application of a radiofrequency pulse results in release of energy as hydrogen atoms return to their relaxed state. MRI coils detect the released energy, and computer software processes the data into anatomic images. Exposure to a magnetic field or radiofrequency pulse with MRI has not been linked to the development of cancer. A paramagnetic contrast agent (gadolinium-containing) is injected to enhance vessels. Because MRI does not use radiation, multiple series of images can be obtained. Vessels usually are first imaged in the arterial phase, and subsequently the arterial/venous phase for visualization of the artery and vein together. Additional series of images are acquired to view the vasculature in multiple planes: axial, coronal, and sagittal.
Gadolinium-containing contrast agents used for MRA have several distinct advantages over iodinated contrast agents used for CTA. The incidence of an acute allergic reaction to iodinated contrast is 3%, which is orders of magnitude higher than the 0.07% incidence of allergic reaction to gadolinium contrast. Furthermore, unlike gadolinium contrast agents, iodinated CT contrast agents can induce renal insufficiency even in patients with normal renal function.
Gadolinium contrast agents can potentially induce nephrogenic systemic fibrosis (NSF), also called nephrogenic fibrosing dermopathy. However, reports of NSF have been limited to patients with impaired renal function. Patients with an acute kidney injury or chronic severe renal disease (glomerular filtration rate <30 mL/min/1.73 m 2 ) are considered most at risk. NSF is a very rare disease, with about 330 cases reported worldwide. Although patients undergoing elective microsurgical free flap are generally healthy and thus are not at significant risk for developing NSF, a creatinine level is drawn preoperatively in patients with a history of hypertension, diabetes, renal disease, or any other indication that renal function may be impaired.
Disadvantages of MRA are contraindication to use with a cardiac pacemaker or in very claustrophobic patients. However, none of the authors’ patients have been excluded from MRA imaging because of these factors. Continuing advances in MRA have decreased the procedure time for a single donor site to as little as 20 minutes and have decreased the actual acquisition scan time to 20 seconds.
MRA is currently the favored modality for preoperative imaging because the authors have found the accuracy to be on par with CTA. With their first MRA protocol developed in 2006, in 50 abdominal flaps, the authors found that the location of the perforating vessel correlated with the intraoperative findings within 1 cm in 100% of the flaps, the relative size (ie, comparing size of one vessel to another for the same patient) of the perforators visualized on MRA correlated with the intraoperative findings in 100% of the flaps, all relatively large perforators visualized on MRA were found at surgery (0% false positive), and intraoperative perforators of significant size were visualized on MRA in 96% of the flaps (4% false negative). By comparison, a study using preoperative CTA on 36 patients found 0% false-positive and 0% false-negative results. Another study using preoperative CTA in 42 patients found one false-positive and one false-negative result. The 2 false-negative results in the authors’ original study were due to inadequate visualization of lateral row perforators secondary to signal interference from the thigh and buttock fat.
Methods
Refinements in the authors’ MRA protocol were made in 2008. The switch was made to a 1.5-T scanner to eliminate inhomogeneous fat suppression associated with a 3-T magnet, for improved visualization of lateral row perforators. In addition, gadobenate dimeglumine (Bracco, Princeton, NJ, USA), a gadolinium-based contrast agent that binds to albumin and has a longer half-life in the bloodstream, was used to extend the craniocaudal field of view. Furthermore, the authors took advantage of the lack of radiation exposure to do serial image acquisitions with a patient in the prone and then supine position. The result of these modifications is that abdominal, gluteal, and upper thigh perforators can be visualized in one study. Also, 3-dimensional (3D) reconstruction was used to view the vessels on surface-rendered images for improved understanding of perforator location.
First, patients were scanned in the prone position because the quality of the images of the abdominal wall perforators is superior to those obtained in the supine position. Respiratory motion is reduced in the prone position and motion artifact is minimized, which enhances abdominal perforator assessment. Fascia is a stable structure in the abdomen, and the location of the abdominal perforators in reference to the base of the umbilical stalk is not affected by the prone position. By contrast, the curved anatomy of the buttock is greatly distorted in the supine position, and buttock perforator location in reference to the gluteal crease is significantly affected. Finally, patients were scanned in the supine position to estimate abdominal flap volume and reconfirm abdominal perforator location.
MRA images and the associated radiology report were reviewed by the surgeon and an optimal perforator(s) was selected. Intraoperative vessel assessment was compared with vessel assessment on MRA, as described in previous articles. Immediately after surgery, surveys were completed by the operating surgeon.
Patients
Thirty-seven consecutive patients were imaged with MRA from August 2008 to June 2009. The inclusion criterion was that all patients referred for breast reconstruction were able to travel to the one radiological center that used the authors’ MRA protocol. Patients located in other states who could not travel were excluded. Exclusion criterion was inability to undergo MRA examination (cardiac pacemaker, severe claustrophobia, and severe renal insufficiency), for which no patients were excluded.
Patients
Thirty-seven consecutive patients were imaged with MRA from August 2008 to June 2009. The inclusion criterion was that all patients referred for breast reconstruction were able to travel to the one radiological center that used the authors’ MRA protocol. Patients located in other states who could not travel were excluded. Exclusion criterion was inability to undergo MRA examination (cardiac pacemaker, severe claustrophobia, and severe renal insufficiency), for which no patients were excluded.
Results
Sixty-two abdominal, gluteal, thigh, and lumbar flaps were used for breast reconstruction in 37 patients. Table 1 illustrates the type of flap and type of perforator used.
| Flap Type | Number of Flaps | Single Intramuscular Perforator | Double Intramuscular Perforator | Septocutaneous Vessel |
|---|---|---|---|---|
| DIEP | 48 | 37 | 9 a | 2 |
| SIEA | 1 | |||
| SGAP | 5 | 3 | 2 | |
| LAP | 1 | 1 | ||
| IGAP | 2 | 2 a | ||
| DFAP | 4 | 4 | ||
| TUG without muscle | 1 | 1 |
a All preoperatively selected vessels were used to carry the flap, except in one patient a second small DIEP was added to a large preoperatively selected DIEP, and in a second patient a backup IGAP was used instead of a DFAP.
The new MRA protocol improved the quality of the images and accuracy of perforator assessment. The relative vessel size (ie, comparing size of one vessel to another for the same patient) on MRA compared with that found at surgery was accurate in all flaps (100%), the predicted perforator location was accurate to within 0.5 cm in all flaps (100%), and there were no false-positive (all relatively large perforators visualized on MRA were found at surgery) and no false-negative results (intraoperative perforators of significant size were all visualized on MRA).
The preoperatively selected vessel was used in all patients except in 2 cases. In the first case, a backup inferior gluteal artery perforator (IGAP) vessel was used instead of a planned deep femoral artery perforator (DFAP) in an inferior buttock flap. The IGAP vessel was identified first intraoperatively by the surgeon, and was of adequate caliber, and thus dissected. In the second case, a second small deep inferior epigastric perforator (DIEP) was added to a preoperatively selected large DIEP because it lined up without necessitating an incision through rectus muscle fibers. The second small DIEP was in retrospect visualized on MRA, but not included in the MRA radiology report because the diameter was less than 1 mm.
The design of abdominal flaps was moved cephalad or caudal to capture the best perforator in 20 of 29 patients (69%). In 20 abdominal flaps, the flap weight estimated from MRA differed from the actual flap weight at surgery by an average of 47 g. MRA determined the design of all buttock flaps (100%). MRA determined the selection of which thigh (ipsilateral or contralateral) was used for a unilateral breast reconstruction.
Discussion on the finer points of MRA and perforator selection
Vessel caliber in conjunction with a centralized location on the flap is the most important factor for optimal perforator selection at every donor site. Caliber measurements are uniformly performed at the point where a vessel exits the superficial fascia. Location measurements are performed in reference to a landmark at each donor site. Specific considerations regarding each donor site are presented here.
Abdomen
The location of the vessel on exiting the anterior rectus fascia is measured in reference to the center of the base of the umbilical stalk for improved accuracy, as seen in Fig. 1 . Vessel caliber measurements are also performed just above the anterior rectus fascia level. An intramuscular course length or a septocutaneous course, as seen in Fig. 2 , can add important information for a surgeon to anticipate a tedious or straightforward dissection. Also, the branching pattern of the vessel in the subcutaneous fat may provide valuable information. In a unilateral reconstruction, it is helpful to see a medial row perforator with branches crossing into the subcutaneous fat on the contralateral abdomen, because zone III is more likely to be well perfused, as seen in Fig. 3 . In addition, DIEP branches connecting with superficial inferior epigastric venous branches may theoretically provide improved venous drainage. An example of a DIEP connecting with a superficial inferior epigastric vein branch is seen in Fig. 4 .
Related posts:
Assessing Perforator Architecture
Acoustic Doppler Sonography, Color Duplex Ultrasound, and Laser Doppler Flowmetry as Tools for Successful Autologous Breast Reconstruction
Maximizing the Use of the Handheld Doppler in Autologous Breast Reconstruction
Noncontrast Magnetic Resonance Imaging for Preoperative Perforator Mapping
Fluorescent Angiography
Near-Infrared Spectroscopy in Autologous Breast Reconstruction
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