Review Article
Imaging Modalities and Image Guided Biopsy Techniques for Lung Cancer Staging and Their Staging Implications for Lung Cancer- A Review for the General Surgeon
Carlos O Encarnacion*, Ahmed Ali, David W Johnstone and George B Haasler
Department of Cardiothoracic Surgery, Medical College of Wisconsin, USA
*Corresponding author: Carlos O Encarnacion, Department of Cardiothoracic Surgery, Medical College of Wisconsin, USA
Published: 14 Jul, 2017
Cite this article as: Encarnacion CO, Ali A, Johnstone DW,
Haasler GB. Imaging Modalities and
Image Guided Biopsy Techniques for
Lung Cancer Staging and Their Staging
Implications for Lung Cancer- A Review
for the General Surgeon. Clin Surg.
2017; 2: 1564.
Abstract
Imaging modalities in thoracic oncology continue to evolve. It is important as a community surgeon
to be aware of all imaging and diagnostic tools available to diagnose potential thoracic cancer. Our
review intends to be a brief overview of the most recent data supporting imaging and diagnostic
procedures to help make informed decision to optimize patient care. We will cover computerized
tomography, positron emission tomography, magnetic resonance imaging, endobronchial
ultrasound-guided transbronchial needle biopsy, and electromagnetic navigational bronchoscopy.
Keywords: Lung cancer; CT scan; PET scan; EBUS
Key Points
1. Integrated PET-CT scan gives highest diagnostic imaging yield for lung cancer staging.
2. Tissue diagnosis of suspicious areas can safely and accurately be obtained via endobronchial
ultrasound- guided transbronchial needle aspiration.
3. PET-CT scan in combination with EBUS-TBNA can guide therapy.
Introduction
There are many new imaging technologies that are available to help clinicians diagnose and
stage patients to determine optimal oncologic therapy. When assessing a patient for suspected lung
cancer all imaging and non-invasive staging modalities should be considered or exhausted prior
to surgical intervention. When a lung nodule is found on routine screening with a chest x-ray the
confirmatory exam is a computerized tomography (CT) scan to further characterize the nodule as
solid or ground glass appearance and to determine presence of or absence of calcium. CT scanning
may also help identify enlarged mediastinal lymph nodes. Staging algorithmic call for a positron
emission tomography (PET) scan to determine parenchymal and mediastinal lymph node avidity
[1].
Once radiological staging has been obtained a tissue diagnosis is appropriate. We will discuss
endobronchial ultrasound biopsy as an option before surgical biopsy of mediastinal lymph nodes.
Diagnostic Imaging
Computerized tomography scan
Once a lesion has been identified on plain chest radiography or low dose CT scan the next step
is to obtain a high resolution computed tomography with contrast if patient’s renal clearance is
appropriate. This imaging allows for better characterization of the nodule such as size, contour,
density, calcification, invasion of surrounding structures, and allows examination of mediastinal
lymph nodes. It is important to note that the characteristics of lung nodules are not enhanced by a
contrast CT scan but the contrast will better assess invasion of surrounding structures. Given the
superior resolution and quicker scan time of CT imaging in the evaluation and follow up of lung
nodules it has been the gold standard for lung cancer investigation [2]. Lymph nodes greater than 1
cm and subcarinal lymph nodes greater than 1.2 cm are defined as enlarged lymph nodes suspicious
for malignancy warranting tissue biopsy. For nodal metastasis CT scanning was found to have a
sensitivity of 57% and specificity of 89% based on detection size of 1 cm3. In order to obtain the
best resolution of hilar lymph nodes, a CT with contrast is recommended or without contrast if the
patient’s renal function is of concern.
Positron emission tomography scan
PET scans detect positrons emitted by low atomic weight
isotopes such as the radioactive fluoride in Fluorodeoxyglucose.
This is an analog of glucose which is preferentially taken up by cells
with increased glycoloysis such as tumor cells, inflammatory lesions
and infectious lesions. PET scans can be used for determining
synchronous lesions of the lungs, nodal metastasis, and distant
metastasis. The degree of FDG uptake can be semi-quantitatively
interpreted using a standardized uptake value (SUV) with a cutoff
of 2.5 for pulmonary nodules larger than 1 cm with a sensitivity,
specificity and accuracy of 91%, 47% and 79% respectively. The two
caveats are that an inflammatory or an infective lesion can imitate
a malignant nodule in its FDG uptake as well as the fact that some
highly differentiated cancers have a relatively low metabolic and
proliferation rate, hence the low specificity. For nodal metastasis
PET scan imaging was reported to have a sensitivity of 84% and
specificity of 89% [3]. In this same study 11% of patients had distant
metastasis to abdominal organs and bones which were not detected
by CT scan making PET scans the imaging of choice for metastatic
disease [3]. Due to the non-specificity of PET/CT scan abnormalities
biopsies are usually required to make a tissue diagnosis of lesions
in question. Essentially the PET scan becomes a staging and target
imaging technique for further intervention. This dilemma raises the
question of whether PET scan alone can be used without biopsies for
treatment planning remains controversial. Certainly, consideration
of nodal patterns which are consistent with standard modes of spread
(e.g. Right upper lobe lesion, right pretracheal or subcarinal node)
can be thought of as highly suspicious of spread without additional
biopsy especially in absence of obstructive pneumonia. An important
rule to remember is that any adenopathy which renders a patient N2
or stage III warrants a biopsy to confirm this, except in the cases of
truly bulky adenopathy with supporting PET uptake.
Magnetic Resonance Imaging
Magnetic Resonance Imaging (MRI) can be used in lung cancer staging but Heelan et al. [4] reported no diagnosistic advantage over CT scans for lymph node assessment and a higher false positive rate. A meta-analysis by Zhang et al. [5] included 90 studies where the sensitivity of MRI ranged between 52% and 93% and specificity ranged between 82% to 100% for nodal disease. In this meta-analysis the pooled per patient sensitivity for nodal disease in MRI was 74% and specificity was 90% [5]. These findings lead us to conclude that given the accessibility and the increased sensitivity and specificity for CT scan modality in lung cancer screening it remains the radiological exam of choice. The role of MRI in thoracic surgical oncology may be best suited for determination of tissue plane invasion of mediastinal tumor threatening aortic invasion and superior sulcus structures.
Combination Imaging is it better?
The combination of PET and CT scan has been studied over the past decade. This combination is thought to increase the diagnostic yield by encompassing biological uptake and radiographic appearance of cancer lesions. A study comparing PET imaging to PET-CT scan of 129 patients yielded superior accuracy for nodular size 47% to 70% and enlarged lymph node detection 56% to 78% [6]. Given these findings and those stated in the prior sections this combined modality would be encouraged in the staging processes of the lung cancer patients. CT-PET has become the standard of care in most academic centers and it is increasingly unlikely for these not to be done concurrently. Of note anatomical structures may appear in slightly different locations because the CT scan done with PET is not a single breath study and therefore chest volume and location of structure may change in subtle manner.
Minimally Invasive Staging Techniques
Endobronchial ultrasound- guided transbronchial needle
aspiration (EBUS-TBNA)
This technique was first described in 2004 as a method for
mediastinal staging in lung cancer [7]. EBUS-TBNA can be used in
the diagnosis of lymphoma and lung cancer. Endoscopic therapies
have proven efficient and in the ACCP guidelines for lung cancer
management these therapies have recently been recommended as
first line before surgical intervention such as mediastinoscopy. This
recommendation was made due to Yasufuku’s conclusion that there
is no diagnostic difference and a cost benefit with EBUS-TBNA
compared to mediastinoscopy [7,8]. Patients who should undergo
EBUS-TBNA according to the American College of Chest physician
guidelines are those that have peripheral tumors >3 cm, central
tumors, suspicion of N1 disease by lymph nodes larger then 1cm on
CT scan, or PET avid hilar and mediastinal lymph nodes. Lymph node
stations accessible by EBUS are 2 upper paratracheal, 3 prevascular
and retrotracheal, 4 paratracheal right and left, 7 subcarinal, 10 hilar
right and left, and 11 interlobar right and left lymph nodes. The
accuracy of EBUS has been reported at 96.3%, sensitivity of 94.6%
and a specificity of 100%. Due to its high accuracy it is becoming
the preferred method of mediastinal staging. When comparing cost
effectiveness EBUS has been compared to mediastinoscopy multiple
times. In a recent U.S. study cost of mediastinoscopy was found to
be $2,356 compared to EBUS/TBNA at $2,503 [9]. In comparison
an Australian study reported EBUS/TBNA to be AU$3754 and
mediastinoscopy cost of AU$8859 [10]. The Australian study seems
comparable to the predominant pattern in the U.S. in which EBUS/
TBNA does offer some cost savings. At this point in time we support
the current recommendations of EBUS/TBNA followed by surgical
staging if the former procedure turns out to be non diagnosistic.
Successful lymph node biopsy is achieved when lymphocytes with
typical appearance are present on the cytology wet smear. In order to
obtain good sampling proper technique must be used by the surgeon
who obtained the sample. Identifying the appropriate lymph node in
correlation to prior diagnostic imaging studies is crucial. The node
must be maintained in central view during the ultrasound imaging
and the needle passed into the center of node without traversing
surrounding structures. The proper use of these techniques combined
with diagnostic imaging will yield the most accurate sample possible.
With any minimally invasive technique, the patient inherits risks
and complications. A post operative chest x-ray may diagnose some
of these complications and is recommended after any procedure.
The main risk associated with any of the techniques mentioned is: 1)
pneumothoraces, 2) hemothorax, 3) endobronchial bleeding, and 4)
parenchymal hemorrhage. Pneumothorax can be treated with pigtail
catheter insertion during or post procedure. For hemothorax that
is hemodynamically stable, chest tube insertion is recommended.
If hemothorax causes hemodynamic compromise due to persistent
bleeding or bleeding does not subside, surgical intervention is
warranted. Endobronchial bleeding may be corrected with cautery
devices deployed via bronchoscopy to control bleeding. In more
persistent endobronchial bleeding tamponade with bronchial blocker
may be appropriate to treat or temporize until surgical intervention
can be provided. Parenchymal bleeding rarely requires surgical intervention and only usually requires supportive therapy with fluid
boluses, blood transfusions and follows up CT scanning. Most of these
patients should undergo observation for 24 h to monitor respiratory
and hemodynamic stability.
ConcElectromagnetic Navigational Bronchoscopylusion
Electromagnetic navigational bronchoscopy (ENB) is another minimally invasive diagnosistic tool that is becoming more readily available. In some institutions ENB falls into the interventional pulmonologist realm of expertise. This technique can safely and accurately be done by surgeons that have access and training on this equipment. Pearlstein et al. [11] reported 86% diagnostic yield in surgeons’ hands with the addition of rapid on site examination for cytopathology. As mentioned earlier a risk to any minimally invasive pulmonary procedure is a pneumothorax which during ENB was found to be 5.8%.
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