Translate this page into:
18F-fluorodeoxyglucose Positron Emission Tomography/Computed Tomography in Postsurgical and Postprocedural Setting in Thorax and Abdominopelvic Malignancies: A Pictorial Essay (Part II)
Address for correspondence: Dr. Archi Agrawal, Department of Nuclear Medicine and Molecular Imaging, Tata Memorial Hospital, E. Borges Road. Parel, Mumbai - 400 012, Maharashtra, India. E-mail: drarchi23@gmail.com
-
Received: ,
Accepted: ,
This is an open access journal, and articles are distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as appropriate credit is given and the new creations are licensed under the identical terms.
This article was originally published by Medknow Publications & Media Pvt Ltd and was migrated to Scientific Scholar after the change of Publisher.
Abstract
This pictorial essay depicts normal appearances, complications and residual or recurrent disease on fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) studies in the postsurgical and postprocedural setting, other than head and neck malignancy. Reading and reporting FDG PET/CT in this scenario is daunting due to the multiple confounding false positives seen during this period. This article which is the second part in this series will familiarize the readers with the normal appearance and pitfalls seen in FDG PET/CT studies in thoracic and abdominopelvic malignancies during the postoperative and postprocedural period so as to avoid misinterpretations.
Keywords
Contrast-enhanced
false-positives
fluorodeoxyglucose positron emission tomography/computed tomography
pitfalls
postoperative
postsurgical
recurrence
Introduction
In the past few decades, fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET CT) has established itself as a very effective imaging modality in staging and restaging of various cancers. Reporting FDG PET/CT in the postsurgical period can be a challenge due the postoperative changes which lead to alteration in normal anatomy and inflammation/infections that occur during this period. FDG accumulates in healing wounds due to the presence of granulation tissue and macrophages.[1] Understanding the changes that take place during this setting will help to avoid misinterpretation and correct reporting. The first part of this article dealt with case scenarios in the postsurgical setting in head and neck malignancies. In this second part, we shall contemplate on the pitfalls in thoracic and abdominopelvic malignancies in the portsurgical and postprocedural period.
Learning objectives
-
Familiarly with normal postsurgical and postprocedural appearances in thorax, abdomen, and pelvis
-
Familiarity with physiological findings and normal variants which are potential mimics for disease involvement
-
Methods to differentiate between recurrent disease and postsurgical/postprocedural appearances and complications
-
Importance of doing intravenous contrast-enhanced CT (ceCT) with PET/CT.
Case Scenarios
Thorax
Extensive surgical procedures are performed for curative treatment of local and locoregional esophageal and lung malignancies. It is important to familiarize oneself with the various transthoracic esophagectomy (TTE) surgeries and the various complications that may occur after these surgeries. One of the most common TTE procedures is the Ivor Lewis procedure, in which the diseased esophagus is dissected out and the stomach is used to create a gastric tube or conduit in place of the esophagus.[2] FDG PET/CT usually shows a photon-deficient area in the right paravertebral region corresponding to the gastric pull-up surgery [Figure 1]. Sometimes, diffuse uptake may be seen around the gastric pull-up due to inflammation postsurgery [Figure 2]. Diffuse nature of uptake with no soft-tissue mass points towards an inflammatory nature. Occasionally, an endoscopy done to diagnose an esophageal carcinoma may cause a perforation in the esophageal wall. It is a very rare complication. It shows diffuse FDG uptake due to inflammation and sometimes due to co-existing infection [Figure 3]. The presence of extraluminal air is the characteristic finding in perforations. This is a life-threatening complication, but small perforations may be managed conservatively.[3] In locally advanced inoperable esophageal cancers, who receive chemoradiotherapy, an esophageal stent is placed to relieve the patient of dysphagia and to improve the quality of life.[4] Recurrence is seen as FDG avid, enhancing soft-tissue mass along the stent [Figure 4].
In patients of lung carcinoma, intractable pleural effusions are usually treated with pleurodesis. The process of pleurodesis involves installation a chemical irritant like talc, which produces inflammation and pleural fibrosis. This is characterized by proliferation of fibroblasts and macrophages, which leads to increased FDG uptake. This may last for more than 10 years.[5] FDG PET/CT shows diffuse or focal areas of intense FDG uptake with corresponding hyper-attenuating areas on CT that are diagnostic of pleurodesis [Figure 5]. These should not be mistaken for pleural deposits, which though FDG avid have a soft-tissue attenuation. The past history of pleurodesis is usually helpful. FDG uptake can also be seen Post-mediastinoscopy at the site of incision in the suprasteranl region, at sites of intercostal drainage for pleural effusion and at scar sites postsurgery, due to inflammation.[1] These show diffuse FDG uptake and can easily be diagnosed as reactive postprocedural changes.
Healing after breast surgery also involves inflammatory reaction with accumulation of leukocytes and macrophages, with a consequence of FDG uptake in the postoperative area. Fat necrosis is a common condition seen after breast surgeries and trauma. It is a benign inflammatory condition and may mimic breast malignancy.[6] This is seen on FDG PET/CT as FDG avid hypodense lesion [Figure 6]. History of previous surgery and hypodense, non-enhancing appearance on CT is giveaway to a benign lesion. Breast seroma is another such condition seen postsurgery or post trauma. This is a collection of serous fluid which gets reabsorbed in a few weeks to months. This appears on FDG PET/CT as a hypodense collection with no FDG uptake [Figure 7].[7] A recent history of surgery is usually diagnostic. These resolve on its own and no intervention is generally needed. In spite of few false positives, FDG PET/CT is a powerful tool for the detection of recurrence in the chest wall [Figure 8], axilla and extra-axillary nodes with a high sensitivity and specificity of >90%.[8]
Abdomen and pelvis
In cancers of the hepatobiliary tract, percutaneous transhepatic biliary drainage is often done to relieve the obstruction along the biliary tract with the placement of metallic stent. Often FDG PET/CT is done for staging of the disease after placement of the stent. Local inflammation occurs which is seen as linear increased FDG uptake along the stent [Figure 9]. This uptake is linear and diffuse and can be easily identified as benign FDG uptake.[9] Cholangitic abscess is another common complication Post-stent placement. These may appear as focal areas with increased metabolic activity and is a potential mimic for metastatic disease. Dilated biliary radicals with increased FDG uptake along the walls of the biliary ducts is typically seen in cholangitis/cholangitic abscess [Figure 10].[10] Tracking these lesions by moving the cursor up and down on the CT image, will show the relationship of these lesions to the dilated biliary radical, helping us to differentiate between metastatic lesions which are focal whereas cholangitic abscess are associated with the dilated biliary radicals.
Abdominal surgeries done for colorectal cancers, may compromise blood flow to the omentum, resulting in omental infarction or fat necrosis. This is an inflammatory, self-limiting process. The appearance of omental infarction of an FDG avid lesion is a mimic for intra-peritoneal metastatic deposit. The presence of fat within this lesion with an enhancing rim helps us to correctly identify this lesion as benign fat necrosis [Figure 11]. Another name for this is epiploic appendagitis.[711] In colonic surgeries, inflammation at the anastomotic site may mimic recurrent disease, because this presents as mass like lesion with increased FDG uptake [Figure 12]. Surrounding fat-stranding may be more profound in an inflammatory condition. The lesion and the uptake gradually decrease with time.[12]
Inflammation and fat stranding is also common after renal surgeries and nephrectomies. The inflammatory fat stranding may be mass like in morphology. FDG PET/CT done too early after the surgery and fat stranding at the operated site should make us suspect an inflammatory etiology. The inflammation and fat stranding generally decrease with time and a follow-up imaging is extremely helpful to precisely differentiate this from recurrent/residual disease. It may be very subtle as shown in Figure 13 and very pronounced as shown in Figure 14.
A very rare and serious surgical complication is a retained surgical sponge or a mop in the abdominal cavity. This leads to inflammation and foreign body reaction leading to formation of a granuloma, which may mimic a soft tissue neoplasm. Due to intense inflammatory reaction, FDG uptake is seen in a retained mop, also known as gossypiboma [Figure 15]. Air trapping within the surgical mop is a characteristic finding seen on CT and is diagnostic [1314] of this potential pitfall.
Response assessment after radiofrequency ablation (RFA) of metastatic liver and lung is commonly done with FDG PET CT. Diagnosing completeness of ablation and residual disease is usually straight forward on FDG PET/CT when the response assessment is done 24–48 h post-RFA. After this period, inflammatory changes start to set in along the periphery of the lesion. These changes usually show low grade, uniform, and diffuse FDG uptake. At times, when the post-RFA assessment scan is done too late after the ablation, it might be difficult to differentiate between residual disease and inflammation.[15]
Another potential pitfall in the pelvis is seen in patients with urinary diversion surgery and postradical cystectomy with ileal conduit due to physiologic excreted tracer. This may mask disease in the lower abdomen and pelvis. Vesicovaginal fistula is a false positive, seen postsurgery and radiotherapy in patients with cervical cancer. Delayed imaging is usually helpful in such cases.[16]
Scar site implants are commonly seen Post-laparoscopic surgeries along the track and also sometimes Post-open abdominal surgeries. These are usually mass like enhancing lesions with FDG uptake [Figures 16 and 17].[17] These should not be mistaken with postoperative inflammation at the scar-site. Postoperative inflammatory changes are usually diffuse with low-grade FDG uptake with fat-stranding. There is the absence of mass-like enhancing lesions in the postoperative changes. PET/CT is the imaging modality of choice for the detection of scar site recurrence.
Conclusion
These are few mimics seen during postoperative period and after invasive procedures. It is necessary to get acquainted with potential false positive mimics due to inflammation, infections, and complications during this period, for confident reporting of FDG PET/CT studies. Proper knowledge of the procedure, correct timing for performing the scan, performing a diagnostic CT with intravenous and oral contrast and awareness of the PET/CT appearances will help in prompt and precise diagnosis.
Declaration of patient consent
The authors certify that they have obtained allappropriate patient consent forms. In the form the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
References
- PET/CT interpretative pitfalls in thoracic malignancies. Semin Ultrasound CT MR. 2018;39:282-8.
- [Google Scholar]
- Postoperative imaging of esophageal cancer: What chest radiologists need to know. Radiographics. 2007;27:409-29.
- [Google Scholar]
- A comprehensive review of esophageal stents. Gastroenterol Hepatol (N Y). 2012;8:526-34.
- [Google Scholar]
- Fluorodeoxyglucose positron emission tomography and CT after talc pleurodesis. Chest. 2004;125:2356-60.
- [Google Scholar]
- Fat necrosis of the breast: A pictorial review of the mammographic, ultrasound, CT, and MRI findings with histopathologic correlation. Radiol Res Pract. 2015;2015:613139.
- [Google Scholar]
- FDG-PET/CT in the postoperative period: Utility, expected findings, complications, and pitfalls. Semin Nucl Med. 2017;47:579-94.
- [Google Scholar]
- Comprehensive imaging of tumor recurrence in breast cancer patients using whole-body MRI at 1.5 and 3 T compared to FDG-PET-CT. Eur J Radiol. 2008;65:47-58.
- [Google Scholar]
- Biliary infections: Spectrum of imaging findings and management. Radiographics. 2009;29:2059-80.
- [Google Scholar]
- FDG PET CT features of an intraabdominal gossypiboma. Clin Nucl Med. 2005;30:561-3.
- [Google Scholar]
- Therapeutic response to radiofrequency ablation of neoplastic lesions: FDG PET/CT findings. Radiographics. 2011;31:201-13.
- [Google Scholar]
- FDG PET/CT pitfalls in gynecologic and genitourinary oncologic imaging. Radiographics. 2017;37:577-94.
- [Google Scholar]
- Surgical scar site recurrence in patients with cervical cancer on 18F-FDG PET-CT: A case-control study. Int J Gynecol Cancer. 2016;26:354-60.
- [Google Scholar]