Atlas of confounding factors in head and neck PET/CT imaging

Diagnostic Performances of Radiolabeled FAPI PET/CT for Lymph Node Staging in Head and Neck Cancer Patients: Comparison With 18F-FDG PET/CT

OBJECTIVE

The purpose of the current study was to compare the diagnostic performances of radiolabeled FAPI and 18F-FDG PET/CT for the detection of lymph node (LN) metastasis in head and neck cancer (HNC) patients.

METHODS

The PubMed, Cochrane database, and EMBASE database, from the earliest available date of indexing through December 31, 2024, were searched for studies comparing diagnostic performances of radiolabeled FAPI and 18F-FDG PET/CT for the detection of metastatic LN in HNC patients. We estimated pooled sensitivities and specificities across studies.

RESULTS

Across 8 studies (14 results), the pooled sensitivity of FAPI PET/CT was 0.89 and the pooled specificity was 0.93. The pooled sensitivity of 18F-FDG PET/CT was 0.91 and the pooled specificity was 0.50. On patient-based analysis, the estimated sensitivity and specificity of FAPI were 0.96 and 0.96, and those of 18F-FDG were 0.95 and 0.34, respectively. On lesion-based analysis, the estimated sensitivity and specificity of FAPI were 0.84 and 0.94, and those of 18F-FDG were 0.86 and 0.78, respectively. On neck side-based analysis, the estimated sensitivity and specificity of FAPI were 0.88 and 0.79, and those of 18F-FDG were 0.91 and 0.29, respectively.

CONCLUSIONS

Radiolabeled FAPI showed a good diagnostic performance for the detection of metastatic LN in HNC patients. Also, 18F-FDG PET/CT revealed low specificity for LN staging in HNC patients. Future large multicenter research with more patients would be necessary to provide a more comprehensive overview of the usefulness of radiolabeled FAPI for LN staging in HNC patients.

Habitat radiomics predicts occult lymph node metastasis and uncovers immune microenvironment of head and neck cancer

BACKGROUND

Occult lymph node metastasis (LNM) is a key prognostic factor for patients with head and neck squamous cell carcinoma (HNSCC). This study was to establish radiomics models derived from intratumoral, peritumoral, and habitat regions for identifying occult LNM in HNSCC.

METHODS

Patients with pathologically confirmed HNSCC from three medical Centers (from March 2014 to April 2024) and The Cancer Genome Atlas (TCGA) were enrolled. Center 1 was split into training (n = 330) and internal test sets (n = 154), while Center 2 and Center 3 served as the external test set (n = 183). Genomic set (n = 50) from TCGA and single-cell RNA sequencing set (n = 6) from Center 1 were used for biological analysis. We used the intratumoral, peritumoral, and habitat volumes of interest (VOIs) to extract radiomics features, respectively. Based on Logistic Regression (LR), Support Vector Machine (SVM), and Random Forest (RF) classifiers, nine radiomics models were built to confirm the optimal predictive performance. The best-performing model, along with clinical-radiologic data, was combined to develop a hybrid model. The log-rank test was used to evaluate the model's prognostic performance. Additionally, bulk and single-cell RNA sequencing were applied for investigating the biological mechanisms underlying the optimal model.

RESULTS

The RF-habitat radiomics model showed the best performance, achieving AUCs of 0.835-0.919 across all datasets. Survival analysis further confirmed the prognostic value of the RF-habitat radiomics model. The RF-habitat radiomics model and the hybrid model notably surpassed the clinical model in predictive performance. Moreover, the RF-habitat radiomics model was associated with the abundance level of exhaustion-associated CD8 + T cells, uncovering the immune microenvironment characteristics contributing to occult LNM in HNSCC.

CONCLUSIONS

The RF-habitat radiomics model demonstrated excellent performance for predicting occult LNM in HNSCC across three cohorts, providing a non-invasive solution for occult LNM. Furthermore, radiogenomic analysis further revealed the biological associations of the model, primarily related to T cell dysfunction.

Cancer Integrin Imaging With 68 Ga-Trivehexin PET-CT in Head and Neck Squamous Cell Carcinoma Improves Diagnostic Accuracy

ABSTRACT

Oral squamous cell carcinoma (OSCC) is one of the most common malignancies worldwide. Locoregional nodal involvement by OSCC is commonly encountered. Current conventional and functional imaging modalities have limited diagnostic accuracy in nodal assessment, particularly in head and neck cancer. Thus, definitive management of head and neck malignancies customarily addresses the locoregional nodes along with the primary malignancy. However, OSCC, particularly tongue cancer, shows erratic lymphatic drainage and thus commonly requires extensive bilateral neck dissection, leading to significant morbidity. Cancer integrin imaging with 68 Ga-trivehexin PET-CT can offer highly specific result and thus has the potential for effective tailored management.

Imaging Modalities for Head and Neck Cancer: Present and Future

Several imaging modalities are utilized in the diagnosis, treatment, and surveillance of head and neck cancer. First-line imaging remains computed tomography (CT); however, MRI, PET with CT (PET/CT), and ultrasound are often used. In the last decade, several new imaging modalities have been developed that have the potential to improve early detection, modify treatment, decrease treatment morbidity, and augment surveillance. Among these, molecular imaging, lymph node mapping, and adjustments to endoscopic techniques are promising. The present review focuses on existing imaging, novel techniques, and the recent changes to imaging practices within the field.

FDG PET-CT for the Detection of Occult Nodal Metastases in Head and Neck Cancer: A Systematic Review and Meta-Analysis

Because of an estimated 20-30% prevalence of occult lymph node (LN) metastases in patients with head and neck squamous cell carcinoma (HNSCC), neck dissection is often proposed, despite its potential morbidity. In this systematic review and meta-analysis, the diagnostic performance of FDG PET-CT in detecting occult LN metastases was evaluated in patients with clinically negative necks (cN0) and in whom histopathology of a neck dissection specimen served as gold standard. Overall, 16 studies out of 2062 screened on PubMed and EMBASE fulfilled the inclusion criteria (n = 1148 patients). Seven of these sixteen studies were split into two or three studies because they contained data that could be processed distinctly in our meta-analysis. For this reason, a total of 25 studies were identified and included in the analysis (n total = 1918 patients). The overall prevalence of metastatic nodes per patient was 22.67%. The pooled sensitivity, specificity, diagnostic odds ratios, and negative predictive value (NPV) were 0.71 (95%CI: 0.66-0.75), 0.90 (95%CI: 0.84-0.93), 20.03 (95%CI: 13.51-29.70), and 0.92 (95%CI: 0.89-0.95), respectively. The main causes of inter-study heterogeneity included different reference standards (evaluation per patient, per neck side, or per neck level). The current meta-analysis showed that FDG PET-CT has a high specificity and NPV for ruling out nodal involvement in cN0 necks, but a limited sensitivity.

Treatment Response to Neoadjuvant Therapy in Squamous Esophageal Cancer-Correlation Between Metabolic Response and Histopathology

PURPOSE

Esophageal cancer is among the leading causes of cancer-related mortality worldwide. Patients presenting with localized and loco-regionally advanced cancer without distant metastases have reasonable survival with multimodality management. Adequate and comprehensive staging is the backbone for proper selection of patients fit for curative treatment. Positron emission tomography (PET) in combination with contrast-enhanced computed tomography (CECT) is utilized as the standard staging modality. Multimodality treatment has been able to achieve evaluable tumor responses including pathological complete response (pCR). It is, therefore, necessary to understand whether the impact of neoadjuvant therapy can be evaluated on imaging, i.e., standardized uptake value (SUV) on PET scan done for response assessment and if this can be correlated with histopathological response and later, with survival. Squamous cell carcinoma (SCC) is more common globally and in the Indian subcontinent; hence, we chose this subgroup to evaluate our hypothesis.

METHODS

This is a single institution, retrospective study. Out of the 1967 patients who were treated between 2009 and 2019, 1369 (78.54%) patients had SCC. Out of these, 44 received NACTRT, whereas 1325 received NACT followed by curative surgery. The standardized uptake value (SUV) of 18-fluorodeoxyglucose was recorded during pre- and post-neoadjuvant treatment (NAT) using positron emission tomography (PET). The histopathology of the final resection specimen was evaluated using the Mandard tumor regression grade (TRG) criteria with response being graded from 0 to 5 as no residual tumor (NRT), scanty residual tumor (SRT), and residual tumor We attempted to find a cut-off value of the post neoadjuvant SUV of the primary tumor site which correlated with achievement of better histopathological response.

RESULTS

Out of 1325 patients of SCC esophagus who underwent surgery, 943 patients had available data of TRG, and it was categorized into the 0-2 category which had 325 patients (34.5%) and 3-5 category, 618 patients (65.5%). The SUV was taken only from the PET scans done at our institution, so as to achieve a more homogenous cohort, and this was available for 186 patients, 151 from the NACT group and 35 from the NACTRT group. The ROC method was used to find the cut-off for SUV (5.05) in the NACT cohort, which depicted significant difference in the outcome. Out of these, 93 patients who underwent NACT had SUV > 5.05 and 58 had SUV < 5.05. It was found that the subjective and objective histopathological scores correlated at a p value of < 0.0001. Specifically, the majority of cases with SRT tended to be in the 3-5 category of TRG, whereas cases with NRT are predominantly in the 0-2 category. In the ≥ 5.05 category of SUV, there were 76 cases with SRT. In the NACT cohort, the < 5.05 category of SUV, there are 26 cases with SRT and 32 cases with NRT. Among cases with SRT, 74.5% had SUV ≥ 5.05, while 25.5% had SUV < 5.05. Among cases with NRT, 34.7% had SUV ≥ 5.05, while 65.3% had SUV < 5.05 (p value 0.007). No significant association was found in the radio-pathological correlation in the NACTRT group.

CONCLUSION

Our study confirms the correlation of post neoadjuvant chemotherapy PET SUV with histopathological response, the cut-off of SUV being 5.05 in our cohort. This confirms the predictive value of FDG PET as demonstrated in other studies. Furthermore, its prognostic value with respect to survival has been verified in multiple other studies. With larger scale randomized studies, we may be able to identify the group of patients who have borderline operability anatomically as well as physiologically, where alternative treatment regimens may be indicated to improve outcomes.

Primary Intraosseous Squamous Cell Carcinoma of the Mandible Mimicking Inflammation on FDG PET/CT

ABSTRACT

Primary intraosseous squamous cell carcinoma (SCC) is an uncommon malignant cancer involving the jaw bones. We herein reported the imaging findings of a primary intraosseous SCC of the mandible in a 47-year-old man. He was diagnosed as cancer of unknown primary in the cervical node. FDG PET/CT revealed a focal hypermetabolic lesion around the tooth root of the right lower molar. MRI showed the lesion had hyperintensity on T2-weighted imaging and significant enhancement on T1-weighted imaging fat saturate images. The final diagnosis of primary intraosseous SCC of mandible was confirmed pathologically.

American Crow Brain Activity in Response to Conspecific Vocalizations Changes When Food Is Present

Social interaction among animals can occur under many contexts, such as during foraging. Our knowledge of the regions within an avian brain associated with social interaction is limited to the regions activated by a single context or sensory modality. We used 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) to examine American crow (Corvus brachyrhynchos) brain activity in response to conditions associated with communal feeding. Using a paired approach, we exposed crows to either a visual stimulus (the sight of food), an audio stimulus (the sound of conspecifics vocalizing while foraging) or both audio/visual stimuli presented simultaneously and compared to their brain activity in response to a control stimulus (an empty stage). We found two regions, the nucleus taenia of the amygdala (TnA) and a medial portion of the caudal nidopallium, that showed increased activity in response to the multimodal combination of stimuli but not in response to either stimulus when presented unimodally. We also found significantly increased activity in the lateral septum and medially within the nidopallium in response to both the audio-only and the combined audio/visual stimuli. We did not find any differences in activation in response to the visual stimulus by itself. We discuss how these regions may be involved in the processing of multimodal stimuli in the context of social interaction.

PET/CT Variants and Pitfalls in Head and Neck Cancers Including Thyroid Cancer

PET/CT imaging is a dual-modality diagnostic technology that merges metabolic and structural imaging. There are several currently available radiotracers, but ¹⁸F-FDG is the most commonly utilized due to its widespread availability. ¹⁸F-FDG PET/CT is a cornerstone of head and neck squamous cell carcinoma imaging. ⁶⁸Ga-DOTA-TOC is another widely used radiotracer. It allows for whole-body imaging of cellular somatostatin receptors, commonly expressed by neuroendocrine tumors and is the standard of reference for the characterization and staging of neuroendocrine tumors. The normal biodistribution of these PET radiotracers as well as the technical aspects of image acquisition and inadequate patient preparation affect the quality of PET/CT imaging. In addition, normal variants, artifacts and incidental findings may impede accurate image interpretation and can potentially lead to misdiagnosis. In order to correctly interpret PET/CT imaging, it is necessary to have a comprehensive knowledge of the normal anatomy of the head and neck and to be cognizant of potential imaging pitfalls. The interpreter must be familiar with benign conditions which may accumulate radiotracer potentially mimicking neoplastic processes and also be aware of malignancies which can demonstrate low radiotracer uptake. Appropriate use of structural imaging with either CT, MR or ultrasound can serve a complimentary role in several head and neck pathologies including local tumor staging, detection of bone marrow involvement or perineural spread, and classification of thyroid nodules. It is important to be aware of the role of these complementary modalities to maximize diagnostic accuracy and patient outcomes. The purpose of this article is to outline the basic principles of PET/CT imaging, with a focus on ¹⁸F-FDG PET/CT and ⁶⁸Ga-DOTA PET/CT. Basic physiology, variant imaging appearances and potential pitfalls of image interpretation are presented within the context of common use cases of PET technology in patients with head and neck cancers and other pathologies, benign and malignant.

Diagnostic value of fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography in sublingual and submandibular salivary gland tumors

The aim of the present study was to compare the diagnostic accuracy of fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (F-18 FDG PET/CT) with that of conventional imaging studies (CIS), such as CT or magnetic resonance imaging (MRI), in the clinical diagnosis and staging of submandibular and sublingual salivary gland tumors. In addition, the data obtained were used to evaluate the significance of maximum standardized uptake value (SUVmax) in diagnosing benign or malignant lesions. For the present study, 18 patients with submandibular or sublingual neoplasms underwent F-18 FDG PET/CT imaging with accompanying CT or MRI. The diagnostic values from 43 F-18 FDG PET/CT scans and 28 CIS of the 18 patients were compared to the gold standard histopathological and/or cytopathological diagnosis. The results demonstrated that the diagnostic accuracy for predicting primary tumors was similar between F-18 FDG PET/CT and CIS. By contrast, PET/CT imaging was more accurate in detecting lymph node metastasis compared with CT or MRI (95.4 vs. 66.7%). F-18 FDG PET/CT had a sensitivity of 88.9% and a specificity of 97.1%, whereas CT or MRI had a sensitivity of 54.5% and a specificity of 75.0%. F-18 FDG PET/CT also enabled screening for distant metastasis, as observed in 10 cases in the present study. Furthermore, there were no significant differences in SUVmax between benign or malignant salivary gland lesions, as high glucose metabolism was also observed in benign tumors. In conclusion, F-18 FDG PET/CT provides more accurate diagnostic information for the evaluation of submandibular and sublingual salivary gland tumors as compared with CIS in terms of lymph node and distant metastasis.

Diagnostic Capabilities of MRI Versus 18F FDG PET-CT in Postoperative Patients with Thyroglobulin Positive, 131I-negative Local Recurrent or Metastatic Thyroid Cancer

BACKGROUND

The detection of recurrence or metastasis might be challenging in patients, who underwent total thyroidectomy and radioactive iodine therapy for Differentiated Thyroid Carcinoma (DTC), with increased serum Thyroglobulin (Tg) levels and negative 131I whole body scan (131I-WBS) results.

AIMS

The purpose of this study was to compare the ability of Magnetic Resonance Imaging (MRI) and 18F-fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (18F FDG PET-CT) to detect recurrence or cervical and upper mediastinal metastases in postoperative DTC patients who had negative 131I-WBS despite elevated serum Tg levels.

STUDY DESIGN

This study has a retrospective study design.

METHODS

We evaluated cervical and upper mediastinal MRI and 18F FDG PET-CT of 32 postoperative patients with DTC (26 patients with papillary thyroid carcinoma and 6 patients with follicular thyroid carcinoma).

RESULTS

We evaluated 44 lesions in 32 patients. For all lesions, the Positive Predictive Value, (PPV) Negative Predictive Value (NPV), sensitivity, specificity, and accuracy of MRI were 81.4%, 76.4%, 84.6%, 72.2%, and 79.5% respectively. The PPV, NPV, sensitivity, specificity, and accuracy of 18F FDG PET-CT were 100.0%, 85.7%, 88.4%, 100.0%, and 93.1%, respectively.

CONCLUSION

Although we could not replace 18F FDG PET-CT, MRI might be used as an adjunct to 18F FDG PET-CT for the evaluation of recurrent or cervical and upper mediastinal metastatic thyroid cancers; however, MRI is inadequate for the detection of metastases in small lymph nodes.

Incidence and Significance of Hypermetabolic PET-CT Findings in Unilateral TVF Motion Impairment

OBJECTIVE

To determine the incidence and significance of asymmetric hypermetabolic laryngeal findings on positron emission tomography-computed tomography (PET-CT) in patients with unilateral true vocal fold (TVF) motion abnormalities.

STUDY DESIGN

Retrospective cohort.

SETTING

Single-center tertiary care institution.

SUBJECTS AND METHODS

The medical records of patients with unilateral TVF motion abnormalities were reviewed. The incidence of normal and asymmetric hypermetabolic laryngeal findings was calculated in patients who underwent PET-CT and laryngeal examination, operative laryngoscopy with biopsy, or injection medialization laryngoplasty.

RESULTS

A total of 135 patients with unilateral TVF motion abnormalities underwent PET-CT. After exclusion of patients who completed new or surveillance imaging for a laryngeal neoplasm (n = 27), asymmetric hypermetabolic findings in the larynx were noted in 21 (19%) cases: 13 (12%) on the contralateral side of the impaired TVF, 8 (7%) on the ipsilateral side. Two (25%) patients with ipsilateral hypermetabolism had concerning subsequent fiberoptic laryngeal examinations prompting operative biopsy. There was no evidence of inflammatory or neoplastic disease in all patients with contralateral hypermetabolic findings. Fifteen patients completed PET-CT scans after injection medialization procedures; 6 (40%) displayed avidity ipsilateral to the side of the injection. The median time from injection to scan was 27 days, as opposed to 193 days in the unremarkable scans (P = .011).

CONCLUSION

Contralateral hypermetabolism in patients with unilateral TVF motion abnormalities may represent a false-positive finding. Ipsilateral hypermetabolic uptake without recent fold instrumentation warrants prompt diagnostic evaluation.

PET imaging of occult tumours by temporal integration of tumour-acidosis signals from pH-sensitive 64Cu-labelled polymers

Owing to the diversity of cancer types and the spatiotemporal heterogeneity of tumour signals, high-resolution imaging of occult malignancy is challenging. ¹⁸F-fluorodeoxyglucose positron emission tomography allows for near-universal cancer detection, yet in many clinical scenarios it is hampered by false positives. Here, we report a method for the amplification of imaging contrast in tumours via the temporal integration of the imaging signals triggered by tumour acidosis. This method exploits the catastrophic disassembly, at the acidic pH of the tumour milieu, of pH-sensitive positron-emitting neutral copolymer micelles into polycationic polymers, which are then internalized and retained by the cancer cells. Positron emission tomography imaging of the ⁶⁴Cu-labelled polymers detected small occult tumours (10-20 mm³) in the brain, head, neck and breast of mice at much higher contrast than ¹⁸F-fluorodeoxyglucose, ¹¹C-methionine and pH-insensitive ⁶⁴Cu-labelled nanoparticles. We also show that the pH-sensitive probes reduce false positive detection rates in a mouse model of non-cancerous lipopolysaccharide-induced inflammation. This macromolecular strategy for integrating tumour acidosis should enable improved cancer detection, surveillance and staging.

Comparative Analysis of Clinical and Pathological Lymph Node Staging Data in Head and Neck Squamous Cell Carcinoma Patients Treated at the General Hospital Vienna

Background

Results from publications evaluating discrepancies between clinical staging data in relation to pathological findings demonstrate that a significant number of head and neck squamous cell carcinoma (HNSCC) patients are not correctly staged. The aim of this retrospective study was to analyze potential discrepancies of radiological assessment versus pathological data of regional lymph node involvement and to compare the results with data published in the literature.

Patients and methods

In a retrospective analysis we focused on patients with HNSCC routinely treated by surgery plus postoperative radiotherapy between 2002 and 2012. For inclusion, complete pre-operative clinical staging information with lymph node status and patho-histological information on involved lymph node regions as well as survival outcome data were mandatory. We included 87 patients (UICC stage III-IV 90.8%) for which the aforementioned data obtained by CT or MRI were available. Overall survival rates were estimated by the Kaplan-Meier method. The Pearson correlation coefficient and Spearman's rank correlation coefficient (non-linear relationship) was calculated.

Results

Discrepancies at the level of overall tumour stage assessment were noticed in 27.5% of all cases. Thereof, 5.7% were assigned to patho-histological up-staging or down-staging of the primary tumour. At the lymph node level, 11.5% of the patients were downstaged, and 10.3% were upstaged.

Conclusions

The study showed that in approximately one-fifth (21.8%) of the patients, lymph node assessment by CT or MRI differs from the pathologic staging, an outcome that corresponds well with those published by several other groups in this field.

Reader performance in the ultrasonographic evaluation of oropharyngeal carcinoma

OBJECTIVE

To examine reader performance in evaluating oropharyngeal anatomy on ultrasonography.

MATERIALS AND METHODS

Ultrasound images of the oropharynx comprising normal and malignant anatomic variants were organized into slideshows. Slideshows were administered to 6 readers blinded to participant tumor status and with varying experience reading oropharyngeal sonograms. A training slideshow oriented readers to images of the oropharynx with and without malignant lesions. Readers then evaluated images in a test slideshow for tumor presence and marked orthogonal long and short dimensions of the tumor. Results were analyzed for accuracy, sensitivity, specificity, inter-reader agreement, and measurement error relative to prospectively-identified reference measurements.

RESULTS

Eighty-seven percent of base of tongue (BOT) sonograms were identified correctly by a majority of readers. In identifying BOT tumors, median accuracy, sensitivity, specificity, and Fleiss's kappa were 79%, 73%, 85%, and 0.51, respectively. Median measurement error in the long and short axes for BOT tumors was -2.6% (range: -40% to 29%) and -2.6% (range: -56% to 156%), respectively. Eighty-four percent of palatine tonsil sonograms were identified correctly by a majority of readers. In identifying tonsil tumors, median accuracy, sensitivity, specificity, and Fleiss's kappa were 77%, 74%, 78%, and 0.41, respectively. Median measurement error in the long and short axes for tonsil tumors was 3.8% (range: -45% to 32%) and -6.5% (range: -83% to 42%), respectively.

CONCLUSIONS

Overall, US has clinically useful sensitivity for identification of oropharyngeal carcinoma among readers of diverse clinical backgrounds and experience. US may be useful for the evaluation of features such as tumor dimensions.

FDG-PET/CT in the Postoperative Period: Utility, Expected Findings, Complications, and Pitfalls

FDG-PET/CT as a modality is increasingly used for detection of recurrence and for restaging in patients with clinical suspicion of malignancy, as well as in patients with elevated tumor markers. However, there are many pitfalls in the interpretation of these scans when the studies are performed after some treatment. Some of these are attributed to normal physiological distribution and are compounded when there are inflammatory changes occurring after surgery. The body's inherent response to the surgical insult results in this inflammation. In addition, there are also complications that can happen following surgery, causing increased FDG uptake. Despite various fallacies, FDG-PET/CT provides valuable information in evaluation of residual and recurrent malignant disease. In this article, we aim to describe some of these postsurgical changes secondary to inflammation, common surgical complications, and finally, the utility of FDG-PET/CT in these patients to detect recurrent disease, even in the background of postsurgical changes.

Impact of combined FDG-PET/CT and MRI on the detection of local recurrence and nodal metastases in thyroid cancer

Background

Suspected recurrence of thyroid carcinoma is a diagnostic challenge when findings of both a radio iodine whole body scan and ultrasound are negative. PET/CT and MRI have shown to be feasible for detection of recurrent disease. However, the added value of a consensus reading by the radiologist and the nuclear medicine physician, which has been deemed to be helpful in clinical routines, has not been investigated. This study aimed to investigate the impact of combined FDG-PET/ldCT and MRI on detection of locally recurrent TC and nodal metastases in high-risk patients with special focus on the value of the multidisciplinary consensus reading.

Materials and methods

Forty-six patients with suspected locally recurrent thyroid cancer or nodal metastases after thyroidectomy and radio-iodine therapy were retrospectively selected for analysis. Inclusion criteria comprised elevated thyroglobulin blood levels, a negative ultrasound, negative iodine whole body scan, as well as combined FDG-PET/ldCT and MRI examinations.

Neck compartments in FDG-PET/ldCT and MRI examinations were independently analyzed by two blinded observers for local recurrence and nodal metastases of thyroid cancer. Consecutively, the scans were read in consensus. To explore a possible synergistic effect, FDG-PET/ldCT and MRI results were combined. Histopathology or long-term follow-up served as a gold standard.

For method comparison, sensitivity, specificity, positive and negative predictive values, and diagnostic accuracy were calculated.

Results

FDG-PET/ldCT was substantially more sensitive and more specific than MRI in detection of both local recurrence and nodal metastases. Inter-observer agreement was substantial both for local recurrence (κ = 0.71) and nodal metastasis (κ = 0.63) detection in FDG-PET/ldCT. For MRI, inter-observer agreement was substantial for local recurrence (κ = 0.69) and moderate for nodal metastasis (κ = 0.55) detection. In contrast, FDG-PET/ldCT and MRI showed only slight agreement (κ = 0.21). However, both imaging modalities identified different true positive results. Thus, the combination created a synergistic effect. The multidisciplinary consensus reading further increased sensitivity, specificity, and diagnostic accuracy.

Conclusions

FDG-PET/ldCT and MRI are complementary imaging modalities and should be combined to improve detection of local recurrence and nodal metastases of thyroid cancer in high-risk patients. The multidisciplinary consensus reading is a key element in the diagnostic approach.

Electronic supplementary material

The online version of this article (doi:10.1186/s40644-016-0096-y) contains supplementary material, which is available to authorized users.

Special Techniques in PET/Computed Tomography Imaging for Evaluation of Head and Neck Cancer

PET with fluorodeoxyglucose F 18 (FDG)/computed tomography (CT) imaging has significantly improved the management of head and neck cancer. FDG, however, is not tumor-specific and various image interpretation pitfalls may occur because of false-positive and -negative causes of FDG uptake. Routine imaging examination of head and neck malignancies does not yield all of the necessary data, even with the most advanced imaging technique. Specific interventions, such as use of different dynamic maneuvers and pharmacologic interventions, may provide useful information about the lesion. This article reviews the use of special techniques in FDG PET/CT imaging and whole-body FDG PET/CT imaging for evaluation of head and neck cancer.

Head and neck: normal variations and benign findings in FDG positron emission tomography/computed tomography imaging

Positron emission tomography (PET)/computed tomography with FDG of the head and neck region is mainly used for the diagnosis of head and neck cancer, for staging, treatment evaluation, relapse, and planning of surgery and radio therapy. This article is a practical guide of imaging techniques, including a detailed protocol for FDG PET in head and neck imaging, physiologic findings, and pitfalls in selected case stories.

Post-treatment appearances, pitfalls, and patterns of failure in head and neck cancer on FDG PET/CT imaging

Majority of patients with head and neck cancer are treated with combined treatment regimes such as surgery, radiation therapy, and chemotherapy. The loss of structural symmetry and imaging landmarks as a result of therapy makes post-treatment imaging a daunting task on conventional modalities like computed tomography (CT) scan and magnetic resonance imaging (MRI) as well as on 18 Fluorine-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (18F FDG PET/CT). Combined multimodality treatment approach causes various tissue changes that give rise to a spectrum of findings on FDG PET/CT imaging, which are depicted in this atlas along with a few commonly encountered imaging pitfalls. The incremental value of FDG PET/CT in detecting locoregional recurrences in the neck as well as distant failures has also been demonstrated.

FDG-PET/CT pitfalls in oncological head and neck imaging

OBJECTIVES

Positron emission tomography-computed tomography (PET/CT) with fluorine-18-fluorodeoxy-D-glucose (FDG) has evolved from a research modality to an invaluable tool in head and neck cancer imaging. However, interpretation of FDG PET/CT studies may be difficult due to the inherently complex anatomical landmarks, certain physiological variants and unusual patterns of high FDG uptake in the head and neck. The purpose of this article is to provide a comprehensive approach to key imaging features and interpretation pitfalls of FDG-PET/CT of the head and neck and how to avoid them.

METHODS

We review the pathophysiological mechanisms leading to potentially false-positive and false-negative assessments, and we discuss the complementary use of high-resolution contrast-enhanced head and neck PET/CT (HR HN PET/CT) and additional cross-sectional imaging techniques, including ultrasound (US) and magnetic resonance imaging (MRI).

RESULTS

The commonly encountered false-positive PET/CT interpretation pitfalls are due to high FDG uptake by physiological causes, benign thyroid nodules, unilateral cranial nerve palsy and increased FDG uptake due to inflammation, recent chemoradiotherapy and surgery. False-negative findings are caused by lesion vicinity to structures with high glucose metabolism, obscuration of FDG uptake by dental hardware, inadequate PET scanner resolution and inherent low FDG-avidity of some tumours.

CONCLUSIONS

The interpreting physician must be aware of these unusual patterns of FDG uptake, as well as limitations of PET/CT as a modality, in order to avoid overdiagnosis of benign conditions as malignancy, as well as missing out on actual pathology.

TEACHING POINTS

• Knowledge of key imaging features of physiological and non-physiological FDG uptake is essential for the interpretation of head and neck PET/CT studies. • Precise anatomical evaluation and correlation with contrast-enhanced CT, US or MRI avoid PET/CT misinterpretation. • Awareness of unusual FDG uptake patterns avoids overdiagnosis of benign conditions as malignancy.

PET/MRI and PET/CT in follow-up of head and neck cancer patients

PURPOSE

Positron emission tomography (PET)/MRI combines the functional ability of PET and the high soft tissue contrast of MRI. The aim of this study was to assess contrast-enhanced (ce)PET/MRI compared to cePET/CT in patients with suspected recurrence of head and neck cancer (HNC).

METHODS

Eighty-seven patients underwent sequential cePET/CT and cePET/MRI using a trimodality PET/CT-MRI set-up. Diagnostic accuracy for the detection of recurrent HNC was evaluated using cePET/CT and cePET/MRI. Furthermore, image quality, presence of unclear (18)F-fluorodeoxy-D-glucose (FDG) findings of uncertain significance and the diagnostic advantages of use of gadolinium contrast enhancement were analysed.

RESULTS

cePET/MRI showed no statistically significant difference in diagnostic accuracy compared to cePET/CT (91.5 vs 90.6%). Artefacts' grade was similar in both methods, but their location was different. cePET/CT artefacts were primarily located in the suprahyoid area, while on cePET/MRI, artefacts were more equally distributed among the supra and infrahyoid neck regions. cePET/MRI and cePET/CT showed 34 unclear FDG findings; of those 11 could be solved by cePET/MRI and 5 by cePET/CT. The use of gadolinium in PET/MRI did not yield higher diagnostic accuracy, but helped to better define tumour margins in 6.9% of patients.

CONCLUSION

Our data suggest that cePET/MRI may be superior compared to cePET/CT to specify unclear FDG uptake related to possible tumour recurrence in follow-up of patients after HNC. It seems to be the modality of choice for the evaluation of the oropharynx and the oral cavity because of a higher incidence of artefacts in cePET/CT in this area mainly due to dental implants. However, overall there is no statistically significant difference.

Detection of synchronous cancers by fluorodeoxyglucose positron emission tomography/computed tomography during primary staging workup for esophageal squamous cell carcinoma in Taiwan

AIM

The aim of this retrospective study was to investigate the ability of fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) in the detection of synchronous cancers during staging workup for esophageal squamous cell carcinoma.

MATERIALS AND METHODS

We performed a retrospective chart review of 426 Taiwanese patients with esophageal cancer who received FDG-PET/CT during their primary staging workup between December 2006 and December 2011. We defined synchronous cancers as those occurring within 6 months of the FDG-PET/CT scan. All of the synchronous lesions were confirmed by histology or imaging follow-up. The study patients were followed for at least 18 months or were censored on the date of last follow-up.

RESULTS

Fifty patients were excluded from analysis because of the presence of distant metastases. Of the remaining 376 patients, 359 were diagnosed with squamous cell carcinoma (SCC). We identified 17 patients with synchronous cancers, and all of them had a diagnosis of SCC. Synchronous head and neck cancers were the most frequent (n=13, 76.4%), followed by gastrointestinal cancers (colon cancer, n=2; hepatocellular carcinoma, n=1), and renal cell carcinoma (n=1). FDG-PET/CT successfully detected 15 synchronous cancers (12 head and neck cancers, 2 colon cancers, and 1 renal cell carcinoma). In contrast, conventional workup detected only 9 synchronous cancers (7 head and neck cancers, 1 hepatocellular carcinoma and 1 renal cell carcinoma). The sensitivity of FDG-PET/CT and conventional workup in detecting synchronous cancers were 88.2% and 52.9% respectively.

CONCLUSION

The most frequent synchronous lesions in patients with esophageal SCC were head and neck cancers in Taiwan. Our data indicate that FDG-PET/CT is superior to conventional workup in the detection of synchronous tumors during primary staging for esophageal squamous cell carcinoma.

Utility of (18)F-FDG PET-CT in staging and restaging of patients with malignant salivary gland tumours: a single-institutional experience

OBJECTIVE

The aim of this study was to evaluate the clinical utility of (18)F-fluorodeoxyglucose ((18)F-FDG) positron emission tomography-computed tomography (PET-CT) in staging and restaging of patients with malignant primary salivary gland tumours.

METHODS

Data pertaining to 30 patients (age: 43.8±16.8 years; male/female: 20/10) with histopathologically proven malignant primary salivary gland tumours who underwent 36 F-FDG PET-CTs were retrospectively analysed. Ten PET-CTs were performed for staging and 26 for restaging. The primary site was the parotid gland in 22 patients, the submandibular gland in seven and the minor salivary gland in one patient. (18)F-FDG PET-CT images were revaluated by two nuclear medicine physicians in consensus. Findings were grouped into local disease, nodal disease and distant metastasis. Results were compared with those of conventional imaging modalities [CIM (CT/ultrasound/bone scintigraphy)] when available (n=28). Clinical or imaging follow-up (minimum 6 months) data along with histopathological information (when available) were taken as the reference standard.

RESULTS

Overall, 25 PET-CTs were positive and 11 were negative for disease. (18)F-FDG PET-CT showed local disease in 21 patients, nodal disease in 17 and distant metastasis in nine (lungs, four; liver, three; bones, four; and thyroid, one). Twenty-three PET-CTs were true positive, nine were true negative, two were false positive and two were false negative. The overall sensitivity of (18)F-FDG PET-CT was 92%, specificity was 82%, positive predictive value was 92%, negative predictive value was 82% and accuracy was 89%. No significant difference was seen in the accuracy of PET-CT between the staging and restaging groups (100 vs. 85%; P=0.468). In patients for whom comparable CIM data were available (n=28), PET-CT did not show any significant advantage over CIM (P=0.012) but was more specific (71 vs. 43%).

CONCLUSION

(18)F-FDG PET-CT shows high accuracy in staging and restaging of patients with malignant primary salivary gland tumours. It is more specific than CIM for this purpose.

Radiographic imaging of human papillomavirus related carcinomas of the oropharynx

Imaging, especially contrast-enhanced computed tomography (CECT) for anatomy and positron emission tomography (PET) with labeled (18)F fluorodeoxyglucose for physiologic detail, is critical for staging carcinomas of the oropharynx. As the incidence of human papillomavirus (HPV) infection and related carcinomas of the tonsil and base of tongue (BOT) increases, experience with CECT and PET for staging HPV+ tumors is growing. No imaging modality, however, can determine whether the tumor is HPV+. There are some unique challenges posed by HPV+ oropharyngeal squamous cell carcinoma (SCC). In most locations of the head and neck, a malignancy enhances more than surrounding normal structures, which facilitates tumor mapping. Unfortunately, normal lymphoid tissue of the oropharynx, in the BOT and palatine tonsillar fossa, enhances on CECT and gadolinium enhanced magnetic resonance imaging in a manner similar to SCC. The primary tumor may be small or even occult at presentation, and easily over-looked on CECT. PET coupled with CECT has made a true "unknown primary" very rare, as the metabolically active tumor is almost always detectable on PET. The nodal metastases, so common with HPV+ SCC, can be truly cystic; and as such, can be misdiagnosed as a second branchial cleft cyst, a congenital benign lesion. These pitfalls, coupled with the complex anatomy of the upper aerodigestive tract, make staging these tumors difficult. In this monograph we describe the anatomy of the oropharynx and review the imaging modalities available for staging. Figures highlight the points raised in the text.