Indian Journal of Nuclear Medicine

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


Archi Agrawal, Anjali Prakash, Sayak Choudhury, MV Manikandan, Yash Jain, Nilendu Purandare, Ameya Puranik, Sneha Shah, Venkatesh Rangarajan 
 Department of Nuclear Medicine and Molecular Imaging, Tata Memorial Hospital, Mumbai, Maharashtra, India

Correspondence Address:
Dr. Archi Agrawal
Department of Nuclear Medicine and Molecular Imaging, Tata Memorial Hospital, E. Borges Road, Parel, Mumbai - 400 012, Maharashtra
India

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.



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 Sep 28 ];36:195-200
Available from: https://www.ijnm.in/text.asp?2021/36/2/195/318875


Full Text



 Introduction



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}

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}

Learning objectives

Familiarly with normal postsurgical appearancesNormal physiological findings which are mimics for disease involvementMethods to differentiate between recurrent disease and postsurgical appearances and complications

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

 Case Scenarios



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

Altered anatomy – due to reconstructive procedures, with the formation of surgical voids and flapsPostoperative complications – infections, inflammation, abscess, fistula, collectionsDisease 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}{Figure 2}{Figure 3}{Figure 4}

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}{Figure 6}

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}

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}{Figure 9}{Figure 10}

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}{Figure 12}{Figure 13}

 Conclusion



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.

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