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PICTORIAL ESSAY
Year : 2021  |  Volume : 36  |  Issue : 2  |  Page : 195-200  

18F-fluorodeoxyglucose positron emission tomography/computed tomography in postsurgical setting in head and neck cancers – A pictorial essay


Department of Nuclear Medicine and Molecular Imaging, Tata Memorial Hospital, Mumbai, Maharashtra, India

Date of Submission25-Sep-2020
Date of Decision18-Nov-2020
Date of Acceptance23-Nov-2020
Date of Web Publication21-Jun-2021

Correspondence Address:
Dr. Archi Agrawal
Department of Nuclear Medicine and Molecular Imaging, Tata Memorial Hospital, E. Borges Road, Parel, Mumbai - 400 012, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijnm.ijnm_204_20

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   Abstract 


This pictorial essay depicts normal appearances, complications, and findings of residual and/or recurrent disease on fluorodeoxyglucose positron emission tomography/computed tomography (18F- FDG PET/CT) studies in the postsurgical setting. Reading and reporting 18F- FDG PET/CT in the postoperative scenario is demanding due to the multiple false positives seen during this period. This article which contains two parts will familiarize the readers with the normal appearance and pitfalls seen in 18F- FDG PET/CT studies during the postoperative period so as to avoid misinterpretations. This pictorial will discuss 18F- FDG PET/CT in the postoperative scenario in head and neck cancers.

Keywords: Contrast-enhanced, false-positives, fluorodeoxyglucose positron emission tomography/computed tomography, postoperative, postsurgical, pitfalls, recurrence


How to cite this article:
Agrawal A, Prakash A, Choudhury S, Manikandan M V, Jain Y, Purandare N, Puranik A, Shah S, Rangarajan V. 18F-fluorodeoxyglucose positron emission tomography/computed tomography in postsurgical setting in head and neck cancers – A pictorial essay. Indian J Nucl Med 2021;36:195-200

How to cite this URL:
Agrawal A, Prakash A, Choudhury S, Manikandan M V, Jain Y, Purandare N, Puranik A, Shah S, Rangarajan V. 18F-fluorodeoxyglucose positron emission tomography/computed tomography in postsurgical setting in head and neck cancers – A pictorial essay. Indian J Nucl Med [serial online] 2021 [cited 2021 Jul 30];36:195-200. Available from: https://www.ijnm.in/text.asp?2021/36/2/195/318875




   Introduction Top


Fluorodeoxyglucose positron emission tomography/computed tomography (18F- FDG PET/CT) has established itself as a very effective imaging modality in the past two decades. It forms the mainstay of oncology practice and is routinely used for the staging and restaging of multiple cancers. Reading 18F- FDG PET/CT in posttreatment setting remains a challenging task, due to treatment-related changes and inflammation. This becomes even more difficult in the postoperative setting due to distortion of the normal anatomical structures, loss of symmetry, and due to the inflammation and fibrosis seen after surgery. FDG uptake is seen in inflammation and postoperative complications such as infection, abscess, fistula, and fat necrosis. [Table 1]; these have confounding features, which at times makes it difficult to differentiate these from recurrent disease. The process of wound healing itself shows increased FDG uptake due to the accumulation of inflammatory cells, fibroblasts, and macrophages in the granulation tissue. This granulation tissue is gradually removed by apoptotic cells, followed by the formation of a mature scar. The FDG uptake gradually decreases from the formation of granulation tissue to the development of a mature scar. These processes make take about 2–3 months to occur.[1],[2],[3] In the postoperative period, it is important to differentiate recurrent disease from normal physiological uptake and postoperative complications.
Table 1: Pitfalls in postsurgical scenario

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This pictorial review is aimed at familiarizing its readers and nuclear medicine physicians with these scenarios so as to help in the reading of 18F- FDG PET/CT studies in this setting. Being well versed with the normal appearance and complications arising in the postoperative setting will assist us in confidently reporting these studies. Some steps taken before doing an 18F- FDG PET/CT will aid in reducing the false-positive FDG uptakes in this period [Table 2].
Table 2: Suggested methods to avoid the pitfalls in the postsurgical setting

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Learning objectives

  1. Familiarly with normal postsurgical appearances
  2. Normal physiological findings which are mimics for disease involvement
  3. Methods to differentiate between recurrent disease and postsurgical appearances and complications


  4. Importance of doing a contrast-enhanced CT (CECT) with PET/CT.



   Case Scenarios Top


The imaging findings in the postoperative setting in head and neck can be divided into three scenarios:

  1. Altered anatomy – due to reconstructive procedures, with the formation of surgical voids and flaps
  2. Postoperative complications – infections, inflammation, abscess, fistula, collections
  3. Disease per se or recurrent disease


Normal appearance postsurgery in head and neck cancers

Multimodality treatment comprising of curative surgical resection combined with radiation therapy and or chemotherapy is generally needed for locally advanced head and neck cancers, in particular in sinonasal and oral cavity malignancies. Curative resection may consist of wide local excision or complex reconstructive surgeries to close the defect, leading to large surgical voids and anatomical distortion. The void may show no FDG uptake [Figure 1] or mild, diffuse uptake around the void, which is physiological. When a large part of tumor is removed along with a part of the mandible to achieve adequate tumor-resection margins, it is repaired using flaps. This may involve placement of either a simple flap made of one tissue type or a composite flap-like pedicle flap or free flap; having two or more tissue types. Pectoralis major myocutaneous flap (PMMC) is an example of a composite, pedicle flap, donor muscle being pectoralis major. The appearance of a flap is a fat density structure with sharp boundaries with adjacent structures. Immediately after the surgery, a myocutaneous flap has muscle/soft-tissue attenuation which gradually undergoes denervation atrophy leading to volume loss and fatty replacement within the flap [2-9]. Postsurgical 18F- FDG PET/CT imaging of these flaps done 8–12 weeks after surgery may demonstrate no FDG uptake [Figure 2] or mild diffuse uptake around the periphery of the flap [Figure 3]. Mild, diffuse FDG uptake around the flap is reactive and often seen in the postoperative period. Apart from the site of the reconstructive surgery, even the donor site of the PMMC flap may show diffuse FDG uptake [Figure 4], these are reactive inflammatory changes seen for a few weeks after surgery and should not be mistaken for disease.[2],[3]
Figure 1: Normal appearance of a postsurgical void. A 50-year-old lady, who had undergone left maxillectomy for an ameloblastoma. fluorodeoxyglucose positron emission tomography/computed tomography was done 7 months after the surgery. Fluorodeoxyglucose positron emission tomography/computed tomography scan shows a surgical void in the left maxillary region with no fluorodeoxyglucose uptake in the axial positron emission tomography and fused positron emission tomography/computed tomography images (arrow a and b)

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Figure 2: Normal appearance (no fluorodeoxyglucose uptake) of a postsurgical flap. A 60-year-old gentleman, squamous cell carcinoma of the right lower alveolus. Underwent right hemi-mandibulectomy with pectoralis major myocutaneous flap. Fluorodeoxyglucose positron emission tomography/contrast-enhanced computed tomography was done 12 weeks after surgery. The axial fused positron emission tomography/computed tomography and computed tomography images show the pectoralis major myocutaneous flap with no increased fluorodeoxyglucose uptake (arrow in a and b). The flap is a fat-density structure having sharp boundaries with adjacent structures. CECT image in b, showing no enhancing soft tissue mass.

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Figure 3: Normal appearance (mild, diffuse uptake) of a postsurgical flap. A 58-year-old gentleman, squamous cell carcinoma of the right buccal mucosa. He had undergone right hemi-mandibulectomy with pectoralis major myocutaneous flap and nodal dissection. Fluorodeoxyglucose positron emission tomography/contrast-enhanced computed tomography was done 6 weeks after surgery. The axial fused positron emission tomography/computed tomography images show mild, diffuse, heterogenous fluorodeoxyglucose uptake at the flap-site (arrows in a), postright hemimandibulectomy. This appearance of diffuse fluorodeoxyglucose uptake around the flap is reactive and often seen postsurgery

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Figure 4: Normal appearance of a postsurgical donor-flap site. The same patient as in case 3. A 58-year-old gentleman, squamous cell carcinoma of the right buccal mucosa. He had undergone right hemimandibulectomy with pectoralis major myocutaneous flap and nodal dissection. Fluorodeoxyglucose positron emission tomography/contrast-enhanced computed tomography was done 6 weeks after surgery. The maximum intensity projection and the fused coronal positron emission tomography/computed tomography images show linear, diffuse fluorodeoxyglucose uptake in the right sternal and axillary area (arrow in a, b). This is due to reactive changes at the donor flap site. Note the absence of pectoralis major on the right (arrowhead in c) in the fused axial positron emission tomography/computed tomography image. The right pectoralis major is the donor for the pectoralis major myocutaneous flap reconstructive surgery done for this patient

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Due to removal of the muscles on the diseased side or due to distortion of normal anatomical structures, a unilateral muscle may show diffuse increased FDG uptake leading to asymmetrical muscle uptake on FDG PT/CT study. This occurs due to altered mechanics of mastication or altered muscle usage often seen post head, neck, and jaw surgeries. This typically appears as FDG uptake along the entire length of the muscle with no enhancing mass lesion[Figure 5].[2],[4]

Such asymmetric uptake is also quite common after partial tongue resection. Physiological uptake in the remnant tongue may appear as focal, intensely FDG avid area, which is a potential mimic for residual or recurrent disease. Reviewing the CECT images carefully helps us to differentiate between the two.[2],[4] Absence of contrast-enhancing mass lesion is indicative of remnant structure, in this case, remnant tongue and not malignant disease process [Figure 6].
Figure 5: (a) Physiological uptake in muscles of the head and neck, postsurgery. A 65-year-old gentleman, post right hemimandibulectomy for squamous cell carcinoma of the right buccal mucosa. Fluorodeoxyglucose positron emission tomography/contrast-enhanced computed tomography was done 3 years after surgery. Axial fused positron emission tomography/computed tomography image shows diffuse increased fluorodeoxyglucose uptake in the right lateral pterygoid muscle (arrow in a) and in right masseter muscle (arrowhead in c). Note the absence of any enhancing mass lesion in the contrast-enhanced computed tomography images in both the muscles (arrow in b and arrowhead in d). Physiological uptake in muscles of the head and neck, postsurgery. A 67-year-old gentleman, squamous cell carcinoma of the right buccal mucosa. Underwent right composite resection with forehead flap. Fluorodeoxyglucose positron emission tomography/contrast-enhanced computed tomography was done 6 months after the surgery. Axial positron emission tomography and fused axial and coronal positron emission tomography/computed tomography images show increased fluorodeoxyglucose uptake in hypertrophied left mylohyoid muscle (arrow in e, f and h). Note the absence of any enhancing mass lesion in the contrast-enhanced computed tomography images (arrowhead in g and i)

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Figure 6: Physiological uptake in the remnant tongue. 58-year-old gentleman, squamous cell carcinoma of left lateral border of the tongue. Underwent left hemiglossectomy. Fluorodeoxyglucose positron emission tomography/contrast-enhanced computed tomography was done 16 weeks after the surgery. Intense, focal fluorodeoxyglucose uptake is noted in the axial positron emission tomography and fused positron emission tomography/computed tomography images in the right side of the remnant tongue (arrow in a, b). This can easily be mistaken for disease involvement. Note that there is no mass or enhancing mass lesion in the axial contrast-enhanced computed tomography image (arrowhead in c)

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Complications, post head, and neck surgery

Complications due to infection and inflammation are common false-positive findings after head and neck surgeries. These could be due to postoperative inflammation of the surrounding tissues [Figure 7], particularly when the 18F- FDG PET/CT scan is done too early in the postoperative period to start the adjuvant chemotherapy or radiotherapy. This is usually diffuse and subsides with time.[5],[7],[8] Infections and abscesses are intensely FDG avid and are a potential mimic for the malignant process. The contrast enhancement pattern of an abscess helps to differentiate the two.
Figure 7: Postoperative inflammation. 56-year-old gentleman, squamous cell carcinoma of right lateral border of the tongue. Underwent wide excision of the tongue mass. Had recurrence and bilateral nodal metastases, 7 months after the first surgery. Underwent bilateral nodal dissection. Fluorodeoxyglucose positron emission tomography/contrast-enhanced computed tomography was done 5 weeks post neck dissection, before starting adjuvant treatment. Diffuse, linear fluorodeoxyglucose uptake is noted in both sides of the neck in the fused axial positron emission tomography/computed tomography (arrows in a). Note the fat stranding on the computed tomography images (arrowheads in b), due to postoperative inflammation

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CECT shows the classical finding of the hypodense collection with an enhancing rim, which is typical for an abscess [Figure 8]. Thus, carefully inspecting the CT images, and doing a CECT helps in correct reporting.[7],[9] Orocutaneous fistula (OCF) is another commonly encountered complication in patients operated for oral squamous cell carcinoma and shows intense FDG uptake [Figure 9]. This is often seen on 18F- FDG PET/CT as a linear area of intense FDG uptake tracking along the entire route of the fistulous track. The patient may present with a discharging fistula. The incidence of OCF ranges from 9% to 20%. This often delays the process of wound healing and also delays the initiation of adjuvant treatment.[10]
Figure 8: Abscess postsurgery. 51-year-old gentleman, squamous cell carcinoma of the left gingivobuccal sulcus, post left segmental mandibulectomy with fibula flap and skin graft. The patient presented with pain in the postoperative site. Fluorodeoxyglucose positron emission tomography/contrast-enhanced computed tomography was done 4 months after the surgery. The fused axial positron emission tomography/computed tomography image shows focal fluorodeoxyglucose avid area posterior to the flap (yellow arrow in a). In the axial contrast-enhanced computed tomography image, there is a hypodense collection, surrounded by an enhancing rim (white arrow in b) – this is a classical finding seen in an abscess

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Figure 9: Orocutaneous fistula at the flap site. 55-year-old gentleman, squamous cell carcinoma of the left retromolar triangle, underwent bite composite resection with pectoralis major myocutaneous flap and neck dissection. 6 months after the surgery, the patient presented with purulent discharge from the left submandibular region. The maximum intensity projection image shows diffuse intense fluorodeoxyglucose uptake in the left side of the face (arrow in a). The fused coronal image shows a fistula opening in the left submandibular region (arrow in b). The fused sagittal positron emission tomography/computed tomography and PET images (arrows in c, d) show the path of the sinus tract, extending from the left maxilla along the left infratemporal fossa and opening in the left submandibular region

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Figure 10: Recurrent disease at the flap site. 60-year-old gentleman, carcinoma of the right lower alveolus, post right marginal mandibulectomy. Fluorodeoxyglucose positron emission tomography/contrast-enhanced computed tomography was done 15 months after the surgery. Fused axial positron emission tomography/computed tomography image shows fluorodeoxyglucose avid, enhancing lesion in the periphery of the flap suggesting recurrent disease (arrow in a and b)

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Recurrent disease in head and neck cancers

18F- FDG PET/CT is the best imaging modality for the detection of recurrent disease in head and cancers, being superior to both clinical examination and conventional imaging.[11],[12] Recurrent disease manifests as FDG avid, enhancing soft-tissue lesion, at the margins of the flap with loss of sharp boundaries with the adjoining structures [Figure 10] and [Figure 11]. Treated cases of head and neck malignancies have 10%–20% higher risk of second primaries.[13] But watch out for lesions in the same subsite in head and neck malignancies because as long as the lesion is in the same subsite, it translates to recurrent disease and not second primary [Figure 12]. In this case, both the lesions are in the same subsite - oral cavity. It is important to recognize the components of each subsite in head and neck cancers.[7] Recurrence of disease can also occur at the site of donor flap [Figure 13]. This is a rare and late complication post oral reconstructive surgery. Its occurrence is likely due to tumor implantation at the donor site during surgery.[14]
Figure 11: Recurrent disease. A 35-year-old young man had undergone left segmental mandibulectomy with pectoralis major myocutaneous flap and nodal dissection for carcinoma of the left retromolar trigone. Fluorodeoxyglucose positron emission tomography/contrast-enhanced computed tomography was done 14 months after the surgery. maximum intensity projection image shows an area of linear fluorodeoxyglucose uptake in the neck (arrow in a). Axial positron emission tomography and fused positron emission tomography/computed tomography shows an area of increased fluorodeoxyglucose uptake in the floor of the mouth (arrow in b, c) which shows intense enhancement on the contrast-enhanced computed tomography image (arrow in d)

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Figure 12: Two sites of recurrent disease in the same patient. 51-year-old gentleman, squamous cell carcinoma of the left buccal mucosa, post reconstructive surgery. Positron emission tomography/computed tomography scan shows fluorodeoxyglucose avid lesion in the anterior aspect of the flap in the maximum intensity projection and axial fused positron emission tomography/computed tomography images (arrows in a, b, c). Another hypermetabolic, enhancing lesion is noted the lower lip in the maximum intensity projection and axial fused positron emission tomography/computed tomography and axial computed tomography images (arrowhead in a, d, e)

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Figure 13: Donor flap site implant. 51-year-old gentleman, post reconstructive surgery (pectoralis major myocutaneous flap) for carcinoma tongue. The donor flap site was the left pectoralis major muscle. Positron emission tomography/computed tomography scan shows fluorodeoxyglucose avid, enhancing lesion in the left chest wall at the donor flap site in the maximum intensity projection and axial fused positron emission tomography/computed tomography and computed tomography images (arrow in a, b, c). Note the absence of left Pectoralis major muscle, being the donor site for pectoralis major myocutaneous flap

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   Conclusion Top


Postoperative FDG uptake due to wound healing, infections, and inflammations are common factors leading to misinterpretation on 18F- FDG PET/CT studies. Knowledge about the procedure, complications, appropriate timing, tailoring of the procedure, and familiarity with the common complications that occur during the postoperative period will assist us in differentiating the false-positive pitfalls from true-positive disease and in making an early, accurate diagnosis.



 
   References Top

1.
Xue M, Jackson CJ. Extracellular matrix reorganization during wound healing and its impact on abnormal scarring. Adv Wound Care (New Rochelle) 2015;4:119-36.  Back to cited text no. 1
    
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Garg G, Benchekroun MT, Abraham T. FDG-PET/CT in the postoperative period: Utility, expected findings, complications, and pitfalls. Semin Nucl Med 2017;47:579-94.  Back to cited text no. 2
    
3.
Purohit BS, Ailianou A, Dulguerov N, Becker CD, Ratib O, Becker M, et al. FDG-PET/CT pitfalls in oncological head and neck imaging. Insights Imaging 2014;5:585-602.  Back to cited text no. 3
    
4.
Purandare NC, Puranik AD, Shah S, Agrawal A, Rangarajan V. Post-treatment appearances, pitfalls, and patterns of failure in head and neck cancer on 18F- FDG PET/CT imaging. Indian J Nucl Med 2014;29:151-7.  Back to cited text no. 4
[PUBMED]  [Full text]  
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Rahman WT, Wale DJ, Viglianti BL, Townsend DM, Manganaro MS, Gross MD, et al. The impact of infection and inflammation in oncologic 18F-FDG PET/CT imaging. Biomed Pharmacother 2019;117:109168.  Back to cited text no. 5
    
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Saito N, Nadgir RN, Nakahira M, Takahashi M, Uchino A, Kimura F, et al. Posttreatment CT and MR imaging in head and neck cancer: What the radiologist needs to know. Radiographics 2012;32:1261-82.  Back to cited text no. 6
    
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King KG, Kositwattanarerk A, Genden E, Kao J, Som PM, Kostakoglu L. Cancers of the oral cavity and oropharynx: FDG PET with contrast-enhanced CT in the post treatment setting. Radiographics 2011;31:355-73.  Back to cited text no. 7
    
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Lonneux M, Lawson G, Ide C, Bausart R, Remacle M, Pauwels S, et al. Positron emission tomography with fluorodeoxyglucose for suspected head and neck tumor recurrence in the symptomatic patient. Laryngoscope 2000;110:1493-7.  Back to cited text no. 8
    
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Garcia MR, Passos UL, Ezzedine TA, Zuppani HB, Gomes RL, Gebrim EM. Postsurgical Imaging of the Oral Cavity and Oropharynx: What Radiologists Need to Know. Radiographics 2015;35:1624.  Back to cited text no. 9
    
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Girkar F, Thiagarajan S, Malik A, Sawhney S, Deshmukh A, Chaukar D, et al. Factors predisposing to the development of orocutaneous fistula following surgery for oral cancer: Experience from a tertiary cancer center. Head Neck 2019;41:4121-7.  Back to cited text no. 10
    
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Abgral R, Ene Querellou S, Potard G, et al. Does 18 F-FDG PET/CT improve the detection of posttreatment recurrence of head and neck squamous cell carcinoma in patients negative for disease on clinical follow-up? J Nucl Med 2009 50:24-29.  Back to cited text no. 11
    
12.
Kostakoglu L, Fardanesh R, Posner M, Som P, Rao S, Park E, et al. Early detection of recurrent disease by FDG-PET/CT leads to management changes in patients with squamous cell cancer of the head and neck. Oncologist 2013;18:1108-17.  Back to cited text no. 12
    
13.
Atienza JA, Dasanu CA. Incidence of second primary malignancies in patients with treated head and neck cancer: A comprehensive review of literature. Curr Med Res Opin 2012, 28:1899-909.  Back to cited text no. 13
    
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Kain R, Dash S. Tumor recurrence at donor site of pectoralis major myocutaneous flap with tumor-free primary oral carcinoma. Gulf J Oncolog 2018;1:64-6.  Back to cited text no. 14
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13]
 
 
    Tables

  [Table 1], [Table 2]



 

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