|Year : 2020 | Volume
| Issue : 1 | Page : 36-39
Diagnostic evaluation of PET CT, USG neck & FNAC in clinically N0 neck
S Piyush1, R Vishal1, S Anand1, S Shivakumar2, S Sudhakar2, K Kallur3, R Veena4
1 Department of Head and Neck Surgical Oncology, HCG Cancer Centre, Bangalore, India
2 Department of Radiodiagnosis, HCG Cancer Centre, Bangalore, India
3 Department of Nuclear Medicine and Imaging, HCG Cancer Centre, Bangalore, India
4 Department of Pathology, HCG Cancer Centre, Bangaluru, India
|Date of Web Publication||22-Oct-2020|
Dr. S Anand
Department of Head and Neck Surgical Oncology, HCG Cancer Centre, Bangaluru
Source of Support: None, Conflict of Interest: None
Introduction : Extent of neck dissection is determined by the neck nodal positivity and indirectly has a bearing on neck dissection related morbidity. The current study prospectively compares the accuracy of these imaging techniques and FNAC to final histopathology. 31 patients of Oral cavity squamous cell carcinoma with no palpable lymphadenopathy were prospectively included in the study.
Methodology : Thirty-one patients of oral cavity SCC who did not have any clinical lymphadenopathy treated at our centre from January 2018 to July 2018 were recruited for the study. All these patients underwent a whole body PET with contrast enhanced CT followed by a high-resolution ultrasound of the neck. Patients then underwent a US guided FNAC of the most suspicious lymph node.
Results: 14 of the 31 patients had pathologically positive neck node. PET CT had 100 % negative predictive value. USG Neck diagnosed 22 patients to have suspicious lymph node with a negative predicitve value of 66.7% and positive predictive value of 50%. The combined yield of PET CT and USG Neck could produce a PPV of 100% and NPV of 68%.
Conclusion : None of the test individually could predict the neck nodal positivity with absolute accuracy in our study. The best accuracy was when a combination of these tests were done.
|How to cite this article:|
Piyush S, Vishal R, Anand S, Shivakumar S, Sudhakar S, Kallur K, Veena R. Diagnostic evaluation of PET CT, USG neck & FNAC in clinically N0 neck. J Precis Oncol 2020;1:36-9
| Introduction|| |
Neck node status is one of the most important prognostic factor (1) in Head and Neck Cancers. Pretreatment assessment of the neck is crucial for staging and planning definitive treatment. Operable disease is best treated with surgical extirpation of the tumour with negative margins and simultaneously addressing the neck even if it is negative (2). It's essential to determine the nodal status accurately before starting treatment. An elective neck dissection has shown definitive survival advantage (3). The extent of neck dissection is determined by the nodal status, and as the extent of neck dissection increases, the morbidities associated with the procedure also increases. The extent of neck dissection changes to at least a modified radical neck dissection in a node positive neck (2,4). The morbidities associated with dissection of the posterior triangle are high (5). This underpins the need for accurately predicting the nodal status before definitive treatment.
With advances in imaging and accessibility to these modalities, one can screen the neck with reasonable accuracy. To be useful as a screening tool the investigation needs to have a high sensitivity and a high negative predictive value (6). Most often the clinicians stage the neck based on their clinical judgement. This has an accuracy of about 60- 70% (7). Ultrasonography used to analyse the nodal status has a positive predictive value of around 90 %. However, this is user dependent (8,9). Studies have also shown that high-resolution ultrasonography has a low sensitivity for detecting neck nodal disease and better methods can detect occult metastasis and avoid watchful waiting. The disease when recurred in patients who underwent watchful waiting was less amenable to salvage surgery and was higher staged with poorer outcomes (3).
With the newer modalities such as PET, the nodal status can be predicted with greater accuracy, even though these have a high false positivity rate (10). It may hence be logical to use a combination of these diagnostic tools to increase the accuracy of staging the neck prior to treatment.
Though previous studies have shown that a combination of investigations offers better accuracy, none of them have cytologically evaluated the nodal status before starting the definitive treatment (11).
The purpose of this study is to validate the hypothesis that a combination of imaging investigations offers better accuracy and can be considered final for treatment planning foregoing a cytological evaluation. The accuracy of PET CT scan, ultrasound of neck and guided FNAC was correlated with the final histopathology report.
| Methods|| |
Thirty-one patients of oral cavity SCC treated at our centre from January 2018 to July 2018. who did not have any clinical lymphadenopathy, were recruited for the study. All these patients underwent a whole body PET with contrast enhanced CT followed by a high-resolution ultrasound of the neck. Patients then underwent a US guided FNAC of the most suspicious lymph node.
A significant nodal uptake on the PET with radiological features suggestive of metastatic lymph node on CECT was considered as a positive metastatic node. Those nodes with sonological features of metastasis were considered as positive for metastasis. When more than one node was positive on ultrasound, FNAC was taken from those with a cytologically positive neck disease after FNAC were considered for a modified radical neck dissection, and those with negative neck disease were planned for a selective neck dissection from level I-III/IV as per the practice guidelines.
All the surgeries were performed either or under the supervision of Senior Head and Neck Surgical Oncologist (V.R) or trained fellows (P.S and A.S). The surgical specimens were sent for histo-pathological examination. The formalin fixed samples were processed and analysed by the pathologist and a final definitive neck node status was reported.
Statistical Analysis: Diagnostic capabilities of individual tests were evaluated by calculating the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV).
| Results|| |
31 patients were finally included in this prospective study [Table 1].
A total of 14 out of the 31 patients who were clinically negative had histo-pathologically proven neck disease.
27 out of the 31 patients had PET positive neck disease. On comparing PET CT scan with the final histopathology, PET had a positive predictive value of 48.15% and a negative predictive value of 100%. The sensitivity of PET CT scan was 100% however specificity was low at 22.2%. The accuracy of PETCT was found to be 53.33% [Table 2].
22 out of the 31 patients had a suspicious node on US neck, which was reported as metastatic. When comparison of ultrasound of neck was done to the final histopathology it was found to have Positive Predictive Value of 50% and Negative Predictive Value of 66.7%. The sensitivity of the ultrasound was 78.5% and specificity was 35.29% with an accuracy of 54.84% [Table 3].
Ultrasound guided FNAC when compared with HPE had a positive predictive value of 100 % and a negative predictive value of 68%. The sensitivity was found to be 42.8% but the specificity was 100%.. The overall accuracy of FNAC was found to be 74.19% [Table 4]. When USG neck and PET was combined it had an overall sensitivity 92.86% with an accuracy of 51.61% [Table 5].
|Table 5: Correlation of combined yield of PETCT and USG Guided FNAC with Histopathology|
Click here to view
| Discussion|| |
Operable oral cavity cancers are best treated surgically. Existing guidelines, advice a more conservative neck surgery in clinically N0 neck (2). Preoperatively knowing the nodal status accurately can help reduce the extended neck dissections without compromising oncological safety. The largest prospective trial on the pattern of nodal metastasis in oral cavity tumour also stressed on the importance of accurately evaluate the neck to pick the stray few cases of metastasis in level IIB and level V (12). Preoperative accurate nodal staging and subsequent elective neck dissection has shown to have better overall survival and disease free survival (3). This in turn would translate into lesser functional morbidities. Shoulder syndrome, which has a high incidence after MRND, has substantial impact on quality of life of patients.
Relying solely on clinical evaluation may not be justified in the current era. High-resolution ultrasound due to its ease of availability and cost suits as a good screening tool. Ultrasonography carefully studies minute details of nodal size, shape, texture, elasticity and other parameters to determine the suspicion of a node being positive for metastatic deposit and definitely offers a higher advantage over clinical examination in predicting the nodal status. In our study the US had a sensitivity of 78 % with an accuracy of 54.4%. This is in concordance with the existing evidence [13-16].
In our study, PET CT had a very high sensitivity but with a low accuracy in predicting nodal positivity. Adams et al  found its sensitivity to be 90 and 94% respectively and its efficiency was found to be superior to sonography. The additional value of SUV when assessed along with the nodal features provides edge to the assessment (17-20).
Current evidence, though extensive, has just evaluated the sole utility of US or PET CT or a combination of these. The inherent deficiency in these studies had been that cytological evidence was not included while considering the efficacy . Despite having a reasonable accuracy none of them individually or in combination reached close to the accuracy offered by FNAC as shown in our study [21-25]. The positive predictive value of FNAC in our study was 100 percent, a negative predictive value of 68%. The overall accuracy of FNAC was found to be 74.19%.
A decision on the extent of neck dissection based solely on PET CT or US neck would result in unnecessarily large number of modified radical neck dissections. Additionally considering targeted FNAC would add to the accuracy and reduce the number of unnecessary posterior neck dissections.
| Conclusion|| |
In our opinion, the current advances in imaging techniques, cannot accurately diagnose the nodal positivity. The treatment planning should not be solely based on imaging evaluation but also include a cytological diagnosis to avoid over treatment of neck in early stage oral cavity carcinoma. To our knowledge this is the only prospective study, which in addition to evaluate the accuracy of the imaging techniques has taken into consideration the cytological diagnosis. The prospective study is underway at our centre with larger number of patients to validate the findings of our pilot study. We recommend that at centres of excellence where resource limitation is not an impediment, this should be adopted as a standard practice.
SCC- squamous cell carcinoma
PET/CT- positron emission tomography/ computed tomography
FNAC- fine needle aspiration cytology
HPE- histopathological examination
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]