Figura 1. Fat graft. Axial non-contrast T1-WI performed in a patient who has undergone a partial lef...

Tabla 1.

Figura 2. Surgical specimen of a fibular free flap. The arrow identifies the native vascular pedicle...

Figura 3. Reconstruction using composite fat flap. A. Axial contrast-enhanced CT shows a large squam...

Figura 4. Reconstruction using fat flap. A. Axial contrast-enhanced CT shows a squamous cell carcino...

Figura 5. Vascularized post-operative granulation tissue. A. Coronal post-contrast FS T1-WI was perf...

Figura 6. Reconstruction using myocutaneous free flap. A. Axial non-contrast T1-WI demonstrates a co...

Figura 7. Reconstruction using fat graft. A. Axial post-contrast FS T1-WI shows an aggressive adenoi...

Figura 8. Composite osteocutaneous flap. Axial contrast-enhanced CT performed in a patient who has u...

Figura 9. Composite flap. Axial (A) and coronal(B) non-contrast T1-WI’s show a composite flap that...

Figura 10. Marginal recurrence. A. Axial non-contrast T1-WI was performed in patient that underwent a...

Figura 11. Composite myocutaneous flap with recurrence. A. Pre-operative contrast-enhanced FS T1-WI d...

Figura 12. Recurrence within region of flap. Axial contrast-enhanced CT was performed in a patient wh...

Figura 13. Fat graft with marginal recurrence. Axial contrast-enhanced CT performed through the oral ...

Figura 14. Free flap with marginal recurrence. A. Axial contrast-enhanced CT shows a right floor of m...

Figura 15. Jejunal free flap. A. Axial contrast-enhanced CT was performed in a patient that underwent...

Figura 16. Liquefaction. A. Axial non-contrast T1-WI obtained in a patient who has undergone a mastoi...

Figura 17. Fat migration. Axial non-contrast T1-WI performed in a patient who has undergone a mastoid...

Figura 18. Abscess. Axial contrast-enhanced CT performed in a patient who underwent segmental mandibu...

Figura 19. Flap hematoma. A. Axial T1-WI shows an aggressive mass in the right retromolar trigone. Bi...

Figura 20. Atrophy of muscular flap component with bone dehiscence. Axial contrast-enhanced CT obtain...

Introduction

Imaging following post-operative reconstruction of head and neck malignancies using grafts and flaps can be very challenging for the radiologist who is not familiar with this topic. The primary tumor can be treated with chemotherapy and radiation therapy versus surgical resection or utilizing a combination of treatment options. Surgical resection can be performed with or without reconstruction using a graft or flap, with the final decision depending on various factors. The goals of reconstructive surgery are to remove the tumor while being able to preserve cosmetic appearance, maintain important functions (breathing, swallowing, eating, talking), and improve the patient’s quality of life.

Before one can interpret the imaging appearance of post-operative reconstructive surgery of the head and neck using grafts or flaps, it is important to be aware of the type of surgical reconstruction that was used. The type of reconstruction depends on the location of the tumor and presence of nodal metastasis. Interpretation of post-operative imaging is challenging due to distortion and alteration of the underlying anatomy1. Treatment with radiation therapy can further complicate post-treatment imaging2.

The goals of this article are to familiarize the radiologist with the normal CT and MR post-operative imaging findings of grafts and flaps, identify findings indicative of tumor recurrence, and review potential complications.

Reconstruction using grafts

A graft is defined as tissue that has been moved from one part of the body to another without bringing the native blood supply. The blood supply will be derived from the surrounding tissues. There are different types of grafts that can be used. An “autograft” is obtained from the same individual’s tissues. When tissue is obtained from an identical twin, it is referred to as an “isograft”. The term “allograft” is used when the tissue is obtained from a donor from the same species, while the term “xenograft” is used when the tissue is obtained from a different species. An “alloplastic” graft is man-made3. The graft tissue may originate from skin, fat, bone, cartilage, or a nerve or tendon (Figure 1).

Reconstruction using flaps

A flap is defined as tissue that has been moved from one part of the body to another with preservation of the native blood supply. The overriding principle when planning an individual patient’s reconstructive procedure is to perform the least complex and safest option while optimizing function and cosmetic outcome. There are various types of flaps which can be classified in various was such as by either the origin of the tissue (“local”, “pedicle (rotational)” and “free tissue transfer”) or by the type of tissue used for the flap. Unlike local and pedicle (rotational) flaps, the vascular pedicle in a free tissue transfer is also transferred and is revascularized to vessels at the surgical site through microsurgical anastomosis3,4. Surgical free flaps have superior functional outcome and cosmetic restoration over local or rotational flaps. The flap classification can also be based on the specific type(s) of tissue used during reconstruction and includes “fascia”, “bone”, “muscle”, or “visceral”3. Descriptive terms such as “myocutaneous”, “osteocutaneous” and “fasciocutaneous” are used if more than one tissue type is used for the reconstructive procedure (Figure 2). This classification system is summarized in (Table 1).

Normal imaging appearance

The principles for evaluating the post-surgical appearance following graft and flap reconstruction are similar. The most important “non-interpretative” information that will help the radiologist is having the pre-treatment imaging and the type of treatment. It is very important to make every effort to compare the post-operative study with the pre-treatment study (Figures 3 & 4). This provides essential information on the primary location of the tumor, expected surgical margins and associated lymphadenopathy. Having a baseline exam improves detection of new or subtle changes on post-operative studies.

Grafts do not typically enhance since they do not have an arterial blood supply. There may occasionally be peripheral enhancement of the graft (Figure 5). This suggests there has been collateralization of blood flow signifying the graft is viable. Flaps differ from grafts in that enhancement is expected since the arterial and venous blood supply has been preserved or anastomosed to adjacent vasculature, as typically performed in a free tissue transfer. In myocutaneous flaps the muscular portion enhances in most cases (Figure 6), however variation in enhancement has been shown ranging from no enhancement to intense enhancement4.

On fat-suppression imaging, the fatty portion of a graft or flap will demonstrate signal loss due to the suppression of fat (Figures 6 & 7). Myocutaneous free flaps will have areas of fat suppression, demonstrating a T1 hyperintense non-enhancing fatty component, and a muscular component which should be isointense to other muscles in the head and neck on T1-WI5. Over time, myocutaneous flaps will undergo atrophy from denervation and develop fatty replacement, becoming heterogeneous on T1-WIand T2-WI3,6. The rectus abdominus muscle is an example of a myocutaneous free flap used to help fill in surgical defects, and has a typical appearance of striated muscle with fat along the margins (Figure 6).

Free flaps containing osseous components are usually composite. For example, an osteocutaneous flap such as a fibula free flap will typically contain bone and surrounding mesenchymal tissue (Figures 8 & 9). One may see bridging bone formation with adjacent native bones, but the osseous portion should maintain smooth margins and no destructive changes3.

In the pharyngoesophageal region, reconstruction may be performed using a jejunal free flap6. This flap may be at increased risk of ischemia due to reliance on blood supply from the superior mesenteric artery.

After surgery, post-operative edema can occur and be present up to 6 weeks after surgery5. The edema can persist for years in patients that have received post-surgical radiation therapy. Resected tumors that require flap reconstruction are often advanced and may require adjuvant radiation and/or chemotherapy. Not only is it important to have information describing the specific type of graft or flap used for the reconstruction, but it also important to know whether the patient has undergone radiation therapy or chemotherapy. An understanding of post-treatment associated changes can help prevent misinterpreting the expected changes from treatment complications.

Recurrence

There are some “pearls” to keep in mind when evaluating for tumor recurrence. It is important to make every effort to compare the post-operative study with a baseline pre-treatment CT or MR exam. The pre-operative study provides essential baseline information regarding the primary site of the tumor and alterations to the surrounding anatomy.

Knowledge of the where recurrence occurs is crucial and guides the radiologist on where to specifically focus. Tumors do not usually arise in the center of the graft or flap since the primary tumor has been removed. Rather, recurrent tumors typically occur at the surgical margins. Specifically, the inferior and superior margins must be carefully scrutinized on all post-operative imaging studies6,7. The recurrence could present as a growing infiltrative mass or thickening of soft tissues deep to the graft or flap6. Thus, any regions of enlarging soft tissue masses should be considered recurrence until proven otherwise8. One should also be aware of recurrence through perineural spread, which will best be evaluated on MRI3.

Recurrent tumor will usually enhance, and unlike grafts, flaps also enhance. Recurrence will demonstrate intermediate signal on T1-WI and intermediate to high signal on T2-WI5. Recurrence should be suspected if there has been replacement of fat inside the flap by enhancing tissue (Figure 12)7. Diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) sequences are helpful in demonstrating increased DWI signal within recurrent and nodal metastasis, with corresponding hypointensity on ADC6. On CT, the characteristic finding is an enlarging soft tissue lesion with attenuation similar to muscle that enhances (Figure 13).

The presence of metastatic lymph nodes is also indicative of underlying recurrence (Figure 14). The recurrent tumor could be due to occult tumor at the primary site or a systemic recurrence (Figure 15). In indeterminate cases, biopsy may be needed for confirmation.

Pitfalls

Several etiologies can mimic tumor recurrence. As described earlier, the muscular component of flaps can have intense enhancement and should not be confused for tumor. One can look for the typical striated appearance of muscle best seen on pre-contrast T1-WI4. Inflammatory changes can have overlap with recurrence, as both can have restricted diffusion on MRI5,8. A vascularized scar or fibrotic tissue can show enhancement (Figure 5). Scar tissue can enhance like tumor recurrence due to vascularized fibrotic tissue but will be hypointense on T1, have progressive decrease in T2 signal, be stable over time or demonstrate tissue retraction1,5,8. Edema in the soft tissues can mimic recurrence due to expansion but can be distinguished from recurrence as there will be attenuation lower than that of muscle on CT6. Muscle atrophy from denervation of a myocutaneous flap can have variable T2 signal or enhancement that can mimic recurrence5,7.

Complications

t is important to be aware of the postoperative complications of grafts and flaps. Graft complications may be seen in superficial skin grafts which do not undergo post-treatment imaging or more complex grafts (such as fat-grafts) and include post-operative seroma, infection, hematoma, liquefaction (Figure 16) or fat migration (Figure 17).

Flaps share similar complications with grafts including seroma, infection (Figure 18) or hematoma (Figure 19). Flaps are also at risk of fistula formation and stenosis (particularly in the hypopharynx and cervical esophagus), radiation-related complications such as osteoradionecrosis, dehiscence and ischemia (Figure 20)7. In cases of suspected ischemia, Doppler ultrasound may be useful for assessing the patency of the arterial and venous anastomoses for free tissue transfer flaps.

Conclusion

We have reviewed the imaging appearances of various types of grafts and flaps including normal appearance, recurrence, pitfalls and complications. A greater understanding of both the surgical technique and the expected normal post-operative imaging appearance will increase both the diagnostic accuracy and confidence of the interpreting radiologist to help differentiate recurrent tumor from expected changes.

1. Wesolowski JR, Mukherji SK. Pathology of the Pharynx. In: Som PM, Curtin HD. Head and Neck Imaging. 5th edition. St. Louis, Missouri: Mosby Elsevier; 2011: pp. 1804-6.

2. Mukherji SK, Mancuso AA, Kotzur IM, et al. Radiologic appearance of the irradiated larynx. Part I. Expected changes. Radiology 1994;193(1):141-8.

3. McCarty JL, Corey AS, El-Deiry MW, et al. Imaging of Surgical Free Flaps in Head and Neck Reconstruction. Am J Neuroradiol 2019;40(1):5-13.

4. Chong J, Chan LL, Langstein HN, Ginsberg LE. MR imaging of the muscular component of myocutaneous flaps in the head and neck. Am J Neuroradiol 2001:22(1):170-4.

5. Learned KO, Malloy KM, Loevner LA. Myocutaneous Flaps and Other Vascularized Grafts in Head and Neck Reconstruction for Cancer Treatment. Magn Reson Imaging Clin N Am 2012;20(3):495-513.

6. Saito N, Nadgir RN, Nakahira M, et al. Posttreatment CT and MR Imaging in Head and Neck Cancer: What the Radiologist Needs to Know.Radiographics 2012;32(5):1261-82. 

7. Syed F, Spector ME, Cornelius R, et al. Head and neck reconstructive surgery: what the radiologist needs to know. Eur Radiol 2016;26(10):3345-52. 

8. Som PM, Lawson M, Genden EM. The Posttreatment Neck: Clinical and Imaging Considerations. In: Som PM, Curtin HD. Head and Neck Imaging. 5th edition. St. Louis, Missouri: Mosby Elsevier 2011:2779-83.

Para descargar el PDF del artículo
Simplified approach for understanding grafts and flaps of the head & neck

Haga click aquí